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Fun & Productive Weeken Antenna Project!

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Airdorn

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#1
Hey all.

I had a very productive weekend!

I went by the office and grabbed some RG-6U coax and a spare mag-mount 800Mhz antenna. I work for an alarm company as a tech and we used to use them with these older cellular alarm transmitters when we had signal problems with the stock stick antenna.

Anyway, I mounted the antenna on top of the furnace ventilation pipe on my roof and ran the cable into the attic.

Inside the attic, I cut off the antenna's wire and soldered the RG-6U to it, as seen in the picture. The braided shields of both are soldered, as are the center taps.

Then I ran the RG-6U straight to my radio room, down the wall, and into my scanner.

I had been using another antenna just like this one, but it was a little bit lower on the roof, and I used all of its cable that came with it, and then used a barrel connector to splice some RG-58 to it and then to the scanner. (ick!)

What a difference this project made!

Before, I was getting 2-3 bars on the S-meter of my BCD996T, monitoring a public safety Motorola type II system about 35 miles away.

Now, with this new setup using the RG-6U and that soldered splice, I get a steady 4-5 bars and the audio is much clearer and consistent.

Total run from antenna to scanner is about 35 feet.

So what about that splice shown in the picture? I know its ugly, but isn't a soldered connection always going to be better than using adapters and connectors and what not? I know a single continuous wire is the ultimate, but that's not possible here. That antenna had that thinner, cheaper coax built right into it.

Any ideas on improving this setup?

Thanks

Airdorn
 

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mancow

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#4
Well..... it's open and exposed. If you could just twist coax together and be done with it AMP, TIMES, Andrew wouldn't be selling those $100 hardline connectors. Unfortunately it just doesn't work that way. You may get by for a simple receive only system like you have going but it's still a place for all kinds of nasty things to get in your system.
 
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#6
the characteristic impedance of the cable (nominally 75 ohm for RG6, 50 ohm for RG8) is NOT the same at that point, it's probably more like 300 ohms or so - try a coax splice (Available at R$), or some other means of keeping the cable coaxial

(a quick and dirty way would be to make the cables run striaght towards eachother, wrap tape around the center conductor, then wrap some foil around the braids and solder it to the braids - This is not meant ot be a permanent or even a GOOD fix, just something to try)

imagine that the signal runs in the insulator between the shield and the center conductor - you've drastically changed that signal path in the joint in that picture. if nothing else, put some connectors (F, PL259, BNC, TNC, Mini UHF, N, SMA, 7/16 DIN, C, SC, anything coaxial) and an adaptor or union in-line.
 

Airdorn

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#7
OK.. I'll cut it down and put a couple of F connectors and a barrel splice.

I just figured soldered connections were always better, hehe. :)

Thanks all.
 
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#8
If you were on 40 meters and using that splice ... I wouldn't say anything, but at 800 mhz those ends are like 1/2 wavelength or better. Jam some F connectors on there and your signal will rise to full scale ... I betcha.
 
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