High SWR during extreme cold/poor rpt coverage

[KitN1MCC]

My little VHF site is having coverage issues when it gets extremely cold. the repeater is mounted in a box on a wooden pole. i did add a heater and i think it warmed up (was warmer out today above freezing) went to the site good output power swr was 1.7 after the cans. I downloaded the log file from XPR8400 and it had SWR alarms that cleared them self. also once the outside warms up it works great. Maybe the heater in the box is just not enough and it needs the sun on the box too. The other idea i had was that once it warmed up something at the antenna messes up due to the extreme cold (ice or what not) but it is fine above 20degrees out. i do need to get it sweeped and getting up the pole needs a bucket truck. so any ideas ??????

[MSS-Dave]

Is there a duplexer in this box? Cold will affect tuned cavities much worse than antennas.....

[Jim202]

My bet would be a center pin either not soldered, or the cold is shrinking the cable enough that the center pin is pulling back and loosing connection at the duplexor or surge protector.

You didn't mention what type of connectors are involved here. If it is type N connectors, you should be able to run your finger nail over the end of the connector and just be able to touch the center pin. Any further back and the connector was made wrong with the center pin too far back in the connector.

If the connector is a PL259 UHF connector, I would look at both the center pin not soldered correctly or the shell not soldered to the coax braid.

Then again the problem could be up at the antenna.

Jim

[nukedude]

I have also seen some of the cheaper connectors (even ones bought through Tessco) where moisture and temperature would cause problems like this. Have a good and solid connection at each end of the coax, using dielectric grease in fittings used in very cold outdoor locations, and making sure drip loops are in place to keep moisture out of connections has helped.

At duplexers, use low loss coax as well. Several times I saw where people used low loss coax to go from the duplexer to the antenna, but then used lossy coax and adapters at the duplexer and radio. Each adapter adds a little bit of loss also.