Re: [Repeater-Builder] Dupelxer wierdness

[safari_tim]

Thanks Bryon.
 
I was using 20 Log Pout/Pin.  My fault.  I should have been using 10 Log Pout/Pin.  Thanks for setting me straight.
 
You're probably right about the 50 ohms difference between the test equipment and the transmitter.   It makes sense.
 
I also have a big difference between the bird and the service monitor.   Since the service monitor goes in for periodic calibration, I always assumed it was correct over the bird readings.
 
Thanks for the feedback
 
---Tim theVAP.com 
 
-------------- Original message -------------- From: Bryon Jeffers K0BSJ <[EMAIL PROTECTED]> Tim,First off lets go over some numbers...38 watts = 45.8dB16 watts = 42dBSo 38 into the duplexer and 16 out is roughly 3.8dB loss not 7.5dB...I don't have a Motorola 2600 but I do have an IFR1500 and it doesn't always measure RF power anywhere close to what my Bird watt meter does...According to Sinclair <http://www.sinctech.com/catalog/series.aspx?id=343> you should see no more than .8dB loss through the duplexer...Your 28 watts which is 44.5 dB is showing about .3dB loss which seems a little too good but is closer than 3.8dB loss....When I see that kind of power gain by tuning the duplexer with low TX power going through it I usually associate it with the fact that when you are tuning the duplexer on the bench you use two of the ports while tuning and terminate the third with a 50 Ohm load. Your service monitor should be fairly close to 50 Ohms as well. When hooked to the transmitter and receiver they are usually not near as close to 50 Ohms as the test equipment that you are using... I will say that usually you won't see that much power to be gained by peaking the TX side under (low) power....  So maybe the transmitter output is not near as close to being a perfect 50 Ohms...I sometimes even use another set of test cables when things start looking weird, just in case.....When you finish re-peaking the TX side under (low) power, always go back and set/re-check the notches on the TX side as well....This is taken from my experience. YMMV..Bryon Jeffers K0BSJAt 05:19 PM 2/6/2006, you wrote:
I got a wierd problem going on. I have a 440 repeater with a Sinclair Q3220E duplexer. I used my Motorola 2600 with the tracking generator to tune it. Then I checked the power.  Power in was around 38 watts, and the power out into the service monitor was around 16.  Or about -7.5 db inserstion loss. So then I just pulled the plungers under power ( I know it's a NO NO), and got the output power up to 28 watts into the service monitor.  Which brought the insertion loss down to -2.6.  Which is still too high, but better. Keep in mind the monitor is a selective watt meter, so its doubtfull that I am measuring garbage.  The spectrum looks fine. So, why when I peak it with the tracking generator, aren't I getting the correct insertion loss or at least comparable to the power tuning method? ---Tim theVAP.com  

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