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1-10 of 11 messages
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Coax / feeder into shack
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by M5AEO on November 7, 2009
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I am feeding my HF and VHF antennas with RG8 coax coming in through a small gap where the window is open. Now that winter is coming on I need to find a way of getting the feeder indoors but with the window fully closed. Would it be acceptable to make up some short 'jumper' cables out of the very thin RG174 coax (which is small enough to enter via the window), just long enough to get through the wimdow gap or would I be creating some sort of feeder 'bottleneck'. Would it effect the efficiency of the antennas?
Jonathan, London.
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RE: Coax / feeder into shack
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by K0BG on November 7, 2009
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MFJ makes an entry device that works quite well. If you don't wish to spend the money, you can make one easy enough.
Alan, KØBG
www.k0bg.com
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RE: Coax / feeder into shack
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by WE1X on November 7, 2009
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I use a piece of plexiglass (Lucite). Drilled several holes in it to accommodate barrel connectors. Feedlines to the connectors, jumpers from connectors to rig. Fits in the opening below the window sash with some insulation.
Harry WE1X
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RE: Coax / feeder into shack
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by K5LXP on November 7, 2009
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Direct answer- yes, you could do that. A better choice would be RG-316 which has somewhat better power handling than RG-174.
You could also do the bulkhead/feedthrough as the others have mentioned, or my favorite, big holes through the wall.
Mark K5LXP
Albuquerque, NM
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RE: Coax / feeder into shack
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by WB6BYU on November 7, 2009
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Generally you can change cable types like that without
problems, as long as the RG-174 meets the power handling
requirements. The loss on 2m in 1/2 metre of RG-174 is
only about 0.2 dB (which is 5 times that of RG-8, so you
don't want to make the cable too long.)
The limiting factor will be the power level and the SWR
on the cable, and these data aren't always as easy to find
as one would hope. Belden type 8216, for example, is
officially rated at only 30V for some purposes, but
at 1100 volts in other places. It is commonly used for
internal wiring of 100 watt HF radios, so should be
safe up to that level if the SWR is not too high.
Belden rate their type 7805 for 25 watts on 2m and the
lower loss 7805R at 30 watts. (Both being "RG-174 type"
cables.) While it isn't uncommon to see small coax
being used with 50 watt radios, you'll have to keep an
eye on it. If the cable is being squeezed in the window
that will tend to compress the insulation and lower the
power rating: I'd make sure that the cable you use
has a solid dielectric type rather than foam in that
case. Solid PTFE would probably be the best choice in
that case - you might look for some RG-178, RG-188 or
RG-316 instead.
You can get a good idea of the various "RG-174 type"
cables from Belden at their web site: www.belden.com
The various types will be around 0.1 inch diameter,
and you can get a good start by entering RG-174 in the
search box.
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RE: Coax / feeder into shack
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by LEEH on November 7, 2009
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Ok Alan. I have searched the MFJ site for the cable entry device you mentioned but am unable to find it.
Can you assist?
LeeH
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RE: Coax / feeder into shack
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by G4AON on November 7, 2009
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I long since drilled a hole through the wall, it doesn't make a mess and is how cavity wall insulation is blown in. Drill from the outside through the mortar between the bricks. If you move you can fill the hole with cement/mortar and the hole will not be visible.
Saves messing around with MFJ low power solutions that are QRP rated and "just works".
73 Dave
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RE: Coax / feeder into shack
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by LEEH on November 7, 2009
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Nice stuff, very handy and I don't have to drill a half a dozen holes thru my wall.
However I did learn therre is a lot of MFJ stuff they dont have on their site and you have to down load their catalog.
But thanks for the help
Lee
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RE: Coax / feeder into shack
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by KB5ZXM on November 7, 2009
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I made an adapter, for my vacuum cleaner hose to collect the filings, I drill a Hole in the glass. < thru duct tape>. I would have made a Plexiglass plate. but there is window AC/Heater in that window also, and I wanted to keep the ladder line away from it.
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