[Elecraft] Antenna matching

[Jack Brindle]

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
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