[Motorola] UHF MICOR Base
Jim
[email protected]
Sun, 20 Jan 2002 14:48:21 -0800
I doubt that the VHF antenna had anything to do with it. You might be wise
to find a channel element in the 450-470 range and verify that there is
rated power out at that frequency.
Doing this before conversion is a MUST!! (Now you know ....heh ....heh)
Otherwise you are just shooting in the dark!!
You can bypass the power amplifier by hooking a SHORT piece of cable with
BNC connectors between the "low level output" and the "pa input" BNC
connectors to see if you have a PA problem. You CANNOT hook a wattmeter to
the output of the low level output and a service monitor or wattmeter and
dummy load! The power control circuits will not allow the low level amp to
get voltage and thus no power output! You MUST have the circulator/filter
hooked up to make the power control work!
You can by-pass the filter that is in the low level amp section and see if
you get about 1.5 to 2 watts output out of the circulator!
When I repaired the power amplifiers on the bench, I used a 2 watt hand held
to drive the amp. IF you don't have 1.6 (absolute minimum for rated power)
to 2 watts into the power amplifier you will not get rated power output!
Again.....The low level power amplifier modules were very reliable! The
circulator modules were also VERY reliable! Even operating into a poor load.
Most of the repeaters that are in commercial operation, don't see the duty
cycle that the typical amateur repeater see. There are exceptions of
course.....Like taxi, data, some law enforcement etc.
What is the rated power of the repeater ??
C64RCB is 75 watts out of the PA (Motorola did not make a 100 watt UHF
repeater/base only 75 watts or 250 watts with a tube final) (They did
however make a 100 watt UHF mobile).
C44RCB is 45 watts out of the PA
C24(or 34) RCB is 12 watts out of the PA (smaller PA than the 45 and 74
watt)
73 and good luck!
Jim W7RY
----- Original Message -----
From: Glenn Little <[email protected]>
To: <[email protected]>
Sent: Sunday, January 20, 2002 14:09
Subject: Re: [Motorola] UHF MICOR Base
| Jim
|
| Thank you for your timely response!
|
| Our transmitter is now on 441.450. When it was abandoned it was on
| 463.775. I am the one that did most of the work in getting the
transmitter
| converted. We have never been able to get more than 30 Watts from the
| duplexer. The transmitter power on the original frequency is
| unknown. During the retuning, I measured the power levels at diffrent
| points that I could get to. The Tripler/Amp was putting out 1.6W when we
| put it into service on our ham frequency. The filter was not retuned, as
| the manual says 1.0 W minimum here.
|
| Now we are getting 0 W at this point. This is with the PA disconnected
| from the tripler/Amp. I had the person at the site check the power from
| the exciter. He does not know how to use his equipment well and did not
| have all of the adapters he needed. He told me that he could see the 150
| MHz signal on his spectrum analysez. His watt mete would not go down low
| enough to measure the power.
|
| He said that he could just see the display move on the spectrum analyzer
| when he looked at the output of the tripler. The manual does not give
| (that I could find) a power level out of the tripler before the amplifier.
|
| My plans are to power up the module on the bench and feed a 400 mw signal
| into the tripler and see if I can get something out. I will check the
| filter on a spectrum analyzer / tracking generator and see what it looks
like.
|
| Since we are operating outside the band that this MICOR was designed for,
| could a filter be mistuned enough to cause the tripler problems and still
| allow the amplifier enough signal to meet specs for drive?
|
| The fact that we met drive specs to the PA, led me to believe that we were
| ok on the stages previous to this.
|
| When we got this repeater, it was still attached to the antenna. The
| antenna that it was attached to was a VHF antenna! The low overall power
| out of the transmitter is caused by a 3dB loss through the circulator.
Not
| knowing a lot about circulators, I think that this one was damaged by
| heat. I think that the VHF antenna presented a mismatch to the
| transmitter. The circulator routed the reflected energy to the load. The
| load heated up. The heat, over time, changed the magnetics of the magnets
| in the circulator. This changed the tuning of the circulator.
|
| Does this make sense?
|
| Would a mistuned UHF filter have caused a problem with the tripler?
|
| Thanks for your help
|
| 73
| Glenn
| WB4UIV
|
| At 01:26 PM 1/20/02 -0800, you wrote:
| >You most likely will need to tune the filter that is part of the low
level
| >amplifier.
| >
| >There is a thin metal cover soldered over the tuning screws and this is
not
| >"field tunable".
| >
| >You should use a tracking generator to look at the filter before you tune
| >it. Then tune for 440-450 range.
| >
| >Do some logical troubleshooting before you assume that there is a bad
part
| >in the low level amp section. They rarely fail. BE SURE to check the
power
| >control section! I have 20+ years working on the Micor UHF (and other
| >bands), the don't fail that often!
| >
| >
| >What frequency are you transmitting on ? When I was using a Micor and
| >transmitting on 444.725, you need to tune it!
| >Good luck!
| >
| >73
| >Jim W7RY
| >
| >----- Original Message -----
| >From: Glenn Little <[email protected]>
| >To: <[email protected]>
| >Sent: Sunday, January 20, 2002 12:43
| >Subject: [Motorola] UHF MICOR Base
| >
| >
| >| Our radio club has a UHF MICOR repeater that was donated to us. After a
| >lot
| >| of work, we got it on the air. This only lasted a day. After
| >| troubleshooting the transmitter problem, we feel that we have a
| >| Tripler/Amplifier (TLE1603B) problem. We have zero power out of this
| >| module, where we had 1.6W out when the repeater was working. We have
| >about
| >| 400mw input at VHF into the tripler.
| >|
| >| Does anyone have any experience with repairing this module? The manual
| >| lists it as not field repairable. The module is currently inroute from
| >the
| >| site to my house for investigation as to repairability.
| >|
| >| Does anyone know where a spare might be obtained?
| >|
| >| Thanks
| >| 73
| >| Glenn
| >| WB4UIV
| >|
| >|
|
>| -------------------------------------------------------------------------
-
| >-
| >| Glenn Little [email protected] QCWA LM 28417
| >| Amateur Callsign: WB4UIV [email protected] AMSAT LM 2178
| >| QTH: Goose Creek, SC USA (EM92xx) ARRL TAPR
|
>| -------------------------------------------------------------------------
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| >-
| >|
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| >
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| --------------------------------------------------------------------------
-
| Glenn Little [email protected] QCWA LM 28417
| Amateur Callsign: WB4UIV [email protected] AMSAT LM 2178
| QTH: Goose Creek, SC USA (EM92xx) ARRL TAPR
| --------------------------------------------------------------------------
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