VHF aerial, SWR meter and lack of range conundrum.

[Simondjuk]

Since finishing the refit on our boat and fitting a new VHF set and masthead aerial, I've been slightly dubious about the range achieved.

Having made a couple of radio checks, I decided it was definitely poor, so set about fault finding.

I got hold of an SWR meter and had a test. SWR of over 3. Not good, bad connection somewhere thinks I. First off though, checked the meter with the emergency VHF aerial and got around 1.25, which is much more like it and shows the meter is good.

Back to the fixed equipment, I started with the PL259 at the back of the radio as it made sense to start at one end, it was the easiest to access and it was dark outside at the time. All looked good there, no shorts, well soldered but I remade it anyway just to be sure and as there was no more to be done until daylight. SWR'd it, no difference.

Come daylight, the next point of call was the deck plug, which in the end I decided was never going to be properly damp free, so best used only as a gland to pass the cable though with a connector in the warm and dry below decks. This I did, using two more PL259s, joined with a back to back barrel connector. I used these as I had them about and since the back to back connector gives me a convenient place to connect the emergency VHF antenna should the need arise without needing to get to the back of the radio itself. Two apparently good connections made. SWR tested, still 3, swore a bit.

By way of a process of elimination, I decided to try the emergency aerial again, this time on the barrel connector. SWR 1.25. This told me that my connector at the radio and my connector into the barrel are both good. Thinking that the only connector which can now be at fault is the last one, which connects to the aerial side of barrel and is on the coax down from the masthead, I remake it. Looks good, no shorts, well soldered. SWR it, still 3! I growl at it.

I then begin to wonder if the new aerial, a Vtronix Heliflex, has a fault. Could it? Really? Nah, surely not. I can't get up to have a look at it anyway, so I decide to experiment. I put the emergency aerial back on and wave it around a bit. Bringing it very close to anything metallic pushes the SWR up to a little over 2, but not well into the red at 3.

The reason I do this is that I'm growing concerned that the aerial may not be faulty, but its positioning may be, since it is not above but alongside the stem of the hawk. Not really close, probably about 6 inches away, and certainly not nearly as close as I have to move the emergency antenna to anything metallic to raise the SWR.

By now I'm running out of ideas and starting to doubt everything. I decide to give the emergency antenna a whirl in anger. Hoist it about 10 feet up on the flag halyards to give a worst case scenario, and shout Solent CG on 67. "Loud and readable, but with lots of interference." Immediately feel rather silly, turn off probably very electrically noisy nearby fan heater and try again. "Loud and clear. Good signal." Thanks muchly to the CG and at least it's nice to know that the emergency aerial works well, as reaching Solent CG from a makeshift aerial at a height of 10 feet in the depths of Chichester harbour seems to me about as good as one can expect.

The only thing left is to try the proper antenna with all its newly made joints in anger in the vain hope that the SWR meter is lying to me. So I connect it back up, SWR it just to make sure I haven't somehow made it even worse than 3, no still 3, and give it a shot on 67. Nicht, nada, not a dickie bird. They can't hear me, and after a while of listening I find I can only hear them in fits and starts.

So, what does the panel think? Has anyone ever fitted a new VHF aerial and found it to be duff? Could the proximity of the shaft of the hawk to the aerial really be obstructive enough to interfere with both transmissions and reception, and also push the SWR up even though moving the emergency antenna much closer to much larger metallic objects had much less effect on the level?

I'm flummoxed and without good reason and exploring any and all other possibilities, don't really relish the idea of a trip to the very top of the mast - the unstayed and elegantly tapered top 1/4 of it doesn't really look man enough to dangle people from.

Any suggestions gratefully received.

Failing a deck level fix, does anyone know of a suitable 30 odd foot high wall one can get a lift keeler alongside?

 

[timbartlett]

The feeder cable isn't overlength, by any chance? Because if so, and especially if you have made it into a nice neat coil, that would do it. Better to cut the feeder cable to the right length.

 

[whipper_snapper]

Well done, a logical and sensible series of tests to narrow down down the source of the problem. You would be amazed how few people seem capable of doing that!


The problem really has to be the coax to the masthead, the connection to the aerial or the aerial itself. And yes, a brand new aerial can have problems, most likely the connection with the coax. If you can only hear in 'fits and starts' that suggests a major problem. Proximity to the windex cannot be the issue. Was the mast down when the new aerial was fitted ? Maybe it was banged when the mast was stepped ?

Looks like you need to go up the mast! Maybe check for crush damage where the coax enters the mast 1st.

 

[john_morris_uk]

Well done, a logical and sensible series of tests to narrow down down the source of the problem. You would be amazed how few people seem capable of doing that!


The problem really has to be the coax to the masthead, the connection to the aerial or the aerial itself. And yes, a brand new aerial can have problems, most likely the connection with the coax. If you can only hear in 'fits and starts' that suggests a major problem. Proximity to the windex cannot be the issue. Was the mast down when the new aerial was fitted ? Maybe it was banged when the mast was stepped ?

Looks like you need to go up the mast! Maybe check for crush damage where the coax enters the mast 1st.

I agree totally - and the problem 'might' be a manufacturing fault in the new antenna - its not unheard of.

 

[uxb]

Slightly OT since you've proved the connections.

But I never use those coax plugs- I solder the cores together, insulate , then re weave ( roughly) the screen.

Hate to say it but it does sound like a duff aerial.

 

[Simondjuk]

Thanks for the responses all.

Tim. No, there's only a small length of spare cable inside the boat and even less in the mast. We're talking a bit of slack to allow a few remakes of connections, certainly not coils of it.

