[AMRadio] Cable splitters for receivers


Donald Chester 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.


Don k4kyv


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