[TowerTalk] Tuning a 20m 4-Square Array - detuning other verticals?

Wed May 13 16:28:09 EDT 2015

OK all, so I ran a quick power dump test with only 100w and my son at the controls in the shack; me at the wattmeter at the array 160-180' away.
At 100w, at 14.000MHz, we saw about 500mW (1/2 a watt) into the dummy load....it steadily went all the way up to maybe 1.5-2w at the very top of 20m (14.350)

Strangely enough, at the radio, the best SWR is at 14.350 (just about 1.1:1) and the worst is at 14.000MHz (1.8:1 or 2.1:1) so I don't really know what that tells me.
(completely opposite to what I would've bet on !)...I have to think SWR curves as viewed through a 4square are odd. On my analyzer I see many dips from 10-20MHz or so.  Vy odd looking.

Presumably at a kW I would see 10-x this amount of power dumped, yes? (I am assuming a max of 20w @ 14.350MHz if running 1kW on 20m SSB) (am I correct?)

Three directions dumped about the same amount of power, but beaming SW dumped about 1/2 of everything the other 3 directions had.  Still all vy low numbers.

Is there more to do or am I ok? Throw me some data ! (hi)

Mike VE9AA

Mike, Coreen & Corey
Keswick Ridge, NB

-----Original Message-----
From: David Robbins [mailto:k1ttt at verizon.net] 
Sent: May 13, 2015 8:39 AM
To: ve9aa at nbnet.nb.ca
Cc: towertalk at contesting.com
Subject: Re: [TowerTalk] Tuning a 20m 4-Square Array - detuning other verticals?

for a comtek box the correct sequence of setup is:
1. setup ONE vertical with 50 ohm feedline(any length), adjust for minimum swr at the frequency of interest 2. duplicate the one vertical to make the other 3 3. connect the 4 verticals to the box with 1/4 wave of 75 ohm line 4. enjoy.

only having 2 radials will degrade performance unless you are on a salt marsh or beach, but f/b should still be good which is why it would be quieter than the single vertical.  do not try to tune the verticals after all 4 are in place, they do interact and will not respond as you would expect... with 20m ones it would probably be easy enough to lay the others down on the ground to check the tuning of each one separately, but the key is you tune them with 50 ohm cable, but connect to the comtek box with 75 ohm 1/4 wave lines.

May 12, 2015 08:53:16 PM, ve9aa at nbnet.nb.ca wrote:

OK, so I just put up a 20m 4-square using a COMTEK box. So far, I'm a fairly happy camper. First real gain antenna on 20m in 11 yrs. (gain being a subjective term here)

Installed the first skinny vertical. 2 raised radials @ 90 degrees to one another. The vert's about 2' off the ground and so are the 2 radials. SWR curve looked really awesome once I tweaked the length of the radials and vertical element. 

I was in heaven.

Unfortunately the way it's arranged, each vert only has 2 raised radials and if you were looking at it from overhead, you would only see a square and a vertical at each corner. The raised radials for each vertical are adjacent to one another. I tried 1 radial each, but SWR was high no matter how much tweaking I did or what angle(s) I had it at. I cannot do ground radials, nor radials extending out past the 4 lines of the 17.5'x17.5' box. I could do one more (very bent) radial towards the center of the box, but that's it. I don't think it would help. I digress.

I put up 3 more verts and built them as close as I could to the original.
Carbon copies.

Let's not talk SWR curves, but how to go back and retweak all the verticals independantly? What I am seeing in the shack baffles me. *(must be the hybrid cct in the external box doing weird things to my SWR analyzer) I am going round and round.

When I was doing the 2nd vertical, I tried shorting the center to the braid on the original but in all honesty I don't think it made much difference.

The array is "working" (F/B great, F/S is "MEH", but I am not really seeing any gain in the favored direction that I can quantify over another vertical 50-60' away. (HF9V). It IS much quieter and that's really nice and I do hear W1's on backscatter (vy weakly) that I cannot hear on the HF9V(QRN) but I see no real difference on the S-meter on signals above the S1-QRNy noise floor. I am looking for 3dB (or that's my hope) Some SSB signals sound different on the 4-SQ compared to the HF9V, so I am presuming a different incoming angle or possible a dB or two of gain, but nothing I can measure.
The quietness is comforting, due to some noise to the NW and other small sources in other directions.

I have a ton of questions and probably could give lots more details on how I have this thing built and why only 2 raised radials etc., but if I could nail down detuning the "other 3", I think I would be on the right road. 

Bottom line, what's the best way, short of taking down the "other 3"
verticals to detune them? (could I clip a 4' wire onto the bottom of them or
something?)

I have not yet measured dumped power into the dummy load. Antennas are ~150' from the house and it's been raining here, so quick dashes outside only...just got control cable working at suppertime. I can enlist my son as a helper to do some key down sessions once the wx clears this weekend. I am told the frequency at which I see the least power dump is where my array is most resonant and has the most gain at ?

TKS

Mike VE9AA

Mike, Coreen & Corey

Keswick Ridge, NB

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