VHF aerial, SWR meter and lack of range conundrum.

[TSB240]

We had a very similar problem to yours.

I eventually replaced the stubby helix aerial with a metz and recabled.

I pulled the old cable out of the mast complete with the mast head stub and found the cable was badly chafed by our wire main haliard.

The chafing had not completely gone through either inner or outer cores but the effect was to make transmit and receive very poor.

For my own benefit I tested with a meter and could not read any visible difference when two cores were shorted or not.

Is it possible that your cable has been similarly damaged hidden inside the mast?

Steve

 

[Simondjuk]

Apologies for not acknowledging all responses and brief reply but on mobile currently.

Steve, Good thought but it's only been in for a few months and not a lot of sailing, so I doubt chafe is an issue, esp given rope halyards.

Starfire, Indeed both masthead and emergency antennas test as open circuit. Obviously, this doesn't allow me to rule out a broken or badly connected conductor at the masthead.

Playtime, the coax appears dry. I've cut back up it a bit and core and shield are both bright.

Bilgediver, The coax/aerial connection was factory made and resin encapsulated I believe. I wouldn't send anyone up the mast, it's 3/4 fractional and very slender at the top as it tapers in both dimensions above the shrouds. It's a lovely spar, but not built for climbing from halyards exiting above the foresaty in my opinion.

Piers, the stub tests open circuit. I'll check the specs and see if this is correct.

Oldgit, No, it's an old CB SWR, but I'm using it for comparative testing against the emergency antenna, so no relying implicitly on the readings. I have a base reference. As for useable, it is but is severely compromised. The emergency aerial at deck level out performs the masthead aerial which simply isn't right.

Good idea on the resistance specs. I shall check to see if this aerial should show a resistance rather than open circuit. If it should, it makes it pretty certain the coax antenna connection is at fault.

Thanks all. Will report back later.

 

[Simondjuk]

Just checked and antenna should test open circuit, so I can't fault find up the coax.

Looks like I need that wall/quay/bridge. Any ideas in the Chichester/Solent area?

 

[William_H]

VSWR of aerial

The 3 to 1 VSWR measured is consistent with a fault in the coax near the top of the mast/cable. What happens is the RF power goes up the cable reflects at the fault and returns to the transmitter. In an ideal situation all the power would return showing infinity to one VSWR. However the natural losses in the cable for the RF in both directions means that only a portion is reflected and is measured at the meter at the bottom. (a perfect antenna does not reflect any power back) So 3 to1 might be measured. 3 to 1 might be OK for an antenna if it was indeed the antenna you were measuring if you measured to the antenna with a short cable. The losses of RG 58 ie 6mm diameter coax are quite significant in a typical 40ft mast run. OK for a good antenna though.
So it is up the mast or looking for a tall quay or lower the mast. good luck olewill

 

[TSB240]

Just checked and antenna should test open circuit, so I can't fault find up the coax.

Looks like I need that wall/quay/bridge. Any ideas in the Chichester/Solent area?

Simple Simon

Put wash boards in.
Attach two or more full 25litre water containers to the main haliard.
Place containers in water alongside.
Lift Keel right up.
Slowly winch mast down until horizontal.
Might need an empty berth or 2 alongside!

You get a free window and deck join sealing test at the same time.

Dont be too surprised how tender she will be with keel up!

If it works tell me and I might try it on my Trapper TS 240 as I need to fit a windyometer

 

[maby]

Just checked and antenna should test open circuit, so I can't fault find up the coax.

Looks like I need that wall/quay/bridge. Any ideas in the Chichester/Solent area?

Find two friendly yacht owners with masts taller than yours, raft up, attach a good strong bar to both their halyards and bosun's chair to the middle of bar, get them to both winch at the same speed? Having a very good head for heights and a lot of confidence in your friends will help a lot!

You probably need to use their spinnaker halyards - main halyards will foul spreaders and all sorts of other things...

 

[Simondjuk]

TSB240, Come on, admit it, you're just curious as to what the AVS of an Evolution 25 with 350 odd kilos of keel suspended in the middle of the saloon might be aren't you?!

maby, That sounds even more dicey than trusting the slender top 1/4 of my own mast. If I knew an professional trapeze artist, I might ask them to give it a whirl.

I know you lot have probably got your boats out of the water, so need some entertainment, but I'm not about to provide it without at least selling tickets I'm afraid.

 

[TSB240]

TSB240, Come on, admit it, you're just curious as to what the AVS of an Evolution 25 with 350 odd kilos of keel suspended in the middle of the saloon might be aren't you?!

but I'm not about to provide it without at least selling tickets I'm afraid.

Go on you know it makes sense

 

[lenseman]

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

There is a very fine bridge just 100 yards upstream of Haslar Marina.

 

[whipper_snapper]

Simple Simon

Put wash boards in.
Attach two or more full 25litre water containers to the main haliard.
Place containers in water alongside.
Lift Keel right up.
Slowly winch mast down until horizontal.
Might need an empty berth or 2 alongside!

You get a free window and deck join sealing test at the same time.

Dont be too surprised how tender she will be with keel up!

If it works tell me and I might try it on my Trapper TS 240 as I need to fit a windyometer

I actually did something similar in Solva harbour once. In a bilge keeler with an inflatable dinghy tide to the back, we dried out overnight and next morning afloat agin could not find the dinghy until we followed its painter and found that it had refloated under the boat, stuck between the bilge keels. There was no way to simply pull it out without destroying it. So we took the main halyard onto an adjacent buoy and winched until the boat was on its ear and the dinghy shot out of the water like a Polaris missile. Isn't the learning curve fun!

 

[Simondjuk]

Thanks for the explanation, William. The intricacies of antenna performance are not something I have much knowledge of, so every bit of information is valuable.

TSB240, No! Actually, I could use a somewhat lower vantage point in conjunction with a bit of heeling, so I may employ some of your idea, if not the full 90 degrees!

Lenseman, That looks perfect. The pontoon is even about the right distance away from the bridge for a nice moderate angle of heel to bring the masthead down to the height of the bridge, and conveniently positioned lamp posts on the bridge to secure the halyard to. The only problem, as I'm sure you know, is that they are JSASTC pontoons, so I rather suspect I'd get turfed off in fairly short order.

 

[lenseman]

. . . . Lenseman, That looks perfect. The pontoon is even about the right distance away from the bridge for a nice moderate angle of heel to bring the masthead down to the height of the bridge, and conveniently positioned lamp posts on the bridge to secure the halyard to. . . .

You attach a painter to the bridge piers and drop a heavy kedge or two from the stern downstream.

All you have to do is work the painter until the Haslar Bridge get nearer and nearer. Hop ashore in the RIB to the public slipway at Haslar Marina and walk onto the road bridge to do the business.

There is very little river traffic below that bridge as it just goes another 200 yards to mud berths. I will have to drop a lead-line down from the top to see the height (bridge parapet to Haslar Creek water).

 

[lenseman]

. . . . . Lenseman, That looks perfect. The pontoon is even about the right distance away from the bridge for a nice moderate angle of heel to bring the masthead down to the height of the bridge, and conveniently positioned lamp posts on the bridge to secure the halyard to. The only problem, as I'm sure you know, is that they are JSASTC pontoons, so I rather suspect I'd get turfed off in fairly short order.

At 1310 today (Low water, just after Springs 13:07UTC) I went up onto the Haslar Bridge and dropped my lead-line over the parapet.

From the hand rail to the water (low tide) was 28 feet (8½ metres) and from the bridge hand rail to the sea bed (low water) was 36½ feet (11 metres) which makes the depth of water under the bridge is 8½ feet (2.6 metres)

 

[Heckler]

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

i thought that is how the vitronix is? i know mine was
stu

 

[Simondjuk]

Lenseman,

You're a top man. It's very kind of you to take the time and trouble to do that. Thank you.

That sounds like just about the right height to do the job nicely if I hop up on the hand rail. Will try and get round there next weekend armed with a new aerial (I'm minded to do a quick swap and fix the duff one later).

Will let you know how we get on.

Thanks again.

 

[lenseman]

Next week will be Neaps so the distances will be slightly different but not by very much but you need to time your arrival so that you can not only look at the area but also be able to do any work in daylight.

Worth arriving and stopping in the visitors mooring at Haslar Marina and walking to the bridge for a look.