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Author Topic: Coax Suitable for VHF/UHF  (Read 264 times)

VE7AXU

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Coax Suitable for VHF/UHF
« on: Yesterday at 05:06:27 PM »

I am getting back on the air after ten years and re-climbing the learning curve. I am erecting a vertical outside for my VHF/UHF base station but cannot figure out what type of coax to use. Is it the same as for HF?

Thanks in advance for setting me on the correct road.
VE7AXU
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KD2HCU

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Re: Coax Suitable for VHF/UHF
« Reply #1 on: Yesterday at 05:53:37 PM »

VHF/UHF  will have higher losses in the cable than hf, so get a good thick low-loss coax.
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K1VSK

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Re: Coax Suitable for VHF/UHF
« Reply #2 on: Yesterday at 06:03:01 PM »

Do a search for coax loss calculator. They are numerous and will give you loss data for whatever choice you plan.
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N8AUC

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Re: Coax Suitable for VHF/UHF
« Reply #3 on: Yesterday at 06:06:50 PM »

If by VHF/UHF you're referring to the 2m and 70 cm bands, I've had good success with LMR-400.

Since insertion loss is usually specified as dB/100 ft, how long of a coax run will you need to get from
the operating position to your antenna? It matters.

LMR-400 has 1.5dB of loss per 100' at 146 MHz, and 2.7dB of loss per 100' at 450 MHz.

Belden 9913 has similar loss specs, but it has that nasty habit of filling up with water.

73 de N8AUC
Eric
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K0ZN

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Re: Coax Suitable for VHF/UHF
« Reply #4 on: Yesterday at 09:32:53 PM »

It kinda comes down to your budget and how much you want to maximize the range of your station. If you just want to work through local and reasonably close repeaters, you don't need to break the bank buying coax.... assuming you don't have a long run of coax.
For reasonable lengths, I also agree that LMR-400 has great bang for the buck. I strongly recommend AGAINST any of the smaller or reduced size coax; use full size. If you want to squeeze every last watt and mile out of your set up use 7/8" heliax. I had that on one of my home station antennas and I definitely could hear mobiles direct at longer distances; it is good stuff....but not cheap.
The mistake a lot of new hams make is they buy a good gain antenna and then "lose" the gain by using small diameter coax which has significant loss.  EVERY antenna is a compromise in some fashion. You just gotta figure out what is the best compromise in your situation.

73,  K0ZN
« Last Edit: Yesterday at 09:38:49 PM by K0ZN »
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KB8VUL

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Re: Coax Suitable for VHF/UHF
« Reply #5 on: Yesterday at 10:02:57 PM »

Oh GOD you HAVE TO USE 1 5/8 at a minimum for ANY run over 3 feet or the losses in the cable will eat up all your signal like the cookie monster on a plate of chocolate chip.  For the love of GOD.... GO take out a second mortgage on your house right now so you can blow a scratch off lottery ticket's worth of money on feed line.

Now for the real truth.
And this isn't some made up, I got my two by three and I am a RF genius ramblings.... It's real radio and real results.

Is there loss in cable runs... yes of course there is.  But there is also over doing things over a few dB of signal level that will have ZERO realized effect in how your station performs.

First off.  And understanding of decibels (dB) and figuring out just what effect losses actually have. 
Look at your HF rig.  Signal meter is in S units S-1, 2, 3 and so on.  To move that needle from S3 to S4 you need to have a 6dB change in signal level. 
A signal level change of 3dB is a doubling of the signal.  So 1 watt (30dBm) the 'm' is an indicator of a SPECIFIC reference that being 0dBm is 1 milliwatt.  30dBm is a watt.  Now, 3 dB increase to 30dBm is 33dBm OR 2 watts. Now when you add 3 more dB, or 6dB (36dBm) the 2 watts double again to 4 watts.  An S unit (from the meter mentioned before) is a 6dB change.  So your 100 watt radio being heard at an solid S-4 by the other guy would need to come up to 400 watts to make his meter show S-5.  And if you played much radio, you know that doesn't change the intelligibility of the signal much at all. 

