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Old October 29th 05, 02:03 AM
TRABEM
 
Posts: n/a
Default HIGH Q CAPS FOR VLF LOOP ANTENNA?

On Fri, 28 Oct 2005 17:03:55 -0700, Richard Clark
wrote:

On Fri, 28 Oct 2005 18:33:23 -0400, TRABEM wrote:

When you said "Well, this is a good opportunity to examine
that tumble down the slope to the Q = 2 (caused by the severe
loading of your proposed design)"...................did you mean
to say or to infer '(caused by the severe loading of your old (now
defunct) series resonant loop design"???


Yes
of course.



Agreed!

Just wanted to be sure I didn't miss something, so I asked.

And, your're right, I haven't formulated a replacement. I bought a 250
foot poll of cable, and it has not been cut. So, it's still in one
piece and returnable if I decide not to use it.

I was just pondering the alternative of allowing the front end to be
untuned. The receiver is susceptible to harmonics, each harmonic of
the tuned frequency is down 6 db though. Since the loop would be
resonant somewhere on HF, it is probably a bad idea to leave the front
end untuned as HF can be unpredictable. so, I am thinking I need some
front end selectivity.

Reg gave me an example of what he might do. And his antenna came out
much cheaper to build and probably easier to put up.

I'm also thinking about the method of feeding the signal to the house.
It will be around 70 feet from the house, so 90 feet of cable of some
sort is needed. I can easily go 700 feet in any of 3 directions, but
there is probably no practical need to go that far out into the woods.
Since the house is a noisy place for LF and VLF, I have to be
concerned about how I feed the antenna. I also think I'd like to have
it fed with balanced line to minimize the possibility of the feed line
acting as an antenna. If a preamp is used, I have to feed power to the
antenna as well, so I will have to wind a common mode filter to do
that job as well. So, I got a lot to think about.

Although I haven't formulated a plan for a replacement antenna, the
series loop is 99.99 percent history.

So, I am thinking about it.

I have a reading session planned for the late night here so I can
reinforce the lesson(s) you and Reg have taught me. And, will probably
work on the actual antenna design tomorrow. My caps are on order from
Mouser, should be here next week

There are a few preamp designs around the web, but none of them seems
very well thought out...although they might be well planned. It's
possible they are solidly designed, but that the authors haven't
shared all the gory details in their web presentation(s).

Thanks again. I'll keep you posted if you like......I'd appreciate
sending up a red flag if I attempt to commit additional acts of
stupidity with regard to whatever I come up with for a design.

Regards,

T