Jumper selection (Radio to Antenna)

[srbecker58]

Pretty simple. I am looking for what you all recommend to run as a jumper(s) from my radio base station to my SWR meter, then from my meter to my bulkhead that my antenna is connected to OR straight from radio to bulkhead if I decide to take out the SWR meter.

I am currently using 2' long LMR-400 jumpers and I get a GREAT SWR with them, BUT they are super stiff and very difficult to deal with as far as cable management. I am looking for something a little more flexible, unless everyone says to just leave it as is and not mess with a good thing?

 

[srbecker58]

 

[mmckenna]

RG-58 would be just fine for a short run. It's cheap and easy to install connectors on.

If you wanted to step up a notch or two, LMR-200 or LMR-240UF would be a good choice. Both are larger than RG-58, so you'd need different crimpers, and you'll need to order connectors specifically designed for them.

But a short 1-2 foot run of RG-58 at GMRS frequencies isn't going to result in enough loss that you'd notice it. It'll take a lot of strain off the antenna jack on your radio. You don't need to go overboard. The difference in loss with 2 feet of RG-58 vs. LMR-200 vs. LMR-240 won't show up unless you have some high end gear to test with. Don't let anyone talk you into LMR-400UF, that's just overkill.

 

[srbecker58]

There must have been something up with or wrong with the cables I had then. I got some of those right angle RG-58 jumpers from Amazon and my SWR went from 1.03 up to 1.32 on repeater channels and then from 1.79 on simplex channels to 2.24 after those cables. I didnt like that much, so I ended up returning them and went back to the LMR-400 jumpers I have in the photo above. With that I am getting 1.00 on repeater channels and 1.79 on simplex channels.

I think I am going to just order up a 4' jumper of something a little more flexible and run it (removing the SWR meter) from a full time install to just when needed since I already know I am getting a good SWR.

 

[mmckenna]

A cable like that shouldn't have a big impact on SWR. In fact, it really shouldn't have any.

If it was a cheap cable, cheap connectors, or improperly assembled, then I think that would be your issue.

If you do this, get name brand cable. While it will be more expensive, it's going to work correctly. www.theantennafarm.com will make custom cables for you, and they sell premade jumpers. They've been a reputable company.

If you really get in a jam, let me know and I can fabricate some for you.

 

[srbecker58]

Thanks mmckenna! If it were your radio, would you leave it as is with the LMR-400 as pictured, or go with something a little more flexible like a 4 foot run of RG-8X directly from bulkhead (antenna) to back of radio and take the LMR-400 and SWR meter out of the equation. Especially now since I know it works properly and I am getting decent SWR readings, I dont really need to be concerned with it anymore.

 

[mmckenna]

I would never connect LMR-400 directly to the back of a radio like that. I've done it in rack mount applications where the radio doesn't/cannot move and I can properly support the cable. I've seen too many Motorola's that had the little mini-UHF connector snapped off the back when someone has tried that.

If you have RG-8X, that would work great.
If the setup checks out, you can take the SWR meter out of the chain. It's likely not impacting things enough to make a big difference, but anytime you can do away with adapters or unnecessary connectors, it's a good thing.

 

[srbecker58]

Ok, that was enough to make me want to change it up lol. I think Ill get a 4 foot RG-8X connector and call it a day. I do have my radio mounted and secured, so the LMR-400 will be fine for now, but I do want to change it out to something more flexible. Is 8X my best bet or would there be something better?

 

[mmckenna]

Is 8X my best bet or would there be something better?

For a cable that short, you won't see a difference between cables on UHF.

 

[mmckenna]

4 foot jumper, 465MHz:

RG-58 = 0.365dB loss
RG-8X = 0.338dB loss
LMR-200 = 0.283dB loss
LMR-240 = 0.215dB loss.
LMR-400 = 0.109dB loss

The difference between RG-58 (least ideal of the 4) and LMR-400 = 0.265dB. Your ears will not know the difference.

You can play with this online calculator and try it out for yourself: Coax Calculator

 

[srbecker58]

Great thanks! So in reality, even that RG-58 I had and returned was likely fine, but maybe the connectors were the problem? Especially the right angle ones I assume? Oh well, I found a nice 4' RG-8X cable with ends on it. Gonna run with that I guess!

Thanks again for everything!

 

[mmckenna]

Great thanks! So in reality, even that RG-58 I had and returned was likely fine, but maybe the connectors were the problem? Especially the right angle ones I assume? Oh well, I found a nice 4' RG-8X cable with ends on it. Gonna run with that I guess!

Thanks again for everything!

The cable shouldn't throw the SWR so far off like that. Makes me think there's an issue with one of them. It's not worth the headache, though. It's not hard to make a cable. If a seller on Amazon screwed it up, there's probably other issues. If your RG-8X is good, roll with that.

 

[n1das]

The cable shouldn't throw the SWR so far off like that. Makes me think there's an issue with one of them. It's not worth the headache, though. It's not hard to make a cable. If a seller on Amazon screwed it up, there's probably other issues. If your RG-8X is good, roll with that.

I suspect the cables are perfectly fine and there's some mismatch at connector(s) along the way from the radio to the antenna. A quick and easy test would be to add adapters in the path and see how the numbers change.

