Radio advice neede please.

[chasroberts]

We have an ICOM fixed radio on board. Radio reception has been pooor for some time and since recently buying a new Icom handheld this has become more obvious.

Replaced all the coax to the base of the mast, checked connections, continuity etc and found a short in one of the connections which has now been fixed and seems fine. Reception now seems better but transmissions are very poor with a boat half a mile away hardly receiving anything from the fixed set although crystal clear from the handheld.

Now I know you can damage a radio by broadcasting without a good aerial. Is this what I have done and if so is there anyway of checking? Plus is the set now stuffed or can it be fixed at a reasonable cost? Bit of an airy post I know but general thoughts would be much appreciated.

Thanks to all in advance.

Chas

 

[captainslarty]

Chas, what do you mean by ´replaced all coax to the bottom of the mast´? ... does that mean you didnt replace the coax in the mast or did you....
Most modern sets are protected against damage from faulty coax / antennas. Have you got an SWR meter ?
Or, can you borrow one.
Any reading under around 3 to 1 is fine.
Joe

 

[orizaba]

aha captain slarty sounds like a familiar problem,think it was how we sort of first met,hope all ok,youve been quiet today

 

[captainslarty]

Ullo Mick, yes fine, got friends over from the uk at the mo, so fairy occupied. Yes, it is how we met me thinks /forums/images/graemlins/smirk.gif
Have you got skype on ?

 

[Kawasaki]

Had the same Prob a few weeks ago.
Stuck a new Spike inc cable on.
"You are Loud and Clear on 16 and 84"
Replied Holyhead Coastgaurd. /forums/images/graemlins/cool.gif

 

[lenseman]

[ QUOTE ]
Replaced all the coax to the base of the mast,

[/ QUOTE ]
You don't say whether you replaced the cabling from the antenna DOWN the mast or whether you replaced the cabling from the Icom transceiver TO the mast? Why did you only replace part of the cabling?


[ QUOTE ]
Reception now seems better but transmissions are very poor with a boat half a mile away hardly receiving anything from the fixed set although crystal clear from the handheld.

[/ QUOTE ]
Are you switched to low-power on the main set?


[ QUOTE ]
Now I know you can damage a radio by broadcasting without a good aerial. Is this what I have done and if so is there anyway of checking?

[/ QUOTE ]
You can damage at transceiver by transmitting with a faulty antenna connection and a good method of checking is to connect a 50 Ohm Dummy Load (capable of handling 20 watts continuous) to the antenna socket and measure the current drawn. If you are transmitting on full power then the radio should be using about 6 to 8amps and the dummy load will be getting slightly warm.. These Dummy Loads can be purchased on-line although I would draw the line on buying one from e-Bay as it could have been overloaded and burnt out. (buyer beware!)

http://www.kcb.co.uk/shop/index.html?target=dept_20.html&lang=en-gb


[ QUOTE ]
Is the set now stuffed or can it be fixed at a reasonable cost?

[/ QUOTE ]
If you have damaged the transceiver, it can be repaired quite easily as it usually is the final RF output transistor (or RF power module). These are relatively cheap compared to a completely new marine radio. As a very rough guide, the RF final stage output power transistors or modules will cost anything from £25 to £75 but please don't hold me to these prices.

One final point, I notice you are in Gibraltar, could it be that the boat who was listening to your transmissions MIGHT have been in an area that caused his radio receiver front end to become desensitised by high power transmissions from other seaborne craft. I am, of course, referring to Royal Navy radar and the like?

 

[captainslarty]

Highly unlikely that the output is fried. If fried there will be no tx at all, maybe slight leakage from an RF driver but that would not be discernable more than a metre or two away.
The ALC on icom sets is also very very good.
Joe.

 

[VicS]

[ QUOTE ]
his radio receiver front end to become desensitised by high power transmissions

[/ QUOTE ] That is ruled out by the fact that he recieved transmissions from the hand held!

If the aerial and the lead from it to the deck has not been replaced that is alogical next step perhaps.

A good test of the radio will be to try it on another boat that has no problems, and the aerial + cabling can be tested with another good radio if anyone is prepared to loan one breifly.

 

[chasroberts]

Many thanks to all of you for your input.

Only replaced the coax as far as the base of the mast as didn't fancy a trip up the mast at that stage to replace the rest (the cable is split at the mast base to allow mast to be taken down and this was all renewed a couple of years ago.)

Will try the not too technical ideas first and if that don't solve it I will be back here crawling for help again.

Many thanks to all once again.

Chas

 

[Shanty]

Do you have an emergency vhf aerial? If so, try connecting that directly to the set & repeat your test with the boat half a mile away.

If reception is OK, then you need to check out the rest of your fixed aerial installation (trip up the mast). If not, your set is the problem.

 

[Kawasaki]

Didn't realise You had a mast!
I can only think mobo!
My symptom origionally, was Reception OK but no Transmision.

I did what VicS suggested and tried the set an another boat.
Luckily twas the same Radio set up an old ICOM IC M80.
Work perfectly.
Back to my boat and nothing at all!!
So new spike ,as mentioned, and all was well.
Easy peasy on a mobo.
Understand , for You it aint so easy!!

 

[mike_k]

Excuse my ignorance but what's a spike ? As in -

Stuck a new Spike inc cable on.