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Old 11 July 2008, 16:04   #1
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Country: UK - England
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Icom 411/ VTronics Rib Raider antenna problem

Can anyone help me. My VHF transmission signal is very weak. I was out on the water last week and called the coast guard. He responded by saying that my signal was barely audible. I called my local marina which was only about 500 metres away and could not make contact. However, on return to the entrance of the marina, I was able to make contact, but then I was just 30 metres or so from the marina office.

I checked the RF cable and found it to be faulty (continuity between core and screen), so I replaced it. I sent the radio back to Icom. They tested it and returned it, confirming that it was well within spec. I installed a new Vtronics antenna believing this was the solution, but it seems not. The only thing that I haven't changed, is the last 15 cm of RF cable that connects to the antenna. Could the problem be with the brass bullet connector that connects into the antenna???

I tested my replacement RF cable for any signs of continuity between the screen and the core cable, and it was fine. Can't figure it out..... pulling the last of my hair out!!!

Other than replacing the whole of the RF cable, I'm lost for next steps. Radio, antenna and boat are brand new.

Any ideas??? Thanks,,,,, Brian
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Old 11 July 2008, 16:10   #2
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I'm getting hopeless performance from my new Standard Horizon GX1500 Class D VHF coupled to a rib-raider. I'm tempted to ditch the rib-raider for a shortish GRP antenna.
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Old 11 July 2008, 18:25   #3
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you will find alot of unhappy customers who have had or still have the rigid Raider aerial,

i have been there also, 50 mtrs away from Chris and he could not hear me,, i ditched it and went to the 1 mtr whip V Tronix aerial and worked superbly!!
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Old 12 July 2008, 04:48   #4
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Brian; have you also checked continuity along each conductor (end to end) on the old piece of cable?

I have had odd problems with the PL-259 connectors; sometimes tweaking the "leaves" of the female socket that the centerpin fits into (push them in towards the center so they hug the pin tighter) helps a bit.

Luck;

jky
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Old 12 July 2008, 12:39   #5
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Quote:
Originally Posted by matt h View Post
you will find alot of unhappy customers who have had or still have the rigid Raider aerial,

i have been there also, 50 mtrs away from Chris and he could not hear me,, i ditched it and went to the 1 mtr whip V Tronix aerial and worked superbly!!
I have an Icom 421/Rib Raider and have had what can only be termed 'structural' problems with this aerial:

http://rib.net/forum/showthread.php?t=20615

However, before they have disappeared into the drink, I have never had any tx/rx problems. From my driveway on the Bristol channel I could hear shipping calling Bristol VTS off Watchet... Bristol was complaining the transmission was broken but both sides were crystal clear for me!

Aerial no. 3 is still present and correct by the way, with no signs of failure thus far!
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Old 13 July 2008, 14:42   #6
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Get an SWR check done, my guess is that all your power is getting lost or bounced somewhere, a duff connector is sufficient.

The following points should be observed when installing a VHF.
1. Fixed VHF take a lot of power from the battery when transmitting, so battery and cable size is important. Long runs need thicker cable to prevent volt drop.
2. Every connection in the antenna wire will lose power, so ideally only have one at the back of the set and the one at the base of the antenna. Using cable joiners etc only saps you power and can introduce noise. Typically 3dB of power per connector, so two PL259's and a joiner would drop 9dB, i.e. you would drop to 1/8 of your input power >> 25W would be reduced to 3.125W
3. Dont be tempted to cut the antenna cable too short, typically try to leave at least 3 metres.
4. Connectors need to be soldered or crimped, simply screwing on and folding the wire over is no good!

Incidentally, some antennas will show a dead short with a multimeter, however at radio frequencies they don't.
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Old 14 July 2008, 06:06   #7
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Quote:
Originally Posted by geoffs View Post
Get an SWR check done, my guess is that all your power is getting lost or bounced somewhere, a duff connector is sufficient.

The following points should be observed when installing a VHF.
1. Fixed VHF take a lot of power from the battery when transmitting, so battery and cable size is important. Long runs need thicker cable to prevent volt drop.
2. Every connection in the antenna wire will lose power, so ideally only have one at the back of the set and the one at the base of the antenna. Using cable joiners etc only saps you power and can introduce noise. Typically 3dB of power per connector, so two PL259's and a joiner would drop 9dB, i.e. you would drop to 1/8 of your input power >> 25W would be reduced to 3.125W
3. Dont be tempted to cut the antenna cable too short, typically try to leave at least 3 metres.
4. Connectors need to be soldered or crimped, simply screwing on and folding the wire over is no good!


