VHF and SWR

[Brian_Richardson]

I have recently fitted a NASA DSC radio to my boat, and I wondered if my antenna was working ok so I found out an old SWR meter from my radio ham days and tested the radio.

when transmitting I am getting an SWR reading of nearly 3 (which is in the red on my SWR meter) my questions are:-

1 - will my SWR meter work ok on marine radio (it was designed to be used on 2meter radio which is about 144 Mhz)

2 - what should the SWR be on a healthy installation (it used to be as lower the better)

3 - if the SWR is wrong what should I do to improve the SWR

Thanks for taking the time to read this

Brian Richardson

 

[ParaHandy]

Don't know swr values, sorry, but, have you been able to interface your gps to it? There was a posting in pbo or ym reporting complete failure of gps when Nasa DSC set switched on.

 

[hlb]

Is it not alot easier to call some one up, to see if the radio is working??

No one can force me to come here-----------
----- I'm a Volunteer!!!

Haydn

 

[DavidJ]

Agree with Haydn
If your mate 10-20 miles away 'line of sight' can hear you there's no problem.
David

 

[Brian_Richardson]

I havent tried transmitting yet as I have only got my boat licence this morning and my operators licence hasent arrived yet (only passed exam 2 weeks ago), however my concerns with very high SWR readings are that in my radio ham days operating long with high SWR can "burn out" the output stage of the transmitter.

and I have sucessfully interfaced my MLR 24 XC GPS to it with no problems at all (I am using this gps on the flybridge) I have purchased a garmin GPS 251 (or is it a 215) to sit at the side of it at the lower helm, I will let you know if I have any problems interfacing this GPS unit

 

[Brian_Richardson]

I havent tried transmitting yet as I have only got my boat licence this morning and my operators licence hasent arrived yet (only passed exam 2 weeks ago), however my concerns with very high SWR readings are that in my radio ham days operating long with high SWR can "burn out" the output stage of the transmitter.

and I have sucessfully interfaced my MLR 24 XC GPS to it with no problems at all (I am using this gps on the flybridge) I have purchased a garmin GPS 251 (or is it a 215) to sit at the side of it at the lower helm, I will let you know if I have any problems interfacing this GPS unit

 

[Brian_Richardson]

I havent tried transmitting yet as I have only got my boat licence this morning and my operators licence hasent arrived yet (only passed exam 2 weeks ago), however my concerns with very high SWR readings are that in my radio ham days operating long with high SWR can "burn out" the output stage of the transmitter.

 

[hlb]

Think your complicating it to much. It's a new radio init!
Just ring some bugger up with it and see what happens.

No one can force me to come here-----------
----- I'm a Volunteer!!!

Haydn

 

[oldgit]

Its a bit on the high side innit, but not high enough to worry about.Your old ham meter should not be far off.In any case no marine aerials can be adjusted so your stuck with what you have got(this is to prevent old marine know alls from fiddling and making lots worse).If lots higher ie.needle on reverse does not move I would be inclined to check stuff.The loss of power between 1:1 and 1:3 is so small as not to be noticed. If your are hearing stuff 10-15 miles away it is prob OK.

 

[Bergman]

Agree with other 3:1 is acceptable.

Unless you decide to recite War and Peace over VHF unlikely to burn out transmitter.

Out of interest you may like to check VSWR accross the whole band, say every 2 or 3 channels.

You may find that it improves at one end or the other, but then again unless you want to start chopping lumps off or adding bits on to aerial not much you can do about it.

 

[Strathglass]

A little on the high side Brian but nothing to worry about. You will loose less than one S point from your ham days. The SWR meter will be fine on marine VHF if it was designed for 2 metres. As stated previously check across the band if it varies on different channels it is probable that your aerial is slightly the wrong length and not worth worying about. However if it is the same on all channels you may have a poorly made joint at a connector in the aerial system which you may wish to investigate as it may deteriorate further.
Iain

 

[Geoffs]

Three is a bit on the high side, as bought marine systems are usually better than that. Check that you don't have any spare co-ax cable coiled up. That will destroy SWR. Loop any spare co-ax around with as large a radius as poss.

Your SWR meter should be OK, but check it's freq range. Should have a plate on it. Want it to extend to 155Mhz, if it cuts off at 145, could be a problem.

My ariel installation instructions say try trimming 100mm at a time off the co-ax lead, to adjust SWR. As installed mine came in at 1.1 low power, and 1.3 high power.

At the end of the day, if you're stuck with 3, not a major problem, just better to get it down if you can.

Old Chinese proverb 'Man who sail boat into rice field, soon get into paddy'