An Easy-to-Build Resonant Inverted Vee Antenna for 17 Meters

I’d been wanting to get on 17 Meters (18.068-18.168 MHz) for some time, and I saw that as solar activity increased, there was more and more activity on it! So, based on my success with my earlier 80 Meter inverted Vee antenna, which always gets very good signal reports with my 200 watts, I resolved to make a single band 17 meter inverted Vee. I already had a home made wooden mast base I had built for an earlier experimental magnetic loop antenna, specifically sized to hold one of the 2.25 inch diameter 48 inch long Army surplus tent poles I had previously bought 24 of. These tent poles fit inside each other making stacking easy, and they’re cheap, and they are perfect for the antenna experimenter. Here is an example listing on Ebay, where I obtained mine.

This is the mast base I built for the flat roof on the back side of our house. The mast section just slips into the wooden cylinder, and it can turn freely if needed. This was a fun little project in itself.

In designing the antenna wires, I relied on the trusty formula 0.95*468/frequency to give the length of the overall antenna in feet. This gives a length of each arm as 12.9 feet. So I built each arm like this, beginning at the feed point at center:

  • 4 feet of 12 AWG solid wire
  • 5 feet of 14 AWG solid wire
  • 5 feet of 18 AWG solid wire

So, this is a tapered wire antenna. The motivation for this is to reduce weight aloft. I mentioned this in an on-the-air conversation and was asked about it, so I guess this is not conventional, so I’ll explain. It’s easy to visualize that using very thin wire for a transmitting antenna will hurt its performance, due to resistive losses. But, the resistance of the wire is only a factor where current is high, and in this antenna the current is only high near the feed point, at the center. The current is zero at the ends of the wires (but the voltage is high there.) So, it is a waste to use heavy copper at the ends of this antenna. Before you consider this idea for your antenna, though there is this one important fact: this only applies to a single band resonant antenna. If I were planning on using this antenna on both 18 MHz and 54 MHz, this would not work well.

Also, this is a direct fed antenna. The RG58 coax with a characteristic impedance of 51 ohms, is connected directly to the two legs of the antenna without any kind of balun, transformer, or matching section. That means that the antenna must be configured so that its feed impedance at resonance is exactly 51 ohms. At the other end the coaxial cable is connected directly to the radio without any tuner (the radio itself has an autotuner, but the object is to have such a good match that it is unneeded). By eliminating tuners and baluns and other hardware, the losses are minimized and the available watts are put to the best possible use. It’s been my impression that hams sometimes rely on tuners and SWR measurements too much — if you add enough hardware, you can, as they say, match your radio to a doorknob. But that won’t radiate any power anywhere. Performance needs to be measured by radiated power, and reducing losses and increasing antenna efficiency is the way to achieve it if you cannot add raw power to your transmitter. An inverted Vee antenna could be thought of as a drooping dipole. A straight dipole has about a 75 ohm impedance at the center drive point, but as the arms are lowered to make the Vee shape, the impedance falls. For a 51 ohm cable as feed, the object is to adjust the arms so that the drive impedance is exactly 51 ohms, giving an ideal match. In an inverted Vee antenna the drive impedance at resonance depends on two things: the angle between the two legs, and the presence of other conducting objects in the vicinity. With the center point as high as I can get it (about 20 feet above roof level) the effect of other objects is not enough to matter, so the rest of the problem is just the tuning of angles and lengths.

Tuning the antenna consists of two related tasks: [1] setting the angle between the two legs so that the drive impedance matches the characteristic impedance of the coaxial cable (51 ohms), and [2] trimming the length of the wires at the ends so that the resonance is at the frequency you expect to transmit the most. If you have 14 feet of wire at both legs, you can fold up one foot of wire on each end, and form a loop there. You do NOT need to cut the wire. Just fold it. Resonance is set by the reach of the wire, not its length. (I would have saved myself a lot of trouble in my first Vee if I’d known this!) Before you start, stretch the wires in a way that results in about a 120 degree angle between them.

  • (1) With the Vector Network Analyzer (VNA) at the cable end, where the radio connects, measure the impedance at the frequency of interest. You are aiming for 51 ohms. If you are on target, go to step 3.
  • (2) Go back to the antenna. If the impedance was over 51 ohms, reduce the angle between the arms. If lower than 51 ohms, increase the angle. Return to Step 1.
  • (3) Measure the resonant frequency with the VNA. Go back to the antenna and either shorten or lengthen the legs, symmetrically. Shorten if low, lengthen if high. Just folding the ends is adequate, no need to cut.
  • (4) Back at the VNA check the frequency and the impedance. If your frequency is right on, and the impedance is 51 ohms, you are done. If not, go back to step 1 or 3 and fix whichever parameter is worse.

The legs don’t have to be symmetrical with respect to the ground — in this case I ended up with a nearly horizontal leg and a steeply sloping leg.

The Vector Network Analyzer I use is this super cheap “NanoVNA” from Amazon which does a surprisingly decent job:

Here below is how the antenna looks on my rooftop, as seen from one of the legs. The nearby leg is tied off to a tree, the far leg is tied to a fixture on the rooftop:

Using the Nano-VNA, after about 10 trips up and down the roof, I got this very good result. The Channel 1 drive point signal magnitude measurement shows a strong dip right at 18.2 MHz (yellow) indicating very good resonance, the Smith Chart shows 49.7 ohms there (green) for an excellent match, and the SWR shows a result of 1/1.04 (blue) which means losses will be very low. My radio (FTDX5000) likes this drive condition very much and shows a nearly 1:1 SWR on its display too.

Here is a closer look at the behavior between 17 and 19 MHz.


So how did it work? Within a half hour, this easy-to-build antenna had given me my very first-ever 17 Meter SSB contact, with N3AIN in Hazleton, Pennsylvania, and a 5-5 report on signal strength for my 200 watts. The next day, I contacted RN3CT, a 100-watt Russian station outside of Moscow. I’m looking forward to having lots of fun on this WARC band in the future as the solar cycle progresses. Not only that, but the WARC bands such as 17 and 30 meters are free of the boring contesters that fill up 80M and 40M on certain weekends, making them good spots to hang out if you don’t want to join the noisy competition.

