Poor radio reception - result

Durcott

Durcott

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Hi folks,

I posted a while back about poor VHF radio reception. Some of you gave your opinions, so I thought I'd report back what I found. There's another question at the end.

I found a reasonable SWR meter, complete with a dummy load, on EBay as suggested. The transmitter worked perfectly straight into the dummy load, but I measured total reflection from the cable between the radio and mast connector (N type socket). [Yes I had moved the load /forums/images/graemlins/wink.gif]

The cable looked like a fairly cheap RG058 clone. The plug at the radio end hadn't been soldered on properly, so I thought I'd 'fix' it.

To cut a long story - 'black wire rot' had got into the cable at least 2' into it and probably more. The centre conductor was brittle and impossible to work, and the braid, though tinned, was equally fragile like rotted cotton.

So there you go. No external indication, but internally ruined and useless.

Well - I can rewire with UR67 say, but I'd never get that up the mast. Is there anything I can do to avoid using relatively lossy RG58 inside the mast?

Thanks

Jeff
 
Durcott, as an ex-field service engineer working on marine comms gear I would say that if you have a rotted braid and a blackened centre conductor, then you can only replace it.
Its reached the end of its life and there is no telling how far that damage has crept up the cable. Cut your losses (multi pun eh) and replace it. Shame about tehe effort but it will be worth it for the increase in performance of the VHF.
When you do replace it, and it usually forms part of the aerial unless you have a wire whip held in to the bracket by a screw, then you will have to replace that as well.
Make sure that when you replace the connector that it is well sealed if it connects to a gland connector on the open deck.
I used to cover the cable and connector with a good wrap of self-annealing tape which wil form a water tight barrier when done properly. Alternatively use heat-shrink tubing over the wire and connector (borrow the wifes hair dryer if she will let you)
 
If I understand your question you are considering replacing the dud cable with the larger sized (i think) UR67 or RG 8. Yes you get less loss but I wouldn't suggest you rush to fit lower loss cable. The losses do not make a lot of difference and most people use RG58. You only need low loss for really tall masts then only if you are fussy. olewill
 
When my boat was designed we did coverage analysis comparisons for RG 58 compared to URM213/RG8 to the masthead. Unfortunately I don't have the analysis any more but roughly speaking the difference was approx another 20 miles reliable range on transmit to a stronger hilltop station for the larger coax and consequent lower power loss.

That was to our mast top approx 16 m above WL so around a little more than 20m total run of coax. Assumed shore station was powerful enuff and high enuff to be reliably received at around 60 nm from memory.

On that basis we figured it was worth the cost of an extra conduit up the interior of the mast to take the larger coax.

However, if you are stuck with no option other than the smaller coax you just have to accept the lesser performance - just buy the best you can.

John
 
[ QUOTE ]
I used to cover the cable and connector with a good wrap of self-annealing tape which......

[/ QUOTE ]"self-annealing tape" - what is that? I have never heard of it. I have heard of, and frequently use, self-amalgamating tape but I might try self-annealing tape - is it any better than self-amalgamating tape? Would you care to post a source of self-annealing tape. /forums/images/graemlins/wink.gif I don't seem to be able to find any in either RS components or Maplins catalogues
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"Artificial intelligence is no match for natural stupidity"
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There is a series of thin, flexible and very low-loss cables called 'Aircell 7', 'Ecoflex10' and 'Ecoflex15'. Sold here. Fully described in a PDF here

I have not used them in a marine environment but their specs look very good, maybe worth a try.
 
You need RG8X cable, good quality marine stuff. It is the best compromise for masthead runs less than about 20m. Nominal diameter is 6.4mm and attenuation is better than 3.7 db per 100 feet at 100 MHz. RG58 is typically 5.0 db per 100'. RG58 is really only for interconnecting equipment. It has grown into the cable of choice for cheap antenna manufacturers, but is rarely offered for long runs by reputable suppliers. RG213 is the best, but probably overkill for the typical small boat.
I declare a commercial interest because we sell cable.
 
