[TowerTalk] K6STI Receiving loop question

[Jan Erik Holm]

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
>>