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A Bench Power Supply That You Can Build Out of Junk – Part 2

Finally, I finished designing, building, and testing this power supply that was intended to be comprised of “junk lying around”. Well, a few new parts did find their way into it, but still, it’s a DIY power supply that any hobbyist could duplicate. This hand built project produces a reliable 0-19 Volts, up to 10 amps, and I’m really pleased at how it has turned out. I put quite a bit of thought and work into this project, and enjoyed every minute of it.

Finished power supply.

So, let’s look first at the design.

The object was to make an “old school” bench supply, with a knob that controls voltage and analog meters that show output volts and output amps. Another feature to add: a knob that sets a current limit, such that if the current reaches that limit, the output voltage drops until the current equals the limit. And the feature that if the current is being limited, an LED comes on. Finally, it was desirable to have some kind of circuit that would measure the temperature at the heat sink and if it is too high, reduce the output voltage as much as necessary to control the heat — and of course, also an LED to indicate the over temperature condition.

As usual, my first step was to simulate the circuit in LTSpice, to see how it works before building it. This was smart, because I stumbled through FOUR different ideas before settling on the final design. My first idea used transistors only, no IC’s [due perhaps to personal pride or stubborness] but when simulated, the accuracy was fairly poor because the gain was so low in the control circuits and it had TOO MANY PARTS. It would be fun to go through each of the earlier designs and explain their pluses and minuses, but let’s skip ahead to the final design. First, here is a SIMPLIFIED SCHEMATIC to help explain how the circuit works, because the topology might be a little unfamiliar to some. This schematic shows just enough to explain how voltage output control works.

In this circuit, “ground” is the negative output of the supply, but it is not the lowest voltage in the circuit. Instead, the power devices have source leads at the lowest DC voltage, with the drain leads going to the “ground”. If you are new to electronic circuits, this might seem odd. There is one and only one reason for this — the drain leads of the Mosfets are connected to the heatsinks directly, for best thermal performance, and it’s easier to make a design with a grounded heatsink since that means that the whole metal box can just be connected to the heatsink. It’s simple and safe and has some immunity to construction mistakes, but it leads to a feeling that most of the circuitry is “floating” at a high level. The Op Amp runs from 6.2 volts generated by the shunt regulator circuit Zener Diode D3 and resistor R16, with these voltages often referred to as its “Rails”. It’s important to notice that the Op Amp has input pins which can be VERY close in voltage to the highest voltage in the circuit. Most Op Amps cannot run with such input voltages, close to a positive Rail. This high level input capability is usually described as “Rail to Rail Common Mode Input Range“. In addition, the Op Amp needs to produce outputs which go nearly from its lowest to its highest voltage, and this ability is called “Rail to Rail Output”. There are not a lot of dual Op Amps which have “Rail to Rail” characteristics for both input and output, but one of them is the MCP6002 [another is TLV2372IP]. (Off topic: as an engineer, I have to admire how clever the IC design is for some of these RR-input amplifiers…) Fortunately I had a couple of the 6002’s in my parts box. So, U1 compares the setting of the voltage control pot R3 with a sample of the output voltage and produces an amplified output at pin 1. This becomes a voltage at the MosFET gates by means of the “level shift” common-base circuit at Q2, whose collector current equals its emitter current – for each volt that U1 output rises, the MosFET gates rise one volt, etc. In summary, the Op Amp increases the drive at the MosFETs until the voltage output corresponds to the pot setting. This is a closed loop control circuit. Now, let’s take a look at the actual, full circuit.

The current control and temperature control circuitry work by overriding the Voltage control circuit. The second Op Amp U1A compares the sensed current with the current limit control pot, and as long as the current does not exceed the limit, produces a “low” output — an output as close to the negative rail as possible. (Note: this op amp characteristic [negative rail output voltage maximum under load] is not especially stable with temperature nor is it tightly specified, so designing this way exposes the design to a little risk, so the engineer must satisfy herself that this works well enough over all conditions…) This voltage becomes part of the reference voltage used by the voltage control circuit. If U1A pin 1 rises in voltage, the voltage control circuit would begin reducing voltage. This means that the current limit pot does not affect the voltage output until the current exceeds the pot setting — and when it does, it “takes over” control from the voltage control circuit, and the supply becomes a current source instead of a voltage source. When it does, the rising voltage at U1A output pin 1 causes the transistor Q1 to turn on, and the Current Limit LED illuminates indicating that it is in constant current mode.

Temperature control is accomplished using a Negative Temperature Coefficient Resistor, a resistor whose resistance decreases as it becomes hotter. These parts are tiny surface mount parts, and two 10K parts in series are used in this circuit in a DIY sensor, soldered to a brass washer with long leads: (photo shown with tenth-inch grid)

In assembling the unit, the sensor was glued to the surface of one of the power FET’s, with the idea that if something gets hot, it will happen there first. [Note, it might have been better to split the sensor into two parts]:

Another view, from the other side.

Referring again to the schematic, the NTC resistors (R11, R21) and R7 form a voltage divider, whose voltage appears at the base of Q2. As the temperature rises, the voltage at the base of Q2 will drop. Notice that PNP transistor Q2 and PNP Darlington transistor Q3 have their emitters connected. Together these two transistors form a crude voltage sensitive switch, such that as the voltage at the base of Q2 drops low enough to turn it on, all the current which had been passing through Q3 then gets shunted into Q2. When this happens, it means that the current, previously supplying drive volts at the MosFETs, instead is “dumped” into the Temperature Warning LED. This drop in gate voltage should turn off the MosFETs, the output voltage should drop and the device, hopefully, should cool down. In the unlikely case that the over-temperature condition is unrelated to excessive current, however, the circuit will not help, except by turning on the warning LED.

Construction of the PCB was definitely old-school. It started with a piece of single sided copper clad board. I drew kind of a general purpose grid of soldering points on it, paying special attention to a place for the 8-pin Op Amp IC, but without planning things out much. Then I cut the lines out using a diamond disk on a Dremel-type tool, while being certain to wear a mask and eye protection. Note: always hold the rotating tool in your LEFT hand, and the item being cut in your right hand (better yet in a vise), below the blade, so that the cut is expelling material away from you. The resulting PCB had lots of room for the circuit, which was made with a rather eclectic mix of leaded and surface mount parts. Small holes were drilled and connecting wires fed in from the back side. Note the authentic 2N2907 (Non-“A”) transistor in the TO-18 case from my old stock, which might be 30-45 years old. Amazingly, still available for sale.

The “E” numbers refer to spots to solder wires.

