Internal SWR meters......accurate or not?

I noticed that the internal SWR meter in my CRT-SS9900 was giving consistently low readings so I decided to test it against my antenna analyser. I took SWR readings on channels 1, 20 and 40 on low-band, mid-band and high band with the internal meter and then repeated the tests using my analyser. These are the results:

                                 INTERNAL SWR METER         ANALYSER
LOW BAND:  Ch. 1                1:1.0                             1:1.3          
LOW BAND:  Ch. 20              1:1.0                             1:1.3
LOW BAND:  Ch. 40              1:1.0                             1:1.3
 
MID BAND:   Ch. 1                1:1.0                             1:1.3
MID BAND:   Ch. 20              1:1.0                             1:1.4
MID BAND:   Ch. 40              1:1.1                             1:1.5

HIGH BAND:  Ch.  1               1:1.1                            1:1.5             
HIGH BAND:  Ch.  20             1:1.2                            1:1.7
HIGH BAND:  Ch.  40             1:1.3                            1:1.8

The readings from the internal meter were all taken in FM mode with 15 watts power input. The analyser is a RigExpert AA-30 and readings were taken at the radio end of the feeder (approx. 5 metres of Mini 8 coax). The antenna is a half-wave Double Bazooka (horizontal). As you can see there is a difference in the results, some of them quite significant. Has anyone else tried this test and if so, what results did you get?

Hi Phil,

I'm not at all surprised with your results and seeing differences like you have, you'll also see differences if you tried an external SWR meter too.

If you tested the rigs SWR readings and the analyser with a 50 ohm dummy load you'll probably get results similar to each other but again not guaranteed.

My own HF rig has a built in SWR meter and even when calibrated will give readings slightly different from an external SWR meter. I don't tend to worry about it using it more as an indicator than anything. If I have a SWR of less than 2 I know everything is good, start worrying & checking if the SWR starts hitting 3 and won't transmit if over 3. Luckily the rig winds down output if a big SWR is present.


I personally wouldn't overtly worry about it and neither should anyone else really, it can all become a bit compulsive, (like the elusive perfect 1:1 SWR )

For my own preference I rate my SWR accuracy as Rig - lowest, SWR meter - more accurate, MFJ Antenna Analyser - most accurate.


There's an old guitar joke that comes to mind....

(Question) How do you keep two guitarists in tune & time with each other?
(Answer)    Shoot one of them!

It's only when we start comparing that we actually notice these things.


All the best,
Victor

I would go with the RigExpert every time over the inbuilt jobby.
And as Victor say's anything under2 is ok but i know everybody wants that 1to1 but it's hard to get(but doable lol).

Yes, well said swr of 2.1 or under, enjoy the radio and relax and chat away the day.

When my antenna analyser arrived and I started using it I noticed the exact same thing but I recalled the topic being discussed on here previously in regard to a linear I think it was and the fact that everybody had experienced the very same thing left me feeling very reassured that everything was quite normal.
The important thing is the SWR protection has kicked in when required on a couple of occasions giving me an instant warning that all was not well, allowing me to search for the fault and rectify it before trying to transmit for an extended period.
Like yourself, I found the analyser far more sensitive than either my external SWR meter or the ones in my radios, and they are tiny increments it is understandable that there would be a little variance between meters I feel.
It looks like your double bazooka has good bandwidth no trouble getting down to the lower bands with that.

Alan - Mirror Man wrote:

It looks like your double bazooka has good bandwidth no trouble getting down to the lower bands with that.

Yes....I did an SWR scan of the analyser's whole frequency coverage and the SWR stayed below 1:2.0 all the way from 24.963 mhz to 27.931 mhz !! The internal meter gives much higher readings at these extremes so I'm wondering if they're only designed to be accurate on the "official" CB frequencies.

I think the answer is they just arent quite as accurate but they seem to give a good enough guideline and let you know when all is not well which is the main thing.

Victor wrote:

Hi Phil,

I'm not at all surprised with your results and seeing differences like you have, you'll also see differences if you tried an external SWR meter too.