Personal experience.
I have a GMRS (actually 3) repeater running at 50 watts out.  That goes into a hybrid transmit combiner that has 6 dB of loss due to the tight frequencies in it.  So my 50 watts becomes 12.5 watts before I ever get to the coax.  Now, while my coax IS 7/8 it's also 350 feet long to the antenna.  SO there is another 3dB of loss.  Now we are at 6.25 watts at the base of the antenna.  It's got 6dBi of gain so my ERP is 25 watts.  THe repeater can be heard 50 miles away.  SO what do you accomplish by running antenna cable that costs more than the radio it's connected to?? Not much. 

Figuring loss per foot requires you to look at your station and the feed line distance.  Can you take a 3or 4 dB hit on the signal level and still be effective.  And the bigger question is if you cut the losses in half, and double your 'watts' to the antenna, is it gonna have a really pronounced effect on the overall ability of the station to talk further.  And you need to weigh the cost vs performance as a consideration as well.

Now, this shouldn't be considered as a license to run 200 feet of RG-58 to your antenna either.  But the folks that get on here and tell you to run 7/8 for a HOME INSTALLATION should fess up about what they are using to feed their antenna's cuz I bet it ain't 7/8.
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G4AON

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Re: Coax Suitable for VHF/UHF
« Reply #6 on: Today at 12:49:42 AM »

I am erecting a vertical outside for my VHF/UHF base station but cannot figure out what type of coax to use. Is it the same as for HF?
If possible use coax with less than 1dB of loss for the length you need. RG213 type coax is typically used, although the slightly less loss foam dielectric types would be my choice.

Here I use Hyperflex 10 for all my VHF/UHF antennas, together with their superb matching plugs. I am sure there will be Canadian equivalents. Details: https://messi.it/en/catalogue/50-ohm-cables-ham-radio/hyperflex-10.htm

73 Dave
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KD7RDZI2

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Re: Coax Suitable for VHF/UHF
« Reply #7 on: Today at 01:18:55 AM »

Cellflex is the right answer. I am fan of Aircell-7 cable, which require its connectors (also excellent) but if you have long run (say 100ft) consider to use a PA with preamplifier that can be put closer to the antenna as possible. In this case both TX and RX will be sensibly ameliorated.
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LA9XNA

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Re: Coax Suitable for VHF/UHF
« Reply #8 on: Today at 02:37:02 AM »

My roule of tumb.
less than 5m (15 ft) RG58.
between 5m and 10m (30 ft) RG 213.
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W9IQ

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Re: Coax Suitable for VHF/UHF
« Reply #9 on: Today at 04:50:37 AM »

I am getting back on the air after ten years and re-climbing the learning curve. I am erecting a vertical outside for my VHF/UHF base station but cannot figure out what type of coax to use. Is it the same as for HF?

It is helpful to know the length of the coax that you need to install.

The coax in your application will have the greatest loss on UHF frequencies. Your reference to a vertical antenna suggests that you are using it for local FM communications. Your choice largely becomes one of economics if there are no other limitations or considerations. Here is a comparison of the UHF loss for some of the commonly used cables (ranked from least loss to most loss):



Then keep in mind these losses are based on a matched load (SWR of 1). If your load is not matched, the losses will generally increase.

- Glenn W9IQ
« Last Edit: Today at 05:05:16 AM by W9IQ »
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

VE7AXU

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Re: Coax Suitable for VHF/UHF
« Reply #10 on: Today at 06:22:03 AM »

Thank you to all who patiently responded to such a rookie question - your answers were really useful and jump-started me back on to the air.

John VA7PX
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N8AUC

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Re: Coax Suitable for VHF/UHF
« Reply #11 on: Today at 06:55:32 AM »

I like KB8VUL's description. Lots of good, specific info.
Bottom line is it's way easier to lose signal in a poor setup than it is to get it back.

As for the dB thing....yes 3dB of gain or loss is doubling or halving of a signal, if the measurement is power.
If you're talking voltage, like on an S meter in a receiver, 6dB is double. Why? Because:

db (volts) = 20 * log (Vout/Vin)
db (power) = 10 * log (Pout/Pin)

In the end, everything is a tradeoff.
How much do you want to spend, vs what level of performance is acceptable for your use case?
Only you can make that decision.

