Good grief, guys. Paul has the solution already. A G5RV is simply a
dipole with some magic consisting of a combination of balanced and coax
line which makes it look like 50 ohms on certain frequencies.
But Paul has a really nice balanced tuner. Now if it were me, I would
eliminate the coax, extending the open-wire feed down to the balanced
tuner. Now he will be able to tune the antenna for any frequency he
wants. Open wire or ladder line has far less loss than coax, and
because of this SWR really doesn't matter. In this case it is the SWR
between the tuner and the radio that needs to be matched, since
that is where the lossy line is.
Paul, it looks like you have the solution at hand, it allows you to
maintain your impecunious image and get the operating capabilities you
desire.
On Sep 26, 2004, at 7:53 AM, Paul Bartlett wrote:
Hi All,
Here's a proper radio question.
I'm still learning about this so apologies for any gaffs.
Questioning things is the right way to go about things. No apologies
needed, just ask! Be sure to question the answers too. Sometimes we get
bad advice, but more importantly as you research and validate the
advice, you give yourself the chance to learn why!
It works tolerably well on 40 but is hopeless on other bands.
I have a horizontal delta loop at 30 feet that works reasonably well on
all bands. It is, of course, fed by open wire line as are all my other
antennas at present.
I'm mean and impecunious so I want to use what I have to hand. I have
an
ex-military ATU built by Redifon. This takes a 50 ohm unbalanced co-ax
feed
and matches to an arbitrary dipole. BNC connector on the front, two
terminals on the back for the antennae and a further terminal for a
ground
stake.
Is it automated, or do you have knobs that need adjusting to get the
tuning?
Of course the best place for the ATU would be at the base of the
antenna but
this is impracticable so the ATU must reside in the shack.
With open-wire feed this is not necessarily bad. Open-wire or ladder
line has such low loss characteristics that you could literaly run
miles of it before you get the same loss figures as a relatively short
length of coax. The problem with Coax is that at medium to high SWR
levels you get heating of the dielectric, resulting in faulty cable and
higher losses. At 10 watts this is not much of a concern, but then at
that power level you want as much RF as possible getting to the
antenna. This makes an even stronger case for balanced feed.
My guess at the moment is that what I need to do is to connect the 50
ohm
output of theK2 into the ATU, take the ATU outputs and feed into a
balun to
drive the coax feed and then have a further balun at the base of the
G5RV to
match to the antenna.
Nah. get rid of the coax completely. Replace it with more ladder line
and you will be happy.
Just remember that the key is to experiment. If you want to try
something go for it. If it doesn't work, try something else. You might
also want to pick up some reference books to study when you aren't
operating. My favorites at the moment were written by Mr Moxon.
Hopefully they will be more available on your side of the pond than
mine. ..
- Jack Brindle, WA4FIB
------------------------------------------------------------------------
---------------------
_______________________________________________
Elecraft mailing list
Post to: Elecraft@mailman.qth.net
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com
