Struggling with SWR...

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Matata

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Whilst resetting our mast it gave me a good opportunity to check out our radio/aerial etc.The Metz aerial is fine, I had it checked out recently. The cabling RG8 cable has no obvious damage. I Have a Nissei digital SWR meter that records on high 25watt FWD 14.5 Ref 0.75 and SWR of 1.66 However on low power 1watt it gives 0.16 FWD Ref0.00 and swr of1.00. Doing a radio check with the coastguard( I know!) we are clear and readable on high and clear and barely readable on low... Any thoughts? I usually leave the radio on 16 just listening to background chat and it seams awful quiet out there. Regards Nik
 
I have no experience of digital SWR meters. Just googled “Nissei SWR” and noticed that one model is also branded as a MFJ. This brand is often known as More F’kin Junk ?

A digital readout to two decimal places seems a bit meaningless to me. My almost 50 year old SWR has two analogue meters. I adjust forward power to FSD and smile if the reflected power meter barely moves.

Clear and readable sounds ok? How far was your transmission when on low power? Perhaps simply not enough power to travel the distance.

Sage advice on a recent, similar thread was to check that the radio is getting a good input voltage, especially when under load (transmitting). A quick application of switch/contact cleaner on plugs, sockets and connections can work wonders.
 
The lower the SWR the better but most of todays modern radio equipment is built to Brick Outhouse standards regards robustness O/P stages.
In the rough and tumble of the mobile commercial world 3:1 was considered good enough and sometimes a lot worse if spending money on new aerial was involved.
Cheapo SWR meters can either reassure or result in concern. Most were rubbish.

Taxi drivers frequently wanted to spent money with us due to the fact that their rivals could hear the base (and get work) in locations that they could hear nothing.
We usually obliged with new aerial as it made them (and us) feel better.
A week later the rival would be in complaining of exactly the same problem.
 
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1.66 is way too high. At the antenna, if that antenna is working, it will be 1.3 or below. A cable from the VHF set to the antenna will have attenuation (how long is it, and what cable do you have?) which reduces the measured SWR, so at your antenna the SWR will be significantly more than the value of 1.66 which you measured. If you have 3dB of attenuation (RG58 cable which is quite commonly used has attenuation of around 0.2dB / m, so that's only 15m of cable) and SWR of 1.66 at the VHF set, the SWR at the antenna will be 3.2. Anything above 3 is broken. Find the fault. This may very well mean replacing the antenna and/or cable, even if not that old.

It's maybe true that very low power systems such as Bluetooth and WiFi have to put up with tiny and inefficient and badly matched antennas when inside a phone (I should know, I designed the radio chips which go inside phones for a living), but no way should a marine VHF antenna have such constraints Last week I measured a new Glomax VHF antenna and cable: it's SWR was <1.1 at the VHF set, which meant that at the masthead (after 24 metres of RG8-X - and so quite low loss - cable) the SWR would have been <1.3. In contrast the old one I threw away had SWR at the antenna of greater than 3, and was broken. 'Radio check please' with the CG tells nothing about this: you could have 60dB - a mere factor of a million - loss both on the way out (Tx) and on the way back (Rx) and still have a good radio check if only a couple of miles from the GC's radio mast!
 
Sorry for the delayed reply...Skylark was on the mark! We took the SWR meter to another vessel with known good aerial /vhf and got better consistent figures. With a known good aerial we replaced it with our suspect VHF. Things were a lot poorer. We tracked it down to poor corroded +ve -ve terminals. The set is probably 15 years old. Rewired the VHF and voila "load and clear"..Back in business. Thanks again for all your contributions Nik
 
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