Finally, I made this little demonstration video to show the power supply in action, using the camera in my new Samsung Galaxy Tab 8 Ultra, which gives really nice video, though it is quite clumsy to hold.

To sum it up, this is quite a nice supply for 12V applications. Hams especially often prefer this kind of all-linear design, which produces no RF interference. (A Ham friend of mine tells me this is no longer true. But I tend to think the noise emitted by a DC-to-DC convertor can never really be zero. What do you think?) The design could be improved in power a lot by a larger heatsink and more fans, and perhaps another MosFET, to spread the heat out to a larger area. The biggest obstacle to large linear power supply designs tends to be the availability of the primary transformer, but this is where the easy availability of low cost Chinese-made Variacs is potentially a big factor. There’s no reason the design could not be upgraded to many hundreds of watts, by upsizing the Variac, heatsink, and drive array. With a 20 Amp Variac core, a 1500-2000 Watt 50V supply is probably possible, which might satisfy the needs of a 1200 Watt Ham RF amplifier. I have an unused 20 Amp Variac sitting in my basement, so maybe it is part of a future project.

If you use this article as the basis of your own project, please write me and let me know how it went.

Finally, for those who want to tinker with the control circuit design, here you can download the LTSpice circuit and listing. As before, paste the listing into a text file and call it Psupply04.asc then open it in LTSpice.Exe.

Version 4
SHEET 1 3268 956
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SYMBOL voltage -640 320 R0
WINDOW 123 24 124 Left 2
WINDOW 39 24 124 Left 2
SYMATTR SpiceLine Rser=.03
SYMATTR InstName V1
SYMATTR Value 20
SYMBOL cap -192 -400 R0
SYMATTR InstName C22
SYMATTR Value 100e-6
SYMBOL nmos 1680 -96 R0
WINDOW 3 -107 -42 Left 2
SYMATTR Value IPP06CN10L
SYMATTR InstName M3
SYMBOL res 2128 -464 R0
SYMATTR InstName R2
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SYMBOL cap 1904 -432 R0
SYMATTR InstName C1
SYMATTR Value 1e-8
SYMBOL LED -64 -608 R0
SYMATTR InstName D1
SYMATTR Value LXHL-BW02
SYMATTR Description Diode
SYMATTR Type diode
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SYMATTR InstName R4
SYMATTR Value 500
SYMBOL res 1712 -640 R0
SYMATTR InstName R11
SYMATTR Value 470
SYMBOL res 1712 -448 R0
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SYMATTR Value 500
SYMBOL LED -480 -176 R0
SYMATTR InstName D2
SYMATTR Value LXHL-BW02
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res -480 -368 R0
SYMATTR InstName R19
SYMATTR Value 10k
SYMBOL zener -272 -544 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D3
SYMATTR Value TDZ6_2B
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL pnp 800 -512 M180
WINDOW 0 70 71 Left 2
WINDOW 3 42 43 Left 2
SYMATTR InstName Q2
SYMATTR Value 2N2907
SYMBOL res 848 128 R0
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WINDOW 0 36 76 Left 2
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SYMATTR InstName R20
SYMATTR Value .05
SYMBOL OpAmps\UniversalOpamp2 1392 -688 M0
SYMATTR InstName U2
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SYMATTR InstName R1
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SYMATTR InstName R9
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SYMBOL OpAmps\UniversalOpamp2 1008 -720 M0
SYMATTR InstName U3
SYMBOL res 800 -736 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R6
SYMATTR Value 2700
SYMBOL res 2000 -448 R0
SYMATTR InstName R15
SYMATTR Value 1e6
SYMBOL res 1808 -976 R0
SYMATTR InstName R17
SYMATTR Value 5
SYMBOL res 1808 -848 R0
SYMATTR InstName R18
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SYMBOL nmos 1824 -96 R0
WINDOW 3 -107 -42 Left 2
SYMATTR Value IPP06CN10L
SYMATTR InstName M1
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SYMATTR InstName R24
SYMATTR Value 10k
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WINDOW 0 70 71 Left 2
WINDOW 3 42 43 Left 2
SYMATTR InstName Q1
SYMATTR Value 2N2907
SYMBOL pnp 576 -512 M180
WINDOW 0 70 71 Left 2
WINDOW 3 42 43 Left 2
SYMATTR InstName Q3
SYMATTR Value 2N2907
SYMBOL LED 624 304 R0
SYMATTR InstName D4
SYMATTR Value LXHL-BW02
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res 480 -336 R0
SYMATTR InstName R26
SYMATTR Value 2000
SYMBOL res 480 -912 R0
SYMATTR InstName R27
SYMATTR Value 22000
SYMBOL npn 16 -416 M0
SYMATTR InstName Q4
SYMBOL res 1200 -384 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R28
SYMATTR Value 8200
SYMBOL res 496 288 R0
SYMATTR InstName R3
SYMATTR Value 33000
SYMBOL res 1712 48 R0
SYMATTR InstName R21
SYMATTR Value 0.1
SYMBOL res 1856 48 R0
SYMATTR InstName R22
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TEXT 848 560 Left 2 !; .tran 0 .25 0 .01 startup\n.op
TEXT 1576 -680 Left 2 ;Current\nLimit\nControl\n100 ohm\npot
TEXT 1192 -1112 Left 2 ;Volts\nControl\n1000\nohm\npot
TEXT -456 -72 Left 2 ;Power\nOn\nLED
TEXT -40 -1072 Left 2 ;Current\nLimited\nLED
TEXT -376 -680 Left 2 ;TL431\nVolt\nRef
TEXT 1216 560 Left 2 !.include opamp.sub
TEXT 2200 -400 Left 2 ;LOAD
TEXT 1816 -1136 Left 2 ;Load\nSensitivity\nAdjust\n10 ohm\npot
TEXT 336 -160 Left 2 ;Temp R\n20C 12.5K\n40C 5.3K\n60C 2.5K\n80C 1.25K\n100C 675\n120C 385
TEXT 624 528 Left 2 ;Over\nTemp\nShutdown\nLED
TEXT 480 -120 Left 2 ;10K\nNTC\nThermistor

A Compact High Current AA Battery Pack For Mobile or Outdoor Applications

In February of 2022 I began using my first prototype of a remotely powered receiving loop antenna system. The unit worked, but I could see that it needed improvement, and it possibly had a lot of potential. So in March 2022 it was time to start working on the next prototype, an antenna array system which will have a number of changes and new features. I am referring to this project as my ESOLA project, standing for Electrically Steerable Orthogonal Loop Array. This is part one. The entire project table of contents is below, including planned future articles.

