Ok, I've got my tech license and am studying for my Gen. I read a lot that references air insulated hardline but I have not found anything that tells me just what it is. Can I get some help here?
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air insulated hard line
- Thread starter john65
- Start date
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BOOTY MONSTER
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Coaxial Coax Cable and moisture and burying
be sure to seal the coax connectors good .
" ......... I can't overlook some of the "air" dielectric cables that have come on the market in the last few years. These generally use a PVC center conductor insulation that is a thin spiral around the center conductor. So air insulation is not 100% accurate but the majority of space around the center conductor is in fact air. Guess what is good at absorbing moisture? Of course - air! A leaking connector can allow rain to literally run into the cable and with air line cable, the water has a large area to fill. Now your coax cable has a center conductor filled with water. It's impedance is no where near 50 ohms, losses can reach to nearly infinity and you can't hear a signal on any band. You think your receiver is deaf, maybe even dead. Well it is deaf, no signal can make it from the antenna to the receiver, the water has created a short circuit. ....... "
be sure to seal the coax connectors good .
" ......... I can't overlook some of the "air" dielectric cables that have come on the market in the last few years. These generally use a PVC center conductor insulation that is a thin spiral around the center conductor. So air insulation is not 100% accurate but the majority of space around the center conductor is in fact air. Guess what is good at absorbing moisture? Of course - air! A leaking connector can allow rain to literally run into the cable and with air line cable, the water has a large area to fill. Now your coax cable has a center conductor filled with water. It's impedance is no where near 50 ohms, losses can reach to nearly infinity and you can't hear a signal on any band. You think your receiver is deaf, maybe even dead. Well it is deaf, no signal can make it from the antenna to the receiver, the water has created a short circuit. ....... "
You have two types of air dielectric hardline...
rigid which resembles conduit. a small pipe supported by nylon bushings "bullets" inside a large pipe.
flexible which more resembles coax or heliax, as mentioned above in the quote from nr6ca.org and pictured below.
flexible is normally found at cell sites in diameters under two inch while rigid is normally found at broadcast stations in diameters over three inches.
Of all the systems that I have installed using air dielectric cable, only one was ever just coax and connectors, and surprisingly it had no problems of moisture intrusion.
The majority of systems used a dehydrator that was connected to the connector at the radio.
The dehydrator would repeatedly pressurize the cable to roughly 4psi then slowly purge the air through silica beads to remove any moisture.
A few of the systems used tanks of nitrogen gas that kept a constant pressure on the coax so that no moisture could enter.
I've heard of and read about "old timer" hams that fabricated their own air dielectric out of whatever they could get their hands on... copper pipe, galvanized fence rail, conduit etc etc.
I never found out how they dealt with moisture other than to have a small drain hole in the "jacket".
rigid which resembles conduit. a small pipe supported by nylon bushings "bullets" inside a large pipe.
flexible which more resembles coax or heliax, as mentioned above in the quote from nr6ca.org and pictured below.
flexible is normally found at cell sites in diameters under two inch while rigid is normally found at broadcast stations in diameters over three inches.
Of all the systems that I have installed using air dielectric cable, only one was ever just coax and connectors, and surprisingly it had no problems of moisture intrusion.
The majority of systems used a dehydrator that was connected to the connector at the radio.
The dehydrator would repeatedly pressurize the cable to roughly 4psi then slowly purge the air through silica beads to remove any moisture.
A few of the systems used tanks of nitrogen gas that kept a constant pressure on the coax so that no moisture could enter.
I've heard of and read about "old timer" hams that fabricated their own air dielectric out of whatever they could get their hands on... copper pipe, galvanized fence rail, conduit etc etc.
I never found out how they dealt with moisture other than to have a small drain hole in the "jacket".
Yes indeed air dielectric line needs to be kept dry either by nitrogen injection or air using a line dehydrator. The line dehydrator we used was basically a molecular sieve. As the air was pressurized it was passed through a membrane that would allow the air molecules to pass but blocked the water molecules. The water simply collected in a small vial and was drained out the bottom. Air dielectric transmission line is not for the faint of heart nor the newcomer. You need a gas block at each end to keep the pressurized gas from escaping the cable unless you also have a pressurized antenna system but that is reserved for broadcast use. I have never heard of a pressurized CB/ham antenna system.
hehehe... at one time in the 90s the KS4UN 147.2 machine used 1 5/8" air core with a dehydrator (freebie pull out & scrap from a cell site change out) but the owner, Jack, didn't like the sound of the dehydrator when it ran.
It turned out for the best, when we removed the air core we also added more tower which gave room for 16 phased dipoles for TX in the middle with RX at the top.
50w would put you in the machine from almost anywhere in Alabama :w00t:
Granted though, most hams won't goto the trouble of a pressurized system just because of the maintenance much less the startup cost.
Here are a few pics of rigid line and patch panels at my work. The molten 25kW dummy load has a 3 inch line on top. In the pic of flexible lines the large ones are 5-inch Andrew HJ9-50.
Ever wonder what it looks like inside the tower? There are a few pictures in and around a couple of towers on this person's site.
Geiser's Hill
And a few other items for bedtime reading... Some pics of hardline sections, as well as nasty burned up cables and antennas.
http://members.rennlist.org/warren/FMCombinerTuningAndTesting.pdf
http://members.rennlist.org/warren/SplitterCableDesign.pdf
http://members.rennlist.org/warren/RelativeHumidityAndDehydrators.pdf
Ever wonder what it looks like inside the tower? There are a few pictures in and around a couple of towers on this person's site.
Geiser's Hill
And a few other items for bedtime reading... Some pics of hardline sections, as well as nasty burned up cables and antennas.
http://members.rennlist.org/warren/FMCombinerTuningAndTesting.pdf
http://members.rennlist.org/warren/SplitterCableDesign.pdf
http://members.rennlist.org/warren/RelativeHumidityAndDehydrators.pdf
Attachments
Here's a picture of a 3-inch patch panel.
Bedtime reading materials with a few interesting pics.
Antenna splitter cable replacement, power divider calculations, etc.
http://members.rennlist.org/warren/SplitterCableDesign.pdf
Relative humidity measurement and remote monitoring, dehydrator theory.
http://members.rennlist.org/warren/RelativeHumidityAndDehydrators.pdf
FM Combiner tuning and testing. Signal flow, intermod calculations, pictures, etc.
http://members.rennlist.org/warren/FMCombinerTuningAndTesting.pdf
Bedtime reading materials with a few interesting pics.
Antenna splitter cable replacement, power divider calculations, etc.
http://members.rennlist.org/warren/SplitterCableDesign.pdf
Relative humidity measurement and remote monitoring, dehydrator theory.
http://members.rennlist.org/warren/RelativeHumidityAndDehydrators.pdf
FM Combiner tuning and testing. Signal flow, intermod calculations, pictures, etc.
http://members.rennlist.org/warren/FMCombinerTuningAndTesting.pdf
Attachments
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