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Field Day 2010 – Preparations Part 2


Field Day 2010 – Preparations Part 2

We first tried using the Receiver Noise Bridge to check the antenna operation, but could not get reasonable nulls an any band.  That was our first sign of trouble.  After hooking up the radio and the bias-T connections, we found the operation of the vertical pretty dismal on all bands.  We hauled out a battery to energize the band switching arrangement as needed while troubleshooting.


After fields day operations had started, we continued to debug the problem, while simultaneously doing some operating with the 135′ doublet (which worked great, as always!)

We found some wiring errors, and fixed them.  Our expectations were high, but again, the antenna just did not perform well.


We decided to go back to basics and check with the simplest configuration.  We took the noise bridge out and measured the resonant frequency of the antenna with no matching network.  At 5.34 mhz, we found a null at 20 ohms resistive and 0 ohms reactive.  Plugging in the formula for a quarter wave antenna, we found:

234/length = Freq
234/43 = 5.44 Mhz — that’s pretty close to expectations.  So we knew the basic vertical was good.

Next, we removed the 4:1 Unun from the matching network and tested it to make certain the wires were connected in the correct manner to give us the required 4:1 stepdown ratio.  We connected a resistor between ground and output side of the Unun.  Again using the Noise Bridge, we were able to confirm that the impedance read at the input was 1/4 of the impedance at the output.  So we knew that the Unun was good, and connected correctly.

At this point, we double-checked the wiring through the relays of the matching network.  We believe they are all correct.  That left the Bias-T arrangement on either end to worry about.

We wired the Unun in line with the antenna at its base, and connected the radio up to the other end of the coax again, through the bias-T box at the radio end.  This configuration worked very well on all bands above 80 meters.  We got good matches, and very good performance with this arrangement (minus the two lower bands, of course).  So this confirmed that the Unun and Bias-T in the shack were working well.

That leaves us with the Bias-T network in the matching box as the likely culprit.  Since the same choke coil was used on both ends of the bias-T, the only real difference is the two 5-kv mica capacitors that I used in the matching network as blocking capacitors.  I suspect these are the problem.

For now, we left the Unun wired haphazardly in place, minus the rest of the low band matching network.  That is how we used the antenna through the rest of Field Day.

Somewhere along the line, we added the ground rods at the antenna base, and at the shack end.  We don’t know if the helped with the antenna operation, but they did help with the RF feedback that we experienced last year on 40 meters.


Field Day Operations begin on next post…

Migrated Comments:

7 Responses to “Field Day 2010 – Preparations Part 2”

  1. Don Rudolph Says:

    I built this same matching network.
    You can see my build on AD5X’s site.
    I am W9BHI.
    Not in the picture is a custom made ferrite loaded rf choke for the bias tees.
    It will handle 1 amp of current and is about 325uHy.
    Very good for 160.
    I had no problem setting the resonance and impedance for my ZeroFive 43 foot vertical.
    You just can’t set it to certain frequencies because of the physical placement of the inductor.(you can’t get to the side next to the case or bottom.)
    The matching network has no trouble with 1Kw on 80 meters but has some arcing on 160 above 400 watts.
    I still have to go out at night sometime and see here the arcing is coming from.
    I presently have fifty 50 foot long ground radials down 2 inches.
    Your build looks great also.
    Thanks for reading this.
    Don W9BHI

  2. Randy Says:

    Hi Don. Wow, great to hear from you. Your very clean build is what inspired me to build this. I copied your layout almost exactly. I had some problems tuning on ALL bands when this was installed with the homebrew 43′ vertical.
    After removing the 4:1 balun from the box and installing it directly connected to the antenna, it loaded up fine on 60 – 6 meters. So after checking the layout for a third time, we decided that the problem is either in the surplus blocking caps or the Radio Shack 1mh rf chokes. I haven’t had a chance to put it back together to do more troubleshooting, but should be able to do some more checking this fall.
    Thanks for your comments. 73 de Randy WB0SMX

  3. Don Rudolph Says:

    Hello Randy,
    I might be missing something but I was looking closely at the pictures of your matching unit and is noticed that the wiring
    is not connected like the schematic.
    In fact it looks like there are some missing connections.
    This might be why the unit is not working properly.
    If you would like,I can send you a physical layout of the wiring.
    I’m not trying to be critical,I’m just trying to be helpful.
    Don W9BHI

  4. Randy Says:

    No Don, you’re not missing anything. We discovered the same thing while we were troubleshooting it at Field Day. I believe I fixed the wiring errors, but still had no luck. Then we removed the Unun and used it by itself for 40 – 6 meters for the rest of Field Day.

    I never took a picture after the wiring errors were fixed, and haven’t gotten back to the project yet. But next time I have it on the bench, I’ll take another picture and post it here.

    My plan at this point is to put it on the bench and install the Unun again. Then I will hook a variety of resistors on the output, and check the impedance with my noise bridge with each one. I’ll work through getting it to work on 60 – 10 meters first, then apply power to the relays to check 80 and 160 meters. I just didn’t have time to do a checkout before Field Day.

    Anyway, if you want to send me a physical wiring diagram, I’m sure it will help me the confirm whether I am correct or not. You can just send it to my callsign at if you don’t have my normal email address.
    Thanks, and 73… de Randy WB0SMX

  5. 43′ Vertical Final Tuning Says:

    […] Field Day 2010  Preparations Part 2 […]

  6. T-Bias interface Says:

    […] Field Day 2010  Preparations Part 2 […]

  7. 43′ Vertical – Part 4 Says:

    […] Field Day 2010  Preparations Part 2 […]


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