Remote tuning a quad reflector
Dr. Duncan Clark
I've just rewired my 4ele quad on 17-10m. Previously I used a stub for
tuning the reflector and had set it up at roughly the book value. This
time I decided to capacitively tune the reflector for best F/B then
replace the variable capacitor with a fixed RG58 capacitor stub. I
already use RG58 capacitors for the gamma match.
The problem is that it has proved darned difficult to adjust for best
F/B when the tower is tilted over. At the low level it is not possible
to really see much F/B. When the quad at 35ft I tried to use a variable
capacitor coupled to a motor and can tune it for a F/B but the motor I
have is too fast, the tuning is very sharp and it is mechanically
unsound (weight distorts the loop etc.).
So am I right in thinking that if I use an electrical half wavelength of
a balanced line from the reflector to a variable capacitor at ground
level the optimum value I find at ground level will mimic the capacitor
I need at the loop itself? If so what sort of balanced line do I use 300
ohm, 75 ohm etc. ?
Finally I'm not worried about losing the 0.5dB or so of gain by tuning
for best F/B. The F/B will help me hear the weak DX that Europe or the
US off the back of the beam obscures.
Many thanks
Duncan
G4ELJ
--
The problem with being on the cutting edge is that you occasionally get
sliced from time to time....
mike....@ziplog.com
>Hi Folks,
>
>The problem is that it has proved darned difficult to adjust for best
>F/B when the tower is tilted over. At the low level it is not possible
>to really see much F/B. When the quad at 35ft I tried to use a variable
>capacitor coupled to a motor and can tune it for a F/B but the motor I
>have is too fast, the tuning is very sharp and it is mechanically
>unsound (weight distorts the loop etc.).
>Duncan
>G4ELJ
Have you ever tried turning the quad straight up when you do the stub
adjustment(s)?
I've never used the trick, but, so said, you can get a far better
adjustment-on-the-ground to as-in-the-air deal, by turning a beam to
point straight up while at ground level.
Others may refute this.. it is just what I've heard from local hams whom
have used this trick..
I never asked how they got to monitor the F/B. I suppose they are using
a monitor point upstairs on some other tower as a reference. Maybe they
even suspend it above the thing and read the F/S needle with a pair of
binocs. I often use the binocs stunt when fooling with field
measurements on the 4 square tuning on low bands ... to read the needle
in the middle of the array or away from it as needed!
As a strictly low-band op on 40 and 80, I doubt I'll ever be able to
afford to try this stunt with a rotatable array on any tilt over tower
though! :)
Just a thought.
//-----------------------------
Mike....@ziplog.com
Mike....@f3000.n117.z1.fidonet.org
ken clark
on to a sure way that works every time [for me] I cut a quarter wavelength
of TV 72ohm coax cable and attach it to the particular full wave driven
element, then from the quarter wave down to the radio, I use 75 twin lead I
buy from Henry Westlake [details in the UK amateur Radio RadComic magazine]
I find it works like a touch of magic.. You can attach all the different
lengths
of 72 coax leads to the twin feeder and then down to the Transceiver... Good
luck de Ken
Dr. Duncan Clark <Dun...@nospam.demon.co.uk> wrote in message
news:3vwVqAAgL$z3E...@genesys.demon.co.uk...
> Hi Folks,
>
> I've just rewired my 4ele quad on 17-10m. Previously I used a stub for
> tuning the reflector and had set it up at roughly the book value. This
> time I decided to capacitively tune the reflector for best F/B then
> replace the variable capacitor with a fixed RG58 capacitor stub. I
> already use RG58 capacitors for the gamma match.
>
Dr. Duncan Clark
writes
>Have you ever tried turning the quad straight up when you do the stub
>adjustment(s)?
I've seen that suggested for adjusting gamma matches on the driven
element but it won't help for optimising F/B.
Dr. Duncan Clark
freeserve.co.uk> writes
>I've built many 3 and 4 element full size HF quads and have finally locked
>on to a sure way that works every time [for me] I cut a quarter wavelength
>of TV 72ohm coax cable and attach it to the particular full wave driven
>element, then from the quarter wave down to the radio, I use 75 twin lead I
>buy from Henry Westlake [details in the UK amateur Radio RadComic magazine]
> I find it works like a touch of magic.. You can attach all the different
>lengths
>of 72 coax leads to the twin feeder and then down to the Transceiver... Good
>luck de Ken
This looks like quarter wave matching for the driven elements but that
isn't my problem.
The problem is finding some way of remotely adjusting the tuning of the
reflectors with variable capacitors to maximise the front to back ratio
with the quad boom at say 30ft on the tower. Once I know the capacitor
value, it will be replaced at the reflector element with a fixed
capacitor etc.
mike....@ziplog.com
>In article <rsvu7r...@corp.supernews.com>, mike....@ziplog.com
>writes
>>Have you ever tried turning the quad straight up when you do the stub
>>adjustment(s)?
>
>I've seen that suggested for adjusting gamma matches on the driven
>element but it won't help for optimising F/B.
>
>G4ELJ
>
>--
>The problem with being on the cutting edge is that you occasionally get
>sliced from time to time....
>
OK .. so noted .. then the old way of placing a remote field strength
meter a few waves away and adjusting at height is still the only way to
optimize it on site.. I guess.
Reminds me of the visit I made to K3TUP's farm. I'd noted that the F/B
on his 7 Mhz yagi was supberb down in Texas. I was shown about the site
by a small slight man, as John wasn't there. As we got to the 7 Mhz
antenna, I remarked to this small slight form below my 6'4", "My that
array has a wonderful F/B ration, I wonder how he does it?"
Answer, "Me."
Puzzled, I retorted, "I don't understand!"
Answer, "He pays me to do it. I crawl out on the boom and adjust it."
No further comment.
--> Sleep well; OS2's still awake! ;)
Mike - W5WQN
Mike....@ziplog.com
Mike....@f3000.n117.z1.fidonet.org
W6RCecilA
> OK .. so noted .. then the old way of placing a remote field strength
> meter a few waves away and adjusting at height is still the only way to
> optimize it on site.. I guess.
Someone once said that works pretty well for vertically polarization
but not well for horizontal polarization.
--
73, Cecil, W6RCA http://www.bigfoot.com/~w6rca
mike....@ziplog.com
OK, so noted.. Then what's the concensus on how far away we have to be
from a horizontal array to take a meaningful look at F/B?
And, whilst we're at it, what's the thought on how high the sensor unit
has to be to deliver meaningful information?
Obviously, if we get into the business of trying to optimize an array
for the average path, we'll likely never get there at skip range, will
we? Grin, but a sincere thought as well.
--> Sleep well; OS2's still awake! ;)
Mike - W5WQN
Mike....@ziplog.com
Mike....@f3001.n117.z1.fidonet.org