At 1/15/2005 12:06 PM, you wrote:
>>"skipp025" wrote:
>>
>>>
>>>Hi Jim,
>>>I really don't want to argue with you, but it can
>>>be done and I've done it numerous times. It all
>>>comes down to a number game (the specs) and a
>>>reasonable approach.
>>>
>>
>>no6b wrote:
>>I'd like to see the specs on what you've come up with.
>>
>>A key advantage of the 2.5 MHz split that I use is that at that
>>spacing the G.E. RX front end has significant rejection: over 40 dB at
>>the TX freq., so it can work with as little at 40 dB of duplexer
>>rejection at the TX freq.
>
>40 dB of rejection of the transmitter power may be enough to make it
>duplex, but I doubt 40 dB would be enough rejection of the transmitter
>sideband noise number.
Yes. I forgot to emphasize that the rejection savings was only for the RX
side notch at the TX freq. But with so many mobile duplexers having
asymmetrical responses, it's worth noting the above RX observation when
shopping for mobile duplexers for this application.
>A 5 watt signal is +37 dBm. *Typical* transmitter sideband noise with a
>good radio set is likely -90 to -100 dB below the carrier at 2.5 mHz
>spacing. Many receivers intended for repeater service will hear a signal
>at -125 dBm. +37 minus 90 is negative 53 dBm. Now take -125 and subtract
>-53, and the duplexer will have to provide 62 to 72 dB of isolation.
That sounds right. Still significantly lower than what's required for 600
kHz spacing.
> Now, use a PLL exciter and your right at that -40 number for both.
>
>Kevin Custer
Interesting. I know about PLL exciters for Mastr IIs but never seen one
for an MVP; do they exist?
Bob NO6B
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