Don't worry, you are putting out 25W. You are not going to see a real difference. The main key, as you have found, is the integrity of the system.

I once bounced the signal off a rock face just off Gomera and talked to a yacht 50 miles away. There is plenty of power considering the advances in receivers.

I would spend the money on the connectors and the aerial and any mast base joints.
 
[ QUOTE ]
You need RG8X cable, good quality marine stuff. It is the best compromise for masthead runs less than about 20m. Nominal diameter is 6.4mm and attenuation is better than 3.7 db per 100 feet at 100 MHz. RG58 is typically 5.0 db per 100'. RG58 is really only for interconnecting equipment. It has grown into the cable of choice for cheap antenna manufacturers, but is rarely offered for long runs by reputable suppliers. RG213 is the best, but probably overkill for the typical small boat.
I declare a commercial interest because we sell cable.

[/ QUOTE ]

I am sure that this is absolutely correct, but in a way it misses the point. With a marine VHF radio you are wanting to ensure good line of sight comms with an MCA station. By and large, they will have an aerial reasonably close to you and receivers with decent sensitivity. So whilst the 0.6 db difference that the cable might make in a 50 ft typical run would matter if you were a radio ham trying to talk to Spain on 2m using 1 watt, it wont make any practical difference for you using 25w on your boat to talk to the local coastguard or your mates nearby. Thats why manufacturers use the cable they do when making aerials and why these aerials actually work.

To put it another way, IMHO its a bit like putting racing slicks on the wife's Astra! Sure its going to improve things but is the difference worthwhile?
 
I agree with the principle of matching the performance of each component in a system, which is why I am happy to recommend RG8X as the best compromise for runs up to 20m. Going to RG58 is a step too far for me; on the other hand the very expensive RG213 is of doubtful advantage, unless you consider the benefit of the greater structural integrity of the larger cable.
Buying an extremely fine radio and then coupling it to a rather dubious antenna system doesn't make much sense - like putting your wife's Astra tyres on a racing car!!
 
A point to keep in mind with the smaller higher performance cables is that they often have a solid centre conductor (RG8X does not tho') and/or foam polyethylene dielectric (which RG8X does normally, but not always, have). Both, in my view, are not wise choices for cables not well supported over their whole length or subjected to tight radius bends.

I personally would not use them up a yacht's mast.

John
 
Hi Cliff and anyone else who read my post. I said to use "self-annealing" tape. I should have said "self-amalgamating" tape, as Cliff correctly pointed out. A slip of the fingers on a greasy keyboard and a lack of editing before posting.
 
"100% tinned copper"

A must to ensure integrity. I assume in your original post the tinned reference was to the soldering not that the braid was manufactured already tinned.
 
Yes, the best coax is manufactured with a tinned copper braid and centre core for best corrosion resistance and easy soldering. Ancor makes marine grade coax this way.
 
I sympathise with the tinned copper and would not distract from its use.

However, for coaxial cable it is not something that I concern myself for my own use, that working on the assumption that once water has wicked in to damage the copper, then the coax losses will have increased anyway just from the water whether tinned or not.

Tinned probably is worthwhile on most boats where the owner would not be expected to be able to pick up increased losses just from water ingress readily and the tinning does limit further consequent losses from corrosion for some time.

Really, the above just a point to demonstrate that just cos tinned does not mean that the coax will not become lossy once water has gotten in (so different in that compared to, say, DC cabling which only becomes lossy through corrosion if water gets in).

John
 
[ QUOTE ]
I agree with the principle of matching the performance of each component in a system...................................Buying an extremely fine radio and then coupling it to a rather dubious antenna system doesn't make much sense - like putting your wife's Astra tyres on a racing car!!

[/ QUOTE ]

Or indeed putting my wife in a racing car /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

I dont think I would describe most marine vhf sets as "extremely fine radios". But then thats a matter of opinion.

I use RG58 for my ham radio set up at home and on the boat - mostly at 4 and 7 mc/c and with 100 watts through a 40 foot run. What cable would you recommend for that application since my aerial is due for renewal anyway.
 
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