73 de N8AUC
Eric
« Last Edit: Today at 07:03:53 AM by N8AUC »
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W1VT

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Re: Coax Suitable for VHF/UHF
« Reply #12 on: Today at 07:01:43 AM »

Depends on the distances your station is expected to cover.
For a few miles it doesn't matter.
But, if  you want to cover 100 miles,  you need a pretty good station with a clear horizon.
If you can do that, propagation theory suggests that improvements to reach 250 miles may be practical, so why not spend a little more to cover a much bigger area?
Surplus Heliax can be quite inexpensive in lager sizes as folks don't really want to deal with stuff bigger than 1/2 inch Heliax.  Low demand drives down the price.

If you are running FM and verticals you can get by with cheaper coax.
If you run SSB/CW/FT8 with a beam on a tower with a clear horizon it can be worthwhile to minimize coax loss.
Folks used to put a brick amp on a tower.  Nowadays one can mount the entire station near the antenna and access it remotely via the Internet.
« Last Edit: Today at 07:03:44 AM by W1VT »
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K1VSK

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Re: Coax Suitable for VHF/UHF
« Reply #13 on: Today at 07:02:43 AM »

if you played much radio, you know that doesn't change the intelligibility of the signal much at all. 


In a world where all of us care about ERP and erecting the most effective antenna we can, a few dB can make a difference, particularly when signals aren’t strong.

It only makes sense that, when it’s a simple matter to choose among feed lines, we try to minimize avoidable loss.
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N8AUC

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Re: Coax Suitable for VHF/UHF
« Reply #14 on: Today at 07:45:42 AM »

Oh GOD you HAVE TO USE 1 5/8 at a minimum for ANY run over 3 feet or the losses in the cable will eat up all your signal like the cookie monster on a plate of chocolate chip.
I wish I could run 1 5/8 hardline, but that's waay outta my price range. So I don't use that.

Now for the real truth.
And this isn't some made up, I got my two by three and I am a RF genius ramblings...
Which you won't get from ham store catalogs...or most places on the internet.
I got a 1x3, been a ham for 45 years, have held an Extra Class license for 30 years, and back
that up with a BSEE with lots of years working with airborne radar, comms, and defense systems.
I'm telling you KB8VUL is 100% spot on. So much for credential waving.....LOL!
I don't consider myself an RF genius, but I do have a lot of "been there, done that" under my belt.

Personal experience.
I have a GMRS (actually 3) repeater running at 50 watts out.  That goes into a hybrid transmit combiner that has 6 dB of loss due to the tight frequencies in it.  So my 50 watts becomes 12.5 watts before I ever get to the coax.  Now, while my coax IS 7/8 it's also 350 feet long to the antenna.  SO there is another 3dB of loss.  Now we are at 6.25 watts at the base of the antenna.  It's got 6dBi of gain so my ERP is 25 watts.  THe repeater can be heard 50 miles away. 
The important fact here is that it's 350 feet to the antenna. That implies some really nice antenna height!
The #1 factor that determines the effectiveness of your station at VHF/UHF is antenna height. There simply is no substitute for that. Your transmitter output power governs how well you saturate that coverage area. After that, you can start considering feed line insertion loss. There is an old (but very true) saying, "At VHF/UHF, sufficient antenna height cures all sins." Yes folks, altitude is your very best friend at VHF/UHF. OMG - he's losing 3dB in his system!!! Yes he is, but with that kind of antenna height it's pretty much a "don't care" condition. Because the desired performance is there.

Now, this shouldn't be considered as a license to run 200 feet of RG-58 to your antenna either. 
That is truly sage advice. One would be well served to adhere to that!

But the folks that get on here and tell you to run 7/8 for a HOME INSTALLATION should fess up about what they are using to feed their antenna's cuz I bet it ain't 7/8.
Exactly right. Which is why I use LMR-400. Acceptable performance at a price I can afford.
Can you get better coax? Sure you can. But just how deep are your pockets?

KB8VUL - keep preaching the truth, my friend!

73 de N8AUC
Eric
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