Why can't I transmit on some VHF channels?

Re: Why can\'t I transmit on some VHF channels?

[ QUOTE ]
Why doesn't it work? He already told us the most likely reason: "the cable run inside the boat from the radio to the deck socket ...... innards were a showing some blackening when I cut it back to re-make the connection yesterday."

[/ QUOTE ]Sounds plausible to me. That black copper is death to wiring....you have to strip it all out. Funny thing that quite a few folk here persist in telling people that it is OK to wire in untinned. You never get black with tinned.
 
Re: Why can\'t I transmit on some VHF channels?

ANT is the radio protecting itself. Bite the bullet, you radio is a safety item, get a new antenna and cable and replace the lot. DOety. NOT skimp on your saf
 
Re: Why can\'t I transmit on some VHF channels?

[ QUOTE ]
ANT is the radio protecting itself. Bite the bullet, you radio is a safety item, get a new antenna and cable and replace the lot. DOety. NOT skimp on your saf

[/ QUOTE ]Why are you telling me this? /forums/images/graemlins/confused.gif
 
Re: Why can\'t I transmit on some VHF channels?

In response to High tech...

Fully agree with your principle that VHF is very important from a safety aspect... that's why I asked a technical question in the first place to help me get the system to work at it's best. I am interested in the significance of the radio working OK on lower frequencies and then dropping out as they rise.

My antenna and wiring down to deck level is only six months old. Of course this doesn't preclude it being faulty, but I will look at the other components first.

I really do appreciate the advice of all of you who have a much greater technical understanding of radio than I.
I just wish I wasn't working all this weekend and won't be get back down to the boat until tuesday... otherwise I'd be a flurry of co-ax, plugs, sockets and solder.. and systematically work through all the permatations.

I look forward to reporting back
 
Re: Why can\'t I transmit on some VHF channels?

My opinion is based on the OP ... where he asks what may be fault. He profers the comment that he found blackening of cable - which as many know is not uncommon in cables not only on boats - but rarely actually fails connection. It may prove higher resistance.
Many then jumped on wagon of Yes it's cable with no other info or detail .......

My suggestion was to test radio with alternative VHF antena or if not available - WE found in my office that a base loaded CB antena worked fine. The radio still in use today.

As to radar etc. - I had the misfortune to have to maintain such 10cm and 3cm and as it happens RT equipment VHF and HF / MF ... so have a reasonable understanding. It may not be text book ... but done. Sad in'it !
 
Re: Why can\'t I transmit on some VHF channels?

"He profers the comment that he found blackening of cable - which as many know is not uncommon in cables not only on boats - but rarely actually fails connection."

Really?! Disturb a cable with blackened copper and you will very rarely get a connection again. At least, not on any boat I ever owned - and I've seen rather a lot of blackened cables over the last 40 years! And had to replace them.....
 
Re: Why can\'t I transmit on some VHF channels?

Agreed, and not only don't you get a connection with black copper, the wire itself seems to go brittle. I've tried various fluxes to remove black, then tin and re-connect, but it's never worked - not even Bakers!! You have to strip it all out and rewire.
 
Re: Why can\'t I transmit on some VHF channels?

[ QUOTE ]
"He profers the comment that he found blackening of cable - which as many know is not uncommon in cables not only on boats - but rarely actually fails connection."

Really?! Disturb a cable with blackened copper and you will very rarely get a connection again. At least, not on any boat I ever owned - and I've seen rather a lot of blackened cables over the last 40 years! And had to replace them.....

[/ QUOTE ]

I totally agree that if disturbed it will need replacement.
 
Re: Why can\'t I transmit on some VHF channels?

[ QUOTE ]
I totally agree that if disturbed it will need replacement.

[/ QUOTE ] coo, Schrödinger's cat





















EDIT>> Did I really waste my 10,000 post on that. I was planning to leave, though I might now just close this login and start a new one, I don't wish to be one of those people! 10,000 I need to go out more.
 
Re: Why can\'t I transmit on some VHF channels?

Ah -see where you're coming from now Refueller.

But unless he had opened the connector, he wouldn't have known it was black. Being a fairly obvious problem, that seems the place to start.
 
Re: Why can\'t I transmit on some VHF channels?

I didn't discount the cable - I just find it strange that it works on some channels and not others. I think the easy step of carry radio to another boat - plug in / connect a known working antena and try it out is a resaonable action to take as well. For me it would be first action. Then to attack cables first of all by metering before dismantling.

I'm talking my method here ...
 
Re: Why can\'t I transmit on some VHF channels?

Well, still not quite there.

I tried with my emergency aerial set up. Plugged it directly into set and all worked fine. i.e straight TX indicator on all relevant channels irrespective of frequency. That gets rid of the voltage and radio queries.

I've replaced the cable inside the boat from the radio to the deck socket. But problem still there exactly the same. so...

