VHF Aerial Check

[LORDNELSON]

My mast is to be taken down for a physical and electrical cable check in March. I thought it would be a good idea before it is down to check the aerial efficiency. I seem to remember that one can install a meter on the aerial circuit and check the strength of transmission. Can anyone point me towards an article or publication dealing with this? I cannot find it in Calder or Payne's books. Thank you.

 

[MGambling]

better idea to instal new one

 

[Billjratt]

http://en.wikipedia.org/wiki/VSWR is what it's all about.
You need to borrow (or procure) a SWR meter from someone - any radio amateur friends?- Depending on the deck connector, it can be done with the mast down -I've just checked mine in the yard as it's an ideal time to fit a replacement if required
http://www.firestik.com/Tech_Docs/Setting_SWR.htm tell how the CB guys do it. We're just the same but at a higher frequency. just google 'SWR meter' or 'vswr' for more.
.

 

[peterN]

You need to make sure the SWR meter covers the VHF marine band (156 to 162 MHz). The cheapest meter I can find is on ebay (buy it now for £27.50). Just search for VHF SWR meter. You will need adapters to convert from N-type connectors to BNC and you need to use your VHF radio for the measurement as this is an in-line meter.

 

[vyv_cox]

Mine has N-type connectors as standard, so they are available. A very useful bit of kit, I'm sure mine has saved me from blowing the output transistors on my VHF a couple of times.

If I was taking the mast down I would change at least the cable as a matter of course. They deteriorate over time: when my son worked for Sunsail he used to change every aerial and cable every winter.

 

[lw395]

SWR will not necessarily indicate excessive loss in a cable. If there is any sign of corrosion to the braid, it is probably worth changing the cable.

 

[lenseman]

I have a fairly good (expensive) SWR Meter which is for the Amateur and Marine Bands.

As you are probably in Brighton or thereabouts (hopefully) I can lend it to you of even come down and assist with the testing current work permitting. /forums/images/graemlins/cool.gif

The actual SWR test would best be performed with the aerial and mast in situ as you could possibly change the test parameters when you have lowered the mast down. /forums/images/graemlins/confused.gif

I only live about 20 miles from that part of the south coast.

Another test which would prove very worth while, before the mast is lowered down, would be to connect an amatuer radio SSB receiver (a Trio 9130 or a Yaesu FT290) to the aerial and tune to the beacon bands which are specifically there to check for enhanced propogation conditions but they can be also used as a go/no-go test on the RF receive path as fitted to your yacht.

And before anyone states the obvious about the beacon being horizontally polarised . . . it would only be 10-12dB down (or so). /forums/images/graemlins/smile.gif