[K3PZN-List] 2M Repeater

[Frank Rodski]

Good job!
Frank K3MTT@ARRL.NET

Lawrence J Solarczyk wrote:

>Greetings,
>
>Wednesday night, Steve N3SB, Bill N3XLY, and I (WX3F) went up to work on
>the 2 meter repeater.  After verifying that the spurs existed, we
>separated the power amplifier from the exciter.  Using Steve's HT, we
>confirmed that the power amplifier was clean and not the cause for spurs.
> We then looked at the exciter output.  After adjusting the power level
>of the exciter to about 400 mW, we looked for spurious emissions.  We did
>not see any spurs.  Since we had the exciter output terminated into the
>station monitor, which is a good 50 ohm resistive load, we concluded that
>the problem may be a result of the interface between the coupling of the
>exciter to the power amplifier.  It appeared that the conjugate match on
>the input of the power amplifier may not have been a perfect 50 ohm
>resistive load.  So we reconnected the exciter to the power amplifier,
>and looking at the configuration of the exciter from the repeater manual,
>we noticed that there was a variable capacitor on the output stage of the
>exciter.  Adjusting this capacitor maybe an eight of a turn eliminated
>the spurious signals.  After several transmit attempts to see if the
>repeater would again spur, a few times hold the transmitter on for
>several minutes to having the fans on the power amplifier start up, we
>verified that the repeater was clean.
>
>In our testing, we did notice that there was no local microphone or
>repeated audio modulating the transmitter. Although, the PL tone was
>modulating the signal.  After going around and around in the schematics
>for the repeater trying to find out where the audio was being lost, we
>concluded that audio loss was at the input of the exciter module itself. 
>The reason for this conclusion came from noticing that the local
>microphone audio and the repeater audio entered the exciter module on a
>different connector pin than the PL tone audio.  So, we were thinking
>that maybe a transistor failed in the exciter.  But, while we were poking
>around the back plane circuit board on the repeater, we would get an
>indication that there may be a loose connection.  I then pulled the
>exciter module out of its holder and reinserted it taking care to insure
>that it was well seated in the connector.  Success, all audio returned.
>
>Before closing up the repeater, we verified that the repeated audio level
>did not exceed 5 kHz deviation and power output at about 100 watts with
>about 80 watts out of the duplexer to the antenna cable.
>
>Before we left the building, Steve mentioned that the power output level
>of the 70 cm repeater may be low.  We found that the output of the 70 cm
>repeater IS low.  The output is less than 500 mW.  We popped the cover
>off of the power amplifier and notice a burn mark.  Checking the circuit
>board, we found a tantalum capacitor blew its top.  That repair will be
>for another day (another round-tuit).  The 70 cm repeater may be used,
>just know that its signal and range is limited.
>
>For the next couple of weeks, I would like all of you that have the
>ability to monitor the output of 2 meter repeater for spurious emissions
>to do so.  Until I receive any more notices that the repeater is
>spurring, I declare that the repeater is available for regular use.
>
>Thanks to everyone who helped in anyway to eliminate the spurs from the 2
>meter repeater.
>
>73,
>Larry WX3F
>-----------------------------------------------------BREAK-------------------------------------------------
>Freedom Park has been conquered.
>
>Mext CCARC Meeting Monday, July 8, 7:30 PM at the Fire Training Center.
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