On Mar 2, 12:39*pm, dave wrote:
- - Robert11 wrote:
- - Hello,
- -
- - Have a Scantenna antenna (receive only) in attic.
- - It came with 75 ohm RG 6 coax, so presumably the output
- - has a 75 ohm impedance.
- - How this varies with freq. I have no idea.

Neither Do I. {You are not Alone}

- - Have a new scanner that says to use 50 ohm coax.

Enjoy You New Scanner.

- - From old posts, the consensus seems to be that it
- - doesn't matter if you use 50 or 75 ohm coax for a run
- - that I have of about 50 feet.
- -
- - Do you folks agree with this ?

I Do. {See the Longer Answer Below}

- - From a somewhat more rigorous and theoretical view,
- - should the coax, even it hardly matters, be matched to
- - the antenna output impedance, or the input impedance
- - of the scanner ? *Why ? *(again, receive only)

It would be 'nice' to have a Signal Path where all the Parts
were the same Impedance : Antenna, Coax Cable and Radio.
-But- Practically Speaking Not Necessary when you are
simply talking 75 Ohm to 50 Ohm Components used for
Receive "Only" Scanner-Radio Listening.

- - Any thoughts on this would be most appreciated.
- -
- - Thanks,
- - Bob

Dave -wrote-
- The mismatch is insignificant. *
- About 1.3 dB of loss or something.

Robert 11,

What Dave says is the Practical Applied Truth : When it comes
to these 75 Ohm to 50 Ohm Mismatches between Antennas,
Coax Cables, Radios, etc for the Average Scanner Radio Listener.

To correct this Mismatch although insignificant; would require
the Insertion of some 'Device' either between the 75 Ohm
Antenna and the 50 Ohm Coax Cable feed-in-line.

This Device would have to be 'connected' between the 75
Ohm Antenna and the 50 Ohm Coax Cable feed-in-line.

Each of the Connections would have a Insertion 'Loss";
plus the Device itself may have some "Loss".

DEVICE = Matching Transformer / Matching Network / etc.

The Total of these "Losses" may be nearly equal to
the original Loss from the 75 Ohm to 50 Ohm 'direct
connection' Mismatch; or could even exceed it.

So the Practical Answer is to accept the small 1.3 dB
Loss due to the Mismatch and have fewer Connection
in the Signal Path from your Antenna to the Radio.

Why Fewer Connections ?
Over time the biggest problem with most Antenna
installations is the Connections in the Signal Path
from the Antenna to the Radio. Two more Connections
may cause more problems then living with the small
Signal Loss due to the Mismatch between the 75 Ohm
Antenna and 75 Ohm Coax Cable and the 50 Ohm
Input of the Radio.

Worry less about these small Mismatches and Losses;
and Learn more about making good Secure Antenna
and Coax Cable 'connections' that are Weather Proof
and will hold-up over years of service.

sorry for the miss-match-of-words )
hope this helps - iane ~ RHF {pomkia}