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@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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