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Author Topic: Using the RigExpert AA-30.ZERO to fix my beverage antenna  (Read 302 times)

Offline ChrisSmolinski

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Using the RigExpert AA-30.ZERO to fix my beverage antenna
« on: January 08, 2019, 1727 UTC »
Obligatory link to the RigExpert AA-30.ZERO: https://www.amazon.com/gp/product/B077B9D18K/ref=ppx_yo_dt_b_detailpage_o00_s01?tag=blackcatsyste-20
Also see my previous post for some background: https://www.hfunderground.com/board/index.php/topic,49903.0.html

My 500 ft northeast beverage antenna has been performing poorly for the last few months, but I haven't had the chance until just now to address it. I've been using the 300 ft south beverage in place of it for DGPS recordings.  The general symptoms are low signal levels on the LW and MW bands, HF performance was difficult to judge, perhaps worse than before, but not as bad as LW/MW.

I first ran some measurements on the south beverage as a baseline, since it generally performs well. Below are the plots of impedance over 0-30 MHz, as well as the TDR (Time domain reflectometer) plot:





The feedline is a little over 200 ft long, made of several lengths of coax. There's a little bump at about 120 ft that should probably be addressed in the future. You can see a bump at the end of the antenna as well, about 530 ft, the termination is not quite right, most likely. It's also possible the taps on the Squid matching transformer could be better selected. Always something to fix/optimize with antennas.  ;D

Next the plots for the 500 ft NE beverage:





Not quite as pretty looking.  My next step was to analyze the coax runs to the beverage feedpoint, to determine the length down the run for each point a new cable begins. For this antenna (as well as all my antennas) there's about a 22 or 23 ft run of coax from my patch board down the side of the house, to the coax grounding blocks. Then this run goes underground for around 100 ft in conduit, then comes up above ground again and connects to the Squid matching transformer and antenna. That end of the coax is *not* grounded (although it is for my other coax runs and maybe something I want to address. But it would need it's own ground rod, as the secondary of the Squid (antenna side) is grounded).

First just the run down the side of the house, the end of the coax was disconnected from the grounding block:



Then including the run to the Squid, but the Squid was disconnected:



So a total underground length of about 110 ft which sounds right, 100 ft underground, and some extra cable at each end of the run.

If you go back to the TDR plot for the 500 ft beverage, there is a reflection at about 280 ft or about 140 ft from the Squid along the wire. I walked along the wire and sure enough at about 130 feet (based on pacing the length) there was an open - location where the wire had broken from a tree falling on it, the wire ends were twisted together to hold them and then a connection with a wire nut, but the connection had opened. I repaired it.

I then ran another set of plots:





That addressed the reflection and the overall impedance plot looks more flat. You can still see a large reflection at the feedpoint, as well as the far end of the antenna. The Squid was set to use the green/white wires for 703 ohms, which is most likely far too high, I recall playing around with the taps after the antenna stopped working well, but did not have the time (or tools it seems) to do a proper job,

So I changed the taps to yellow/white and 378 ohm with these results:





A bit of an improvement, next I switched to to the black/yellow pair and 253 ohms:





Slightly better still. Perhaps I overshot a bit, but there's no intermediate set of taps to use.

While making these changes I also noted signal strengths of several MW stations (shortwave stations signal levels vary too much to be useful here, but I included CFRX 6070 as it is more stable than most):

Initial readings: 1280 -33 dBm, 1090 -49 dBm, 1470 -44 dBm, 6070 -85 dBm
Fixed open in wire: 1280 -31 dBm, 1090 -42 dBm, 1470 -41 dBm, 6070 -83 dBm
Squid now yellow/white 378 ohms.  1280 -29 dBm, 1090 -41 dBm, 1470 -41 dBm, 6070 -73 dBm
Squid now black/yellow 253 ohms.  1280 -29 dBm, 1090 -42 dBm, 1470 -41 dBm, 6070 -66 dBm

I also tried it on the DGPS band (305 kHz) and while local noon is not the best time for propagation on LW/MW, I did notice stronger signals vs the 300 ft south beverage. Previously the south beverage was producing much stronger signals.

So I think it's fixed!  Next step would be to improve the termination resistors of both beverages.
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 270 ft west-south-west beverage / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop

Offline Josh

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Re: Using the RigExpert AA-30.ZERO to fix my beverage antenna
« Reply #1 on: January 08, 2019, 1738 UTC »
Something else you might try is to use a variable pot at the terminated end to fine tune the response, might help with directivity and so on. Then after finding the best termination, replace the pot with a suitable fixed resistance, might want to go with even a 5 watt part as lightning sometimes pops bev terminations.
Conveniently located near Vincennes Indiana.

Offline ChrisSmolinski

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Re: Using the RigExpert AA-30.ZERO to fix my beverage antenna
« Reply #2 on: January 08, 2019, 1745 UTC »
Something else you might try is to use a variable pot at the terminated end to fine tune the response, might help with directivity and so on. Then after finding the best termination, replace the pot with a suitable fixed resistance, might want to go with even a 5 watt part as lightning sometimes pops bev terminations.

Yes, using a pot to find the ideal termination is on my to-do list. I need to get the RigExpert mounting in an enclosure so I can take it outside with a laptop (right now it is on the desktop Mac, so it's a hassle to run outside to tweak something and note the change, let alone run outside and then through 500 ft of brush in the woods).
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 270 ft west-south-west beverage / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop