VSWR meter - bad results!!

Richard10002

Richard10002

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Just plugged in my new VSWR meter to find the following, (which was not unexpected:

Img_0564small.jpg


reading when not transmitting

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reading when transmitting High Power - approx 4.5

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reading when transmitting Low Power - hard to tell

Looks like I'm going up the mast!!

But not for a few days!!

Richard
 
Smart looking meter! Much nicer looking than mine, which was used by Noah until he replaced it with a better one.

Not a nice reading though, looks like there's a problem. When this happened to me last season with a new Vtronics aerial it was because the core wire wasn't making contact with the antenna spike. If the screw in plastic plug is not set up quite right the core can slide back inside the sleeve, and doesn't make contact. Took me about two hours to find that out, several times up and down the mast, withdrew the cable and brought the antenna down, and about 30 seconds to fix.
 
DOn t worry....you are not alone...Life would be boring if the starboard needle looked stuck /forums/images/graemlins/smile.gif

Before climbing the mast check the deck connection if there is one. I have seen more failures here than up the mast.

I find it is safer to feed the coax from the mast through the deckand make the connection inside the boat where it lives in a dry environment.
 
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Before climbing the mast check the deck connection if there is one. I have seen more failures here than up the mast.

I find it is safer to feed the coax from the mast through the deckand make the connection inside the boat where it lives in a dry environment.

[/ QUOTE ]

My coax comes down the mast, through a deck gland, and a PL259 connection is made under the deck. I have opened and closed the connection with no effect, which is what suggests that the problem is up the mast.

However... before going up the mast, I have a spare aerial up the mast, with a coax terminating under the deck near the existing connection... so I am going to get a PL259 put on the end of that and see if it resolves things. (I cant do it myself because I always make a mess of the soldering bit, such that the prong wont go in the hole.

Should be sorted, one way or the other, in the next day or so.

Richard
 
For the cost of a few squid you might find it worth while to make a dummy load. You need a total resistance of 50 ohms across from inner to outer of a PL259 plug. Using a dummy load you should find that VSWR is perfect into the dummy. So confirming meter and connections are good.

The dummy load needs to have a power capability of 25 watts. It needs to be made of carbon resistors not wire wound high power Rs. (too much inductance) (If you can get 2w resistors you need 12 x 600 ohm. If you can only get 1w resistors you need 24 x 1200 ohm resistors all wired in parallel.
But yes if your radio performance is not brilliant you probably have a problem up the stick. good luck olewill
 
[ QUOTE ]
My coax comes down the mast, through a deck gland, and a PL259 connection is made under the deck. I have opened and closed the connection with no effect, which is what suggests that the problem is up the mast.

[/ QUOTE ]

Do you mean that the SWR is the same with this plug disconnected??

I suspect that you have a short on the under-deck connection - try un plugging the coax at each end and checking resistance between the centre pin and the connector body (of the section of cable going back to the set). It should be open circuit. Then use a piece of wire to short the centre pin to the connector at one end, and check the resistance between the centre pin and connector at the other end of the cable - it should be very low - 1 or 2 ohms, maybe. (Then remove the shorting link!).

Speaking personally, I would verify the integrity of every section of cable below decks in this way, including the 'patch' lead that came with your meter, before ventruing aloft.

Andy
 
Out of curiosity, have your tried moving the VSWR meter to a different location and rechecking the measurements?
 
[ QUOTE ]
[ QUOTE ]
My coax comes down the mast, through a deck gland, and a PL259 connection is made under the deck. I have opened and closed the connection with no effect, which is what suggests that the problem is up the mast.

[/ QUOTE ]

Do you mean that the SWR is the same with this plug disconnected??

I suspect that you have a short on the under-deck connection - try un plugging the coax at each end and checking resistance between the centre pin and the connector body (of the section of cable going back to the set). It should be open circuit. Then use a piece of wire to short the centre pin to the connector at one end, and check the resistance between the centre pin and connector at the other end of the cable - it should be very low - 1 or 2 ohms, maybe. (Then remove the shorting link!).

Speaking personally, I would verify the integrity of every section of cable below decks in this way, including the 'patch' lead that came with your meter, before ventruing aloft.

Andy

[/ QUOTE ]

Andy,

Firstly... I hadnt tried the SWR with any plugs disconnected. I merely meant that I had made and broke the connection under the deck at the mast to see if it improved things in a wiggling kind of way /forums/images/graemlins/smile.gif

First test I did was Richards where I put the meter between the connection at the underdeck connection - no movement. Checked with the meter at the set - same bad reading as before.

