Coax To Coax Noise transfer ?
 

Hello:

Am about to start stringing some coax from an outside Receive-Only antenna's
Balun up to
my study where the receiver is. (30 MHz on down listening)

The easiest thing for me is to run it alongside an existing (looks like
coax, but am not sure) wire
that Comcast has strung for my broadband service to the PC. Actually to
their always-on modem which is then
connected to the PC.

Was wondering about coax to coax noise transfer into the receiving antennas
coax from being right alongside
this Comcast stuff.

Think there's any reason for concern ?

If so, worth the trouble to find a new route for the receiving antenna's
coax ?

Thanks,
Bob

Coax To Coax Noise transfer ?
 

In article ,
Robert11 wrote:

Hello:

Am about to start stringing some coax from an outside Receive-Only antenna's
Balun up to
my study where the receiver is. (30 MHz on down listening)

The easiest thing for me is to run it alongside an existing (looks like
coax, but am not sure) wire
that Comcast has strung for my broadband service to the PC. Actually to
their always-on modem which is then
connected to the PC.

Was wondering about coax to coax noise transfer into the receiving antennas
coax from being right alongside
this Comcast stuff.

Think there's any reason for concern ?

If the Comcast cable was installed properly, there shouldn't be a
problem. Coax cable with high-quality shielding leaks very little
signal, and the cable companies have to use well-shielded cable in
their plants in order to avoid leakage of channels whose fall into the
airband, amateur, and public-safety allocations.

Also, I don't think that Comcast's plant is likely to carry much, if
any content below 30 MHz.

There's some possibility, I suppose, of some leakage of noise from the
cable modem itself back up along the outside of the Comcast coax. You
might want to consider buying a few snap-on interference-suppression
ferrites, and snap 'em onto the outside of both cables (e.g. where the
Comcast cable leaves the building, where your receiver coax enters the
building, and maybe a few more scattered along one or both coaxes).
This would help block or dissipate any RF currents flowing on the
outsides of the coaxes.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Coax To Coax Noise transfer ?
 

In message , Dave Platt
writes
In article ,
Robert11 wrote:

Hello:

Am about to start stringing some coax from an outside Receive-Only antenna's
Balun up to
my study where the receiver is. (30 MHz on down listening)

The easiest thing for me is to run it alongside an existing (looks like
coax, but am not sure) wire
that Comcast has strung for my broadband service to the PC. Actually to
their always-on modem which is then
connected to the PC.

Was wondering about coax to coax noise transfer into the receiving antennas
coax from being right alongside
this Comcast stuff.

Think there's any reason for concern ?

If the Comcast cable was installed properly, there shouldn't be a
problem. Coax cable with high-quality shielding leaks very little
signal, and the cable companies have to use well-shielded cable in
their plants in order to avoid leakage of channels whose fall into the
airband, amateur, and public-safety allocations.

Also, I don't think that Comcast's plant is likely to carry much, if
any content below 30 MHz.


You're forgetting about the UPSTREAM data and interactive signals (QPSK
and/or QAM, from the cable modem or the set-top TV box). These will be
in the range of (probably) 15MHz to 42MHz. The max transmit level will
be typically 40dBmV (max around 56dBmV). The actual frequency used will
depend on the local area (segment).

The upstream levels are higher than the downstream (typically 10dBmV
analogue, 0dBmV QAM). However, where possible, the cable operator may be
avoiding the HF amateur frequencies, in order to minimise any problems
of ingress.

There's some possibility, I suppose, of some leakage of noise from the
cable modem itself back up along the outside of the Comcast coax. You
might want to consider buying a few snap-on interference-suppression
ferrites, and snap 'em onto the outside of both cables (e.g. where the
Comcast cable leaves the building, where your receiver coax enters the
building, and maybe a few more scattered along one or both coaxes).
This would help block or dissipate any RF currents flowing on the
outsides of the coaxes.


This is certainly a good idea 'just in case', and won't hurt any.
Ian.
--