|[AMRadio] Cable splitters for receivers|
k4kyv at charter.net
Sun Jan 12 14:04:18 EST 2014
> From: Bill Guyger <bguyger at yahoo.com>
> We'll, the most obvious point is that the splitters are 75 Ohm. If you
> can take the impedance bump and not not mind the mis-match you still
> have to take into account Mr. Kirchoff saying you loose part of the
> original signal every time you add another branch off the feed line.
> Bill AD5OL
The bump in impedance from 50 to 75 ohms is not going to make a
discernable difference in receiving. Impedance matching is not critical
with a receiver like it is with a transmitter. The worse thing that
would happen would be a fraction of a dB of signal loss. Besides, very
few receivers present a perfect 50-ohm non-reactive load to the incoming
transmission line. As I recall, the 75A-4 manual says its input
impedance is something like 150 ohms. Not sure of the exact figure, but
far from 50 ohms. I use an attenuator on mine, because my transmitting
antenna delivers too much signal and I could use a little attenuation
to avoid cross modulation.
The splitter will reduce signal levels at both receivers. Theoretically
it should be at least 3 dB, if the signal is divided equally between the
two receivers. If it is a resistive network, the attenuation will be
much more. The greatest likelihood will be extreme attenuation on 160m
if the gadget is rated down to only 5 mc/s.
I once used two receivers, a 75A-4 and a R-390, just by connecting the
same transmission line to both receivers using a T-connector. It didn't
seem to attenuate either receiver's signal level noticeably. The
greatest danger in doing that is that spurious products from one
receiver will show up in the other.
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