Hi Richard,

En Richard Clark va escriure en Wed, 15 Sep 2004 15:43:55 GMT:

On Wed, 15 Sep 2004 11:08:21 +0200, Toni
wrote:

I have a Sony radio for SWL and I have seen that if I parallel a
300 ohm resistor to the antenna input the received signal drops
considerably

This is something you could test yourself:
- Having a 50 ohm feedline, would I benefit by using a 4:1 balun
in reverse at the rcvr input?
with a before/after 300 ohm resistor application. Sure it isn't a 330
Ohm resistor? 300 is not a standard value. Also, is there any chance
this resistor is wire wound? Makes an important difference!

It probably is 330 ohm, it wrote 300 ohms just to show in what
order of value it was. It is not a wire wound, probably a bad
quality carbon resistor, but even in the firs case I think it
would only affect if used in series, not if used in paralel
(where the extra inductance would simply put a higher value Z in
parallel to the source)

Alternatively, the same phenomenon should occur if you put the
resistor in series. Be careful to maintain ground in all tests.

Yes, the series circuit would also probably work foro estimating
the input Z, but with the parallel it is easier to solder one leg
of the resistor to ground and touch/don't touch the signal wire
to compare both situations.

Finally, what are you using as an input reference? The signal from
this same 50 Ohm feedline?

Yes, I just turn to SSB where AGC seems to have much less effect
(if working at all) and "touch/don't touch" the resitor. The
effect on volume is very noticeable. Unfortunately the ICF-7600G
has no s-meter.

73's
Richard Clark, KB7QHC

Thanks,

--
Toni

"Auto" = prefijo griego que significa "no funciona"