75 olm coax resolve?

[pede69]

Hi Guys...

Quick question please...

Good 50 ohm coax is expensive. But I just happen to have 3 500 foot rolls of high grade 75 ohm coax.

What can I do for using it for cb's. Auto and/or base.

Just getting back into 11 meter after years of having no clue what is going on in the CB world. I do know that new high grade 50 ohm coax is expensive.

I would prefer to not build (or buy) a matching box for every application.

Are there any other solutions?

Thanks much,
John

 

[Moleculo]

You could run equal odd 1/4 wave lengths soldered together into a single PL-259 (for the radio side) and run a cophase setup at your house or in your mobile.

 

[pede69]

Thank you...

Anyone else?

Thanks,
John

 

[wcsd106]

Use it for feedline.

75ohms isn't far enough off of 50ohms to give you too much trouble... just remember you're going to be looking at a 1.5SWR as your theoretical "perfect match" with a good 50 ohm antenna.

If it's what you have and will let you get an antenna in the air, go for it.

 

[pede69]

Thanks wcsd106...

You don't know of a small inductor or resistance circuit I could throw together to match it up?

Thanks again,
J

 

[DJboutit]

75ohm coax is used for setting up dual antennas like running 2 hot coil antennas 7ft to 9ft apart

 

[Beetle]

Go ahead and use it. Experiment and see what works well and what not so well. I've used RG-59 and RG-11 (both 75 ohm stuff) for dipoles and yagis in the days before antenna analyzers were even thought of.

 

[jazzsinger]

If your using a dipole antenna it has a characteristic 72 ohm impedance,so feeding it with 75 ohm coax is exactly the same as feeding it with 50 ohm coax,either way you'll have a 1.5:1 mismatch.instead of the mismatch being a the antenna end as is usual using 50 ohm coax,it will be at the radio end with 75 ohm,the end result will be the same.

you can also use it as others have said to cophase mobile whips using odd mutiples of a quater wave (allowing for velocity factor) on each leg of the cophase harness,by running them right back to the radio you can connect them to the rig/swr meter with a t splitter,if using a swr meter you will only need a short 50 ohm connection to the radio.same applies to two base station antennas cophased.

you could also use it to feed a quad,again with odd multiples of a 1/4 wave.

you can basically use it with odd 1/4 wave multiples on any antenna that has a 100 ohm or thereabouts characteristic feed impedance,as it will transform that feed impedance to approximately 50 ohms at the radio end.

 

[tracker1962]

If you google "convert program", you should be able to find (mine is the first hits) a free program from a Josh Madison.
With this tool, my friend in the cable business helps me to calculate 75 Ohm coax lengths to use for my radios as I have lots of RG-11 kicking around.
Hope this helps.
tracker.

 

[Shockwave]

For low power stuff (250 watts PEP or less) where a perfect match is not required RG-59, RG-56, and RG-11 will work in place of 50 ohm cable with no noticeable change in performance in nearly all applications. That is unless your rig has very fussy VSWR foldback. If the run is long (100 feet or more) consider that smaller RG-59 and RG-56 cables have more loss then RG-8 or LMR-400. RG-11 is low loss 75 ohm in the RG-8 size. I agree if you have quality 75 ohm coax and new 50 ohm coax is not in the budget, by all means use what you have. Even if you don't calculate ideal cable lengths, the stuff will work fairly well.

 

[jessejamesdallas]

Strip it down, and use the shield for ground strap....Give the Copper Center conductor wire to some poor crack-head standing on the corner...