VHF question again, SWR meter and forward power

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santavey

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From previous good advice given by formites VHF performance much improved.
P*ss poor performance was caused by voltage drop when TX on 25 watts.
Was down at 9.6 volts, set requires 10.2 min. Now still drops a bit but from 12.2 V to 11.8 V
Having sorted that bit out I used a SWR meter to see the results.

Mast head antenna FWD 22 watts reflected 1.4
Is that good or bad?

Pushpit antenna FWD 30+ watts reflected 1.3
The pushpit antenna is a 5 ft hi gain affair with better quality co-ax.

How is it possible to push out more than 25 watts?

I also arranged for another boat when 10 miles out to give me a call.
We received him OK. He could not hear us.
How can that be? What else is left to check?
 
VHF

With forward power of 22W and reflected power of 1.4W this represents a VSWR of 1.67. Of course cable losses will make it look better than it really is at the antenna base. It is not brilliant but is workable. It does not explain why you couldn't get ten miles. Perhaps there is a michrophone or modulator fault in the transmittr. You are pehaps transmitting the full carrier power but with no modulation. Try using a hasnd held to listen to your transmission.
 
Tried listening with Handheld. Sounds OK to me.
How do you calc VSWR.
What gives the best results, more fwd power or lower reflected.
i.e. is 20 watts with no reflected (if thats possible) better than 30 watts with 1.3 reflected?
 
At an SWR of 1.3, the total line losses will be less than 1.1 times the cable losses which you can do nothing about anyway since you have to have a cable to reach the aerial. The cable loss will be about 0.2db ( I cannot find a proper figure but this wont be far out) so the total will be 0.22db and the smallest change that is detectable to the human ear is around 1.0 db.

In short the difference between an SWR or 1.3 and one of 1 will be undetectable to the listener and it wont damage your radio.

Why could you hear him and he not hear you? Who knows? Even with identical set ups, propagation is very variable.
 
Bosun Higgs said:
At an SWR of 1.3, the total line losses will be less than 1.1 times the cable losses which you can do nothing about anyway since you have to have a cable to reach the aerial. The cable loss will be about 0.2db ( I cannot find a proper figure but this wont be far out) so the total will be 0.22db and the smallest change that is detectable to the human ear is around 1.0 db.

In short the difference between an SWR or 1.3 and one of 1 will be undetectable to the listener and it wont damage your radio.

Why could you hear him and he not hear you? Who knows? Even with identical set ups, propagation is very variable.
Click to expand...

What's the human ear got to do with this? The transmission is FM so differences in power will be undetectable above the lower limit of the sensitivity of the receiving set.
 
First the watts reading

A VSWR meter will only give a reasonably accurate measure of power into a true 50ohm resistance - which is a rare thing with an aerial

Its the inability of your mate to hear you needs looking at first -

First question has to be does your mike work. You need to establish that it will transmit audible signals even if its only a few yards, even if it is only breaking his squelch without modulation. Find a friend with a handheld.

If it does you can start to look at the antenna - most obvious thing would be a partial short somewhere thats looking like a load to the set - bu it may be something trickier.

If it doesn't then there's a fault of some sort with the set.
 
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Most low cost VSWR meters should be used more as a guide than an absolute. I hasten to add that my experience is by having held an amateur licence A since 1982, by profession I'm a mechanical engineer, not an expert in electrickery.

The very-easy-to-use meters have two gauges; transmit and set the power out to FSD and read VSWR on the reflected wave meter. Generally, solid state devices are quite content with a VSWR less than 2.0.

VHF is, ignoring exceptions like sporadic E propogation, line of sight. The higher the antenna the greater the range, put simply. Many transceivers are better at receiving than transmitting (based upon my own anecdotal observations). 10 miles doesn't sound very good from the top of your mast.

Sounds like it's back to the proverbial drawing board. Can you try an alternative set? Perhaps connect your handheld to the mast head antenna and seek feedback from your 10m distant pal? Try to systematically work through the input power, transceiver, connections, cabling and antenna until you're satisfied.

Good luck.
 
savageseadog said:
What's the human ear got to do with this? The transmission is FM so differences in power will be undetectable above the lower limit of the sensitivity of the receiving set.
Click to expand...

It is relevant when comparing the audibility of the received signal with the background noise level. I would expect any line of sight fixed marine VHF transmission to be received on a properly functioning set at the other end - the question is whether the signal you want to hear is intelligible above the background noise level, and I can't see the difference between a perfect swr of 1 and and swr of 1.3 being sufficient to make an otherwise inaudible signal audible. Its not something that would be perceptible to the listener.
 
davidjackson said:
Most low cost VSWR meters should be used more as a guide than an absolute. I hasten to add that my experience is by having held an amateur licence A since 1982, by profession I'm a mechanical engineer, not an expert in electrickery.

The very-easy-to-use meters have two gauges; transmit and set the power out to FSD and read VSWR on the reflected wave meter. Generally, solid state devices are quite content with a VSWR less than 2.0.

VHF is, ignoring exceptions like sporadic E propogation, line of sight. The higher the antenna the greater the range, put simply. Many transceivers are better at receiving than transmitting (based upon my own anecdotal observations). 10 miles doesn't sound very good from the top of your mast.

Sounds like it's back to the proverbial drawing board. Can you try an alternative set? Perhaps connect your handheld to the mast head antenna and seek feedback from your 10m distant pal? Try to systematically work through the input power, transceiver, connections, cabling and antenna until you're satisfied.

Good luck.
Click to expand...

Have tried everything apart from a new set.
1. Replaced masthead antenna & new co-ax jointed below deck using barrel connector (2009)
no better
2. Replaced internal co-ax from set to connector (2010)
no better
3. Discovered voltage drop (2011)
Better! Much clearer for receiving station but still not got the range I would expect.
4. Tried calling various people at relatively short range. All reported clear & audible.
5. Connected another antenna to set to see if SWR readings different.
Very similar

The only thing left is to try another set and if that doesn't work..........
leave the mast ladder permanently rigged and climb to the top with the handheld!
 
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