picking out the best coax ?

#335817

I,m trying to decide which coax is best for picking up 800-900 mhz plus the normal 150-453 mhz conventional channels. I tried the rg 58 100ft and that cut out all my 800-900 mhz. Is the jetstream JT 400 that's equal to LMR 400 best or foam core RG 8? I guess I have to solder on PL 259's and adapt that to BNC? Thanks for any help.

'Doc · #335821

Of the three you listed, use the LMR-400 equivalent. It will be the better of the three. Still going to have losses with that length of run, but not as much.
- 'Doc

(An LMR-600 or equivalent would be even better... till you get to the price.)

#335846

Is this for transmitting or just receiving those frequencies?

3's

Greg

#335865

Just for receiving. I'm going up 10 more feet for a total of about 30 ft high to base of antenna and reducing coax length to 60ft. I hope that helps. Is there any loss going from the PL-259 to BNC adapter on both ends? Thanks

'Doc · #335867

There's always ~some~ loss when using adapters but unless they are absolutely total trash there won't be a significant amount. Generally, it's not something to waste a lot of worry on, usually a small fraction of a dB of loss.
- 'Doc

#335883

I used RG6 (72 ohm) for my scanner and discone antenna. It was only about 35 feet, but I received the 850 mhz band just fine. I have a bnc connector on the scanner end. I think you can get an inline preamp that is powered thru the coax for longer runs. I don't think you need 52 ohm cable just for receive.

H T

'Doc · #335900

Want to try something 'odd'?
(If you had an SO-239 connector on that scanner instead of a BNC it's much easier to do, but even with that BNC connector it's possible.)
Very simply, disconnect the feed line and only connect the center pin of the connector back to the scanner's antenna center pin. I think you will see a 'difference'. May not be an improvement, but in most cases it will show one. That's NOT easy with a BNC connector, it requires that you have to do some 'shade treeing'. A straight pin and short piece of wire can be used.
What that does is make the entire feed line and antenna into an antenna. If the antenna isn't resonant in the places you want it to be, the difference in performance can certainly be beneficial. In some cases, not so beneficial.
It's just something to try. If it's done carefully it isn't destructive at all and can be 'put back' like it was easily.
- 'Doc

#335920

I occasionally use one of those adapters to connect my old Bearcat scanner to my Imax antenna coax, it seems to work well for receiving the 2m band. I haven't tried any other freqs though.

#335969

The antenna I'm using is from rat shack. Its a magnetic with two center loads and 16 ft of rg 58 made onto it. My brother swears by this antenna that it worked better that his discone. Was thinking of chopping that off ( just leave 4 inches) and splicing on the LMR 400, soldering center to center and shield to shield and wrapping with electrical tape. That should help some with the loss by getting rid of the 16 ft of rg 58? Thanks

'Doc · #335996

I very much doubt if the losses in 16 feet of RG-58 coax is going to make a noticeable difference in reception.
- 'Doc

#336278

Got antenna up yesterday. I ended up using the RG8 foam core braided instead of LMR 400 solid its too stiff for my app. The antenna is 30 ft to tip and I cut out all but 4 inches of the made on to antenna RG 58 and used 67 ft of RG8. Slight improvement from 1st attempt when using antenna on metal roof half way to peak w/ 16 ft of RG58 stock coax on antenna, was only about 12 ft above ground. Was hoping for a big improvement, very disappointed. What about T-ing off the coax and putting up a home brew 800 mhz beam antenna run off the same coax w/ a T connector? That way the other antenna can still pick up the lower freq's. Two antenna hooked to 1 coax, how would that work? Thanks

'Doc · #336292

Using one feed line with two antennas get's sort of complicated. Yes, it can be done, but it's not all that simple and it will require some additional effort/expense.
There are always compromises with 'multi-band' antennas, some bands are just not going to be as 'good' as others, no way around that. For 800 Mhz, getting the antenna higher would probably be the simplest way to 'help' things. Getting the antenna above the roof line would be a definite help, that roof will attenuate signals especially on 800 MhzI don't know of any good/simple/cheap answer for you. Good luck.
- 'Doc

#336344

Thanks Doc for all your help and knowledge. Its already about 20 ft above the roof. Do you have a link for running two antenna's w/ one feed line? Thanks

'Doc · #336356

No link, sorry. It has to be done on an individual basis, no two installations are ever the same. It involves making the impedances of both antennas such that they can be combined to give you something that your radio will 'like' and that doesn't produce excess loss from either antenna. That's really not that simple. There are things called 'splitters' that do that in various 'degrees'. It's all frequency sensitive and always means a loss in something. I haven't had to do any of that 'figuring' in a hundred years and I'm too lazy to re-learn it, sorry.
- 'Doc

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