st599
Well-Known Member
I normally go to Nevada in Portsmouth - specialist supplier with decent stock.
Salty John Metz VHF Antenna
- Thread starter Jokani
- Start date
Rappey
Well-Known Member
I don't really see why someone would spend over the average price for a antenna and use it with rg58 coax. Rg58 coax can be bought for as little as 30p/metre.
Buy a really cheap antenna and use a better coax, that will probably outperform any expensive one using rg58.
100ft cable run with rg58 using 25w, output at antenna about 7.5w.
100ft cable run using rg400 @25 w , output at antenna around 23w.
Use a antenna such as the one suggested by momac which takes a pl259 plug and you can use a higher grade coax of your choice.
I was given a lot of rg400, double braded and silver plated. It was truly amazing the difference it made over the rg58.
Buy a really cheap antenna and use a better coax, that will probably outperform any expensive one using rg58.
100ft cable run with rg58 using 25w, output at antenna about 7.5w.
100ft cable run using rg400 @25 w , output at antenna around 23w.
Use a antenna such as the one suggested by momac which takes a pl259 plug and you can use a higher grade coax of your choice.
I was given a lot of rg400, double braded and silver plated. It was truly amazing the difference it made over the rg58.
st599
Well-Known Member
Yep - or go for RG8 mini which is available in all good radio stores for a similar price to RG58 in a chandlers. The key is getting a decent antenna with a proper connector you can use it with.
Also - PL259/SO239 - a shrouded banana jack of unknown impedance (and hence loss). Use BNC or TNC for any inline connections.
dgadee
Well-Known Member
They suggested a Sirio SB2/S
Seems to have moved to Milton Keynes.
Will get decent cabling, too.
IanCC
Well-Known Member
Isn't 7.5 w overkill for say 15 mile range anyway? Genuine question.
st599
Well-Known Member
If you fire 25W in to a system and lose 75%, you're heating up a lot of components.
The highest power gives you the best chance in an emergency.
The highest power gives you the best chance in an emergency.
andsarkit
Well-Known Member
I have just replaced my antenna with a Metz that I got from Salty John a few years ago before he closed.
The 30 year old antenna with RG 58 had been bashed and the coax had worn through the insulation and braid where it rubbed on the bolt for the lower shrouds ( no mast conduit).
I was expecting great improvements with the Metz and RG 8 coax but the VSWR only improved from 1.77 on the old antenna to 1.74 on the Metz.
What sort of VSWR are people getting on their installations? I was hoping for about 1.5 or thereabouts as at the moment I am only transmitting about 18W. I know it is an inverse square law but I would still like to push out another couple of watts if possible.
The 30 year old antenna with RG 58 had been bashed and the coax had worn through the insulation and braid where it rubbed on the bolt for the lower shrouds ( no mast conduit).
I was expecting great improvements with the Metz and RG 8 coax but the VSWR only improved from 1.77 on the old antenna to 1.74 on the Metz.
What sort of VSWR are people getting on their installations? I was hoping for about 1.5 or thereabouts as at the moment I am only transmitting about 18W. I know it is an inverse square law but I would still like to push out another couple of watts if possible.
Refueler
Well-Known Member
You have to look at the example he gave ... over 100ft .... that's 30m approx ... so the losses are spread over a long length .. so negligible temp rise in the co-ax. Think of actually how much length is really in your boat ...
If really concerned - there are boosters you can get hold of ..
Of course max power is desired ... but often the limitation is the fitting of plugs / connectors and threading the cables through ... RG58 is common because it fits the plugs and connectors easily ... it is usually easily passed through and formed round bends etc.
If you ever decide to take the better cable - you will find a) those connectors you have will not fit and you need bigger for the increased diameter ... b) quite often its not the most flexible or easily worked cable ...
Often its RG58 that is supplied with antennas !
st599
Well-Known Member
Checked one of the boats I worked on a few weeks ago, 1.08:1 at the top of the mast, 1.18:1 at the VHF. RG8 mini in to a Metz Manta with TNC joins at the mast base.