From the photo it's hard to tell what connectors are on each piece of the setup. The mobile radio usually has an SO-239 to accept a cable with a PL-259 connector on it. I have a love/hate relationship with PL-259 and SO-239 connectors. They are called UHF connectors but they absolutely suck at UHF and aren't 50 ohms at UHF. They are more like 45 ohms at UHF instead of 50 ohms. I have a love/hate relationship with them because I absolutely love to hate them. I also hate their mechanical design. What I do on a mobile is put an N-female to PL-259 adapter on it and deal with all N connectors the rest of the way to the antenna and including the connector on the antenna. My old Bird 43 Wattmeter even has N connectors instead of SO-239s on it. Ideally I would want the mobile to have an N connector instead of an SO-239 or Motorola's mini-UHF connector. I don't know why the LMR industry continues to use a sucky SO-239 or mini-UHF connector instead of an N connector.

OP, What connector(s) and/or adapter(s) does each part of the setup have? Eliminating mismatches at all connectors from the radio to the antenna should help improve the SWR across the entire band.

I prefer to use my trusty old Bird 43 Thru-Line Wattmeter instead of a "SWR meter" and simply measure the forward and reflected power directly. If I want to know SWR, I can calculate SWR from the forward and reflected power numbers measured on the Bird 43. Tuning to minimize SWR translates to tuning to minimize reflected power so just measure reflected power directly on the Bird 43 and then calculate SWR if you want to know the SWR.

 

[srbecker58]

Everything is UHF connectors except the adapters on the SWR meter.

 

[mmckenna]

Yeah, UHF connectors are not ideal, but adding adapters to the rear of the radio can be problematic.

I'd ditch the SWR meter once you've checked everything out. Keep everything else N connectors, which I think is what I suggested in your original post. Issue is, I don't think good ol' Ed Fong uses N connectors on his antennas. That goes back to the ham radio roots, and hams just LOVE them some UHF connectors.
Most higher end commercial stuff has N connectors on it.

But I don't think the UHF connector on it's own is your problem. A lot of perfectly good UHF commercial radios come with UHF connectors on them. It was sort of an industry standard for a while. Now some companies that sell top of the line radios use better connectors.

The idea that the specific length of the coax was changing your SWR crossed my mind, but I don't think that's your issue. I think you said you tried it without the SWR meter and it was still bad. I still think bad cable, and by 'bad cable' I mean some part of the whole thing. Absolutely could have been poor connector installation.

If replacing it with the RG-8 fixes is, then I think there is your issue. Length of coax shouldn't make that much of a difference if the antenna SWR is good. But again, Ed Fong…..

 

[mmckenna]

You need to be really cautious with inexpensive pre-made coaxial cables. While it's kind of hard to screw up, it's absolutely possible. Usually a simple continuity check is enough to tell you if it's good or not.

But I ran across some Tram NMO mounts that had pre-installed UHF connectors that were truly awful when I disassembled them.

I'm fortunate that I can roll my own cables and have good results with them. Most reputable companies can do a good job. But low buck Amazon/e-Bay cables can be pretty crappy.

 

[n1das]

Everything is UHF connectors except the adapters on the SWR meter.

UHF connectors as in N or PL-259/SO-239?

I dealt with this years ago on a Kenwood TKR-820 repeater I was setting up for GMRS. The repeater came with SO-239 connectors. I had short coax jumpers (RG-142/U) from the repeater to an external duplexer. I rolled my own cables too. The transmitter was putting out 25W but I was only getting about 5W at the end of the jumper connection to the duplexer. The power measured on the Bird 43 would change by using a longer or shorter jumper. The cabling inside the repeater used BNC connectors and the SO-239 connector was bulkhead mount BNC to SO-239 adapter. Changing the adapter to a bulkhead mount BNC to N adapter fixed the issue and then the length of the jumper connection from the repeater to the duplexer wasn't critical anymore and I got full power to the duplexer. The problem was due to mismatch caused by the SO-239/PL-259 connection.

 

[srbecker58]

I think we went down a rabbit hole didn't maybe my lack of explanation?

To clear up things. I had the following first.
Ed Fong Antenna with UHF > 40' run of LMR-400 with UHF connectors > bulkhead in the wall for a nicer finished look > 2' LMR-400 jumper UHF > UHF to N adapter > SWR meter > N adapter > 2' LMR-400 adapter UHF > radio. This setup gave me 1.79 on GMRS channels and 1.00-1.03 on repeater channels. Everything works great, great audio, great range, lots of compliments on clarity and signal strength.

Tried to swap ONLY the 2 jumpers with same length (2 feet) RG-58 jumpers for better flexibility and cable management, SWR readings nearly doubled. All I changed were (2) 2' jumpers for the same length jumpers also with UHF ends, but was RG-58 instead of LMR-400.

Hopefully that clears up what I did?

 

[srbecker58]

UHF connectors as in N or PL-259/SO-239?

I dealt with this years ago on a Kenwood TKR-820 repeater I was setting up for GMRS. The repeater came with SO-239 connectors. I had short coax jumpers (RG-142/U) from the repeater to an external duplexer. I rolled my own cables too. The transmitter was putting out 25W but I was only getting about 5W at the end of the jumper connection to the duplexer. The power measured on the Bird 43 would change by using a longer or shorter jumper. The cabling inside the repeater used BNC connectors and the SO-239 connector was bulkhead mount BNC to SO-239 adapter. Changing the adapter to a bulkhead mount BNC to N adapter fixed the issue and then the length of the jumper connection from the repeater to the duplexer wasn't critical anymore and I got full power to the duplexer. The problem was due to mismatch caused by the SO-239/PL-259 connection.

Yes, everything is SO-239 and PL-259 except the meter came with N connections and adapters

 

[n1das]

What are the "UHF connectors" in the setup, N or PL-259/SO-239?

EDIT: You answered while I was typing. D'Oh!