Other Car Tips: Convert from RG-58 to LMR-240-UF or RG-213.
I'd take that with a grain of salt. The length of coax in a car is about say 10 feet. The loss of 100 feet of RG-58 is say 5 dB? and the loss of fancy stuff might be 3 db? But the diffrence for only a 10 foot run is only .5 dB versus .3 dB or only 0.2 dB. Nothing at all to even consider compared to all the work it will take, and the lack of flexibility and trying to run something almost like pipe through places where a simple wire (RG-58) fits.
My lesson was learned 40 years ago when I go my first 100 lb UHF mobile rig (tubes) just after highschool. The boat anchor filled the entire trunk of my MGB. But the first thing I did when we go the lot of them in my club was spend a day replacing the 8" internal piece of RG-58 in mine from the Transmitter output over to the chassis connector with a 8" run of RG-8. It was hard work getting that 8" piece of RG-8 coax inside the radio and routed all around the internal chassis.
The elmer at the time laughed. He said you just wasted a day and all that work to save 0.01% of loss. So now your radio works at 100% where as before it worked at 99.99%. Losing 3 dB of course is one thing (50%), but trying to worry about that last 1% when the effort is tremendous is just not effective.
Anyway, just my 2 cents...
Bob, Wb4APR
At 06:48 AM 5/30/2009, Bob Bruninga wrote:
Other Car Tips: Convert from RG-58 to LMR-240-UF or RG-213.
I'd take that with a grain of salt. The length of coax in a car is about say 10 feet. The loss of 100 feet of RG-58 is say 5 dB? and the loss of fancy stuff might be 3 db? But the diffrence for only a 10 foot run is only .5 dB versus .3 dB or only 0.2 dB. Nothing at all to even consider compared to all the work it will take, and the lack of flexibility and trying to run something almost like pipe through places where a simple wire (RG-58) fits.
My lesson was learned 40 years ago when I go my first 100 lb UHF mobile rig (tubes) just after highschool. The boat anchor filled the entire trunk of my MGB. But the first thing I did when we go the lot of them in my club was spend a day replacing the 8" internal piece of RG-58 in mine from the Transmitter output over to the chassis connector with a 8" run of RG-8. It was hard work getting that 8" piece of RG-8 coax inside the radio and routed all around the internal chassis.
The elmer at the time laughed. He said you just wasted a day and all that work to save 0.01% of loss. So now your radio works at 100% where as before it worked at 99.99%. Losing 3 dB of course is one thing (50%), but trying to worry about that last 1% when the effort is tremendous is just not effective.
Anyway, just my 2 cents...
Bob, Wb4APR
Yep. Commercial NMO mount mobile VHF/UHF antennas typically come with 17-feet of RG-58 and a connector to install when coax is trimmed for the particular installation. I have way too many 100w mobile installs in my past ;-) Of course, FM repeater design is for overkill on signal margins so no one sweats coax loss for mobiles.
The repeater sites may see 100-150 foot hardline runs, though. I have one 120-ffot tower with 17 antennas and the coax are 1/2 or 7/8 inch Heliax with the longest run 180-feet.
73, Ed - KL7UW
On May 30, 2009, at 10:15 AM, Edward Cole wrote:
Yep. Commercial NMO mount mobile VHF/UHF antennas typically come with 17-feet of RG-58 and a connector to install when coax is trimmed for the particular installation. I have way too many 100w mobile installs in my past ;-) Of course, FM repeater design is for overkill on signal margins so no one sweats coax loss for mobiles.
While I agree with the comments that typical mobile installations have no need for low-loss coax, I've started using the slightly more expensive NMO mounts with low-loss coax in mobile installations for a different reason... the mounts are typically installed once and left alone, but someday I might want to hook up the 927 MHz FM rig and put an antenna on one of those mounts... and at 927 (or higher... say an Icom ID-1 for D-STAR use at 1.2 GHz), that lossy coax on the typical Larsen NMO mount becomes a problem. Larsen (and others) make the mounts with better coax on them for only a few more dollars, and amortizing that cost out over the 8 years I've owned the current vehicle (and counting), I think mobile installations fall under the same old Elmer's line "buy the best coax you can afford and you'll only have to install it once!".
Of course, if all you're ever planning on doing in the mobile station is VHF/UHF... it definitely doesn't matter. I want the flexibility to swap the antennas and run higher bands.
The repeater sites may see 100-150 foot hardline runs, though. I have one 120-ffot tower with 17 antennas and the coax are 1/2 or 7/8 inch Heliax with the longest run 180-feet.
Good repeater builders/designers treat the installation almost exactly the same as good weak-signal terrestrial or satellite folk's installations, for sure... we're trying not to lose any of that 100 mW pip-squeak signal from an HT in some guy's basement 20 miles away who is too lazy to do the math to figure out his path loss, when he calls complaining that the repeater is "deaf". LOL! Hardline on everything, commercial quality high gain antennas, appropriate levels of band-pass or window filtering and pre-amps... a good repeater site looks a heck of a lot like a station set up to receive satellites or terrestrial weak-signal SSB... other than the antennas are fixed, and they're vertically polarized...
Repeater installations also mean avoiding cabling with foil-over-braid and other things that don't duplex well, and various other things that satellite and weak-signal enthusiasts DON'T usually have to worry about at home stations... I have no qualms with using LMR-400 here at the house... using it at the repeater site can quickly become a disaster that eats up multiple weekends.
A good repeater, done right, isn't cheap... nor is it as simple as slapping up a cheap Diamond antenna on a tower in a good location and calling it "done"... and the money isn't in the radios. It's (just like weak-signal terrestrial and satellite work) in the antennas! :-)
-- Nate Duehr, WY0X nate@natetech.com
participants (3)
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Bob Bruninga -
Edward Cole -
Nate Duehr