Any 460 mhz antenna recommendations?

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odlaw

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Hi,
I am looking for a good antenna for 460 for an apco 25 system. My RS discone isn't cutting it and back of set antenna although better than the discone still isn't dependable.
Thanks
Dave
 

amedik

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Any 460 mhz antenna recommendations

The Discone should be more than adequate. Are you running at least LMR 400 (50 ohm) with "N" connectors or RG-59 and "F" connectors for the coax?

RG-58 is extremely lossy at 460 MHz, and RG-8 or Mini-8X really isn't much better at these frequencies. PL-259s (UHF connectors) are lossy as well at these frequencies.

Check out these charts.
Coax Attenuation Chart

If you have a weak signal, and have lssy coax, and lossy connectors (PL-259s), then it is likely that this is the problem. This would also explain why the antenna direct to the scanner is better than the Discone.... No loss.

Alan
N1KAK
 

odlaw

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The discone worked for about a year then gradually degraded. I replaced the coax with two different types including cablevision brite wire 75ohm which has a lot less loss at that freq vs rg8 etc. and still only get a 40% signal compared to 80 using back of set ant. I am ready for a different antenna with gain for 460. By the way the RS discone comes with a PL-259. I am now using f connectors with the brite wire as it is a stainless type of cable.
 
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Hi,
I am looking for a good antenna for 460 for an apco 25 system. My RS discone isn't cutting it and back of set antenna although better than the discone still isn't dependable.
Thanks
Dave
First of all what radio are you using to scan that system? It is hard to tell you an antenna when we dont know what connecter you radio is. The antenna also has alot of varibles to it. Are you in a urban enviroment or in the county part of the city? If you are in an urban enviroment you probaly need a 1/4 wave UHF antenna and if you are in the county you probaly need a dB gain antenna.
 

odlaw

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The radio is a radio shack 197 with a bnc connector however my current thruwall feedline is terminated with a F connector on the outside of the house. I live in the country in central ny. I am 15mi away from the system I need to listen to. The antenna will be exposed to snow and occasional 40 mph gusts. The mast is a 8ft chimney mast on a ranch style home.
 

davenlr

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Try the scanner on the discone at the end of the cable from the roof before it connects to the cable running through the wall. Sounds like you have a bad connection somewhere in that thru wall setup. My discone picks up UHF great on systems 50 miles away. 15 miles should be a slam dunk for it. F-connectors are used for satellite IF's in the Gigahertz with no issues, so I doubt you are getting that kind of loss just because of the connector.
 

odlaw

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I did that previously with the same results. Thats when I decided to buy a new antenna cut for the freq I use. I don't remember if the antenna is coil loaded or not. I am suggesting a break of the coil or corrosion of the whip where it attaches to the base of the antenna. The radials have always been fine as I used thread lock on them during the original install.
Thanks
 
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davenlr

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If you suspect its the coil or whip, take it off. Its not used for 450Mhz at all, only for a very narrow section of the 30-50 Mhz band. If its shorted out, removing it should allow the actual discone to work. Then you can put a Ohm meter on the disc and the cone, and see if there is any continuity which there should not be if the coax is unplugged from the scanner. That would narrow down the problem.

Mine is picking up several sites right now, and I have it sitting on a tripod 3 feet off the ground in the back yard, for maintenance (two radials broke off during the ice storm, and Im going to replace them all with solid rods instead of those floppy tubes radio shack used).

But to answer your original question, you can make a 450 Mhz coaxial dipole very easily. It will have about 2dbi gain, and can be shoved up into a piece of PVC if you wanted to permanently mount it. You can use 50 or 75 ohm coax, to match whatever coax you use for a downlead, and radio shack has the connectors for a couple bucks. Whole thing shouldnt cost more than $10.

You basically take a section of coax, measure 1/4 wavelength from the end, and at that point cut off the outer jacket (without cutting the sheild wires) and remove it. Then carefully roll the shield backwards over the jacket leaving you with a 1/4 wave of plastic or foam covered center conductor on top, and shield over the outer jacket on the bottom, Seal that in a pvc pipe, and solder the coax end to a female jack and mount it in a pvc cap at the bottom.
 
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