QRN( Forum) have you seen/used........

[AudioShockwav]

There has been a lot of discussion about coax as of late, have you ever worked with pressurized, ceramic-insulated transmission lines?
I was doing some digging around about Coax ( transmission lines) and ran across this stuff. Is it gold or ????.
I like the idea of a pressurized coax, if it leaks, it gets out, not in.
And you would know by a slow pressure drop.
Thought I would run it by you .
73
Jeff

 

[Captain Kilowatt]

Well Jeff, I have worked with Andrews LDF12-50. It is 2 1/4 inch heliax which has a hollow centre and is suitable for gas pressurization.We did run it pressurized with dry air generated by a line dehydrator.The dehydrator ensures dry air and that is fed through a special gas block fitting that allows the gas,in this case air but some use a nitrogen bottle,to pass through the heliax up and into the antenna system without leaking back into the non-airtight hardline cable connected to the transmitter.Even the antennas are pressurized.The dehydrator is needed if nitrogen is not used as the gas in the line MUST be dry or arcing can result.They work just like a water pump and sense a drop in pressure and turn on when needed to maintain line pressure. They have a running time meter to tell how much the unit has been running in a given time.One of our sister stations,K100 in Saint John, New Brunswick, suffered ice damage to their antenna system and had cracks in the welded joints of the FM antenna.It was a 12 antenna system configured as four bays of three antennas each covering 120 degrees.IIRC 5 out of 12 had cracks and they had a real problem maintaining line pressure as they were using nitrogen cylinders. A full cylinder would only last a little over a day and a half. :shock: The road up Mount Champlain was impassable at the time except for snomobile/ATV or by help from the CBC who had a 4X4 truck with the CAT tracks instead of tires.Eventually the antennas were taken down and welded on the spot and put back up.That solved the leakage problem but after that they decided to go with a dehydrator due to the thousands spent on nitrogen in a short time. Pressurized line is great for high power and high budgets but not really practical for you and me.

Forgot one thing,the line I was using did not have ceramic insulation (?) but rather had a spiral wound teflon spacer that kept the centre conductor aligned and still allowed the gas to pressurize the centre conductor and the outter shield to keep any moisture ingress away.

 

[C2]

A big problem for us is snippers...

 

[Captain Kilowatt]

With that kind of cable they would need a hacksaw.