Re: [amsat-bb] Yeasu 736-R Question

[Bruce Bostwick <lihan@xxxxxxxxxxxxxxxxxx>]

On Wednesday, May 16, 2001, at 02:23 PM, Douglas Cole wrote:

> Bruce Bostwick wrote:
>>
>>> Please be careful not to change transmit modes while d/c is on! The 
>>> other
>> night
>>> I was changing band by pushing the band button and it threw a spike 
>>> up the 2
>>> mtr.
>>> coax. Sounds really strange, but I guess anything is possible.
>>> Steve / KB8VAO
>>
>> Pity there aren't any circulators/isolators for 2m .. this would be 
>> just
>> the application for an isolator .. downconverter sees in the input of 
>> the
>> radio, radio sees a 50 ohm dummy load.  If the IF was on 432, an 
>> isolator
>> would be a little more feasible, but for this application I don't think
>> it's possible.  Something to think about though ..
>>
>
>
> Ok , so I am a little confused here , as there -are- vhf isolators that
> will work on amatuer bands ( I am using one on my IRLP repeater) , the
> only trouble I can see is they don't give you -complete- isolation (
> around 30db ) so there will be a sizeable signal going back to the IF
> output of the converter ...
>
> Maybe using pin diodes to shunt the leftover rf to ground would work
> ....

Might, although PIN diodes have been known to generate mixing products 
with lots of RF around -- if the downconverter is near the transmit 
antenna, you might end up mixing in a lot of local junk to the IF.  
Thought about switching 2.4 GHz antennas with PIN diodes a while back, 
and decided not to for just this reason -- the ambient RF was just too 
nasty where it would have been installed .. your mileage may vary ..

I didn't know there were VHF isolators, although if they only get 30dB 
of backfeed isolation that is understandable ..

           --... ...-- -.. . -. ..... ...- -...
                   Bruce Bostwick N5VB
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