Coax query for uhf, vhf

Hi all putting up a 2m,70cm sharman , I have some rg58 left over is it OK to use this... Thanks...

Hi Chris,

All depends on how long your coax run is going to be.

When you get into the world of coax and it's losses you'll have typical lookup tables for 100ft lengths, (30m in new money). But it should be obvious that if you use much shorter lengths, (my attic antenna run is only about 12ft), the loss issues will be far less. It's quite common for VHF 'marine' installations on small boats to be fitted with RG58.

I have no idea where you'll be installing your antenna or where the radio will be so ultimately your coax length. If you're making a long run, (antenna on top of the house, radio on the ground floor), then the longer lengths will start making a dramatic difference. At 100ft a 10W transmission on RG58 may be cut down to 2-3W reaching your antenna on VHF and you might get as little as 1W on UHF!! 

Of course the situation will be worse for your UV5r as you more than likely have much less than 10W to start with.

If you're doing a big installation such as fitting the antenna to the roofline, chimney or some such then it's probably best to start with the best coax you can afford. The last thing you want to do is go to all that trouble then have to get back up there just to change your coax(!)

If you're bolting the antenna to a fitting on the side of the house at the gutter line and only using a shorter coax run into the house to the radio then you'll more than likely get away with the RG58.

As I mentioned, my VHF/UHF antenna, (dipole), is in the loft space just above my radio room and as such I knew I'd get away with my RG58.


Hope that helps you mate.

All the best,
Victor

Hi Victor thanks for that help, it's going to be bolted about gutter line, probably be about 20ft of coax at the moment while its all setup in the dining room, until I can get it into the spare room, then it will only need approx 8,10ft, might just order some rg58x to play safe, my missus says you just like to spend, oh well you can't take it with you... Thanks...

No worries Chris. Nice to see you excitedly getting your Ham station setup after gaining your new qualification. 

Got a good price on the aerial from your location £49 Cranfield Rd, I think it's the sharman 2m,70cm, good gain 7.5db on uhf..

RG8x do you mean lol.
Soon have that shiny new m7.

Yep getting my coax wrong,, will be on nervous pacing all week...

I would look at Thursday and if it comes before a bonus.
Did my test on a Tuesday it came on the Saturday.
Victor got his quicker think he got his in 2 or 3 days.
From what i believe it is a lady that does them one at a time i would think as i think she is a volunteer but i could well be totally wrong on that.

Just had a email from moonraker UK, they said rg58 is ok for short lengths I said 12, 15ft..

Aircell 7 is pretty good stuff ,dual screened .

They're a great lot at Moonraker Chris, (my local outlet ) Alway give good and sensible advice.

Don't wear out your carpet pacing on that certificate arrival.
Got mine quickly but I'm only spitting distance from RSGB headquarters. The mule pack tends to take longer travelling out to the wilds and fringes

26ct954 wrote:

Just had a email  from moonraker UK,  they  said  rg58 is ok for short lengths I said  12, 15ft..

Depending on whose RG58 you use, you’re looking at about 10dB of loss per 100’ at 450MHz.

Now, and forgive me if I’m teaching you what you already know, remember that 3dB equates to half power, and 6dB is quarter power....so if you had a 100’ run, you’d be losing 90% of your signal!

Scale that back to your 15’ though, and you’re only losing 1.5dB which is easily tolerable (a mere sixth of your power lost)....but for the cost of 15’, I’d probably run something better anyway! 

What do reckon rg8x

26ct954 wrote:

What do reckon rg8x

You’re asking a cable snob. 

For that run, anything will work....but whatever you go for, get quality branded cable, not eBay crap where the shield hardly covered the dielectric! 

Personally, I’d go a thicker cable, but that’s just me, and not because you need to. I usually buy lengths of coax whenever I see it at a good price, and then over engineer everything.

Up to you.
Main thing is you want that 2/70m aerial up as high as possible so you don't want to be going up there again in a hurry.

Alan Pilot wrote:

Up to you.
Main thing is you want that 2/70m aerial up as high as possible so you don't want to be going up there again in a hurry.

Ah, the beauty of double story houses with chimneys! I remember those! 

Oh, and just to add, seal the connector, or you’ll be cleaning it all up sooner than you’d like when your SWR goes through the roof one day....I usually use self-amalgamating tape with insultating tape over the top, to stop the Sun’s UV rotting the sealing tape...but that will be less of an issue back in the UK.