1.00 SWR?

[Coffeemaker]

I have an old rat shack CB swr meter, but they are reported not to work well on UHF.  So, I bought a Surecom SW-102.  Connected to my Wouxun KG-905G, I get an SWR of 1.00 to a Midland MXTA-26 antenna on the roof of my SUV on all GMRS channels, and about 5 watts.  Is that believable?  I get 1.25 to 1.33 and 4+ watts on the repeater channels.  Darned Good. 

 

I've never seen 1.00 SWR.  I have a Firestik CB antenna with sloped ground radials in my attic that shows 1.02 -1.03 after several trips to tweak it and I thought that was amazing. 

[OffRoaderX]

I often get 1.1:1 - 1:2:1 on my MXTA26 and when I put it on a good groundplane I have seen 1.0:1 more than once. 

[KAF6045]

I don't think I'd trust Surecom for precision... Even the MFJ-847 costs twice as much, and MFJ is often considered a lower-grade product (many items are built into what can be called "hobby" project boxes, rather than engineering a custom case, but this is an exception) https://mfjenterprises.com/collections/mfj/products/mfj-847?_pos=4&_sid=b976da1f8&_ss=r

The fact that it shows some variation when you jump 5 MHz at least proves some function.

Note that SWR is computed from comparing forward power to reflected power... If the power measurement circuits are "sloppy" (a very low reflected power may not even be detected) then 1.0:1 is a reasonable display, even if false (any reflected power will raise SWR, but if the meter can't detect it...). The spec for the Surecom states 0.5W minimum (with 5% accuracy -- so 0.475-0.525 to my mind). Given that "channels" 8-14 are 0.5W ERP maximum, you wouldn't expect to detect any reflected voltage unless the antenna is pretty much unusable -- send 0.5W out, and have 0.5W reflected!). Even on 5W output, you'd need a 1.9:1 to have 0.5W reflected https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwiMj_39_e_5AhUPlGoFHUGxBQkQFnoECAkQAQ&url=https%3A%2F%2Fwww.arrl.org%2Ffiles%2Ffile%2FTechnology%2Ftis%2Finfo%2Fpdf%2Fq1106037.pdf&usg=AOvVaw3UXQaeDbAlSg1tPOEUuz0Z Ugly Google tracking garbage.... Even 1.3:1 implies only 0.1W reflected, so getting that measurement almost seems a miracle. I can only hope the spec is for /forward/ power, and sensitivity for /reflected/ is better: 0.05-60W perhaps

 

ADDENDUM: Also -- any non-exact match at the antenna may show different SWR depending on the length of the coax. There are points where the forward&reflected will add together, and others where they subtract. Just adding a foot extension between meter and antenna coax could change your results.

[OffRoaderX]

24 minutes ago, KAF6045 said:

don't think I'd trust Surecom for precision

My Surecom SW-102 gives the same SWR readings as my RigExpert AA-650 antenna analyzier..

But the rest of your post was very impressive - You must be very smart!

[marcspaz]

2 hours ago, Coffeemaker said:

Is that believable?

 

Yes. 

[kidphc]

10 hours ago, Coffeemaker said:

I have an old rat shack CB swr meter, but they are reported not to work well on UHF.  So, I bought a Surecom SW-102.  Connected to my Wouxun KG-905G, I get an SWR of 1.00 to a Midland MXTA-26 antenna on the roof of my SUV on all GMRS channels, and about 5 watts.  Is that believable?  I get 1.25 to 1.33 and 4+ watts on the repeater channels.  Darned Good. 

 

I've never seen 1.00 SWR.  I have a Firestik CB antenna with sloped ground radials in my attic that shows 1.02 -1.03 after several trips to tweak it and I thought that was amazing. 

1.0 is what you are shooting for. Anything below 1.5 hell 1.7 is acceptable. Just a tad more power loss on transmit. Will you notice difference? NAH.

Normally, if I can get an antenna system to get around 1.2 I close my eyes and forget it all happened. No need to be OCD about it. 

[Lscott]

There is a lot of misinformation and myths surrounding SWR and coax cables. I would recommend reading the book at the following link.

  http://www.w3pga.org/Antenna Books/Reflections III.pdf

[Coffeemaker]

19 hours ago, marcspaz said:

 

Yes. 

But mostly due to built-in error in the meter? 

The ultimate question was, "do I need to adjust the antenna?" And the answer is clearly enough, no. 

 

I'll repeat the test on my Miata.  It is shorter and MA's much Al in it. 

[marcspaz]

17 minutes ago, Coffeemaker said:

But mostly due to built-in error in the meter? 

The ultimate question was, "do I need to adjust the antenna?" And the answer is clearly enough, no. 

 

I'll repeat the test on my Miata.  It is shorter and MA's much Al in it. 

 

The meter is what some of us refer to as 'close enough' for what we do.  Keep in mind, the meter is user adjustable. It likely is calibrated fairly close from the factory. 

You want to keep your SWR under 3:1 for best performance.  I wouldn't touch it.

[tcp2525]

On 8/30/2022 at 10:05 PM, KAF6045 said:

I don't think I'd trust Surecom for precision... Even the MFJ-847 costs twice as much, and MFJ is often considered a lower-grade product (many items are built into what can be called "hobby" project boxes, rather than engineering a custom case, but this is an exception) https://mfjenterprises.com/collections/mfj/products/mfj-847?_pos=4&_sid=b976da1f8&_ss=r

The fact that it shows some variation when you jump 5 MHz at least proves some function.