I then did all your tests except the shorting one, but got 1-2 ohms resistance with the cable connected to the set, (which I guess is almost as good as shorting it.

With a variety of open circuit, 1-2 ohms, 0 Ohms etc., I lost track of things after a bit but, during the wiggling of the connectors, I eventually got a decent reading on the meter fitted at the set. I then tried the meter at the underdeck connection - no reading.... then wiggled the wires at the underdeck connection - decent reading.

So it looks like I have a bad connection at the underdeck - which is great!!! I'll have this remade, and see what happens.

As a matter of interest, when I have the VSWR meter set on High, and the transmitter on High, the Forward reading is 15W at the set and 10W at the underdeck connection ... presumably it will be even less at the aerial.... Is this a problem, or is it what happens when you have cables?

Thanks to all for the help - I'll report back when I've had the connectors sorted.

Richard
 
Had a connector fitted to the spare aerial but it made no difference /forums/images/graemlins/frown.gif

The problem is clearly in the cable from the set to the under deck connection.

Bought some PL259 connectors with converters for RG58 5mm cable, and decided to have a go at soldering.

Soldered connectors onto each end of a spare length of aerial cable, which is long enough to reach from set to underdeck connection - it works!! So now I have an emergency aerial cable if the current one packs up. Also means I can connect the aerial on the pushpit - so lots of spare VHF aerial capacity.

Bit the bullet and chopped the connector off the under deck bit of the cable from the set.. soldered a new connector on and, BINGO! it works. Not the neatest bit of soldering, but successful!

IMG_0591.jpg


This is how a VSWR screen should look.

As a matter of interest, the spare aerial only shows 15Watts - any ideas why?

Thanks to all for the help - that VSWR gizmo at £40 or so could turn out to be a life saver.

Richard
 
It's been like someone turned a light on!! I think I've had a bad connection getting progressively worse since I bought the boat.

Sadly, I've been listening to Valletta Port Control all day, and it's like Piccadilly Circus! previously I would hear the odd transmission from port control and none of the ship/yacht responses.

Did a radio check and they hear me "555" - whatever that means /forums/images/graemlins/smile.gif
 
[ QUOTE ]
Bit the bullet and chopped the connector off the under deck bit of the cable from the set.. soldered a new connector on and, BINGO! it works. Not the neatest bit of soldering, but successful!


[/ QUOTE ]

Just seen this - glad to hear you've got it sorted /forums/images/graemlins/smile.gif Looks like a very well matched set-up now.

[ QUOTE ]
As a matter of interest, the spare aerial only shows 15Watts - any ideas why?

[/ QUOTE ]

What's the SWR reading for the spare aerial? I'm guessing it might me up at around 1.5 for that forward figure? If so, everything is working as it should. Don't worry about it. A lower SWR reading would be nice, but unless the aerial is permanently mounted it's a bit pointless to try and tune it .

On your other point about getting a different reading at different places - I'm prepared to be corrected, but I think it's fairly normal - stick with measuring it at the set.

Well done !

Andy

P.S. '555' - was it 5 by 5? If so, it was probably related to the ham radio RST code for Readability, Signal & Tone (but tone not relevant to voice). If so, it translates to perfectly readable, reasonable signal strength (i.e. good!) - read more here
 
Richard, hate to be a wet blanket but that last photo of the meter rings BIG alarm bells.

An SWR of 1.0:1 is, frankly, impossible with this class of equipment so there is a measurement problem.

If you can hear well and get out well, then that is a very good sign. Another good sign is to feel behind your set (if you can) for a heatsink. If you can find one, transmit on full power on a clear frequency, while modulating 'testing 10, 9, ... for a while and see that the heatsink isn't getting uncomfortably hot. Not all sets have external heatsinks, though.

You said....[ QUOTE ]
As a matter of interest, when I have the VSWR meter set on High, and the transmitter on High, the Forward reading is 15W at the set and 10W at the underdeck connection ... presumably it will be even less at the aerial.... Is this a problem, or is it what happens when you have cables?

[/ QUOTE ] What this suggests is that you have a massive mismatch between the set and the underdeck connection. Possibly in the cable itself, or in one of the connectors or thru-decks. The power meter is telling you that five of the fifteen watts is not getting to the deck. Some is being reflected back, or being absorbed in loss in a cable (e.g. wet cable getting warm -- dielectric has a high 'tan delta'). This also means that the mismatches from your cable to the masthead, the connectors on the masthead and the mismatch in the antenna itself (huge, these VHF marine antennae are crap) will be attenuated (disguised, buried, covered-up) when you are measuring at the set.

