Connectivity/Loss Question

[jjudson]

I currently have my RS discone and Wilson Yagi antennas connected with 50 feet each of RG6/U coax. I am replacing the cable with Belden 7810 coax.

7810 is substantially thicker, heavier, and stiffer than the RG6/U. I'm concerned that having it hang directly off of my BCD396XT will put undue strain on the antenna connector over time. I was thinking about running the 7810 to a wall connector, then connecting something lighter like RG6/U from there to the scanner antenna input. The question I have is this:

Using this scenario, would connecting about six feet of RG6/U to the tail end of the 50 feet of 7810 coax (running it from a wall mounted connector, then converting it with an adapter to the SMA connector) cause more loss than just leaving the RG6/U up in the first place?

I don't want to go through all of this work just to have the benefits negated by all of the connectivity conversions.

 

[N_Jay]

My guess is for use under 1 GHz, you will never notice the difference between the RG-6 (assuming it is in good condition) and the new cable with, or without the jumper.

 

[prcguy]

Your starting out with reasonable antennas and very nice 50ohm coax for the main run, why compromise with an RG-6 75ohm jumper? A few feet of RG-58 or maybe some LMR-200 as a jumper would seem more appropriate.
prcguy

I currently have my RS discone and Wilson Yagi antennas connected with 50 feet each of RG6/U coax. I am replacing the cable with Belden 7810 coax.

7810 is substantially thicker, heavier, and stiffer than the RG6/U. I'm concerned that having it hang directly off of my BCD396XT will put undue strain on the antenna connector over time. I was thinking about running the 7810 to a wall connector, then connecting something lighter like RG6/U from there to the scanner antenna input. The question I have is this:

Using this scenario, would connecting about six feet of RG6/U to the tail end of the 50 feet of 7810 coax (running it from a wall mounted connector, then converting it with an adapter to the SMA connector) cause more loss than just leaving the RG6/U up in the first place?

I don't want to go through all of this work just to have the benefits negated by all of the connectivity conversions.

 

[gewecke]

Prc guy has a good point. But I wouldn't think the smaller diameter feed to your radio would increase loss unless you drastically changed your impedance. Another idea would be a 90degree bnc adaptor? Those can help with the strain problem too.
N9ZAS

 

[prcguy]

Not enough loss in a few feet of RG-58 to worry about up to a GHz or so. It just seems odd that you would build a nice system with 50ohm components and then toss in a very inexpensive part that doesn't match.
prcguy

Prc guy has a good point. But I wouldn't think the smaller diameter feed to your radio would increase loss unless you drastically changed your impedance. Another idea would be a 90degree bnc adaptor? Those can help with the strain problem too.
N9ZAS

 

[jjudson]

Not enough loss in a few feet of RG-58 to worry about up to a GHz or so. It just seems odd that you would build a nice system with 50ohm components and then toss in a very inexpensive part that doesn't match.
prcguy

Actually, I didn't think ahead a bit when I wrote RG-6/U. It just popped into my head as that's what I have laying around (a good amount of it if I'm replacing my current antenna coax with the 7810). You are correct, I will be impedance matching the setup by going with another 50 ohm connector cable.

I guess that said, though, what can I expect going from my current 75 ohm setup to a 50 ohm one? How does this impact my performance?

 

[nanZor]

One option you can get right from RS is either:

1) #278-0011 sma-female to bnc-female jumper. It is about 20 inches of small flexible RG-316 (50 ohms) (alternate #278-011)

or

2) #278-0012 (alternate 278-012) sma-female to SO-239 female made with the same RG-316.

AND, you'll need the male-male sma adapter: (I wish their jumper was male instead of female...)

#278-009

Works fine on the 396's, and the Pro-137 race scanner if you need a low-stress jumper connection..

 

[jjudson]

AND, you'll need the male-male sma adapter: (I wish their jumper was male instead of female...)

Yeah, that's weird. Why would they make a device advertised as an female SMA-to-something adapter, then advertise it as a "Connect your scanner or handheld 2-way radio to an external antenna with this cable" adapter? Do any scanners or radios take a female antenna connection?

Sometimes I scratch my head over Radio Shack.

 

[rvictor]

You can use the calculator that's here to calculate the loss for different types and lengths of coax.

Coax Calculator

Dick