Incidentally, some antennas will show a dead short with a multimeter, however at radio frequencies they don't.
Geoff, Thanks for that. I didn't realise the effect of adding joints on power. The cable that comes with the antenna is just 6 metres long, which is around a metre too short to couple VHF to antenna on my boat. Consequently I have a crimped BNC connection which is adding an additional 60 cm of cable. I'll see if I can get a single cable with an appropriate antenna connector.

Thanks for everyone's advice....

Cheers,,,, Brian
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Old 14 July 2008, 13:48   #8
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Often the case. When I install cables for customer they are usually too short, if the cable can be removed from the antenna then I will replace it with one of the correct length, if not then I will crimp a BNC male and a BNC female on and extend as required. Yotties often want to be able to take their masts down so a joint is inevitable but unaviodable.
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Old 20 August 2009, 04:31   #9
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Vtronic arials

We have always had problems with the Raider Whip Antenna's over a period of
time as they seem to allow water via the top. We recently replaced them
with 2 4' GRP made by Shakespeare for Vtronic's and had the same
problem communicating with the Coast Guard. While our second Antenna
for our PMR had a very short range. Our Coms expert decided to look inside.
The C G only had about 8" of ordinary co-ax linked to a small brass
tube , and the open end inner core and cox ax were soldered together.
All enclosed in a 4, GRP Rod ! The PMR just had about 6" of the main
co-ax and no brass tube. Our Coms Expert replaced them with 2
hi tec short stubs and perfect long range communications has been
established. As a Rescue Service this poor communication with Coast
Guard had put lives at risk , and I wonder why it was neccessary to use
a 4, impressive looking rod for a 8" stub. We also had a old broken GRP
antenna which when we cut in half had a proper copper tuning coil and
full length steel rod. Tiffy Venturers Search and Rescue.
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Old 31 August 2009, 07:10   #10
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Founf (and fixed) the problem

Quote:
Originally Posted by Tiffy View Post
We have always had problems with the Raider Whip Antenna's over a period of
time as they seem to allow water via the top. We recently replaced them
with 2 4' GRP made by Shakespeare for Vtronic's and had the same
problem communicating with the Coast Guard. While our second Antenna
for our PMR had a very short range. Our Coms expert decided to look inside.
The C G only had about 8" of ordinary co-ax linked to a small brass
tube , and the open end inner core and cox ax were soldered together.
All enclosed in a 4, GRP Rod ! The PMR just had about 6" of the main
co-ax and no brass tube. Our Coms Expert replaced them with 2
hi tec short stubs and perfect long range communications has been
established. As a Rescue Service this poor communication with Coast
Guard had put lives at risk , and I wonder why it was neccessary to use
a 4, impressive looking rod for a 8" stub. We also had a old broken GRP
antenna which when we cut in half had a proper copper tuning coil and
full length steel rod. Tiffy Venturers Search and Rescue.
Tiffy, Thaks for that.

I have after just over 12 months of frustration, fixed the problem.

I eventually contacted Shakespeare who manufacture the VTronix antennas. I was told that I should be able to measure 10,000 ohms accross the PL259 plug which connects the antenna cable to the back of the VHF radio. When I checked with my multi-meter, I found it to be open circuit. I then connected the original Rib Raider that was installed by Humber when I bought the boat. It was short circuit.

I called Shakespeare and informed them of these readings, and they asked me to return the antennas to them, which I did. The guy that I spoke to in their Product Support department was very helpful and told me that they had found water in one of the antennas. Consequently, they replaced both faulty units with good, tested units.

I wish I'd contacted Shakespeare a lot earlier as I could have saved myself a lot of anguish and expense in replacing cables, sending the radio back to Icom twice. I never expected two consecutive antennas to be faulty. I the end, I was very pleased with their service. My VHF reception is excellent now, and I have a spare antenna in the cupboard, as a back-up, just incase the worst should happen again.

Cheers,,,, Brian
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