[AMRadio] I'm not an antenna expert


John Lawson jpl15 at panix.com
Wed Jan 11 13:05:59 EST 2006



On Wed, 11 Jan 2006, W5OMR/Geoff wrote:

> There's no law that says you have to run full power output, to tune SWR on an 
> impedance matching device...


    Ooops - I should have clarified that  - I do not run full power to play 
with the tuning - actually I run the minimum I can get the Valiant to put 
out, by decreasing the coupling to as little as possible, and tuning the 
transmitter up at that output - usually 20-30 watts. THEN I load 'er up to 
full blast.


>
> I'd just as soon use a solid state rig, that has SWR protection in it... 
> slowly adjust the impedance matching device, until you get full output of the 
> ricebox, and minimum standing wave ratio.  Then, DON'T TOUCH IT!  Just switch 
> rigs, and tune the transmitter to that setting.  it's resonant.

    Except that I don't seem to be able to achieve much in the way of 
'resonance' on the affected bands - the tuner settings get very 
'squirrely' and of course the transmitter tuning goes wildly off as those 
adjustments are made - as opposed to the bands where the antenna/feedline 
is "happy" - then it's stable, and an easy matter to arrive at a logical 
setting for the system.

   One of the drawbacks to the pseudo-NVIS arrangment is that it is like a 
'searchlight' directed straight up to a cloud-deck in the sky - the light 
is diffused back down, as opposed to a more directional distribution of 
radiated flux - so I really need to have an electrically efficient antenna 
system as I can, give my particular constraints.



   But the question I still have is - what do you think of modifying the 
Loop into a dipole - I'm going to try it anyway, just for the halibut - 
but I have also thought of replacing the ladder-line with coax and a balun 
at the feed point - dunno yet.


    Cheers

John   KB6SCO




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