RF signal mixing mystery
les wrote in message ...
Hello....
I have a peculiar problem that I can't understand, so I can't reslove it
I'm using a few CCTV cams into a 8 channnel DVR, and have tried to
then piggyback the auxiliary composite signal using a Ch. 4 modulator.
This RF then mixes into the regular antenna cable (OTA) that feed four
digital TV's throughout the house.
I figured this simplistic RF mixing would avoid redundant cabling, but have
been
surprised that I havea poor signal issue. I assumed that with one signal
being
around 70 MHZ, and the remainder in the UHF bands, any heterodyning
would be unlikely. At this point I'm not sure if this is THE issue, or
something else.
My arrangement is this:
l------l
Antenna--------l l
l l-----combined coax-----To
distribution Amp----
local modulator-- -l l
l------l signal splitter/mixer
The symptoms are that if I run the above arrangement shown above WITHOUT
the
antenna attached to the splitter, the local signal looks great. When I
reattach, the signal
drops dramatically, becomes noisy. I attached a 75 ohm load to the open
port
to see if
a termination would simulate the antenna load, but the picture looked great
as usual.
I tried an 12dB amp prior to the mixer, but it had no beneficial result. It
seems no matter
what I try, the external antenna somehow interferes with the modulator.
Help! Any ideas?? What am I missing?
Les
I had the same problem. The cure was to put a pad between the antenna and
distribution amp. I'm not sure if the antenna was over driving the input or
there was feedback from the amp output back into the antenna. Whatever the
case, try padding the antenna level down.
bg
|