Standard Horizon: Standing Wave Ratio

[nigelmercier]

The manual for the Standard Horizon GX2100 says to have a marine technician check the Power Output and Standing Wave Ratio.

I've got my own Power/SWR meter, so I can do this myself. Although the ideal SWR is 1, anything under 2 is normally considered OK, a least it is in most Amateur Radio bands.

Has anyone actually got a technician to check, and got what they consider an "acceptable" figure for the SWR?

 

[Playtime]

Has anyone actually got a technician to check, and got what they consider an "acceptable" figure for the SWR?

No but I have some practical experience.

My new AIS aerial on the pushpit has a SWR of 1.5.

My old (12 years) masthead aerial, with a coax lead that was dribbling water, showed a SWR of 5. Amazingly, it still works pretty well - raising Solent CG from mid channel and Jersey Radio from off Lezardrieux this summer (after I measured the SWR).

I plan to replace it with a new Metz antenna and coax over the winter!

 

[nigelmercier]

Has anyone actually got a technician to check, and got what they consider an "acceptable" figure for the SWR?

I found the attached on my new antenna, might be a handy guide.

 

[rob2]

I think you've answered your own question. The SH graph suggests that the manufacturing spec for the aerial is less than 1.1 SWR in the middle of the marine band.

I borrowed a meter from a ham when I was making an emergency aerial of the Slim Jim type. The antenna was made from the parralel 50 ohm feeder cable usually seen as a dipole for domestic VHF use. Although the meter is nominally set up for the 2m band and so should give a slightly high reading, the homemade aerial came in at below 1.2 SWR. It performed really well in practice too, giving greatly improved performance on my handheld. My masthead aerial, which I am perfectly hapopy with, measured 1.4 SWR.

Rob.

P.S. A ham may also be able to test the output on the bench using a meter and dummy load.

 

[Playtime]

The masthead antenna gives a minimum (best) SWR round about the Ch 16 frequency (156.8) which is good. However, the curves presented are for idealised coax, I would guess. The figure you could obtain in practice would be slightly worse, probably around 1.5 with a new antenna and coax and progressively worse for older equipment.

 

[Skylark]

Anything under 1.5:1 is very good. 1.5 to 2.0:1 is probably perfectly acceptable but if everything is new it will annoy to the point of searching for the culprity (have you soldered / applied the PL259 plug?).

Depends upon the spec of the radio (I'm talking ham, no experience of marine vhf) power output may be reduced to protect the amp if the vswr is higher than around 2:1

Good old valves were much more tolerant of a high standing wave.

Checking vswr across the available frequency range and plotting the result is usually informative.

On the other hand, I haven't really dabbled with radio for a while so I could be talking bolox.