Have now got an SWR meter, but have not idea what do do with it....!

Andrew_Trayfoot said:
I have some issues with my VHF transmission power from the masthead antenna.
It appears to work better with the AIS antenna on the pulpit.

So I now have a SWR (correct frequency range) meter so i can try and work out which bit of coax is causing the issue.

ZETAGI 102 SWR METER 3-200MHZ CB HAM RADIO. | eBay

Question is how do I interpret the results?
Click to expand...
First, do you know how to get an accurate reading (or at least as accurate a reading as that instrument is capable of providing?
 
What you are trying to do is compare the transmitted power to the reflected power. Obviously the more power that goes out the better.

Connect the short cable between the radio and meter and the antenna to the ANT connector.
Set switch to SET and knob to minimum.
Switch radio to a free channel (NOT 16) and transmit at 25W.
Turn the knob clockwise until the meter reads MAX or infinity.
Switch to REF and transmit again and read on the VSWR scale.
A reading of 1 is perfect but unobtainable and should ideally be about 1.2 although up to 2 is considered acceptable.

If you have a slightly faulty coax you may still get good readings because the power is attenuated on the way up and also on the way back which gives the illusion of a low reflected power when the transmitted power is also reduced.
 
andsarkit said:
What you are trying to do is compare the transmitted power to the reflected power. Obviously the more power that goes out the better.

Connect the short cable between the radio and meter and the antenna to the ANT connector.
Set switch to SET and knob to minimum.
Switch radio to a free channel (NOT 16) and transmit at 25W.
Turn the knob clockwise until the meter reads MAX or infinity.
Switch to REF and transmit again and read on the VSWR scale.
A reading of 1 is perfect but unobtainable and should ideally be about 1.2 although up to 2 is considered acceptable.

If you have a slightly faulty coax you may still get good readings because the power is attenuated on the way up and also on the way back which gives the illusion of a low reflected power when the transmitted power is also reduced.
Click to expand...
Thank you
 
Andrew_Trayfoot said:
I have some issues with my VHF transmission power from the masthead antenna.
It appears to work better with the AIS antenna on the pulpit.

So I now have a SWR (correct frequency range) meter so i can try and work out which bit of coax is causing the issue.

ZETAGI 102 SWR METER 3-200MHZ CB HAM RADIO. | eBay

Question is how do I interpret the results?
Click to expand...
Looks very similar to the Tandy SWR Meter which were quite good.
 
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The meter if attached at the transmitter end will give an accurate representation if VSWR at that poin. However as already said the attenuation losses of the cable will tend to show a better reading than is in fact the c ase for whole system. The attenuation of the cable depends on the length of the cable and the quality (size) of the cable. So generally the 6mm RG58 has much more losses than 10mm RG8 type cable. This is a generalisation because some small cables are better than others. nB the higher the frequency the greater the losses. The reflected power which is the one you measure and don't want is lost both on the up trip to the antenna and the return trip.
So if you had a very long cable you could get perfect VSWR regarless of what antenna if any you connect at the end. So for a true measure of antenna tuning you shoud check the VSRW near the base of the antenna. Never the less checking at the transmitter hopefully will give you a good indication of the condition of the cable and antenna itself. ol'will
 
An SWR meter is a very simple and versatile instrument to help fault find and diagnose RF cable and antenna issues. I prefer a dual meter version personally. It’s usefulness is further enhanced when used in conjunction with a dummy load.

I’m sure that a Youtube search would be helpful and informative.
 
andsarkit said:
What you are trying to do is compare the transmitted power to the reflected power. Obviously the more power that goes out the better.

Connect the short cable between the radio and meter and the antenna to the ANT connector.
Set switch to SET and knob to minimum.
Switch radio to a free channel (NOT 16) and transmit at 25W.
Turn the knob clockwise until the meter reads MAX or infinity.
Switch to REF and transmit again and read on the VSWR scale.
A reading of 1 is perfect but unobtainable and should ideally be about 1.2 although up to 2 is considered acceptable.

