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Author Topic: UHF mobile duplexers, rang and performance?  (Read 1870 times)

NA4IT

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RE: UHF mobile duplexers, rang and performance?
« Reply #15 on: February 11, 2019, 02:40:55 PM »

Best write up on how to tune a mobile duplexer...

http://www.repeater-builder.com/antenna/notch-duplexer-tuning.html
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KK6RPX

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RE: UHF mobile duplexers, rang and performance?
« Reply #16 on: February 12, 2019, 03:43:42 PM »



Ahaha! I love the "Sandlot" analogy. Great movie. And I will grant that I share Small's profound ignorance. To continue the Sandlot analogy, I hope that despite my ignorance that the team rallies and helps me learn what I need to know.

I have been looking into the SINAD method of testing receiver sensitivity. I see that Comtekk has some software for measuring SINAD http://comtekk.us/sinad.htm. Has anybody used this or have an opinoin if it is wirth the $39? My SSG can do the 440 range but on harmonics and is a little touchy to get set. I use my RSP2 SDR as a frequency counter. I know that may seem pretty cheesy but I nailed the last ARRL frequency contest within a couple hertz using it a while back. Buying a proper counter is on the agenda but not in the immediate future.

Thanks for the detailed write up on how to do desense test properly. I will be acquiring the equipment needed but it won't be overnight. I have ordered some RG400, it will be here soon. I also do have a directional couple that I got from mini-circuits. While I do have a nice step attenuator I have been cautioned that it should not see the 5 watts out of the repeater. I will have to get a more power capable attenuator. I think I may have a 12 or 24dB unit in the junk stash, I'll dig. I am trying to find a way to do some work with what I have and then improve as I can.

I see why the SINAD method is best for testing actual measured receiver sensitivity. However, I am not too concerned in this case of getting accurate numbers as I am being able to determine at least roughly how much desense the system is experiencing and if I am making improvements. In that case, is there any real problem using the signal generator to use the break in squelch level as the baseline and then use the break in squelch while transmitting to determine how much desense is being experienced? I think I have most of the equipment to do this as detailed here:

http://www.repeater-builder.com/antenna/desense-testing/desense-testing.html

Finally, and I know Smalls (ME!) will be killing you, why would having only the center conductor connected appear to improve the sensitivity? Type slowly and use small words.  ;)

NA4IT, good link. Much useful information on the RepeaterBuilder site.

Many thanks for all of the help.




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WB8VLC

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RE: UHF mobile duplexers, rang and performance?
« Reply #17 on: February 12, 2019, 08:40:00 PM »

I was watching the sandlot while reading this post and I didn't mean any disrespect, after all Smalls eventually became a good ballplayer.

If you were closer to Northern Oregon I'd help with it but I never venture south of Eugene.

You should be able to find a repeater group/club that has the tools to help/mentor you.

Better to have someone local show you, I used to work with a group called CARS, CALIFORNIA ARIZONA REPEATER SYSTEM, helping with their 6 meter repeater near Prescott Arizona.

If you are close to San Fernando and you have 6 meter fm capability you could get on the Mt. Frazier 52.56 repeater and ask for Dan N6BKL, the owner/trustee and pass my call along to see if he is possibly available for a help session
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KK6RPX

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RE: UHF mobile duplexers, rang and performance?
« Reply #18 on: February 12, 2019, 09:00:48 PM »

No offense taken at all. Great movie and I have no problem confessing my ignorance.

I live in the middle of nowhere. There really isn't anyone close to me. I have gotten hold of someone who maintains a wide area repeater system fairly near me but he is an hour and a half away. So he and I will get together but for now I just gotta keep plugging away. I am sure that with your and others help I can at least get to a functional level.

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