I believe my receiver is microvolt sensitive and that the loop will
deliver a relatively good signal to the receiver even though the loop
isn't terribly efficient. If I build selectivity into the front end of
the receiver, do I really need high Q (200)??

I think the answer is NO.....

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).

The correlative to this is, how much selectivity do you need in a
field where stateside VLF is relatively rare? Further, by the action
of the strong filtering that usual attends the "I" and "Q" channel
processing, you could easily repair any shortfall.

However, back to that Q = 2. That still offers respectable (not
fantastic) selectivity against signals out at the bottom of the AM
band which is 10f (one decade) away.



OK, I'm not sure how we got back to the Q=2 scenario. I think my
proposed design is the old series tuned loop, which I have firmly
rejected.

With no tuning in the front end, the Q of the receiver would approach
1.......Yes, I understand that.

I understand the answer you gave initially, which was 'I think the
answer is NO....'.

I understand the degree of protection against signals in the bottom of
the bc band.

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"???

All is in agreement above EXCEPT in not sure why the reference to the
old design.

Thanks again.

T

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.

You have asked a number of questions outside of this old (now
defunct) design, but you haven't, as far as I can tell, formalized a
replacement.

The ancillary point that I've made is that the original could work.
However, you've never stated any operating specification to test that
against. I've offered that all components need to be scrutinized in
the face of your goal. We saw where that lead.

You've only specified your desire for High Q capacitors (properly, low
D capacitors). I offered that ESRs vary widely and could easily
derail your goal. The presence of an ESR equal to the 0.06 Ohm of the
loop is very well within being guaranteed. It still is. Reg
dismissed this as inconsequential. So be it, but being that it is
easily remedied through selection, then why toss away half your Q to
casual indifference?

What Reg actually meant, and he has a hard time with that given he can
often be found on both sides of an argument, is that such loss may not
matter. There I agree, but this does not advance the topic of High Q
Caps for VLF Loop Antenna when they can be obtained.

73's
Richard Clark, KB7QHC

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