If you have a slightly faulty coax you may still get good readings because the power is attenuated on the way up and also on the way back which gives the illusion of a low reflected power when the transmitted power is also reduced.
Click to expand...

If you're measuring the antenna, surely the meter needs to be plugged in at the antenna base.

I remember the great joy of having to haul a vector network analyser up 7 decks - back in the days when they weighed 25kg and cost £50k.
 
st599 said:
If you're measuring the antenna, surely the meter needs to be plugged in at the antenna base.

I remember the great joy of having to haul a vector network analyser up 7 decks - back in the days when they weighed 25kg and cost £50k.
Click to expand...
I agree that in an ideal world you would measure at the antenna but a lot of marine antennas have a continuous coax and no connector at the antenna. Also the practicality of climbing the mast and then having very long arms to press the transmit button means that most of us have to make do with a measurement at the radio. At least this will show up any serious faults.
 
Andrew_Trayfoot said:
I have some issues with my VHF transmission power from the masthead antenna.
It appears to work better with the AIS antenna on the pulpit.

So I now have a SWR (correct frequency range) meter so i can try and work out which bit of coax is causing the issue.

ZETAGI 102 SWR METER 3-200MHZ CB HAM RADIO. | eBay

Question is how do I interpret the results?
Click to expand...
If the VSWR is high, you probably have a break in the cable. Or a loose connection or a short.
If the VSWR is not particularly high and the aerial doesn't work, then the cable is probably lossy. Corroded braid or water inside?
To fully test the cable as best you can with a SWR meter, you need a dummy load to replacce the aerial. That should give a low VSWR. With nothng connected at the far end of the cable you should get a very high SWR if the cable is low loss. But this could damage a cheap transmitter or cause the transmitter to shut down. A lot of transmitters can measure SWR themselves and turn the power down, maybe even read out the SWR in a service menu, so you don't need to buy the meter.
 
TernVI said:
If the VSWR is high, you probably have a break in the cable. Or a loose connection or a short.
If the VSWR is not particularly high and the aerial doesn't work, then the cable is probably lossy. Corroded braid or water inside?
To fully test the cable as best you can with a SWR meter, you need a dummy load to replacce the aerial. That should give a low VSWR. With nothng connected at the far end of the cable you should get a very high SWR if the cable is low loss. But this could damage a cheap transmitter or cause the transmitter to shut down. A lot of transmitters can measure SWR themselves and turn the power down, maybe even read out the SWR in a service menu, so you don't need to buy the meter.
Click to expand...
Can you point me at an appropriate 'dummy loads on eBay/Amazon please
 
Andrew_Trayfoot said:
Can you point me at an appropriate 'dummy loads on eBay/Amazon please
Click to expand...
I can't recommend anything unbranded, but this is the kind of thing,
1 Pcs RF Coaxial 25W U Style UHF PL259 M Male Connector 50 Ohm DC-1GHz DummyM3B6 | eBay
You might want a different connector type or gender.
You might prefer to pay a little more for a higher power rating.
If you know your antenna is good, then it should look like a reasonable 50ohms on the middle channels.
If the VSWR is fair with the antenna connected and high when it's removed, coax open circuit that would indicate the cable is not completely shot.

I think most amateurs would be better just buying new cable than buying test accessories, but of course the cost of installing new cable can be terribly high if it means taking down the mast.
It's easy to get into a nightmare of confusing results due to using adaptors and other untrusted gear.
Buying a cable a few metres long and testing the aerial with that might be an option?
 
So...
I went out to the boat today and did some tests.
AIS antanna SWR 1.2 and a good and readable from Solent Coastguard.

Got the same results with all the coax to the mast foot and then back to the panel and on to the AIS antanna, so no issues there.


Mast Head antanna SWR 15!
So put a new plug at the bottom of the mast and got the same result

Got pretty much the same with nothing connected.

So my guess is the connection at the top of the mast to the V-Tronix Hawk..

Next step stick my son in the bosan's chair....
 
Well done. It's great when you get some solid information when fault finding. So much better than randomly swapping bits and hoping for the best.
 
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