Slightly worse on the emergency antenna, but that's a small compromised size.
(10 years old - only issue we've had is having to replace self amalgamating tape every year)
dgadee
Well-Known Member
PBO needs to do an article on this stuff.
OCuea
N/A
I think they did decades ago about antenna separation distance ….. made great sense…… the days when the magazine was thick in size. Or else I read it somewhere else, or discussed it with a friend working at BAE (uk) but most people know 2 antennas should not be ‘next’ to each other if they have read a bit about the subject.
Refueler
Well-Known Member
I think they did ? Or at least one of the sailing mags did.
OCuea
N/A
I would think you need better coax - over 20 years ago I measured the vswr of my Metz and it matched the marketing value …… it was superb. At £60 I was very happy.
There are so many types of coax and my memory fails to remember the names and I can’t be bothered to google . I once messed around with coax that was almost half inch thick and stiff as heck ( may have been rg8 ? Or 213 …. sorry….. memory failure ) but excellent at reducing losses ( I remember that much) . Overkill for my modest needs but I was just experimenting. When I did sail I used a good co a. That was flexible and low loss (it was red coated sheath …. all I can remember….. the web will have all the info on good co ax)
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OCuea
N/A
I have not found an emergency antenna that is anywhere near as good as masthead ones , let alone the Metz. Those short stubby antennas are poor (according to my measurements and real life tests). I could not be heard with a standard horizon handheld radio as standard (well ‘barely readable was coastguard reply), but when I attached an antenna I had made ( held at same height as stubby) I was ‘loud and clear’
Refueler
Well-Known Member
Refueler
Well-Known Member
It was something I liked about my old hand-held M100 Icom ... actually the ONLY thing I liked !! The supplied antena could be removed and another screwed on to give better range ..
I still have it and it now has a LiPo battery connector to give decent battery life... instead of the crap oem pack.
st599
Well-Known Member
The best I've seen is an inflatable based on a scuba marker boy.
It contains a full size J-pole or helicoil antenna, folds down to a small pouch and if you're in a real rush, will inflate off a CO2 canister. Can be held aloft or raised on a string.
Refueler
Well-Known Member
Another was a measured length and then a Kite to get it aloft ...
Rappey
Well-Known Member
Back in 82' when cb radio (27 mHz) was polular many were obsessed about getting a 1:1 swr or close. Who could contact someone over the greatest distance was another. Many of the antennas had ajustable tips enabling fine tuning. A few mm could move the swr a noticable amount.
A vhf marine antenna is usually set for 156 mHz (ch 16) giving a half wave length of 95.1cm
Ais antenna (162mHz) is 88.1cm. I wonder what range difference 7cm makes as many use their radio antenna for ais.
My coax is 10.8mm. Certainly not for everyone. 3 times the power output at the antenna and probably 3 times more reception compared to rg58.
A vhf marine antenna is usually set for 156 mHz (ch 16) giving a half wave length of 95.1cm
Ais antenna (162mHz) is 88.1cm. I wonder what range difference 7cm makes as many use their radio antenna for ais.
My coax is 10.8mm. Certainly not for everyone. 3 times the power output at the antenna and probably 3 times more reception compared to rg58.
andsarkit
Well-Known Member
Thank you for that link.
This is the chart they provide::
I have 15m (50ft) of RG8X so I would expect to lose 2.3dB in the coax and so my output of 18w is about right. This doesn't consider the losses in the two PL259 connectors . Why don't VHF radios use BNC or even better N type connectors as the PL259 is rubbish in comparison. N types have the added advantage of being waterproof.
My tests were done with the Chinese electronic device and also with a dual needle meter.
For work I always used a Bird meter that seemed indestructable but they are really expensive even second hand.
How does st599 above manage to get a VSWR of 1.18 if there is a reasonable length of coax?