Note that SWR is computed from comparing forward power to reflected power... If the power measurement circuits are "sloppy" (a very low reflected power may not even be detected) then 1.0:1 is a reasonable display, even if false (any reflected power will raise SWR, but if the meter can't detect it...). The spec for the Surecom states 0.5W minimum (with 5% accuracy -- so 0.475-0.525 to my mind). Given that "channels" 8-14 are 0.5W ERP maximum, you wouldn't expect to detect any reflected voltage unless the antenna is pretty much unusable -- send 0.5W out, and have 0.5W reflected!). Even on 5W output, you'd need a 1.9:1 to have 0.5W reflected https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwiMj_39_e_5AhUPlGoFHUGxBQkQFnoECAkQAQ&url=https%3A%2F%2Fwww.arrl.org%2Ffiles%2Ffile%2FTechnology%2Ftis%2Finfo%2Fpdf%2Fq1106037.pdf&usg=AOvVaw3UXQaeDbAlSg1tPOEUuz0Z Ugly Google tracking garbage.... Even 1.3:1 implies only 0.1W reflected, so getting that measurement almost seems a miracle. I can only hope the spec is for /forward/ power, and sensitivity for /reflected/ is better: 0.05-60W perhaps

 

ADDENDUM: Also -- any non-exact match at the antenna may show different SWR depending on the length of the coax. There are points where the forward&reflected will add together, and others where they subtract. Just adding a foot extension between meter and antenna coax could change your results.

Best to go with a Bird meter if you can find one at a good deal. Right now I got five of them.

[marcspaz]

Martin has new 43's for sale for about $650... including the PEP module.  Another $450 for the elements and you have a rock star meter for life.

[WROZ250]

Personally, I would question any reading that suggests no reflected power. 

Even a quality dummy load will normally have enough of a mismatch to make the meter 'twitch'.  The possibility of a 'perfect match' is highly unlikely.

Another factor is the meter's range setting.  If you measure a 5W transmitter with a 50-100W setting (or slug with a Bird meter), you're not likely going to show any reflected power on a close match.  The reason being is that vswr is a ratio measurement.

Additionally, where the meter is located in the antenna feed will also affect the reading.  It's possible to have, for example, an antenna with a 1.5:1 vswr, as measured at the antenna. However after 100ft of line, the line loss measured at the transmitter will normally cause the vswr to read far lower.

Not saying such a 'perfect reading' is impossible to obtain, just extremely unlikely.

[WROZ250]

3 hours ago, tcp2525 said:

Best to go with a Bird meter if you can find one at a good deal. Right now I got five of them.

Agreed, but even a Bird has a margin/percentage of error in a reading.  It's typically posted on the back of the meter.

[Lscott]

5 hours ago, WROZ250 said:

Agreed, but even a Bird has a margin/percentage of error in a reading.  It's typically posted on the back of the meter.

I wouldn't mind having one myself. I've been on the look out for a good deal on one. For $150 and no slugs I can get one that's beat to crap, or for $250 to $300 and still no slugs I can get a nice one in very good condition. Don't forget you an buy them with different connectors. They can be swapped but you're better off getting it with the ones you want. Also the slugs aren't cheap either.

[tcp2525]

On 9/6/2022 at 10:20 AM, WROZ250 said:

Agreed, but even a Bird has a margin/percentage of error in a reading.  It's typically posted on the back of the meter.

True, but but you get what you pay for. I have two Daiwa meters and they are pure crap. I always thought Daiwa was a great brand, but the wattmeter movement burned out on the 901 so I either have to find a replacement meter from a scrapped one or just throw it away. The 801 had a diode crap out, which was an easy fix and then I spent some time recalibrating it. All of these are known and documented problems. I'm sticking with Bird since they have been around since the 50s and kept a tried and true design. 

[WROZ250]

On 9/7/2022 at 9:38 AM, tcp2525 said:

True, but but you get what you pay for. I have two Daiwa meters and they are pure crap. I always thought Daiwa was a great brand, but the wattmeter movement burned out on the 901 so I either have to find a replacement meter from a scrapped one or just throw it away. The 801 had a diode crap out, which was an easy fix and then I spent some time recalibrating it. All of these are known and documented problems. I'm sticking with Bird since they have been around since the 50s and kept a tried and true design. 

To be clear, I was absolutely not dissing Bird (I own one and love it).  My point was regarding the OP's comment about 1.00:1 vswr.  Specifically, even a Bird meter will almost always display some reflected power even while on a dummy load.  There is always some margin/percentage of error with any measurement even with the best test equipment, ergo, always question a 'perfect reading'. :-)

[tcp2525]

15 hours ago, WROZ250 said:

To be clear, I was absolutely not dissing Bird (I own one and love it).  My point was regarding the OP's comment about 1.00:1 vswr.  Specifically, even a Bird meter will almost always display some reflected power even while on a dummy load.  There is always some margin/percentage of error with any measurement even with the best test equipment, ergo, always question a 'perfect reading'.

I didn't take your post as dissing Bird at all. I agree that ALL equipment has some degree of inaccuracies and accept that. Of course, one can meet a point of diminishing returns on any piece of test equipment. I don't need a $20K piece of equipment for doing what I am doing. Just saying the Bird is a great economical choice for the average hobbyist, especially considering the money I wasted on two Daiwa meters.