The first step is to build a 6.8V battery pack, one that is large enough for extended operation. It needs to be compact enough to fit inside this nice waterproof plastic box that I bought. AA NiMH batteries looked like the right choice for this, even though the project might have been done with Lithium Ion batteries such as the 18650 size. One reason was that the ideal voltage range for the RF transistors was easier to get (5.7-7.2V) with the NiMH batteries — a single Li-Ion battery wasn’t enough voltage, and two in series were too much.

With NiMH AA batteries, 4 parallel sets of 5 in series gives 8 AH (if you can believe the manufacturer’s 2000 maH rating, which I don’t) which at 1/2 amp drain will nominally run 16 hours, but with conservative charging and discharging, should give practical use of at least 8 hours. That’s 20 batteries, and with them in a very compact arrangement they could fit into the lid of the box. So, I ordered these battery holders:

These are terrible! I left a bad review for them. These are obviously meant FOR TOYS. The wire is so thin that they amount to a half ohm in series, so high current is impossible with these battery holders. Furthermore, the button end is a brass rivet, cheaply holding the thin red wire to the contact, and in most of these it is NOT STRAIGHT, such that the pressure of the anode spring is enough to “pop” the battery’s cathode off the button with the slightest vibration (with the exception of the singles, which hold the battery on the sides with the plastic shell). These can’t be used for any serious application requiring a secure battery connection.

Instead, I set about to try to design a battery pack using single sided 0.065 inch copper clad board and Keystone 590 battery clips, a part that I happened to have a bag of 100:

The clip isn’t perfectly suited to this application because there would be no holes for the contacts, so it needs modification to use on an undrilled PC board. If there were room, the contacts could just be bent at right angles and soldered that way, but the closest possible spacing was desirable, so I used wire cutters to cut off the contacts flush with the bottom. In addition, these contacts are not ideal for the cathode end, so it was necessary to remove the spring leaf for the cathode ends by gripping it with pliers and bending up — the metal fatigues and it snaps off easily leaving a flat surface perfect for the cathode button, having a “lip” which contributes to battery retention.

It’s important to measure carefully for the PCB planning, allowing for closest packing. As they say, “Measure twice, cut once.” The interconnection can be done almost entirely by cutting grooves in the PCB using a rotating tool such as a Dremel, so the first step was to mark the places to cut using a marker. Setting the distance between the clips is CRITICAL because that determines the holding force. By experimentation, I found the ideal distance and then cut a short brass strip to use as a template for mounting the clips. Soldering was tricky, because the clips had a tendency to walk away while waiting for the solder to wet their surface. The clip sides did better by running them over a piece of sandpaper before soldering, so that the solder would run up the metal quickly. Using tweezers to hold the clip snug against the brass template while soldering did the trick and gave very consistent results, as measured by the battery insertion force.

  • Battery to battery width spacing: 0.565 inch (14.1 mm)
  • Battery end-to-end spacing with clips, approximate: 2.6 inch (66 mm)
  • Brass template for clip spacing: 2.084 inches (52.93 mm)

Below is the unfinished battery pack, showing the layout, the cutting marks, and the destination box lid. Each 5-battery series set is labeled 0-9 for the order in which the batteries stack, with 0 volts at “0” and 6.8V at “9”. The odd numbers are the cathodes, and they need the clips which have the spring bent off.

Finally, here is the completed unit. In building this, I had to use two boards since my raw PCB sizes were not large enough. The two boards are splinted together with some short brass strips soldered to both at three points. Completing the connections to join the 4 sets of batteries in parallel required two extra wires.

Overall, this took quite a bit of manual work trimming the battery clips and doing the precision soldering, but I enjoyed it a lot. Sometimes doing things the hard way is the most satisfying. This home built battery pack has a secure grip on these AA-size batteries and the unit is as compact as possible. The next part of the project will be to design, build and test the battery management circuit.

Receive-only Loop Antenna with Wideband Amplifier (Part 1)

Receiving loop antennas are a good solution for the ham who has an electrically noisy environment. Loop receiving antennas are superior because:

  • They can be positioned far from local noise sources. Today, one’s house is a major source of wideband noise.
  • Because they are more sensitive to the magnetic component of the RF than the electrical component, they are relatively insensitive to nearby power line discharge noise.
  • Being directional, they can be positioned to null out a specific nearby noise source.
  • Because they are not used for transmitting, they can be lightly built and near the ground.

So I set out to design and build one. This article describes my first version. (I was so impressed with it that I went on to design a much more elaborate receiving loop system. The first entry of that design work is here. That project and its several entries has the acronym of ESOLA. As of June 2022, it is still in development. Return for updates!)

Design considerations: Loop antennas are high impedance antennas, and the smaller they are the smaller the signal they produce, so they always need an impedance converting amplifier to amplify and match their tiny signal to a 50 ohm coaxial cable. The smaller the loop, the smaller the signal, and the more amplifier gain is required. Amplifiers add noise, and as one shrinks the antenna, the noise added by the amplifier begins to offset the noise eliminated by the loop configuration, until a point of diminishing returns is reached. So, the smaller the loop, the less noisy the amplifier must be, and the more gain. This wideband amplifier (WBA or LNA) has to be located near the loop, and far from the receiver. To get power, there are two strategies: one is to have power storage at the WBA (batteries) and the other is to feed power down the coaxial cable. Most of the commercial powered loop antennas receive their power down the cable, but the experienced ham eventually learns that coaxial cable conducting DC current generates a bit of RF noise itself. This means, to get the lowest possible noise, power should be stored at the WBA, with recharging done when the amplifier is offline via the cable, or by solar power. I chose the cable charging method for my design.

Today, many WBA’s are designed using Gallium-Arsenide transistors (GALI-74) and other technologies, but I wanted to start with something I was more familiar with, the classic J310 (or U310) depletion mode N-channel junction FET, combined with a fast bipolar transistor. Doing a dual amplifier and then combining the signals using a transformer was a good way to get added amplitude. I did some hunting and found I had some 2N5770 transistors, so I chose to use them. Operating voltage of 5V would be all that was needed, so 5 NimH batteries would supply enough voltage, though of course it would need to be regulated. In addition, I’d need the charging circuit to stop charging when the total battery voltage went too high. And a power-on LED, and a switch.

