question about RG6

[davidgcet]

i noticed in reading on here that a lot of folks here use RG6 for their connections. is there a reason for this other than cost? RG6 is a 75ohm cable, RG8 is 50 ohm which is what the antennas are matched for. we have used 7/8" 75 ohm hard line cable for a community repeater before, but put impedence matchers on it to use it.

i'm not saying what you are doing is wrong, i honestly want to know why and if there is any benefit to it.

 

[gewecke]

i noticed in reading on here that a lot of folks here use RG6 for their connections. is there a reason for this other than cost? RG6 is a 75ohm cable, RG8 is 50 ohm which is what the antennas are matched for. we have used 7/8" 75 ohm hard line cable for a community repeater before, but put impedence matchers on it to use it.

i'm not saying what you are doing is wrong, i honestly want to know why and if there is any benefit to it.

If you're not transmitting,then the mismatch of 75ohms vs. 50ohms is not really a problem. Rg6/quad shield has pretty low loss figures so it works well if you're receiving above 400mhz.
The smaller diameter size is probably liked by many users too.
n9zas

 

[davidgcet]

just wondering because for maximum signal transfer you want a circuit at resonance, and having 75 ohm cable in a 50 ohm circuit is not at resonance. it is not as critical as transmitting, but it will have an affect on the signal level that makes it to the radio/scanner. i guess it is not enough to matter for most folks, and the ones trying to pick up far off signals are going to run preamps anyway.

our only venture into trying 75 ohm was 1 because it was free, and 2 because it was not a critical repeater. it definitely had decreased range vs the other repeater sitting next to it with the same style antenna at the same height, though it was only a minor decrease. and like i said we had tuned impedence matchers, without them the SWR was nearly 2:1.

 

[W6KRU]

Yes a resonant circuit would be better but what frequency should it resonate at?

 

[SCPD]

I used it for 2 reasons.

1: Took it from work we had an extra spool.
2: I did not know any better between the miss match in 50 & 75. I was just happy to get free coaxial cable and use it for my new antennas.

 

[jackj]

It's not a mismatch

i noticed in reading on here that a lot of folks here use RG6 for their connections. is there a reason for this other than cost? RG6 is a 75ohm cable, RG8 is 50 ohm which is what the antennas are matched for. we have used 7/8" 75 ohm hard line cable for a community repeater before, but put impedence matchers on it to use it.

i'm not saying what you are doing is wrong, i honestly want to know why and if there is any benefit to it.

I've gotten into this discussion before on different threads. A lot of very vocal folks here don't really understand antennas and transmission lines. They seem to think that if you are not transmitting then a mismatch doesn't matter. Like you, I have used 7/8" 75 ohm hard line here at my station on both HF, feeding an old Tri-bander and 2 meters feeding a yagi as well as a j-pole. I used it because I got it from the cable company for free. It worked but the reflected was higher than I liked.

You are wasting your time if you try to get them to change. There is something about being able to say, "It isn't designed to do this but I'm so smart I was able to make it work anyway."

 

[Thunderknight]

I use RG-6 Quad for most of my receive antennas. It's cheap, the connectors are cheap, and it's easy to run. F to BNC connectors for scanners are cheap and plentiful.
For receive, you are only going to be at 50 ohms at a particular frequency(ies) at the antenna. For a lot of other frequencies, it will not be a 50 ohm match. I guess if you were building antennas for resonance at a specific receive frequency, it might matter...but most scanner antennas and uses are broadbanded.

 

[davidgcet]

if the antenna is a multiband antenna it would be resonant at all matched frequencies. naturally full resonance would only occur at a few freqs that matched best.

anyway i was just curious if there was a reason for it's use other than cost/availability of RG6. heck, i have used RG59 for 30' runs before because it was all i had at the house and did not feel like goign to the office to get RG8 or LMR, so i understand the availability part!

 

[eaf1956]

Rg6

Most people use it cause they have it laying around. I use BURY FLEX cable myself. Some may say that is excessive but I use it for 2m 440 radios anyway so why not on the scanners too.

 

[W6KRU]

Thunder has it right. The scanner/coax/antenna has to be looked at as a system. The total system is resonant at a particular frequency but if you are listening to everything from vhf-lo to 800MHz then the total system impedance is all over the place and making one particular piece of the total system resonant at a particular frequency isn't going to be very beneficial. How many people worry about the resonant frequency of the antenna that is hooked to their scanner?

 

[davidgcet]

jack, i learned long ago that nothing you cna do or say will change someone else's mind on a forum, so i don't even try. i figured that was why it was used, but just wanted to make sure if they knew something i did not! i saw no mentions of impedence matchers, so i was curious.

