UHF channel spacing,avoiding intermod
 

We have a number of UHF television channels as well as
VCR's, Satellite decoders etc. all with UHF modulators.
One needs to carefuly choose which UHF channel to modulate on when setting
up the VCR, decoder etc. so that they dont interfere with each other or the
off air UHF signals.

Some time ago I came across a table that assisted with the choosing of
various UHF channels (taking into account the off air channels) to avoid
multiples and adjacent channel interference. I can not seem to find this
table anymore.

Do you know of an algorithm to use to assist with the above? The UHF
spectrum for TV video is from 21(471.25 Mhz) to 68 (847.25Mhz) with audio
being 6Mz higher in frequency.

If for example we have UHF signals on channels 39, 43, 37 and 47 which of
the remaining channels would be acceptable to use for the modulation of the
other devices.

It has been suggested to avoid n-1,n+1,n+5 and n+9 where n is a UHF channel
currently in use. Is this correct?

Thanks

Joel

ZS6CBA

IM is the product of at least two signals.

One third order IM will be found at 2*A-B where A and B are two signals.

For example:
X=100 MHz
Y=101MHz

2*100-101 = 200-101 = 99 MHz IM product
2*101-100 = 202-100 = 102 MHz IM product

The original are 1 MHz apart and the products are one MHz either side of
them.

Then there is a three signal third order. I think it is A+B-C.
A=100
B=101
C=102
100+101-102=99
etc.

It just gets worse from there.

Time for a spreadsheet with all the possible formulas, then plug-in the
frequencies.

--
Steve N, K,9;d, c. i My email has no u's.


"Joel Dorfan" wrote in message
...
We have a number of UHF television channels as well as
VCR's, Satellite decoders etc. all with UHF modulators.
One needs to carefuly choose which UHF channel to modulate on when setting
up the VCR, decoder etc. so that they dont interfere with each other or
the
off air UHF signals.

Some time ago I came across a table that assisted with the choosing of
various UHF channels (taking into account the off air channels) to avoid
multiples and adjacent channel interference. I can not seem to find this
table anymore.

Do you know of an algorithm to use to assist with the above? The UHF
spectrum for TV video is from 21(471.25 Mhz) to 68 (847.25Mhz) with audio
being 6Mz higher in frequency.

If for example we have UHF signals on channels 39, 43, 37 and 47 which of
the remaining channels would be acceptable to use for the modulation of
the
other devices.

It has been suggested to avoid n-1,n+1,n+5 and n+9 where n is a UHF
channel
currently in use. Is this correct?

Thanks

Joel

ZS6CBA

Joel:

Avoid adjacent channels, your n=1, n-1; and then have no two channels spaced
by the same separation. Starting with 39 and 43, have no other pair 4
channels apart. So, you are already in trouble with off air signals (47 -
43 = 4). And so on for the rest of the channels. The n+5 or 9 is for IF
beats which will depend on the image rejection of your particular equipment.
Difficult to predict exactly without performance data. There has been
published an algorithm for most effective use of channels, but you don't
have enough channels to need that sophistication.
"Joel Dorfan" wrote in message
...
We have a number of UHF television channels as well as
VCR's, Satellite decoders etc. all with UHF modulators.
One needs to carefuly choose which UHF channel to modulate on when setting
up the VCR, decoder etc. so that they dont interfere with each other or
the
off air UHF signals.

Some time ago I came across a table that assisted with the choosing of
various UHF channels (taking into account the off air channels) to avoid
multiples and adjacent channel interference. I can not seem to find this
table anymore.

Do you know of an algorithm to use to assist with the above? The UHF
spectrum for TV video is from 21(471.25 Mhz) to 68 (847.25Mhz) with audio
being 6Mz higher in frequency.

If for example we have UHF signals on channels 39, 43, 37 and 47 which of
the remaining channels would be acceptable to use for the modulation of
the
other devices.

It has been suggested to avoid n-1,n+1,n+5 and n+9 where n is a UHF
channel
currently in use. Is this correct?

Thanks

Joel

ZS6CBA