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Author Topic: Cold temperature desense  (Read 609 times)
K6ECS
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Posts: 58




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« on: December 04, 2017, 06:07:07 PM »

Our repeater site vendor does not provide heat for the vault. Ironically, he does provide air conditioning. Now that it has turned cold again our duplexer seems to be desensing even though during warmer times of the year it does not. What are some ideas available to keep the duplexer at close to a nominal temperature? I am blessed with LIDS that know of this anomaly and come by and key the machine up just to trigger the desense. Over and over and over and... The duplexer is a Sinclair Res-Loc Q2330e.

Thank you in advance.
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K5LXP
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« Reply #1 on: December 04, 2017, 09:23:59 PM »

Just to be accurate, duplexers don't desense, receivers do.  I'm not sure what you mean by "trigger desense", you don't hear desense with just a kerchunk.  You're implying that the repeater cycles on its own, which is a different problem.

In my experience duplexers don't shift that far over their spec'd temperature.  The data sheet for the model you listed shows -40 to +60C, so if yours are drifting out of spec at temperatures within this range either there's a defect, or it's something else in the system that's inducing your symptom.

It would seem then you need to isolate the problem to the root cause, than to just assume it's the duplexer.  May mean a trip to the site when it's cold, and verify the subsystems independently.

Mark K5LXP
Albuquerque, NM
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NA4IT
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« Reply #2 on: December 05, 2017, 04:03:34 AM »

100 watt light bulb next to the problem child.

I actually installed a small 12V DC bulb inside a RX compartment with a small thermostat mounted to the case of the box. The bulb would turn on at 40F. Drilled a 1/16" hold in the lid to see if the bulb was on. Worked well.
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K4JJL
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« Reply #3 on: December 05, 2017, 07:11:43 AM »

It could be a buildup on condensation, too, especially if it's large temperature swings a short period of time.

Try the technical tap.  Sometimes you can narrow down the issue by banging on it with a screwdriver handle.
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NA4IT
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« Reply #4 on: December 05, 2017, 11:30:35 AM »

Come to think of it, I think the 12VDC bulb was put in the TX compartment. Probably wouldn't hurt to have one in each. Thermostat was a simple HVAC wall thermostat.
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N8EKT
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« Reply #5 on: December 08, 2017, 03:58:14 PM »

Sinclair specs are from -40 to 140 degrees so i would call Sinclair and ask them why this is happening.
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K3GAU
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Posts: 14




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« Reply #6 on: Today at 08:21:52 AM »

It could also be that the squelch sensitivity changes with temperature. 
In any case, you might try using a battery warmer for heat.  It is kind of like a heating pad for batteries. They are usually wrapped around the outside of the battery to help keep it warm in very cold temperatures.  It may even have a thermostat built into it.
GL
Dave K3GAU
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