Do you have an emergency aerial? I highly recommend that you get one for your trip back to Blighty...if you lose your mast, or if your masthead VHF aerial fails (the do, frequently) that is the only way you'll be able to get out. The best £50 insurance you will ever spend in your life. Try checking the SWR on the emergency aerial. Mine is pretty good on short leads.... 1.25:1 which is GOOD/EXCELLENT for this sort of kit.

There are some tech issues about SWR that are non-obvious. For example, if there is a mismatch at a deck connector then the mismatch at the aerial head will simply be reflected back up the line....making the aerial mismatch look much better than it really is.

Have a fiddle around, check heatsink temperature and try an emergency antenna. Before saying "job jobbed" try to get a credible reading -- something like 1.25:1 or worse. If you are better than 1.25:1 there is possibly something wrong.
 
I just bought one of these - as I've had doubts about my masthead (though have another on pushpit which is better).

After getting nothing for a few minutes I discovered the patch cable they supplied had a dead short in it /forums/images/graemlins/mad.gif - so after cutting the ends off and remaking them (which is what I didn't want to do in the first place!) I started to get some readings.

Identified another bad connection in the masthead aerial cable - remade that and readings started to look sensible (reflected probably just under 1.5)

What I don't quite understand is that the forward power didn't seem to match the 1 / 25 W of the set (though it did sometimes). The VHF says it has some protection against burning out the transmitter - so I wondered if it has a temperature sensor or something to step down the power ?

Readings with a 5W dummy load didn't seem to get the full power showing either - so either the radio is adjusting the output power, or my patch lead is still not that great (though at least is not shorting now!) or maybe the dummy load is not right.

Anyway - I'm happy I have a much better setup now - on a rainy day I may have another go - so any suggestions would be appreciated.

Thanks
 
[ QUOTE ]
P.S. '555' - was it 5 by 5? If so, it was probably related to the ham radio RST code for Readability, Signal & Tone (but tone not relevant to voice). If so, it translates to perfectly readable, reasonable signal strength (i.e. good!) - read more here

[/ QUOTE ]

It must have been 5 by 5 .. somebody else I mentioned it to said the same.... a CB radio term.

The guy at Valletta Port Control yesterday wasnt too constrained by VHF radio technique and etiquette - it was quite amusing /forums/images/graemlins/smile.gif

Richard
 
"Do you have an emergency aerial? I highly recommend that you get one for your trip back to Blighty...if you lose your mast, or if your masthead VHF aerial fails (the do, frequently) that is the only way you'll be able to get out. The best £50 insurance you will ever spend in your life. Try checking the SWR on the emergency aerial. Mine is pretty good on short leads.... 1.25:1 which is GOOD/EXCELLENT for this sort of kit."

I have 2 aerials at the top of the mast, and one on the pushpit. The pushpit aerial I class as the emergency aerial, although it currently needs a connector on the end of its cable, which I will be doing soon. Also have an ICOM handheld.

Getting to the rear of the VHF set is quite fiddly and, whilst many sailors could probably make the connection, I dont think Janet could.

In light of what you say, I wonder if I should use the patch lead to bring the connection to the exterior of the panel, so that either the pushpit connector could be easily plugged in or, alternatively, the extension lead.

I wonder if anyone has done this, and how?

I'll have a look at the SWR issues when I get settled at the marina.

Many Thanks for the pointers

Richard
 
Might you find that Janet can do it more easily than you if it is a question of smaller hands? Bringing out the cable is less desirable as each connector is a 'discontinuity' and each discontinuity causes mismatches and reflections. My emergency antenna is about the size and shape of a para rocket, it has plastic caps on either end of the tube, which is bright yellow with clear simple instructions on the side. I have shown S. how to use it and have no doubt there would be no problem....it clips onto its own mount when not in use in a locker under the radar...dry and warm. In our case, we can plug it in and then feed the cable out through a roof hatch, lashing the antenna to a bit of rail. Very simple, non-techie and foolproof. An extra masthead aerial is a very mixed blessing; it needs to be some distance from the active one or it can interfere badly even if it is not connected down below. The antenna people do quote a figure, ISTR.

SWR readings can be tricky. At RF things are not always as clear-cut as you'd think. Let's hope that you can make your SWR a little bit worse /forums/images/graemlins/wink.gif
 
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