here's the plan

[joetnymedic]

OK, before anyone says it, I know it's crap but I've had about a 30ft run of RG-58 going to a radio shack 30-176 for a couple of months now. Obviously crap cable so crao signal although it was a tad better than just the base antenna to the back of the scanner via bnc adapter. So, went out and got (actually got the wife to buy it for me which is cool cuz she hates me scanning and anything else going on with them. So her buyiing this was just SO awesome- sorry had to gloat) bought some RG-6 quad shielded cable. Next step is the f to BNC and F to pl-259 adapters and then replacing the current rg-58 and putting the antenna a bit higher on the roof. So that's the plan. Any idea what this is gonna do for me sgnalwise? I mean I know the 58 is crap but my question is just how much of a difference in the RG-6 going to make? I only stayed away from the RG-8 and Beldon because of how thick they were and the pain running them through, by the new windows would be. I'm hoping this is gonna be at minimal pretty good as far as pick up goes. Mostly vhf/uhf scanned couple of 800 systems but they are so good I get them in the clear on a rs 800 duck. I'm thinking at minimal they should be the same on the outside antenna.

 

[crayon]

I mean I know the 58 is crap but my question is just how much of a difference in the RG-6 going to make?

You can run the numbers yourself here:

http://www.timesmicrowave.com/cgi-bin/calculate.pl

 

[mass-man]

It's hard....

To predict just what will happen...

But throw the new coax into the system...raise the antenna and only THEN will you know what improvement you have made.

Honestly antennas, feedline, HAAt, etc. are hard to calculate...you have to throw it up there and see if it works for you.

 

[kf4lne]

it cant hurt, just do it. i used some RG6QS for a scanner for a long time before I moved and it worked great. I am currently using RG11 for my scanner and RG6QS for the weather radio. Works great, but your milage may vary.

 

[Woodie]

OK, before anyone says it, I know it's crap but I've had about a 30ft run of RG-58 going to a radio shack 30-176 for a couple of months now. Obviously crap cable so crao signal although it was a tad better than just the base antenna to the back of the scanner via bnc adapter. So, went out and got (actually got the wife to buy it for me which is cool cuz she hates me scanning and anything else going on with them. So her buyiing this was just SO awesome- sorry had to gloat) bought some RG-6 quad shielded cable. Next step is the f to BNC and F to pl-259 adapters and then replacing the current rg-58 and putting the antenna a bit higher on the roof. So that's the plan. Any idea what this is gonna do for me sgnalwise? I mean I know the 58 is crap but my question is just how much of a difference in the RG-6 going to make? I only stayed away from the RG-8 and Beldon because of how thick they were and the pain running them through, by the new windows would be. I'm hoping this is gonna be at minimal pretty good as far as pick up goes. Mostly vhf/uhf scanned couple of 800 systems but they are so good I get them in the clear on a rs 800 duck. I'm thinking at minimal they should be the same on the outside antenna.

Your scanner, and antenna for that matter have been engineered to operate @ 50 ohms impedance. RG 6 is 75 ohms. This will bring about a feed line mismatch.

At vhf it will not pose to much of a problem since a damp noodle performs better than RG58. However at 800 megs there will be considerable loss.

Go to your local Amatuer radio supply store and buy some RG 8M or RG 8X. Its onlt about 20 cents a foot. Or if your feeling rich - go for the gold and buy some Belden 9913.

Cheers

 

[kf4lne]

Unless the scanner and antenna are tuned to the same frequency all the time it is NOT going to be 50 ohms. In fact, because of the large amount of spectrum covered by a scanner the impedence of the entire antenna system can range anywhere from just a few ohms all the way to to several thousand ohms, causing an overall impedence mismatch depending on the frequency it is tuned to at the time. The RG6 will work fine. basically the scanner doesent care if you use 50 ohm coax or lamp cord, as long as the overall antenna system is sensitive enough to provide the scanner with enough signal to open squelch. Chances are that your antenna is not tuned to a perfect match, or even anywhere close to a match for the frequencies you are listening to so the difference between 50 and 75 ohm coax is nothing to worry about. if I can find it again I will post a link to a impedence calculator, it shows how dramatic a change in antenna impedence can be over just a few MHz away from the freq the antenna is matched to. basically, in just a few MHz difference you can expect an antenna to vary several ohms above abd below the 50 ohms it presents at its primary frequency. use the RG6, it will work.

 

[Woodie]

Unless the scanner and antenna are tuned to the same frequency all the time it is NOT going to be 50 ohms. In fact, because of the large amount of spectrum covered by a scanner the impedence of the entire antenna system can range anywhere from just a few ohms all the way to to several thousand ohms, causing an overall impedence mismatch depending on the frequency it is tuned to at the time. The RG6 will work fine. basically the scanner doesent care if you use 50 ohm coax or lamp cord, as long as the overall antenna system is sensitive enough to provide the scanner with enough signal to open squelch. Chances are that your antenna is not tuned to a perfect match, or even anywhere close to a match for the frequencies you are listening to so the difference between 50 and 75 ohm coax is nothing to worry about. if I can find it again I will post a link to a impedence calculator, it shows how dramatic a change in antenna impedence can be over just a few MHz away from the freq the antenna is matched to. basically, in just a few MHz difference you can expect an antenna to vary several ohms above abd below the 50 ohms it presents at its primary frequency. use the RG6, it will work.

Sorry Dan,

As an RF Engineer, I cant help but totally disagree. Before I explain think about this. Across a discones designed bandwith, the impedance will only vary from 44 to 56 ohms. Now think about modern wide band tuned circuts and the front end of the receiver.

Cheers

 

[prcguy]

Dan and Woddie are both correct. A multiband antenna like a Scantenna or RS “Sputnik”, etc are resonant with a corresponding good match at a few specific frequencies only. Everywhere else they present a widely varying match to the feedline with additional losses adding up outside the resonant spots. One nice thing about a Discone is it has a good match across most of its design bandwidth, which is about 100 to 800MHz for most scanner types, not the 25 to 1300MHz they lie about. If you were to add a preamp to the base of an antenna a Discone would be a good choice to keep the preamp stable with less chance of oscillation. Modern wide band receivers probably match well to 50ohm coax across their entire bandwidth. Using 75ohm coax will introduce a slight mismatch to the receiver or a Discone but probably not enough to notice in most cases. On most other multiband antennas, losses from using the wrong coax will be dwarfed by the additional losses from the antenna being operated nowhere near resonance.
prcguy