[AMRadio] Valiant and Loop progress


Jim Candela jcandela at prodigy.net
Mon Dec 5 07:34:41 EST 2005



John,

   I wonder what your loop looks like at the feed
point to your tuner. Do you have an impedance
analyzer? Just curious. As for me, I like to steel
ideas from those that have already been there, and
done that. Once such example is at:

http://www.sirinet.net/~mars/hor_loop.pdf

Since you are modeling this antenna, consider the
counterpoise as described in the PDF file. Maybe this
can be attached to the bottom of your fence with
periodic 4' ground rods every 30' or so. I'd be
curious if this helps either with Eznac, or actual
usage with your loop.

Also since you have a 35 foot tower up already,
consider that as a means to support say a 3/8 wave
inverted L for 80 meters (3/4 wave on 40) with a
single wire counterpoise in your fence. With the
current maxima up high (80m), and dual polarization,
good all around performance is possible. This would be
a 30' vertical, and 60' horizontal sloper down to your
fence. This wire will be nearly invisible if you use a
small gauge wire (maybe 22 awg).

Good luck with the "taming of the shrew (Valiant)".

Regards,
Jim

--- John Lawson <jpl15 at panix.com> wrote:

> 
> 
>     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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