Mr Snapper, I should have pointed out that the Heliflex is a stub aerial, so shorter than the windex with no clear radiating length above it. Could that make a difference? The mast was down when it was fitted, but I did it myself, grommeted the cable's entry and exit holes in the mast carefully and for the aerial to have been bashed whilst the mast was down or being lifted, the windex would have had to have been bent first, which it hasn't been.

John, I'm starting to think it is a duff aerial. Of all the things, it would be something at the masthead which doesn't work out of the box.

uxb, I agree about not being keen on extra connectors but wanted a place to quickly connect the emergency aerial, so they've provided that, and they are fully soldered, both conductor and screen, so have half a chance of working reasonably.

Looks like I might need a suitable wall to go against.

 

[starfire]

worthwhile borrowiing or buying a dummy load, even one rated for less than 25W as you can do the tests on low power.

even this may not show 1:1, anything below 1.5:1 is good enough.

 

[Reverend Ludd]

Have you tried anther length of coax to eliminate the one running in the mast from the equation.
If you need a dummy I could post you one and when you have tested your rig you could send it back.

 

[Seajet]

I don't know about the stub versions, but my old V-Tronix stainless whip aerial had the cable disappear into the base in a pre-made join, which seems the likely culprit in your case.

I have just replaced it with a Glomex stainless whip, and notice that has a connection to the base, which seems a much beter idea.

This aerial is about 6" away from a Hawk, no problems there - though it's a lot taller than the Hawk.

Does sound like a duff factory join to your aerial.

 

[nigelmercier]

I'd put my money on a dodgy connector the mast end, which was disturbed when you fitted the new antenna.

 

[Simondjuk]

Starfire, Excuse my ignorance, but what's the purpose of the dummy load when testing?

Rev Ludd, No, I've not been able to substitute the coax in the mast. If I were to go up there I'd probably just swap the aerial out on the first trip anyway to save a second. The coax is permanently attached to the aerial anyway, I think in a resin filled connector block. Thanks for the offer of the loan of the dummy load, but before I go further, as per my question to starfire, what will it tell me that an SWR comparison to a known good aerial won't. I'm not familiar with their use, so completely ignorant.

Seajet, Indeed, the Heliflex is the same. Not ideal.

Nigel, It's looking that way I guess. What a pain.

 

[whipper_snapper]

Starfire, Excuse my ignorance, but what's the purpose of the dummy load when testing?

It cannot add anything to what you already know. You have already done much better by using your emergency aerial.

 

[starfire]

It cannot add anything to what you already know. You have already done much better by using your emergency aerial.

I agree with that, but a dummy load is a known good test for the coax & connectors, the plus point is you do not radiate (perhaps a little) when doing tests.

 

[oldgit]

Real world.

Is that a good quality proper VHF SWR meter you are using ?.
The length of the cable including patch lead can affect SWR.
IF ......you are getting a sensible range forget that 3.1 its perfectly acceptable.
If it works OK just use it

 

[Puggy]

I read your posts with interest as I am in the process fitting both a Vtronix whip with RG58 cable (AIS) and Metz with RG213 (VHF) to my main mast whilst it is removed from the boat

I notice the in the instructions for the Vtronix, they suggest testing the resistance across the core to shield: 10,000 ohms is good, 0 indicates a short etc. might be worth checking this before pulling everything apart at the top of the mast? Also, my Vtronix has a small ferrule type connector between the RG58 and the antenna, I think it would be checking this is properly assembled, especially if it was supplied already assembled.

P

 

[Bilgediver]

Any suggestions gratefully received.

Failing a deck level fix, does anyone know of a suitable 30 odd foot high wall one can get a lift keeler alongside?

Some current antennas need the coax very carefully prepared before making the connection at the antenna. They have a pin in the antenna connection which must pierce the centre conductor stranding. The centre conductor and insulation must be cut flush and a specific distance longer than the braid and outer insulatlion and the braid is folded back over a washer. Any departure from this can create a short in the antenna. Hope you find a high wall or wee assistant with a head for heights

 

[Playtime]

I
I notice the in the instructions for the Vtronix, they suggest testing the resistance across the core to shield: 10,000 ohms is good, 0 indicates a short etc. might be worth checking this before pulling everything apart at the top of the mast? Also, my Vtronix has a small ferrule type connector between the RG58 and the antenna, I think it would be checking this is properly assembled, especially if it was supplied already assembled.

P

This test only works on some aerial types. Unless the instructions for your particular aerial specifically recommend this test, don't bother as you could be misled by the result.

 

[st599]

Slightly OT since you've proved the connections.

But I never use those coax plugs- I solder the cores together, insulate , then re weave ( roughly) the screen.

Hate to say it but it does sound like a duff aerial.

You'd be better off with correct impedance connectors.

 

[Playtime]

Water in the coax down the mast is quite common. I had this problem. I discovered it when checking the underdeck connector - water actually ran out of the coax after I disconnected the connector. The SWR was reading around 5 but, amazingly, the radio still worked with reasonable range (mid channel to SCG).

 

[starfire]

I read your posts with interest as I am in the process fitting both a Vtronix whip with RG58 cable (AIS) and Metz with RG213 (VHF) to my main mast whilst it is removed from the boat

I notice the in the instructions for the Vtronix, they suggest testing the resistance across the core to shield: 10,000 ohms is good, 0 indicates a short etc. might be worth checking this before pulling everything apart at the top of the mast? Also, my Vtronix has a small ferrule type connector between the RG58 and the antenna, I think it would be checking this is properly assembled, especially if it was supplied already assembled.

P

Some aerial types appear as open circuit at DC, one of the tricks is to wire a high value resistor across core/shield inside the antenna, no effect on the RF side, but allows you to check for open/short circuits with multimeter.

Other aerial types appear as short circuit at DC, so not possible to check.