Tuning one element as you describe is for preliminary adjustment only. When
all elements are in place you tune it as a system.
I assume you are feeding the 4 square with a phasing box such as Comtek.
The way I tuned my 4 squares was to measure the power loss into the dummy
load. The frequency where the minimum power goes into the dummy load is the
system resonant frequency for that direction. If all elements are equal
(they seldom are) the resonant frequency will come out the same for all
directions. But when it doesn't you just allow a little Arizona windage for
tuning, and make sure all elements are as physically identical as possible.
With buried radials I found the system was flat DC to light. When I went to
elevated radials I found the system tuned very sharply, which to me
indicates the RF is going into the ether rather than into the ground losses.
I do not use shunt coils at the feed point on my elements as I believe they
would introduce phase shift and screw up the pattern. If you are talking
about a parasitic array you should certainly remove the shunt coils as they
will screw up the inductance of the open feed line.
Your smileage may vary.
de Paul, W8AEF
ZF2TA FO8DX FO0PLA 8Q7AA XZ0A
----- Original Message -----
From: "Dana Roode" <email@example.com>
To: "TowerTalk" <firstname.lastname@example.org>
Sent: Monday, August 25, 2003 12:40 AM
Subject: [TowerTalk] Tuning a four square
> Towertalkans -
> I am retuning my 40m 4 square - for some reason it started tuning high in
> the band after I found a faulty dummy load (gory details below). The
> procedure is to tune a single vertical to about 100khz lower then the
> frequency you are after, then duplicate the resulting length in the other
> identical verticals.
> Question: Should I tune the first vertical fed with the quarter-wave 75
> coax used in the array, or with a random length 50 ohm coax? For some
> reason my vertical tunes to 7.1 mhz with the 50 ohm random length coax,
> to 6.5 and 7.4 mhz (double dip!) when fed with the quarter-wave length of
> ohm. Does this make sense?
> Dana, K6NR
> I've had the array working for quite sometime but when I went to use it
> weekend the SWR was bad (2:1+) except at the top end of 40, about 7.290.
> don't recall what the SWR was previously, but it was under 2:1 on most of
> the band. I originally tuned it for 7050 as Im a CW op. I did not check
> the power dumped to the dummy load this weekend, but when I first setup
> array it was very low across the 40m band.
> I went out to check on the array and found the dummy load, a very old one,
> was intermittently open. I replaced it with a good dummy, and the SWR was
> better, but still skewed high. I checked it with an antenna analyzer and
> saw two SWR dips - one above 7.3 and a deeper one below 7.0. Seemed like
> the verticals were adjusted too low in frequency.
> I decided to verify the tuning of the verticals and took all but one down.
> It had the lowest SWR at 6.950, which was I what I recalled tuning it to
> (your manual says to tune individual elements 100khz lower than the
> frequency). However, when I checked the 1:1 frequency at the end of
> feedline to the shack (about 200' long) it was lower, 6.820.
> I shortened the vertical to resonate at 7.080 when measured at its base,
> which was 6.950 at the end of the feedline. I reset all the other
> to the same length and put it all back together.
> Now the system has 2 1:1 SWR dips when measured at the end of the
> 6.589 and 7.475. The array has about a 2:1 SWR across most of the 40m
> I feed the bases of the vertical through a base tuning coils to keep the
> elements at ground potential.
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
> TowerTalk mailing list
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
TowerTalk mailing list