Don't forget velocity factor, quarter wave length will be different in coax to in free air.
If this was a tech support Q& A page i would agree with you.... but it isnt.
This is not an encyclopedia. It is not a technical journal. It is a discussion forum like many others.
The primary function is discussion.
As I mantioned other threads on this and many other boards get a great deal further off the subject than this one and no body seems to care in fact many enjoy where the thread takes them.
As I said before.. if they want to know if the should cut their coax... they have their answer in the first half dozen posts..........
no on with some further information
The GME site its self is pretty poor as far as information on marine areials.
but some of the marine catalogues are more helpfull.
in 27Mhz gme have three areials
AE364H which has loading coils and a cap in the base... fitted with a 5M cable
AE96 the 2.4M double swivel.... fitted with a 4M cable
AE66 the 1.8M double swivel that has a 2M cable
in VHF they have four areials.... there may be one more
AE31 which is designed to mount up a mast and has a socket on the bottom.
AE30 which has a bas like the AE346H.... there may be stuff in the base fitted with 3M of cable
AE87 2.4 m double swivel has a coil half way up and fitted with 3M of cable
AE346V 1.8m double swivel fitted with 5M of cable.
I note that there are a number of differing cable lengths and none of them are a neat multiple of a quarter wave length.
cheers
Don't forget velocity factor, quarter wave length will be different in coax to in free air.
wave length at 160Mhz = 1.875m
velocity factor of RG58CU 66% = 1.24m
still nothing comes up even.......I supose if 3meters was approximate 10 x quareter wave length is 3.090 meters..... and 5 meters is close to 16 quarter wave lenghts.
I can not believe that cable length could be that critical 4 full wave lenghts down a transmission line......
cheers
Nah I was just putting it out there, easy to forget. I agree that there is a high probability of cable length not being critical. Here's another idea, maybe many many years ago when they first started making the antennas it mattered. Then it was just carried over into newer models because it used to be a rule....
If there wasn't some sort of design requirement, why would you supply aerials with such a variety of different length cables?
Now here is a good one.......one of the marine catalogues lists a 5m GME extension cord and states that it is only suitable for 27Mhz areials.
What the.......
Baffelin'... just baffelin'...eh jock.
cheers
Ah and now the plot thickens........seems the boys at GME use some other sort of measurement other than SWR in assessing these aerials.
I seem to remember something about this from the dim dark past.
Seems to be that these ground independent aerials don't look good with an SWR meter..... never did and never will.... they are suposed to radiate well regardless.
any way my contact is making enquiries of some fomer work mates who will remember the full story.......
cheers
CUT!!
A direct cut and paste from an email direct from Navman
My question...
Message: Hello, Can the coax cable on a Navman VHF aerial be cut to a
more suitable length?
Thanks Scott
The answer....
Hi Scott,
Shortening the cable should not cause any problem.
Regards
Paul Godfrey
Product Support Technician
Navico Asia Pacific
His e-mail address.... Paul.Godfrey@navico.com
Seems pretty open and shut case to me
Just another reason not to touch the GME stuff in my books.
I intend on living for-ever....so far so good
I have broken my VHF aerial... not on purpose! I just forgot to lay it down when I left Yamba to head back up to the Gold Coast... By Broadwater I realised that I had left it up and had a look at it... the fibreglass tube was about a foot shorter than it used to be and there was just two stiff (~1.5mm dia) single core wires sticking out of the snapped tube. It still works though, I just tucked the wires back into the tube and siliconed the end up again...
I tested it the other day up the Terranora Inlet on the Tweed and the VMR said they could hear me loud and clear but it was very staticy when they replied... Maybe I should bite the bullet and get a new aerial?? Off shore (being that theres no structures in the way) it is clear as anything and I can hear the GC seaway as well so I figure its all good
Some information has finaly come back to me from ex GME employees.
Aparantly the GME ground independent areials are tuned using a sweep generator and a spectrum analiser......using this equipment they are tuned for best resonance with the measuerd coax attached......."the coax can be extended but not shortened".
I have no detail as to the areials being tuned "by design", by batch or individulally.
No replies from GME themselves yet.
cheers
Sounds like a lot of pelican poo to me and just another reason not to touch GME stuff
I intend on living for-ever....so far so good
If In doubt, just leave it as is and hide it out of sight with a few plastic cable ties
Especially if it is only for looks, I am sure you could tuck it away and cable tie it somwhere out of sight.
Always better to have too much than not enough, if you cut it you can not reverse that.
cheers
Aparantly the GME ground independent areials are tuned using a sweep generator and a spectrum analiser......using this equipment they are tuned for best resonance with the measuerd coax attached......."the coax can be extended but not shortened".
Now that's surely got to be codswollop from your source !!!!
A tuned length is a tuned length so if you lengthen the antenna you have to change the impedance either inductively or capacitively but I'm not going into that again!
Cheers