Owen Duffy wrote:
Tony Giacometti wrote in
news:geadnZCVBcuhxdnanZ2dnUVZ_ojinZ2d@hawaiiantel. net:
Owen Duffy wrote:
Tony Giacometti wrote in
news:bMednQ1HY8JTVN7anZ2dnUVZ_gGdnZ2d@hawaiiantel. net:
...
sorry, I'm not trying to be an ass here but the diagram I have shows
3 connections to the cap. 2 for the loop and one for the center
conductor of the feedline.
Is my diagram whats confusing the issue?
Here is a diagram of what I suggested:
http://www.vk1od.net/SmallTunedSquareLoop/index.2.gif .
The variable capacitor needs to be 0-400pF. The fixed capacitor
should be at least 1000pF.
If you couldn't arrive at this circuit from the word description, and
you aren't being silly, then it questions whether your intial
construction was based on misinterpretation of the original article.
Here is an even better idea:
http://www.vk1od.net/SmallTunedSquareLoop/index.3.gif .
There is only one change here, the inner conductor is bonded to the
outer conductor at the left hand side of the shield gap. Ask yourself
why that improves things... some will suggest it just halved the loop
size, but it hasn't.
Owen
I understand now, seeing your drawing clears it up for me.
No, I wasn't being difficult or silly, I kept thinking of how I have
the unit wired and I couldn't picture in my mind (senior moment?) the
changes. Anyway now I see what you are asking me to try and I will
give this a try. Hopefully tonite after work.
I will let you know the results. Thank You.
Tony,
Keep in mind this scheme improves the impedance match (ie reduces the
mismatch "losses", but it doesn't approach an MPT match unless the fixed
capacitor is very large, and in that case bandwidth would probably be too
narrow for your use. The trick is to improve the system gain enough to be
usable without making the system unusable because it is too narrow. The
suggested fixed capacitor of 1000pF should win you enough system gain, if
it doesn't try larger values (eg 4,700pF).
I will be offline for a few days, I look forward to hearing of the
outcome.
Owen
I tried both configurations, both raised the noise level which I am thinking
must be related to the gain you said I would get, I didn't need the preamp
at all. I didn't get the nulls like I get from the original loop - that was
a mild surprise - there was only a 2-3 S unit difference between noise peak
and noise null, The original loop normally has S1-2 99% of the time when
nulled. The current loop has a difference between noise peak and noise null
of 7-9 S units. Now don't misunderstand me, but I like the low noise level.
What concerns me with the other 2 configurations is the gain makes the
noise increase so much that I am not so sure I would be able to hear the
weaker ones.
I think this project as simple as I thought it would be ...... just isn't.
What I would like to accomplish with this loop idea is to have the low noise
and the ability to null out the noise from my neighbors houses. But at the
same time have enough gain to be able to hear the weak signals. Now I don't
have preference for using the preamp or not. Whatever works is what I want
to go with.
Maybe changing the type of loop to a different style of loop would be the
way to achive what I would like to obtain.
Obviously, there is a miriad of designs and configurations. Since I need the
loop only for 75 meters and have a limited amount of real estate this cuts
the pile down to a lesser amount.
What to do...................well, maybe I should start over - why not try
a different type/style of loop. A larger loop might be better for gain but
how big before its not able to null out noise cause I can't rotate it due
to its size?
Does the loop have to be coax? can it be some other type of wire?
Your input is much appreciated.