I did the WBA design using LTSpice. Here is the design I ended up with, after a few iterations (click to enlarge):

I cannot attach the LTSpice source file directly (this hosting service will not allow that file type) so I will append it to this post in Text format, and you can copy it off and save it as an ASC file if you want. Ask me questions if you need help. Below, we see the amplifier throughput characteristic simulated in LTSpice, showing it is fairly flat from 3 MHz to 30 MHz, and usable output gain from 500 kHz to 100 MHz.

The LTSpice design led to the final schematic, after a few alterations and tests: (click to enlarge)

I need to admit that the battery management circuitry is unnecessarily complicated. I designed it using discrete parts because that’s what I had on hand, but there are better approaches using linear ICs. Do me a favor and redesign it yourself, and send me an update! [Edit: my redesign of the battery management section is here.] I’ll skip a detailed circuit description — if you’re an experienced electronics hobbyist, there’s probably enough information in the schematic above for you to duplicate the design, but feel free to ask me questions. If I’m asked questions about this, I’ll probably include my answer text in the post here.

Below, the WBA section as built. Note that the output RF connector is floating, not grounded to the chassis. The box is not especially weather proofed. In my next version I’ll do a better job with that.

Below, a photo showing the entire assembly, with batteries and the battery management circuitry.

The actual wire antenna can be any loop. This leaves lots of room for experimentation. I plan on testing different size loops, to compare their signal to noise ratio for different bands. Also, I’ll be trying some twin-lead loops. At present, the loop is a vertical one, about 10 feet on a side, square, with the WBA mounted on a fence at the bottom of the loop. Note the grounding strap going from the chassis to the 1/2 inch pipe, pounded into the ground:

The practical results with the amplified loop antenna on the 80M band are quite dramatic: I see noise reduction of about 12 db over the phone bands. Some conversations which were detectable but not readable are now quite easily readable. Improvement for weak signals on the 40M band seem to be about 10 db, with some very weak CW signals seeming to “emerge” from the noise when the loop is switched on. In general, I’m quite happy with the unit, and now I’ll begin experimenting with it to see if I can improve it. Remember: when running the unit, turn off the charging supply for best results. Then turn it back on once you are done, to bring the batteries back up to full charge. Charging current will automatically limit to about 0.25 amps. When you see the charging current fall to about 0.12 amps, that means that the batteries are fully charged, but there is no need to disconnect the power supply because the circuit will not overcharge the batteries. Use about 11-12 VDC as your charge voltage. I built a small charger interface box to use with the amplifier box — see the schematic for the details.


I looked around the web and found some more reading on the subject, if you’d like to see designs by others.

I found a ham who published a WBA design, single ended, using only one J310 transistor.

Someone is selling a dual J310 circuit on Amazon, but it has a single ended input, which is not as good a choice for a loop input. It looks like a near copy of this circuit.

This ham experimented with a J310 circuit in his Youtube video.

This ham had a circuit which was the most similar to mine (using a NPN rf transistor to drive the 50 ohm cable), though again, it was single sided only.

For a theoretical analysis of the optimum low noise amplifier design problem, this article by VA3IUL is a good introduction. It emphasizes the noise in the amplifying component and is an alternate to the mostly-experimental approach I used here. The collection of links on his web site is a treasure trove.

The MFJ-1886 receive-only loop antenna is a double ended input like mine, and it uses the GALI-74, so it’s a more modern device. I would love to compare this commercial unit’s performance to mine but I’d have to buy one, and I’d rather not do that. I think it’s possible that the J310 FET might do as good or better job when compared. But see David Casler’s video on it. He has good things to say about dedicated receiving loops in general, though MFJ’s loop is tiny compared to my 10 foot square vertical – signal strength increases with loop area and number of turns.

So, this quick look at the web did not find a close match to my circuit. There are dozens of good ways to design with these parts, so perhaps this is one of them, but I have no illusions that this circuit is highly optimized. If you use my circuit as a starting point, please mention my call sign NK6Y and leave a link back to my article here.

Next, I’ll try to figure out how to measure the performance of the loop. My purpose is to improve on the signal to noise ratio. I want to try a 2-turn loop, using 450 ohm twinlead wire, and see how it does.


Below is the LTSpice drawing file. Copy the following into a text editor and save it as a file with extension “.ASC” and open that in LTSpice. Because of limitations of this hosting service, I can’t put the file here any other way.

