wrote:

On Nov 17, 11:36 am, Tony Giacometti wrote:


Anyone familiar enough with receiving loops to be able to assist me in
figuring out whats wrong here?

TIA

Tony


I use a lot of solenoid loops. You should not need a preamp
with a decent size loop using an R4C in most cases.
I'm wondering if you are actually tuning the loop to resonance.
Do you notice a sharp, fairly high Q peak of noise and signals
at the point where you think it is tuned?
There will be no mistake hearing this peak if it's working
correctly.
400 pf seems kind of low to me...
IE: lets take a regular solenoid loop, being calculated by
Reg Edwards loop program rjeloop3.exe..
It's fairly accurate.
I set up a one turn loop using a 20 mm wire, each side
of the loop 5 ft, or 1525mm. I set 1900kc as the
desired frequency, which is the middle of the band.
It shows a stray capacitance of appx 9 pf, and requires
appx 1350 pf to tune to 1900 kc.
See my problem with your meager 400 pf?
Of course, you using coax instead of plain wire may
be effecting the results..
I'm just not sure if you are actually tuned.
I have two solenoid loops that I often use. One is a
16 inch circle, and the other is a diamond loop
44 inches per side.
The 16 inch loop uses appx 12 turns. The larger
loop, 5 turns. I still use fairly large values of caps
to drop down low in frequency. IE: a dual 365pf BC
radio cap, with both gangs tied together is usually
needed to cover the whole BC band.
On my large loop, the various gangs of the cap
add up to a good bit more than 730 pf..
More like 1000+ pf or so.. So I get a wider tuning
range, and can switch gangs out to get small
values for the higher bands.
Anyway, when building small loops, you usually must
build the loop around the cap at hand, rather than
try to match the cap to a set number of wires.
You would think a "planned" loop would work though..
Anyway, the first thing I would need to know is
do you hear a sharp noise peak when "tuned"?
You should. And you really should have enough
signal to not need a preamp in most cases.
As an example, the loss in comparing the 5 ft
per side loop vs a 1/4 wave monopole is appx
-21 db according to the program. "1900 kc"
That should not be enough to kill you on the lower
bands.
I run both of my loops straight to my IC-706mk2g
most of the time, and need no preamp at all on
160m or BC. And I don't have to enable the radio
preamp either.
It's possible you could have a problem with the
preamp. :/
If you want to try a solenoid loop, here is the program.
http://home.comcast.net/~nm5k/Rjeloop3.exe
I put it on my server, as I forgot where the archive
of all his files are..
A simple way to make a PVC frame is here..
http://home.comcast.net/~nm5k/loop5.jpg
The loop you have should work ok once tuned, but
there seems to be a problem of some kind.
Is your feed line ground shield making a connection
to the loop on the other side of the cap from the
center pin connection?
I use separate coupling loops on mine and the coax
feeds that loop. The variable cap is connected in parallel
across the main loop connections.
I get better balance and cleaner nulls if I use a
coupling loop vs feeding directly at the cap/loop
connection. But of course, I'm not using a "shielded"
loop to aid in balance. But in the end, I get just
as clean nulls as the shielded loop.
MK


Lots of good info, thanks!

This link was the guide I used to build the loop, I am only using the 80
meter loop.

http://www.qsl.net/kc2tx/

Without the preamp I do get a noise spike when I tune the cap.
Its very noticeable also.

I would have thought that the signals I have heard would be much louder
especially using the preamp.

I have 2 different types of preamps and they both behave the same way.

For what its worth, I have never considered just plain wire for the loop.
I do use coax RG-6 - its all I can get, no RG-59 around here.
Another ham mentioned to me that using 75 ohm hardline would be the best.
None of that stuff here either.

I am beginning to think my feedline could be a problem. I can replace that
stuff rather easily.

I like your idea of a separate coupling loop.

Any idea what the loop would need to be electrically and physically?
Do I need to change my tuning cap if I change to a coupling loop?

Anyway, thanks for your input - great stuff.