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Re: [TowerTalk] K6STI Receiving loop question

Subject: Re: [TowerTalk] K6STI Receiving loop question
From: Jan Erik Holm <>
Date: Fri, 19 Nov 2004 10:33:58 +0100
List-post: <>
No not unless your feedline has very high losses.

73 Jim SM2EKM

Pete Smith wrote:

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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