Version 4
SHEET 1 2668 680
WIRE 1056 -912 656 -912
WIRE 1056 -848 976 -848
WIRE 2112 -768 496 -768
WIRE 2112 -736 2112 -768
WIRE 496 -720 496 -768
WIRE 496 -608 496 -640
WIRE 656 -608 656 -912
WIRE 656 -608 496 -608
WIRE 688 -608 656 -608
WIRE 800 -608 768 -608
WIRE 848 -608 800 -608
WIRE 976 -608 976 -848
WIRE 976 -608 928 -608
WIRE 2112 -608 2112 -656
WIRE 2112 -608 976 -608
WIRE -48 -544 -944 -544
WIRE 336 -544 -48 -544
WIRE 496 -544 336 -544
WIRE 1568 -544 496 -544
WIRE 1952 -544 1568 -544
WIRE 2112 -544 1952 -544
WIRE 2272 -544 2112 -544
WIRE 336 -480 336 -544
WIRE 1952 -480 1952 -544
WIRE 496 -432 496 -544
WIRE 2112 -432 2112 -544
WIRE 496 -256 496 -352
WIRE 2112 -256 2112 -352
WIRE -48 -208 -48 -544
WIRE -48 -208 -192 -208
WIRE 400 -208 208 -208
WIRE 432 -208 400 -208
WIRE 1568 -208 1568 -544
WIRE 1568 -208 1440 -208
WIRE 2032 -208 1824 -208
WIRE 2048 -208 2032 -208
WIRE -192 -160 -192 -208
WIRE -48 -160 -48 -208
WIRE 208 -160 208 -208
WIRE 1440 -160 1440 -208
WIRE 1568 -160 1568 -208
WIRE 1824 -160 1824 -208
WIRE 400 -144 400 -208
WIRE 2032 -144 2032 -208
WIRE -192 -48 -192 -80
WIRE -48 -48 -48 -80
WIRE -48 -48 -192 -48
WIRE 1440 -48 1440 -80
WIRE 1568 -48 1568 -80
WIRE 1568 -48 1440 -48
WIRE 208 -32 208 -80
WIRE 336 -32 336 -400
WIRE 336 -32 208 -32
WIRE 1824 -32 1824 -80
WIRE 1952 -32 1952 -400
WIRE 1952 -32 1824 -32
WIRE 336 0 336 -32
WIRE 400 0 400 -64
WIRE 400 0 336 0
WIRE -48 16 -48 -48
WIRE 1568 16 1568 -48
WIRE 1952 16 1952 -32
WIRE 2032 16 2032 -64
WIRE 2032 16 1952 16
WIRE -512 96 -800 96
WIRE -496 96 -512 96
WIRE -304 96 -416 96
WIRE -160 96 -224 96
WIRE -96 96 -96 80
WIRE -96 96 -160 96
WIRE 1104 96 912 96
WIRE 1120 96 1104 96
WIRE 1312 96 1200 96
WIRE 1456 96 1392 96
WIRE 1520 96 1520 80
WIRE 1520 96 1456 96
WIRE -512 160 -512 96
WIRE 1104 160 1104 96
WIRE 336 176 336 0
WIRE 1952 176 1952 16
WIRE -1120 240 -1232 240
WIRE -944 240 -944 -544
WIRE -800 240 -800 96
WIRE -352 256 -400 256
WIRE -160 256 -160 96
WIRE 496 256 496 -160
WIRE 496 256 464 256
WIRE 592 256 496 256
WIRE 1264 256 1216 256
WIRE 1456 256 1456 96
WIRE 2112 256 2112 -160
WIRE 2112 256 2080 256
WIRE 2208 256 2112 256
WIRE 208 288 208 -32
WIRE 1824 288 1824 -32
WIRE -400 304 -400 256
WIRE -352 304 -352 256
WIRE 464 304 464 256
WIRE 1216 304 1216 256
WIRE 1264 304 1264 256
WIRE 2080 304 2080 256
WIRE -1120 320 -1120 240
WIRE 592 320 592 256
WIRE 2208 320 2208 256
WIRE -1120 448 -1120 400
WIRE -944 448 -944 320
WIRE -944 448 -1120 448
WIRE -400 448 -400 368
WIRE -400 448 -944 448
WIRE -352 448 -352 368
WIRE -352 448 -400 448
WIRE -160 448 -160 320
WIRE -160 448 -352 448
WIRE -48 448 -48 112
WIRE -48 448 -160 448
WIRE 208 448 208 352
WIRE 208 448 -48 448
WIRE 336 448 336 256
WIRE 336 448 208 448
WIRE 464 448 464 384
WIRE 464 448 336 448
WIRE 592 448 592 384
WIRE 592 448 464 448
WIRE 800 448 800 -608
WIRE 800 448 592 448
WIRE 1216 448 1216 368
WIRE 1216 448 800 448
WIRE 1264 448 1264 368
WIRE 1264 448 1216 448
WIRE 1456 448 1456 320
WIRE 1456 448 1264 448
WIRE 1568 448 1568 112
WIRE 1568 448 1456 448
WIRE 1824 448 1824 352
WIRE 1824 448 1568 448
WIRE 1952 448 1952 256
WIRE 1952 448 1824 448
WIRE 2080 448 2080 384
WIRE 2080 448 1952 448
WIRE 2208 448 2208 384
WIRE 2208 448 2080 448
WIRE -944 480 -944 448
WIRE -800 512 -800 320
WIRE 912 512 912 96
WIRE 912 512 -800 512
WIRE -1232 576 -1232 240
WIRE -512 576 -512 240
WIRE -512 576 -1232 576
WIRE 1104 576 1104 240
WIRE 1104 576 -512 576
FLAG -944 480 0
SYMBOL voltage -944 224 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 4.8
SYMBOL voltage -800 224 R0
WINDOW 123 24 124 Left 2
WINDOW 39 24 152 Left 2
SYMATTR Value2 AC 120e-6 0
SYMATTR SpiceLine Rser=50 Cpar=22e-12
SYMATTR InstName V2
SYMATTR Value SINE()
SYMBOL res 944 -624 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R4
SYMATTR Value 25
SYMBOL ind2 512 -736 M0
SYMATTR InstName L1
SYMATTR Value 29e-6
SYMATTR Type ind
SYMBOL ind2 480 -448 R0
SYMATTR InstName L3
SYMATTR Value 140e-6
SYMATTR Type ind
SYMBOL njf -96 16 R0
SYMATTR InstName J1
SYMATTR Value J310
SYMBOL res 320 -496 R0
SYMATTR InstName R6
SYMATTR Value 12000
SYMBOL res 320 160 R0
SYMATTR InstName R8
SYMATTR Value 10000
SYMBOL cap 192 288 R0
SYMATTR InstName C4
SYMATTR Value .01e-6
SYMBOL res 448 288 R0
SYMATTR InstName R9
SYMATTR Value 32
SYMBOL ind2 -64 -176 R0
SYMATTR InstName L2
SYMATTR Value 330e-6
SYMATTR Type ind
SYMBOL cap 576 320 R0
SYMATTR InstName C5
SYMATTR Value 220e-12
SYMBOL ind2 224 -176 M0
SYMATTR InstName L4
SYMATTR Value 33e-6
SYMATTR Type ind
SYMBOL ind2 -320 112 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 4 56 VBottom 2
SYMATTR InstName L5
SYMATTR Value .12e-6
SYMATTR Type ind
SYMBOL cap -176 256 R0
SYMATTR InstName C1
SYMATTR Value 15e-12
SYMBOL res -528 144 R0
SYMATTR InstName R1
SYMATTR Value 500
SYMBOL res -400 80 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 5
SYMBOL diode -368 304 R0
SYMATTR InstName D1
SYMATTR Value 1N4148
SYMBOL diode -384 368 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D2
SYMATTR Value 1N4148
SYMBOL npn 432 -256 R0
SYMATTR InstName Q2
SYMATTR Value 2N5769
SYMBOL ind2 2128 -336 R180
WINDOW 0 36 80 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName L6
SYMATTR Value 140e-6
SYMATTR Type ind
SYMBOL njf 1520 16 R0
SYMATTR InstName J2
SYMATTR Value J310
SYMBOL res 1936 -496 R0
SYMATTR InstName R2
SYMATTR Value 12000
SYMBOL res 1936 160 R0
SYMATTR InstName R3
SYMATTR Value 10000
SYMBOL cap 1808 288 R0
SYMATTR InstName C2
SYMATTR Value .01e-6
SYMBOL res 2064 288 R0
SYMATTR InstName R7
SYMATTR Value 32
SYMBOL ind2 1552 -176 R0
SYMATTR InstName L7
SYMATTR Value 330e-6
SYMATTR Type ind
SYMBOL cap 2192 320 R0
SYMATTR InstName C3
SYMATTR Value 220e-12
SYMBOL ind2 1840 -176 M0
SYMATTR InstName L8
SYMATTR Value 33e-6
SYMATTR Type ind
SYMBOL ind2 1296 112 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 4 56 VBottom 2
SYMATTR InstName L9
SYMATTR Value .12e-6
SYMATTR Type ind
SYMBOL cap 1440 256 R0
SYMATTR InstName C6
SYMATTR Value 15e-12
SYMBOL res 1088 144 R0
SYMATTR InstName R10
SYMATTR Value 500
SYMBOL res 1216 80 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R11
SYMATTR Value 5
SYMBOL diode 1248 304 R0
SYMATTR InstName D3
SYMATTR Value 1N4148
SYMBOL diode 1232 368 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D4
SYMATTR Value 1N4148
SYMBOL npn 2048 -256 R0
SYMATTR InstName Q1
SYMATTR Value 2N5769
SYMBOL res 784 -624 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R12
SYMATTR Value 25
SYMBOL ind2 2096 -640 M180
WINDOW 0 36 80 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName L10
SYMATTR Value 29e-6
SYMATTR Type ind
SYMBOL res 384 -160 R0
SYMATTR InstName R13
SYMATTR Value 390
SYMBOL res 2016 -160 R0
SYMATTR InstName R14
SYMATTR Value 390
SYMBOL res -208 -176 R0
SYMATTR InstName R15
SYMATTR Value 5000000
SYMBOL res 1424 -176 R0
SYMATTR InstName R16
SYMATTR Value 5000000
SYMBOL voltage -1120 304 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value -.8
TEXT -816 -216 Left 2 !.ac oct 8 .1e6 300e6
TEXT -808 -152 Left 2 !K1 L4 L2 1\nK2 L3 L1 1
TEXT 1200 -696 Left 3 ;5 to 2 turns ratio
TEXT -24 -248 Left 3 ;3 to 1 turns ratio
TEXT -808 -72 Left 2 !K3 L7 L8 1\nK4 L6 L10 1
TEXT 1592 -248 Left 3 ;3 to 1 turns ratio
TEXT 1064 -880 Left 2 ;Output to 50 ohm cable

