which one for my setup??

[boomer92266]

I just bought a digital scanner and have bought 40 feet of rg6 dual shield coax, I will be using an outside antenna, on the inside is where my question is. I have found bnc connectors that will connect the rg6 to fit on the scanner, however I see some that say copper inside and 50 ohm and some that say plated 75 ohm but they look the same. Is there a difference in them or will either work with my scanner? looking at pics I can't tell any difference. Thanks for any help.

 

[K4EET]

RG-6 is 75 ohm and is not what should be used on the scanner which is 50 ohms. You really should be using LMR-400 since scanners receive above 1,000 MHz.

 

[majoco]

Now I've just gone through the specification pages of my two base scanners and a portable and neither of them mention a specific impedance for the antenna terminal. I run RG8 from a discone to the nominal 50ohm input of my Icom R7000 but RG6 quad shield from a aero band antenna to one scanner and another bit of RG6 quad to the other from a low VHF band antenna to the other scanner - both antennas are either a folded dipole through a 300ohm to 75ohm balun or a straight dipole and 1:1 balun - so theoretically I'm running a 75ohm system - but both receivers work very well at all sorts of other frequencies other than the intended 'tuned' antenna. The portable is mainly used on its rubber ducky but occasionally on a 2m band 50 ohm J-pole and to tell the truth it works better on the J-pole than either of the base radios on their frequency matched antennas - so to my mind it matters diddley-squat what impedance the antenna/cable combination presents to the receiver - as long as it works then it's fine by me. BUT if I was using a transmitter then I would pay much more attention to a proper match through the system - like the J-pole connected to my 2m transceiver through more RG8!

 

[Ubbe]

Here is the SWR of a discone. If the SWR are 2:1 it means that it is either 25 ohm or 100 ohm. Higher SWR are even more from a 50 ohm impedance.

Here are a Uniden BCD536 scanners impedance at 400MHz and 800Mhz.

It's far from a perfect 50 ohm. If you did have a perfect 50 ohm scanner and used a 75 ohm coax it would be a 1.5:1 SWR which can be pretty much ignored even when using transmitters.

/Ubbe

 

[boomer92266]

Thanks for the help, I went and bought one of each and found there is a difference on reception even tho they both look just alike. I put up a 36" steel scanner antenna outside on a cb mount and I grounded it, I ran 40 feet of RG6 dual shield coax. I used a Rg6 to cb mount adaptor on the mount, on the scanner I tried the 50 ohm bnc connector that said copper for better signal but I had some static in the reception, I tried the 75 ohm bnc connector that was advertised as plated, but signal came through much clearer and with no static. So I am gonna stick with the 75ohm connector as long as I use Rg6 coax. I am on a tight budget and had to save over a year to get my scanner but do plan on getting scanner coax some time in the future if I can. thanks again.

 

[mmckenna]

I am on a tight budget and had to save over a year to get my scanner but do plan on getting scanner coax some time in the future if I can. thanks again.

As was so well stated above, neither the scanner antenna port or the scanner antenna provide a perfect 50Ω impedance across their usable bands. There's zero need to replace your RG-6 if it's working to your satisfaction.

It's easy for us to quote all kinds of specifics about what you 'should' use, but the reality is that for many, this is just a hobby. Like yourself, not everyone has a large discretionary budget to throw at this sort of stuff. The RG-6 will work just fine and if you are happy with the coverage, there's no need to change it. It's unlikely that you'd be able to tell the difference between LMR-400 and the RG-6 you have. Yes, there is a slight improvement on paper, but your scanner and your ears may not be able to tell the difference.

Instead, take what money you have available for hobby activities and put it towards a good antenna. Also, make sure you -fully- waterproof all outdoor connections. Leaving your outdoor connections unprotected will result in water ingress, either from rain or condensation, and that will result in corrosion. That corrosion will really impact your listening.

 

[K4EET]

@boomer92266, listen to what @mmckenna has to say because he does have a lot of wisdom as well as technical knowledge. In an ideal world I would go with LMR-400 but due to your situation, I have to agree with @mmckenna. Enjoy your scanner with the RG-6 coax!

 

[rescuecomm]

I ran RG6 to a 75 and 40 meter dipole back in the 1980's although it was on a Kenwood TS 830 with tube finals. Didn't have the money for a trap dipole so used alligator clips at the midpoint. Signal was good to Charleston SC. The RG6 was a present from a ham who didn't have a use for it.

Bob

 

[Ubbe]

...I tried the 50 ohm bnc connector that said copper for better signal but I had some static in the reception, I tried the 75 ohm bnc connector that was advertised as plated, but signal came through much clearer and with no static.

It's more a mechanical issue than anything else. Some BNC's have the center pin very thin and pointy as a needle and others are very thick over its whole lenght.

Sometimes a bad connector will help reception as some scanners overload easily and desense and attenuating some dB makes the signal stay below the overload point. It's always a good tool for external antenna use to have a variable 0-20dB attenuator to adjust while listenining to a weak signal in analog mode. Perhaps a FM broadcast filter are needed or a pager filter or it just needs 6 dB loss and you can still receive the systems you are monitoring. I have not heard of copper connectors. They are usually made of brass and a center pin of silver or plated.

/Ubbe

 

[jonwienke]

A 75-ohm BNC has a smaller center pin than a 50-ohm, and plugging a 75-ohm male BNC into a 50-ohm female BNC means a loose connection.

 

[boomer92266]

A 75-ohm BNC has a smaller center pin than a 50-ohm, and plugging a 75-ohm male BNC into a 50-ohm female BNC means a loose connection.

The center pins look the same size on both but eyeballing them with my eyes may not be too accurate, I just know using the one that says 75 ohm has almost no static and most local channels are crystal clear but using the 50 ohm causes static on most channels with just a few good and clear. I may take my 50 ohm back and get another 50 ohm in case I got a bad one. thanks