[AMRadio] Valiant and Loop progress


John Lawson jpl15 at panix.com
Mon Dec 5 00:13:33 EST 2005



    A dozen folks have written me, privately and on the List - with advice 
about my loop antenna. The consensus is: it doesn't matter much - so I 
connected the balanced feedline to the loop with no 'spread'.

   First off - there have been a couple of 'why do you want to do *that*??" 
questions - and the answer is of course - brand new housing development, 
and CC&Rs.  Now, here in No. Nevada - folks are pretty much live and let 
live - and I do have a VHF/UHF stick up on a 35' pole - but putting up a 
'real' antenna is not a good idea...  so I have run mine around the 
perimeter of my back yard, just under the top of my 6' wooden fence. Until 
I shift QTHs - perhaps as soon as this spring - this is what I have to 
work with.  I had considered an all-band vertical, and have owned a couple 
of Butternuts in years gone by - but the Loop must do for now.

   At 100W RF output on 80M - the Loop is tunable to 1:1.1 using an 
Ameritron ATR-15 tuner.  Before I had a chance to try a Real QSO on that, 
or any other bands, the Valiant puked up Yet Another Capacitor.

   Which brings me to:  The Valiant.

   I have recieved much helpful advice and experience from many folks as I 
have been involved in electrically refurbing my Valiant I.  Of course I 
couldn't have finished the Project w/out the help I have recieved - so my 
thanks to all of you who have been so kind with your advice and 
experience!!

   And this much I have learned: just because a capacitor is a certain 
value and voltage, doesn't mean it's going to be able to stand RF 
current...  ;}

   There is a fine reason the Johnson engineers used the capacitor configs 
they did in the pi-net and coupling circuits - it's the "divide and 
conquer" strategy.  Now, I imagine a few folks are rolling their eyes and 
saying things on the order of "No shit, Sherlock!" - but I have next to no 
RF repair or design experience - most of my work professionally and 
privately has been in audio and music and film systems...  even hi-power 
PA-amp output coupling caps don't have to stand the gaff that occurs in RF 
work.

   And even though I rebuilt the bandswitch stacks twice - I didn't use the 
topology that existed - two 'series pairs' in parallel - mainly due to not 
having the right units and to getting 4 350pF micas that are marked on the 
package "350" - the color code is '350' - but they're 560pF every one of 
'em.  No wonder they were surplused!  Imagine the hours of Fun that 
caused...  now I just check 'em no matter what.


   So the Valiant is putting out 100 - 130 watts into my load or antenna on 
all bands - I put it back in it's cabinet (mistake..) and cabled it up. 
Having previously set the mod bias, I tuned 'er up, opened the Audio pot, 
gave a couple of whistles and the 160/80 M capacitor stack "deviated from 
spec" in a rather spectacular and stinky fashion.  O well - at least I 
understand completely what needs to be done - and about $60 worth of the 
correct RF units will be delivered to me on Tuesday.  Wouldn't have been 
so much, but I bought heavier than required and also spares, just in 
case....


    Thats where it lies as of this Weekend - if I have paid my dues 
sufficiently I oughta be on the air by the weekend - and I'll be happy, 
until I set my fence on fire - snowing or not.   ;}



   Cheers

John  KB6SCO



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