Yaesu FTDX3000 For Sale [Sold!]

For sale is my Yaesu FTDX3000, in excellent condition, used lightly for 4 months for $1199. The unit includes the optional XF-127CN 300 Hz CW filter, which is already installed in the unit. Also included: 12V power cable, MH31B8 microphone, manual, and remote control. This transceiver requires an external 12V power supply, which is not included. I operated it using an MFJ-4035MV power supply, but I need that supply for use elsewhere, and you probably want to pick out the right power supply for you. I loved this transceiver, especially the incredible Yaesu DNR system, and I’m sure you will enjoy it too. It has no significant dings, dents, scratches or other damage. I can pack this in mostly-original Yaesu boxes (I will have to add stiffeners and cut some new styrofoam) and ship it for $75 anywhere in the continental USA, or you can pick it up locally by appointment in Scotts Valley, CA. I can also ship to Canada — ask me for the rates. I can accept payment by Paypal, cash, check (10 day delay), USPS money order, or cryptocurrency. Sale is final, no returns (due to scammers, sorry). I’m willing to hold the unit for up to a week for a non-refundable deposit – ask me for details if you need extra time. Feel free to contact me with any questions. I’ve upgraded to the FTDX-5000 now, and am enjoying it too. [PS: the unit has NOT received a firmware update — it is exactly as-delivered from HRO.]

Automatic Half-Duplex WebSDR Audio Switch for Yaesu and Similar Radios

Band conditions on 75M lately have been terrible. So bad, that our long-time scheduled 75M SSB meetup of our four hams on the West Coast can’t work radio-to-radio due to high levels of noise. Also, propagation seems to favor distant stations over nearby ones, due to the inability of the ionosphere to reflect a near-vertical incidence wave at frequencies over 3 mHz.

We have been forced to use the Internet to make up for our inability to receive the distant station. One way to do this is to connect via Internet to a WebSDR page. A WebSDR is like a remote receiver that you can control yourself. Once you are connected to it, you specify the frequency and mode, and you can listen to the demodulated audio on your computer. By picking a WebSDR which is located in an area that your distant station can transmit to, you can listen in on your station even if the noise entirely drowns them at your own receiver. So this is what we do, when it’s necessary.

Some may say this is not how Ham Radio should work. That using someone else’s receiver, and the Internet, is cheating. Perhaps that’s true for contests, but networking with other radios in order to break thru propagation blocks is just another part of the hobby’s advance through the years. And it’s only fair — if Ham radio is a backup for the Internet, then the Internet should be the backup for Ham Radio. Right?

But manufacturers of modern transceivers haven’t kept up, of course. Our problem is that if we are listening to the WebSDR on our computer speakers, and we begin speaking into the microphone, we get feedback started and an embarrassing buzz or howl ensues. So to go from listen to speak, we have to shut off the computer audio at the same time we activate the push-to-talk button. It can be awkward and it invites mistakes, especially since it usually involves a mouse click. Then we have to reverse the process. Being forced to switch between sending and receiving is sometimes called “half duplex” operation. So the hobbyist’s answer is — design and build a device to switch between computer audio and radio audio. So here is such a box. Before we go too far I want to apologize for the shoddy construction methods and the reuse and abuse of old parts — I made this out of stuff that was within reach. If you make a version of this, yours can be pretty and professional if you like.

Rough interconnection diagram
Detailed Schematic (click for full size)

Operation is simple. There are two front panel switches, one marked “Radio” and the other “Computer”. As wired, turning on one or the other connects that source to the output. Turning on neither switch connects the computer UNTIL the radio goes into transmit mode, when it switches to the radio automatically. This will be the normal mode when listening to a conversation via the WebSDR. (Note: turning on both switches forces the computer to the output.) If you choose to use headphones, plugging them in will shut off the audio to the speakers. There is an output for an oscilloscope, to monitor the audio, if you like. Here are some photos.

