VHF aerial tester

[yotter]

I am having VHF aerial issues and and was very kindly loaned tester from a local marine electrics/electronics business, this was very useful to fault find. I would like to buy one, but not an expensive professional type since they are pretty expensive. I wonder if anyone could recommend a reasonable priced good quality tester.? I see that Shakespeare do a ART-3 for approx £120, any comments are (hopefully) welcome.

 

[srm]

My ICOM AIS class B transciever has an antenna test function. Simply OK/Not OK. I can plug either antenna into AIS or VHF and have used it to confirm VHF antenna function.

 

[KompetentKrew]

I have one of these: Nanovna-h 2.8" Touchscreen Antenna Analyzer

It is presently with my radio consultant, who informs me that it works.

There are two competing NanoVNA groups - the above link is a supplier approved by one of them.

 

[smert]

I have one of these: Nanovna-h 2.8" Touchscreen Antenna Analyzer

It is presently with my radio consultant, who informs me that it works.

There are two competing NanoVNA groups - the above link is a supplier approved by one of them.

What sort of things can this tell you? I think we have a intermittent fault with our antenna - likely at the top of the mast of course - that I'd like to investigate.

 

[Skylark]

I am having VHF aerial issues and and was very kindly loaned tester from a local marine electrics/electronics business, this was very useful to fault find. I would like to buy one, but not an expensive professional type since they are pretty expensive. I wonder if anyone could recommend a reasonable priced good quality tester.? I see that Shakespeare do a ART-3 for approx £120, any comments are (hopefully) welcome.

I have no experience of it but a quick read suggests that it is a VHF SWR and Power Meter. I like analogue equipment. It is expensive and quite restricted to the task in hand. Not flexible nor versatile but will give you a single frequency check of antenna SWR. It would be possible to sweep the marine vhf frequency range but would require a fair amount of effort.

It conveniently has a built in power meter but these are notoriously inaccurate. A basic analogue SWR meter, preferably twin meters to show forward and reflected power simultaneously and a dummy load would probably cost half as much, give the same results but not be as convenient.

I have one of these: Nanovna-h 2.8" Touchscreen Antenna Analyzer

It is presently with my radio consultant, who informs me that it works.

There are two competing NanoVNA groups - the above link is a supplier approved by one of them.

I also have one of these. I've used a twin meter, analogue SWR meter for more than 30 years but was introduced to the NanoVNA a couple of years ago. They can give more information than 99% of owners need (me included). Fairly easy to set min and max frequency band of interest and the screen will show a dynamic sweep of SWR across the set frequency. Instructions are lacking but there's a ton of YouTube videos to show their use. Some care is needed. The unit has to be calibrated before use. At this price, I wouldn't trust the accuracy nor the precision of the numbers, a Lab quality VNA costs thousands. The screen graph of SWR against frequency is good enough to see if the antenna is working reasonably well, or if there's a problem. Very powerful piece of kit, it measures SWR, resistance, reactance, Smiths Chart and lots more.

 

[yotter]

Skylark, KompetentKrew,
Many thanks for your views, much appreciated. Its a fairly idiot proof solution I am looking for and not sure the Navovna will provide me with much more than the simple analogue meter, perhaps it may be useful to fault find a GSM or WiFi aerial if I fitted one at some point.

 

[st599]

Skylark, KompetentKrew,
Many thanks for your views, much appreciated. Its a fairly idiot proof solution I am looking for and not sure the Navovna will provide me with much more than the simple analogue meter, perhaps it may be useful to fault find a GSM or WiFi aerial if I fitted one at some point.

The analogue meter will show you the SWR at the frequency your radio is transmitting (and therefore needs a working radio) - the NanoVNA doesn't need a radio attached so you can check the antenna independently. It will also do a frequency sweep, so you can check easily that the antenna is working over the entire marine band.

 

[KompetentKrew]

What sort of things can this tell you? I think we have a intermittent fault with our antenna - likely at the top of the mast of course - that I'd like to investigate.

I am only a foundation level radio boffin, so hopefully some top tier radio boffins will reply.

My understanding is that an SWR meter shows whether the antenna is the optimal length for a specific frequency (e.g. 156.8mhz of channel 16), and the normal use of a NanoVNA is for showing the antenna's performance over a range of frequencies (e.g. the whole marine VHF band). They do the same thing, but the NanoVNA is very accurate and shows the whole band at once, instead of having to test separate frequencies individually.

The length of the antenna is relevant because radio waves have a length, which has a relationship with their frequency (i.e. longwave is actually longer than shortwave) and transmission and reception are best when the aerial is the same length as the radio wave (or certain multiples of the wave's length).

The problem with this is that the length of the antenna never changes - providing you use a marine VHF aerial and the right kind of coaxial cable, the SWR will always be right and should always stay the same.

It seems to me that corrosion in the connectors due to salt water ingress must be the most common mode of failure of marine VHF aerials, and it's not clear to me that an SWR meter (or NanoVNA) will diagnose that. Similar to how a bad cable or connection can test ok with a continuity meter (because a very low current is being used) but cause resistance and voltage drop when an actual load is applied.

I'm sceptical of the value of a meter for testing a boat's VHF antenna. I think you're better off taking your radio to another boat and testing it with a known-good aerial and if it works there you just have to inspect the cable manually.



(I think you can also use the NanoVNA to test traps, bu those are only useful for radio boffins and only for sailors who want to make aerials to work on the marine VHF bands).

 

[europe172]

I once got my Tv antenna mixed up with the vhf radio antenna, my Nano was able to show which was which which

 

[Daverw]

Most vhf issues I get asked to help with as the club radio guy, luckily I’ve got the test gear as I’m also full licensed Ham are loose connections or badly soldered connections along with corroded coax. The first thing I do is replace them, crimping the plugs on takes a few minutes and also allows you to have a look at the condition of the coax cable.
only after this do I test the antenna with antenna analyser with sweeps for SWR and frequency tuning.

 

[srm]

What sort of things can this tell you? I think we have a intermittent fault with our antenna - likely at the top of the mast of course - that I'd like to investigate.

Firstly check all the connections, and hopefully none are out in the elements.
If the problem persists perhaps, rather than spend money on analysing the problem and then probably having to replace the antenna anyway the simplest solution is a new antenna and cable. I have two VHF antenna, one at the top of the mast and a second for the AIS on the stern gantry with enough cable so they can be interchanged between equipment at the chart table. I also carry a new spare with sufficient attached cable to replace the mast head antenna. Can not remember the price, but probably somewhat less than the £120 mentioned in the OP.

Unless of course trying to trouble shoot intermittent faults is really your thing. Personally, I have had more than enough experience of that type when working as a surveyor offshore and having to set up the equipment on a new vessel at the start of every contract.