For years I used an inline LED SWR meter in the field using VHF. 160(ish) MHz
Tuning a simple tripod vertical until the LED went out.

Accuracy wasn't exactly great and better at night as you could see the LED dim to almost black.

Checking it against a meter in ideal conditions, it was usually between 1.5 and 2. If it wasn't pouring with rain.
PaulGray

Love those little LED SWR indicators Paul and they're usually good enough for a quick check.

Somewhere I have a little three LED unit, SO259 either side and handy as heck for a quick field test. So small and handy I can't find the damn thing!

I did build it though so suppose I could ways construct another, but you can bet I'll find it the moment I build another!!!

Funny you should say that, I couldn't find mine after I thought of adding a picture of it in my post.
Happy Days. At least I haven't lost my soldering iron!

For me in built SWR meter is just useful for telling if you have a problem.  If it's reading very high then it's obvious something is wrong.   But I wouldn't rely on it for tuning my antenna.

Mine seems pretty accurate compared with my external meter but who’s to say that one is accurate?

26uk81 wrote:

For me in built SWR meter is just useful for telling if you have a problem.  If it's reading very high then it's obvious something is wrong.   But I wouldn't rely on it for tuning my antenna.

I agree with Chris.

When out mobile/portable, I use the internal meter as a guide.

If the SWR reading goes high, check the antenna, plugs & cables

Victor wrote:

Love those little LED SWR indicators Paul and they're usually good enough for a quick check.

Somewhere I have a little three LED unit, SO259 either side and handy as heck for a quick field test. So small and handy I can't find the damn thing!

I did build it though so suppose I could ways construct another, but you can bet I'll find it the moment I build another!!!

Do you have a picture and where can i find a schematic for this?

I never did find it again Karel and knowing me I probably stripped it apart to use the SO239's on another project. (I don't 'document' every project I build. )

If you search Google for "LED SWR meter" you'll get loads of hits starting with the commercially available units but change to 'images' on the search and you'll find a shed load of circuit diagrams. Some of these projects come with great documentation others a little more scant so best to make your own choice from them.

From what I remember I used a 'Stockton' bridge type unit but there are 'Bruene' bridge types as well. With the resistive types they are very wide frequency but at only QRP power depending on the resistors you use in them. A true 'stripline' type would probably be too big for a miniature unit and are very frequency dependent. (Used in many 'cheaper' commercial SWR meters and specified for 1 band such as CB so land up less sensitive on lower frequencies and much more sensitive on higher frequencies.)

I probably wouldn't build such another miniature unit with my failing eyesight and hand problems.

73
Victor

Alan Pilot wrote:

Dejan
Connect the external mete the wrong way round and see if you get the same results.
You will find it all works opposite the forward and set that is but it will tell you if the meter is working spot on r not.
It should give the same readings as it did the correct way round.

Hello Alan,
I did as you said, and I got the same readings. 
I also tried with an SWR calculator and obtained an accurate result. 
It seems that SWR meter is functioning correctly. 
I accepted it as it is, but the mystery remains as to why the radio measures half the SWR. 
Could this possibly indicate that the radio may not be in proper working condition? 

The second thing: 
If I assume that SWR meter is working correctly, I encounter a new issue. 
I can't set SWR on the Boomerang 27A antenna below 2.0. 
I've tried various combinations with angles and length, but it's not working. 
I am tired of everything, but I don't want to give up. 
I don't have the conditions to set up a regular antenna on the balcony.
 Any advice would be appreciated. 

Hi Dejan,

Your internal SWR meter hasn't got a length of patch lead connected to it which judging by your setup will make a difference. (How long is the patch lead you're using? Is it a good quality item? I'll bet a shorter/longer one will show differences.) I wouldn't start thinking that your radio has an apparent fault.

The Sirio Boomerang is sensitive to it's surroundings and shouldn't be mounted too close to other metal fixtures except obviously the balcony fixing. (It may even make differences if it's grounding to a metal fixture or not.) This is explained in the documentation the antenna comes with.

