Tony Giacometti wrote in
news:A5SdnQdv8vz466LanZ2dnUVZ_t2inZ2d@hawaiiantel. net:

Owen Duffy wrote:

Tony Giacometti wrote in
news:suednRqSYJd58aLanZ2dnUVZ_uDinZ2d@hawaiiantel. net:

also, if these loops don't work then why do these designs exist?

Tony,

A few questions:

1. With a 50 load on the preamp input, when tuned to a quiet spot in
the band, RF gain full, preamps on, telephony bandwidth, does the S
meter deflect at all?


not noticeable



2. If no s meter deflection, note the receiver audio output voltage.

125mv


3. With the loop connected on the preamp input, when tuned to a quiet
spot in the band, RF gain full, preamps on, telephony bandwidth, does
the S meter deflect at all?


not noticeable



4. If no s meter deflection, note the receiver audio output voltage.

150mv


5. What is the ratio of the voltage at 4 to the voltage at 3? If it
is more than about 3:1, you have achieved nearly as good a S/N ratio
as is possible.

So, the ratio is 1.2.

Two thirds (actually 1/1.2^2) of your total noise is from the receiver
internal noise. That is not a good situation, S/N on signals will be
degraded by relatively excessive contribution from the receiver, actually
caused by inadequate antenna gain.

Expected ambient noise level from a lossless antenna in 2kHz at 3.6MHz
should be around -82.9+33dBm or -49.9dBm. The 80m loop gain is about -
47dBi, so expected receive level would be -97dBm which is some 40dB above
your receiver noise floor.

Things aren't working like they should, so you need to localise the
problem.

I have no idea of the sensitivity or bandwidth of your receiver, but a
good (not outstanding, just good) (bare) receiver with a noise floor of -
130dBm should see a large increase in noise moving from dummy load to the
loop. (Ambient at -97dBm would be equivalent to S5 if your S meter was
accurate.)

Just for verification, I performed the same test you did, but with a
600mm a side untuned loop and an ICR20 receiver, and I got a 10 fold
increase in noise from the loop compared to the dummy load. Your loop is
larger and tuned, so it should be a 10dB more sensitive.

BTW, I didn't state it, but those noise measurements MUST be made in SSB
mode.

Owen