View of the chassis rear.
View of the front. This was before the circuit board was screwed into place.
The LED is the little round indicator at the front top.

Finally here is a photo of the finished unit snuggled up alongside my Yaesu FTDX5000MP radio. It operates flawlessly so far. If you need to use an Internet device to receive sometimes, you need one of these too. Write me if you have any questions.

Hams Want Spectrum Displays! The Solution is the Panadapter. (SDRPlay RSPdx/RSP1a/RSPduo and Yaesu FTDX3000)

Yes! Hams have made it clear that they want spectrum displays on their radios. So what did HF receiver manufacturers do? They included REALLY BAD displays in their new receivers, dooming those designs to quick obsolescence. Ask yourself — would you like a display like this?

“Spectrum” display on my $1800 Yaesu FTDX3000.

Or, would you like something more like this?

SDRuno software main control and spectrum display.

The latter display is the SDRuno software running on my Lenovo Yoga Laptop. The key is the inexpensive black box “SDRPlay RSPdx” which can do two things at once: (1) Mirror all settings of common, modern HF transceivers on the PC screen, allowing control from the PC, and (2) analyze the RF input to the transceiver, displaying it as a spectrum, and optionally demodulating it into whatever mode you need: CW, SSB, RTTY, etc. All this for about $199, assuming you have a laptop and transceiver. Here is a nice Youtube summary of how to set it up.

My setup. Left side: the RSPdx unit. Bottom: the Yaesu FTDX3000 transceiver. Top: the Lenovo Yoga laptop, in reversed orientation with downward-facing keyboard. I use a bluetooth keyboard/mouse.

It’s a trend, and as I said, conventional HF base stations, even with touch screens showing a poorly-displayed spectrum scan, are doomed to becoming obsolete. As an engineer, I feel certain this is happening, and I needed to rant a little about it. So then, where is this going? It can only go in two directions, and of course, it will end up going both directions at once. One direction is the premium transceiver with LOTS of physical dials, buttons, and direct hands-on control for the ham operator who wants the kenetic, haptic, and tactile experience that only old-school equipment can deliver. (Example: the FTDX5000) The other direction is the box-plus-pc solution in which the ham relies on their computer for ALL control and display. And it’s here already: the Expert Electronics SunSDR2-Pro transceiver, the ultimate in PC transceivers. I’m not in the market myself, but my message to other hams is this: FORGET the Icom 7300, it is a Frankenstein’s Monster, a patchwork of concepts that you love today but will not stand up to time’s progress well. Forget FlexRadio, whose quality (and price) is sky-high. Even my FTDX3000 will look sad ten years from now. At least I can hide it and use the computer interface for nearly everything. If you are like me, the $199 SDRPlay RSPdx box will allow you to convert your modern receiver to a fancy panadaptor spectrum display, as I did above. But seriously, check out the SunSDR2-Pro, and especially, check out those upcoming PC-only transceivers that should be coming out in the near future. They are the new direction. The next great radios will be boxes that you put in the corner out of sight – or boxes you can install at the top of a mountain a mile away – yet control with your laptop while relaxing in your hot tub.

Ad for the SunSDR2-Pro by the Russian company Expert Electronics.

12 Volt Power Supply Made From Random Junk – Part 01 [Design]

[Note, this is Part One. The project is completed in Part Two.] I need a power supply that can supply about 14V at loads of at least 10 amps. This need came about because of my 45 ft sailboat, which last year lost all its batteries. It had been moored on an inaccessible piling without power for its trickle charger. So, we bought a new deep cycle battery, but it needs more than a trickle charger to keep charged. Actually, the battery may already have been damaged. Ugh. I can’t afford to keep buying these big batteries. This power supply not only needs to be able to trickle, but to pump out a lot of amps when it is loaded by, say, the 12V pumps.

And, my challenge to myself is to make this power supply out of junk I have lying around my workshop. To be honest, I do have a LOT of such junk, so making a decent power supply should not be too hard. I shouldn’t have to buy anything to make this.

In designing it, the first question is – switcher power supply or linear? I have lots of linear parts, so that’s easily answered. For the transformer, I’ll use a Variac core, with a secondary winding done by hand. I’ll sketch out a design that is simple and easy to throw together. And uses no integrated circuits. Just for fun. Preliminary sketch — something to start with: (See my final design, which is very different.)

A quick sketch, just to get started.

I relented on my “junk only” resolve and bought the diode bridge – I ordered a couple of these from Mouser: KBPC5004W-G. Having a rating that is 100% higher than the design goal is just a few cents more than one that is just good enough. The power FETS came out of an old junked Pioneer Stereo Receiver. The current sense resistor is a hand made and calibrated one. (More on that later.) The Variac is one that had been on the boat for 25 years, that I’d used to correct for bad harbor AC volts (often as low as 105VAC).

The unit needs a heatsink and a fan. As I thought of simple ways to accomplish this, I remembered an old Packard Bell PC in the closet. I found it had a nice clean boxy power supply complete with fan and HP-type 120V power receptacle. I told myself, well I’ll just take it apart and use its fan and especially use its air flow venting as part of the design. Below, is a shot of the old supply with its cover off. I tore out all its electronics (saving the heatsinks and the two capacitors) and cut up the metal.

Old computer supply from a 1998-era PC. On the left is the Variac core showing the hand-wound secondary.

For the main chassis, I have this 12x10x6 18G steel box. (Ugh. I hate having to cut steel.) So, I joined the halves of the old 1998 supply together to make part of the chassis front, and installed it into the steel box, like this. Imagine that the fan is pushing air INTO the box. Air will emerge from the grillwork. So, under the grillwork is the preferred location for the heatsink.

Steel box, plus the PC supply panels

Then finally, I laboriously cut the original steel box front panel with a Dremel-type tool, and voila, we have a usable chassis. Again, imagine that the heatsink will go behind the fine grill. Then by running the fan backwards it will “suck”. (Heehee) That will cause the hot air to leave the top of the unit. One should never use a fan to force hot air to descend — hot air always needs to be allowed to rise. The blank side of the panel will still need an ammeter, a voltmeter, banana jacks, a couple of potentiometers, and maybe an indicator light. I don’t have a plan for those parts yet. This ends this update — more to come.

So, here is a usable chassis to start mounting parts onto and into.