Yagi Antenna & Coax

[radio69]

I am putting up a 8 elements yagi antenna for the 462mhz band. I would like to know what kind of coax should I use. I will be running a 100' coax. Some people recommended me the RG8-X , RG-213 and the RG-223. Thanks for the advices.

 

[kb0nly]

I would stick with RG8 size. I know a lot of guys will chime in and suggest LMR400, yep its good stuff, but spendy compared to other options, not to mention its stiffer than you know what and you can't make sharp turns with it.

I used to use 9913 but i don't like the hollow air core types unless your really careful about sealing it up, otherwise you end up with a water pipe.

I use a lot of Jetstream JT2015F, its the flexible variant of their RG8. They also make other versions of it as well. It's affordable, comparable specs to 9913 type coax and much more flexible with its stranded center.

Jetstream

Click on the pictures for the specs.

Either way, no matter what you do, at UHF try for the larger RG8 lower loss variants. Not some cheap RG-8X, RG-58, etc..

 

[James04TJ]

If I were installing an 8 element yagi for use on UHF with a 100' cable run I would not use anything short of LMR-400... My first recommendation would be to run Andrew Heliax LDF4-50A for everything up to the bulkhead and then LMR-400 or LMR-600 from the bulkhead to the base station depending on the length of that run. LMR-600 would be another option for the run from the antenna to bulkhead. Where Heliax is considered a semi-hardline, the LMR's are considered semi-rigid. I would prefer Heliax to LMR for a run from the antenna to the bulkhead any day. In fact you will find that a hardline or semi-hardline is all that is permitted up the tower at most commercial sites. I would not under any circumstances run RG-8x, RG-213, or RG-223. With any of these you will be loosing any gain that you are picking up with the yagi. Here is an estimated breakdown of feedline losses for your run.

RG-8x: 8.4dB (Belden 9258)
RG-213: 5.1dB (Belden 8267)
RG-223: 8.7dB (Coleman 991079)
RG-8: 2.9dB (Belden 9913)
Andrew LDF4-50A: 1.47dB
LMR-400: 2.7dB
LMR-600: 1.7dB

 

[kb2vxa]

James has the right idea, in a nut shell for UHF you need transmission line with the lowest loss possible because loss rises sharply with frequency. What I should mention because nobody else did is you MUST run a short, flexible jumper around the rotor from the top of the tower to the antenna or metal fatigue will snap the internal conductors. Ordinary RG-213 is just fine for the purpose only give it a wide loop, all coax hates a sharp bending radius as the center conductor migrates through the dielectric causing a lumped impedance at that point and a possible short eventually.

 

[James04TJ]

Absolutely correct Warren. Since he mentioned that it was on 462MHz I assumed that it would be a fixed side mount but a loop of a highly flexible cable is a must for any antenna that is mounted on a rotor. The loop need not be very long but must be enough to allow for the full rotors full rotational range.

 

[N_Jay]

What are you trying to receive, and why did you chose an 8 element yagi?

With that information MAYBE some of these guesses would be right.

 

[kb2vxa]

N_Jay, all he wanted to know is what sort of coax to use and we gave him all he needs to know, the exact choice is up to him with a wide selection to choose from. Why muddy the waters with pointless discussion when the question has been answered?

Fret not, you're only the first and there always is a first when opening a can of worms so guys, let's not start this nonsense all over again shall we? When the question has been satisfied move on to the next one... please.

 

[N_Jay]

N_Jay, all he wanted to know is what sort of coax to use and we gave him all he needs to know, the exact choice is up to him with a wide selection to choose from. Why muddy the waters with pointless discussion when the question has been answered?

Fret not, you're only the first and there always is a first when opening a can of worms so guys, let's not start this nonsense all over again shall we? When the question has been satisfied move on to the next one... please.

and if the yagi was to avoid a signal from a different direction, your answer would be the same as if it was to receive a distant station?:roll::roll:

 

[screenersam]

would RG8 be a good generic choice for antenna line? I'm hooking up a j-pole for 2 m outside my bedroom (only 10-12 feet high).

 

[W6KRU]

would RG8 be a good generic choice for antenna line? I'm hooking up a j-pole for 2 m outside my bedroom (only 10-12 feet high).

What is the total length of the coax going to be? It sounds like you might be OK with RG8X.

 

[K2QI]

For 462Mhz, Belden 9913 RG-8 gets my vote as total loss at 100ft is only 2.9db at 100w.

It's a good trade-off between price and performance compared to LMR600.

 

[nexus]

Times Microwave LMR-400

 

[gcgrotz]

For 462Mhz, Belden 9913 RG-8 gets my vote as total loss at 100ft is only 2.9db at 100w.

It's a good trade-off between price and performance compared to LMR600.

Keeping in mind that it represents half your hard earned transmitter power.

On RX however, I used to like to show people the difference using a service monitor to generate a signal producing 12db SINAD, which is very audible but noisy. Turn up the generator 3 db and it is still noisy, only slightly less so. Unless you are trying to reliably work a very marginal distant station, I would save the money and use good quality RG213 mil-spec. If you want every last drop of performance, then use 1/2" or even 7/8" hardline.

 

[kb0nly]

LMR-400 to 9913 you get a whopping difference of .2db, oh wow...

And for the record the Jetstream JT2015F that i use is 2.6db of loss at 400Mhz. So its about the same as the other variants of 9913 and LMR-400.

Why pay for the brand name and get LMR-400??