[AMRadio] I'm not an antenna expert


John Coleman ARS WA5BXO wa5bxo2005 at pctechref.com
Wed Jan 11 21:41:34 EST 2006


I would be curious as to what the fundamental resonance frequency is and
what the high impedance and low impedance actually is at the feed point
of the antenna without balanced line.

If the feed point at the transmitter end of the line is too low, add or
subtract some feed line.  You can also add and subtract line from the
opposite side of the antenna.  You mentioned earlier about opening up
the opposite end.  This could be a good experiment. And also consider
capacitance or inductance added where you make the cut or adding
transmission line at that point with and open or closed end going
nowhere except to a stick to hold it up off of the ground.  

It doesn't take a mathematical antenna expert to experiment You only
need some extra wire. 

Fun Stuff

John,
WA5BXO


-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of John Lawson
Sent: Wednesday, January 11, 2006 10:44 AM
To: amradio at mailman.qth.net
Cc: johnson at mailman.qth.net
Subject: [AMRadio] I'm not an antenna expert


I don't even play one on TeeVee...

   So, in advance of a lot of EZNec work (and I don't have the
experience 
with that program to derive much 'good' out of it right now) - I'd like 
to ask what may seem to be a rather obvious HF antenna question.

   Due to the usual reasons - my HF antenna is a loop suspended from my 
backyard fence - approx 430' total, closed loop, 5' off the ground, fed
by 
450 ohm ladder line back into the shack, using an Ameritron ATR-15 tuner

to match the system to my Valiant.  The tuner and transmitter are bonded

to a very heavy ground system via an 8' stake less than 3' from the
gear. 
There is no ground system under the antenna, other than that which
Nature 
provided - and with the current winter conditions, the ground is rather 
wet and conductive.

   This antenna system exhibits the following SWR:

160M - 1.3:1
  80M - 1.1:1
  40M -  +3:1
  20M -   2:1
  15M -  +3:1
  10M -  +3:1

  The tuner capacitors end up being  all-the-way-meshed on the 
'misbehaving' bands - not so on 160, 80, and 20.


   So I'll see Y'all on 3880 and just fergit the rest.   ;}


   No but seriously folks: obviously the feedpoint resistance is outside

the tuner's ability to cope with it at various frequencies.

   I'm thinking the first unscientific experiment might be to go to the 
opposite side of the loop from the feedpoint and cut it into a big 
horizontal bent dipole - mainly because that will take about 45 seconds
to 
accomplish - one of the benefits of having one's entire antenna at 
ahoulder-height.

   But I'd like to get some other opinions - I know there's an
electrical 
Pattern here from the info - and I have some other ideas based on that.

   And no, I can't put up a "real antenna" so I'm pretty much comiited
to 
making this one work as well as I can. Until I move the QTH to somewhere

with a few acres and room for Lots of Wire.


   Cheers

John  KB6SCO


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