Although frustrating it's best to tackle these things methodically as haphazard desperation can lead to nothing but a hair pulling exercise!

First thing I'd check for is an obvious but often missed inspection of the coax you're using to feed the antenna. If it's crushed in any way by feeding it through a balcony door/window the coax properties will be changed and affect your SWR readings.

Secondly only adjust one thing at a time....If you extend the top section right out then adjust it bit by bit and read your SWR it should get lower and lower until you hit a point where it starts getting higher again. Fix it at the lowest SWR reading point, (mid band such as 27.5MHz). After that the bottom radial section should only make minimal differences to your SWR readings if at all. Worth trying different mounting points along the balcony in case that makes a difference too.

If your SWR is 2 or less (people still clamber for that elusive 1:1 SWR!) then your setup will be running to at least 90% efficiency and shouldn't trip the radios internal protection. Better would be great but don't fret too much.

With the sunspot activity we've had more recently you should get some great DX opportunities even with such a humble setup when the 'skip' is in.  


Keep it calm and more importantly enjoy yourself.

73
Victor

Fun, i found this one:
The best part of it is that i understand how that works .

Victor wrote:

Hi Dejan,

Your internal SWR meter hasn't got a length of patch lead connected to it which judging by your setup will make a difference. (How long is the patch lead you're using? Is it a good quality item? I'll bet a shorter/longer one will show differences.) I wouldn't start thinking that your radio has an apparent fault.

The Sirio Boomerang is sensitive to it's surroundings and shouldn't be mounted too close to other metal fixtures except obviously the balcony fixing. (It may even make differences if it's grounding to a metal fixture or not.) This is explained in the documentation the antenna comes with.

Although frustrating it's best to tackle these things methodically as haphazard desperation can lead to nothing but a hair pulling exercise!

First thing I'd check for is an obvious but often missed inspection of the coax you're using to feed the antenna. If it's crushed in any way by feeding it through a balcony door/window the coax properties will be changed and affect your SWR readings.

Secondly only adjust one thing at a time....If you extend the top section right out then adjust it bit by bit and read your SWR it should get lower and lower until you hit a point where it starts getting higher again. Fix it at the lowest SWR reading point, (mid band such as 27.5MHz). After that the bottom radial section should only make minimal differences to your SWR readings if at all. Worth trying different mounting points along the balcony in case that makes a difference too.

If your SWR is 2 or less (people still clamber for that elusive 1:1 SWR!) then your setup will be running to at least 90% efficiency and shouldn't trip the radios internal protection. Better would be great but don't fret too much.

With the sunspot activity we've had more recently you should get some great DX opportunities even with such a humble setup when the 'skip' is in.  


Keep it calm and more importantly enjoy yourself.

73
Victor

Hi Victor,
First of all, I would like to thank you for this post.
It's been some time, in the end, I gave up on the boomerang antenna.
Simply, my balcony has too much metal (fence, posts, partition between my terrace and the neighbor's), and it wasn't possible to adjust the SWR within acceptable limits.
The only solution would be to move it considerably away from the balcony railing, which was not acceptable to me (I live on the 4th floor, and I'm afraid it might fall onto a car or a passerby).



The next thing I did was buy a Nano VNA and save myself a ton of nerves with adjusting the SWR.

I decided to try with an inverted V dipole, and in the end, I achieved an exceptionally good SWR thanks to the ingenious Nano VNA device.

I will write about other things that still interest me in the Maas DP-27 antenna thread, so as not to go too off-topic.

Sorry to hear that the boomerang antenna didn't work out for you Dejan but very pleased to hear that it didn't dissuade you from continuing your efforts to enjoy your radio pursuits.

The NanoVNA is a marvelous bit of kit for such antics (I am fortunate to have had one gifted to me by a fellow CT member) and helps immensely with such projects.

I wish you the very best of luck with all you do and look forward to hearing from you further on the forum.

73,
Victor