 

[CalebATC]

I plan to get my setup moved over to RG-8X for all my scanners, since the extremely low loss. Also, it will be better fitting for HAM equipment. RG-6 is just a very accesable cable, not hard to get, and usually cheap. And the connectors are fairly easy to assemble.

Caleb

 

[DPD1]

I plan to get my setup moved over to RG-8X for all my scanners, since the extremely low loss. Also, it will be better fitting for HAM equipment. RG-6 is just a very accesable cable, not hard to get, and usually cheap. And the connectors are fairly easy to assemble.

Caleb

I think you mean RG8. 8X is actually quite a bit smaller. Confusing I know. They should have made it a different number besides 8.

 

[CalebATC]

I think you mean RG8. 8X is actually quite a bit smaller. Confusing I know. They should have made it a different number besides 8.

Well, I never understood that either. Anyway, I will probably use RG-8X, and maybe RG-8 for my main antenna.

 

[n5ims]

I plan to get my setup moved over to RG-8X for all my scanners, since the extremely low loss. Also, it will be better fitting for HAM equipment. RG-6 is just a very accesable cable, not hard to get, and usually cheap. And the connectors are fairly easy to assemble.

Caleb

Actually 8X has pretty high loss (about 12 dB @ 800 MHz) at the higher frequencies, much more thank RG-6 (under 9 dB). RG8 would have about 6 1/2 dB (about 4 dB for the better 9913 grade) and LMR 400 about 3 1/2 dB. 8X does work well in fairly low power HF use on ham stations, however.

 

[kb0nly]

Well, I never understood that either. Anyway, I will probably use RG-8X, and maybe RG-8 for my main antenna.

The RG-6 Quad is going to beat that RG-8X for loss if your using it for the scanner, the RG-8X is ok at HF, and 2m its "ok" for short runs, but anything longer and you need to bump it up to RG8.

I have seen so many scanner installs using RG-6 and did some side by side comparisons, and i don't think the impedance mismatch with a hundred feet or so of 75 ohm cable with a wideband antenna is going to matter much. Look at the ST-2 antenna, a bunch of different length elements all fed in parallel to the feed point, no way is that antenna 50 ohms, more like 2-300 ohms i bet, not having one myself i can't confirm, but they do put a impedance transformer at the feed point. Wouldn't be hard to build a transformer to go to 75 ohm cable instead of 50 ohm, and then use an impedance transformer again at the scanner to go down to 50 ohms, but overall the difference isn't noticeable to most.

As a simple comparison, while arguing this a while back, i took a 200' roll of RG6 and strung it out with an antenna at the end, measured the signal level on a bunch of frequencies, then we took 200' of RG8 and measured again, only a VERY SLIGHT improvement, less than one S-Unit on the scanner and no noticeable increase in the noise floor going to the RG-6. The RG-6 quad shield is also better suited to keeping out interference as well, especially in a case when your running next to other cables.

Overall, i wouldn't worry. I used RG8 sized cable myself but only because thats what i had and its lower loss than the RG8X and RG58 that i also had on hand. If i would have had a roll of RG-6 laying around i would have used that!

 

[bob_c_89431]

Let's not forget that the Z of the antenna is going to be all over the place based on freq.
Also, the rcvr input is not going to be 50 or 75 ohms on every band (or any band).
Of the cable models suggested, go for the lower loss or better shielded cable for a rcv only situation.

Now you know......as little as I do.

bc

 

[smason]

Wow. Another thread on Rg6, how many is this now?
Seriously this horse has been dead for a long time

To the O/P do a search, there are a few good threads on this.

For the money, you get very low loss, easy to work with, cable. You can get good compression BNC connectors for it too. What's not to like about RG6?

 

[davidgcet]

smason, i personally have a lot against RG6 since it is the wrong impendence and the fact that i have plenty of the correct impenedence cable at hand. everything from flimsy RG58 to 1 1/4" hardline, so i don't have a need to "engineer" my connections. it's no skin off my back what others do with their setups, i honestly was wondering if there was a valid reason beyond it being at hand. and now i know there is not.

as to the search i did do one first. it returned a whole bunch of recent posts about running RG6 for scanner antennas but none as to WHY they would. thus my question.

 

[W6KRU]

smason, i personally have a lot against RG6 since it is the wrong impendence and the fact that i have plenty of the correct impenedence cable at hand. everything from flimsy RG58 to 1 1/4" hardline, so i don't have a need to "engineer" my connections. it's no skin off my back what others do with their setups, i honestly was wondering if there was a valid reason beyond it being at hand. and now i know there is not.

as to the search i did do one first. it returned a whole bunch of recent posts about running RG6 for scanner antennas but none as to WHY they would. thus my question.

Wrong. Did you read my reply? I explained why the impedance is quite irrelevant. It is explained in a lot of old threads but since you are kind of new, I went ahead and explained it again as many have before.