Re: [TowerTalk] K6STI Receiving loop question

[Jan Erik Holm <sm2ekm@telia.com>]

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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