Re: [TowerTalk] K6STI Receiving loop question

[Pete Smith <n4zr@contesting.com>]

OK -- well, the program says that at the RX end this particular length of 
cable and other conditions presents a 23+smallj mismatch to a presumably 
50-ohm receiver.

The point I was trying to make is that this magnitude of additional loss is 
of little consequence in a simple low-band receiving antenna.  Is that wrong?

73, Pete N4ZR

At 06:40 PM 11/18/2004, Tom Rauch wrote:

> >Well, as a 'frinstance, if he's using RG-6 75-ohm cable,
> say 100 feet
> >long, and the antenna is presenting 240 ohms to the cable,
> on 1.8 MHz the
> >additional loss in the cable due to the mismatch is about
> .4 dB out of a
> >total of .8db, according to TLW.
>
>
> The source never sets feedline SWR. The SWR on the line in
> receiving is set by the receiver, not the transmitter. The
> receiving feedline loss is calculated using receiver input
> impedance. The antenna mismatch only adds mismatch loss at
> the source (the antenna).
>
> Lossy systems are often not bilateral. Take for example an
> antenna tuner. When it has loss, the impedance
> transformation is not the same in both directions.
>
> If I have a 35 ohm load I can match it to a 50 ohm
> transmitter by adding a series 15 ohm resistor. The load,
> looking back at the transmitter port, sees 65 ohms when a 50
> ohm receiver is attached. Woops!
>
> 73 Tom
>
>
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>
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See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.

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