what is the different cable and antenna spec for vhf vs 27mhz?

[Shanaly]

[Wotname]

I assume this is a serious question despite the devil.

Both use 50 ohm coax (RG58/RG213/LMR400 etc etc).
Marine VHF uses an antenna tuned for about 155 MHz
Marine 27 MHz uses an antenna tuned for (you guessed it), 27MHz.

Sometimes a antenna tuning unit is used with a 27MHz radio.

Do you have a specific question?

[Shanaly]

thnx 4 that! yes: i have to connect the coax to my 27mhz radio/antenna - do i need a specific 27mhz fitting at each end - and is a marine 27mhz th same as land cb radio in all important respects?! thnx again

[Wotname]

Originally Posted by Shanaly

thnx 4 that! yes: i have to connect the coax to my 27mhz radio/antenna - do i need a specific 27mhz fitting at each end - and is a marine 27mhz th same as land cb radio in all important respects?! thnx again

Marine 27MHz is not the same as land CB in any technical aspect, (except they both have microphones and speakers )
CB radio operates in the UHF band and the 27MHz operates in HF band.

Please note that Marine 27 MHz is very much an Aussie thing; very few (if any) other countries use it.

The usual connector found on these radios is the PL259 (AKA UHF), see UHF connector - Wikipedia, the free encyclopedia

Being as you are in Perth, send me a PM if you need a hand with basic radio stuff.

[denverd0n]

In the USA, CB frequencies range from 26.965 MHz to 27.405 MHz. Not UHF. Is "CB" a completely different frequency range in Australia?

[SoonerSailor]

May be a matter of definition. What we call FRS or Family Radio Service is UHF at around 462 mHz. What we in the USA call CB is where DenverDon says, around 27 mHz.

[hellosailor]

You could get away with, and many adapters are sold for, using a standard "UHF" aka PL259/SO239 connector for both frequencies. While there are good technical reasons for using something better matched for the marine VHF, the "UHF" conenctors are common and if anything less suited for the marine VHF use. It is totally acceptable for the 27MHz use.

The VHF antenna may be more of a problem, I'd strongly suggest using an SWR meter and checking for a mismatch before trying to transmit the 27MHz radio on the VHF antenna.

[Wotname]

Originally Posted by SoonerSailor

May be a matter of definition. What we call FRS or Family Radio Service is UHF at around 462 mHz. What we in the USA call CB is where DenverDon says, around 27 mHz.

Yes & no to the matter of definition.
In Oz, we do have a Citizens Band 27 MHz service but it has a very small usage. The "normal" CB usage is the UHF service and what USA calls FRS, we just call CB (sometimes UHF CB or Public CB).

We also have a Marine CB service (known as 27MHz Marine) which operates of different frequencies to the land service.

This service had an enormous uptake and was for many years was sole radio in recreational boats. Over the past 20 years, VHF has become more common but the 27 Marine is still popular especially in smaller boats. All sea rescue services use it (along with VHF & SSB of course).

For frequencies see here Australian CB & Marine

[Shanaly]

hello and thanks to all for such helpful data - one other query: the bottom of my 27 MHZ antenna has only a tiny stub of coax cable coming out. i wish to join it to the rest of the coax - it parted by accident. the antenna appears to be permanently sealed, do i dare to break in to the bottom fitting to expose more cable? (ii am ok to glue any bits together with epoxy afterwards)

[Wotname]

Originally Posted by Shanaly

hello and thanks to all for such helpful data - one other query: the bottom of my 27 MHZ antenna has only a tiny stub of coax cable coming out. i wish to join it to the rest of the coax - it parted by accident. the antenna appears to be permanently sealed, do i dare to break in to the bottom fitting to expose more cable? (ii am ok to glue any bits together with epoxy afterwards)

You can try but usually it is unsuccessful and you end getting another antenna

However are you really sure you want to keep the Marine 27 MHz service, assuming you have a VHF service? There is no real advantage with the 27 MHz radio and once outside Oz, no use at all.

[hellosailor]

If the cable was torn, the odds are that the stub will have to be removed (unsoldered) and the entire cable replaced. So unless you are willing to solder and OK with soldering coax in particular, that could be a vote for "toss it".

The base probably was sealed in order to keep out water damage. If you can chew it open and then reseal it after soldering in the new cable. great. If not...the worst that can happen is you'll find that out and then toss it.

But if there's no other internal damage, sure, replacing the coax and resealing the base should be possible.