Now working on last three possibilities... deck plug joint... masthead connection to antenna.... antenna itself.

Don't you just love boats
 
Re: Why can\'t I transmit on some VHF channels?

[ QUOTE ]

Now working on last three possibilities... deck plug joint... masthead connection to antenna.... antenna itself.

[/ QUOTE ]

I will bet anything that it is the deck plug or the connections you just made on the new coax inside the boat. Deck plugs for VHF are a menace. If you can take the opportunity to get rid of it, then I suggest you do.
 
Re: Why can\'t I transmit on some VHF channels?

[ QUOTE ]
Deck plugs for VHF are a menace. If you can take the opportunity to get rid of it, then I suggest you do.

[/ QUOTE ]

My boat came with deck plugs for most stuff. I changed them for glands and all joins are now under deck.
 
Re: Why can\'t I transmit on some VHF channels?

OK - so radio is fine ... so it's down to cable and joints.

Out comes the multi-meter ... and prod round find where the faults are.

Glad to see someone doing 'elimination testing' instead of just jumping ! /forums/images/graemlins/wink.gif
 
Re: Why can\'t I transmit on some VHF channels?

Had a bit of a breakthrough today.... It works.

I examined both parts of the deck socket/plug and tested with a mulimeter. Was getting continuity through at whatever part of the circuit I tested.

Plugged the emergency aerial into the deck socket and... all worked. So this eliminated the wiring between the set and the deck socket.

I then read the masthead antenna instructions to remind me of the cable joint system up there (that I had fitted in a gale on the Deben). There was a note saying that "if the SWR is too high then cut 12" off the cable".

I tested the radio again and found that I was OK up to channel 15 now. On the basis that my new cable run inside the boat was a slightly different length to he one I'd taken out, I figured this could be relevant.

Snag is I haven't got a foot to cut off so I went the other way a connected-in my extension lead (say 5 meters) and.... All is well. "TX" displayed across the frequencies and contact with CG on 16 from Woodbridge.

I now plan to make-up a shorter extension, test it progressively and, hopefully, the job's a good'un

Many thanks for all the suggestions with this post. Turns out that all connections and the antenna were servicable but, as far as I can work out, the problem was with the cable length.

I certainly don't know why..... do you?

cheers
 
Re: Why can\'t I transmit on some VHF channels?

[ QUOTE ]
Turns out that all connections and the antenna were servicable but, as far as I can work out, the problem was with the cable length.

I certainly don't know why..... do you?

[/ QUOTE ]

No! It makes no sense at all. I can only imagine that after cutting 12" off you made a better connection. So you probably/possibly still have a dodgy connection. A multimeter will not tell you much - you will still see continuity if yu have a short across inner and outer or a break in inner r outer.
 
Re: Why can\'t I transmit on some VHF channels?

[ QUOTE ]

I certainly don't know why..... do you?

[/ QUOTE ]Yes, as any radio ham will tell you VHF frequencies don't behave like mains and dc. Completely different rules apply. It gets a bit mathematical and probably isn't of interest to most -- and would be hard to explain! Basically, the length of the cable is a significant proportion of a wavelength. When that happens 'different' electrical rules apply and you can throw Ohm's Law out into the trash bin (sort of).

Pleased that it is sorted.
 
Re: Why can\'t I transmit on some VHF channels?

Thing is I didn't cut 12" off... I actually added 5m. All the joints are still there in the line... I've actually added to them.

Whatever... I'm happy as long as Mr Ohm lets me hear the VTS, pick up a weather forecast and, heaven forbid, shout "help" if I need to.
 
Re: Why can\'t I transmit on some VHF channels?

Thing is I didn't cut 12" off... I actually added 5m. All the joints are still there in the line... I've actually added to them


it is not the cutting off that is important, it is the overall length of the cable. By adding 5m you have changed the length. If you understand frequencies have wavelengths, then try to imagine for simplicity, the sine waves travel up the cable to the aerial, added to this complication you get a reflected wave back from the aerial as no aerial will ever transmit 100% of the forward wave, this is the SWR, a reflected wave can cancel out the 'good' wave travelling up from the radio. You can not remove the reflected wave, but you can reduce it's affect by balancing the cable length and thus the point at which the reflection hits the forward wave. This is what you have done be changing the cable length.

I could get more technical, but my theory is rusty and my notes are in the loft. It sent me to sleep, it will send most on PBO catatonic.

This is also the reason most manufacturers suggest not cutting the cable unless you know what you are doing, they will send the cable at the best length for the aerial and frequency.

I suggest at this point you get a man in, or buy and learn to use a SWR meter as Richard posted above.

I would also suggest, if you have black cable under the socket, the main cable up the mast will be rather suspect, personally I would change mine if I found damage as you described.
 
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