I'm not Scott, but maybe I'll do... <grin>
See Below....
[EMAIL PROTECTED] wrote:
For Scott:
With respect to using the GE MII mobile frame for repeater applications:
1. Can you say categorically that there is sufficient TX/RX shielding
to prevent any desense at any power level the conversion is capable
of operating?
Yes, there is sufficient isolation for single box conversion with
absolutely no internal desense from the MASTR II Mobile, with the
exception of the frequency ranges between 223T940/222R340 thru
224T060/222R460. Why don't these frequencies work?
<http://groups.yahoo.com/group/GE-MastrII/message/6972>
I have built intermittent duty 2 meter repeaters from Mastr II and Micor
Mobiles with 110 watt PA running at 140+ watts and have seen no sign of
internal cabinet desense.
2. When these converted mobiles operate with reduced TX power, what
happens to the output impedance of the TX? Is it still 50 ohms? If
not, does this affect the physical length of the half wave
interconnect cables often suggested between the TX and an isolator
and/or the cavities?
We don't recommend operating a mobile conversion at greatly reduced
power because the amplifiers are run in Class C, and reducing the power
will generate spurious emissions. For the 220 conversion, we totally
build a new power amplifier as seen in this Micor 220 conversion - GE is
similar. See here:
http://www.repeater-builder.com/pix/220micorpa.jpg
http://www.repeater-builder.com/products/ampbd.html
For other bands, we recommend the 45 watt version of the PA which will
run rated power, continuously.
3. If the output of the TX is other than 50 ohms as a result of a
power level change, does it upset the adjustment of the downstream
isolator that has been tuned by a tracking generator?
Any time you convert commercial equipment to ham band operation, you
likely won't have a perfect 50 ohm terminal impedance at the receiver or
transmitter port, so yes, as all better repeaters builders know, the
equipment might have to be tuned as a system using custom cabling
lengths or Z Matchers for optimal performance.
Kevin Custer
Repeater Builder (the company)
