[UK-CONTEST] Inverted V help

[G3SJJ]

John, a couple of things to check :

1 What length of wire did you cut? 65ft per leg would be a good start. The
90 deg bend may effectively reduce the electrical length.

2 - You ought to see some kind of dip in SWR as you swing the MFJ across say
3.0 to 5.0 MHz. If you can find that you should be able to tell if the
antenna is too long or too short. Once you have found the point of minimum
swr you can then check its impedance to see what matching you might need.

The feed impedance will vary from say 15 to 150 ohms depending on the
variables you have stated, so you ought to be able to see an SWR of less
than 3:1, I would have thought. An internal matching would then cope with
this to give you the full rated power of the radio.

73 Chris G3SJJ


-----Original Message-----
From: uk-contest-bounces at contesting.com
[mailto:uk-contest-bounces at contesting.com]On Behalf Of john lemay
Sent: Tuesday, February 18, 2003 12:34 PM
To: uk-contest at contesting.com
Subject: [UK-CONTEST] Inverted V help


Hello all

In one of my very rare forays below 50MHz, I decided to try an inverted V
for 80m. It would use my modest Versatower for the central support, and the
ends would end up where-ever.

I knew it would be a compromise :-

I probably could not get enough height
I probably could not get the right apex angle
One end in particular would need to be close to the house and bent through
90 degrees
The other end would be in trees.

Even so, I thought that at least I would get an antenna that would be within
the limits of a typical internal ATU on my rig.

Wrong !

It received quite well, and nicely quiet compared to my HF6V. But the match,
checked out on the MFJ analyser was about 10 to 1. I have done the obvious
tests, such as continuity of wire, continuity through balun etc.

Today, I have taken down the 1:1 balun (Watson) and checked it out with a
resistor across the terminals. Interesting: - Using a 50ohm resistor which
is suitable for low frequency rf use, the match through the balun at 3.0MHz
is about 2 to 1. It gets worse going lf, and improves to 1.2 to 1 by about
10MHz. Then not surprisingly above 40MHz the match gets lots worse.

What I need help in deciding, is whether my abysmal match with something
resembling an inverted V is due to too many antenna compromises or is it due
to a dodgy balun ? (Preferably without too many more sessions freezing in
the garden, or hauling the tower up and down).

Regards

John G4ZTR




_______________________________________________
UK-Contest mailing list
UK-Contest at contesting.com
http://lists.contesting.com/mailman/listinfo/uk-contest