How accurate is the SWR meter?

Ben Sinclair

How accurate is the SWR meter on my 6300? I use a magnetic loop, and when I tune it up I can usually get my external meter to read close to 1, but the software meter usually shows around 1.5.

I know my other radios have matched the external meter pretty well.

Thanks!

Duane_AC5AA

Heh, I don't know the answer to your question, but I have two external SWR bridges outside the rig and the Flex, just like the Orion before it, doesn't agree with either of them, and they don't agree with each other.  So, for me, I just choose which one I'm going to believe and use that one!  :-)

  73, Duane

John n0snx

Well as I see it any meter is nothing more than a reference guide..... If the radio isn't folding back on power all is good...

pa0bie

The internal software SWR meter is situated in front of the internal ATU.  Your external SWR meter is behind the ATU. This can give differences in meter readings I think.

DrTeeth

Another thing I have noticed about the internal meter (which does reasonably match that on my ATU) is that I can get a better SWR when using 30W (JT65) than 20 on 'tune'. I always use the radio's SWR to fine tune as I think that reading is the more important of the two for the radio itself.

Al_NN4ZZ

Another potential reason for different readings is reflected RF.  In my setup with a linear amp and external tuner I corrected it with ferrites on the coax jumper between the 6700 and linear.  More details on my web page:

http://www.nn4zz.com/FLEX6700.htm#RF_issues_and_solutions

Regards, Al / NN4ZZ  
al (at) nn4zz (dot) com

Burch - K4QXX

I was messing around with my 5000 and 6500 this weekend on 6 meters.  I have a 5 element beam for 6.  My MFJ antenna analyzer said my SWR was 1.3:1 on 50.125.  Flex 5000 said SWR was 1.4:1 on 50.125 and my 6500 said it was 1.7:1 on 50.125.

Ben Sinclair

I don't have a tuner in my 6300, and don't need one since I'm using a magnetic loop

 I can get it down to 1:1-1.2 on the loop's meter, and if I plug in my analyzer it reads about the same. The Flex always reads around 1.5.

I don't think it's a big deal, I just wanted to make sure it was okay.

Duane_AC5AA

Thanks, Al, I'll give that a shot.  I've just lived with the differences since I use my PowerMaster meter to tune my antenna system through my TenTec238B tuner and I know once it's correct, everything from the linear back is happy.  But if I use the rig's ATU when running barefoot, the PowerMaster will often show 3:1 or so SWR where it is measuring.  I'll give the toroids a shot.

Jim Hawkins / K2JHV

I don't know about SWR, but someone I worked did measurements on the S readings on his Flex 6000 box and it was right on the money!  S1 = 0.2 μV, S2 =  0.4 μV and so on.
So, if that is any hint of the accuracy of Flex metering, my guess is that all the Flex 6000 series equipment is very uncommonly accurate on receive and transmit measurements.
http://en.wikipedia.org/wiki/S_meter
I find that the readings I get on average are lower than others using older analog equipment so, when I give someone a report of S9, they are pounding in as if it were yesterday's 10-20 dB over.

I upgraded from Flex-3000 to 6500 and one thing I miss on the 6500 that was on the 3000 is a digital readout of the SWR, output power and reflected power.  However, I can get a numerical reading using the SWR Plotter 6K, so it is available internally.

Al_NN4ZZ

Hi Jim,
Take a look at this idea on the SWR readout and add your vote and comments if you would like to see it.  It is to improve the readability and add a digital read out.  

Regards, Al / NN4ZZ  
al (at) nn4zz (dot) com

https://community.flexradio.com/flexradio/topics/idea_to_improve_the_swr_and_power_scale_readability

***** two options for the readout are shown ****

Al_NN4ZZ

Here is the POWER change also requested in the same request.   Digital and analog scales vary based on the RF power slider setting.

Regards, Al / NN4ZZ  
al (at) nn4zz (dot) com

Jay Nation

Burch
Were you using a switch or just moving the coax?

Burch - K4QXX

Just moving the coax from one radio to the other (and to the MFJ analyzer).

Duane_AC5AA

Of course - but only if the internal ATU is engaged.

Jay Nation

Ok that would eliminate the feedline length being a factor. Now I suspect the actual impedences of the radios/analyser may not be totally identical. Or it could be an accuracy problem. I've got 4 SWR meters inline counting the one in the radio, and the one in the amp, none ever match, I'm only concerned about the match between my amp and antenna, If I get that matched, the rest are all below 1.5:1. 
My antenna isn't actually resonant within any ham band. It's below 1.5
without a tuner around 7.2mhz and useless for 160m.

DH2ID

I had the Flex-3000 on my bench today. according to my HF-wattmeter bei R&S the S-meter is extremely accurate, more, in fact, than the S-meter of most conventional rigs. Measurement is done with an ideal 50 Ohm dummy load first and changing resistance and hence SWR later. I will put my new Flex-6500 on the bench next week and post the results.

DrTeeth

Alex, as I mentioned above, I do the final SWR tweaking in SSDR figuring that what the rig sees is the most important thing.

I wonder if you could check the SWR you can get with different power levels? Here I tune my 6300 with 20W to get the best SWR - but when transmitting JT65 at 30W I can tune to get a better SWR. It's not really a significant difference but should it be there at all. I wonder if you could check this too if you could be so kind.

L.Kubis

Try a good RF choke ahead of your Flex, Ben. Mag loops can have high common mode RF on the coax which will throw you VSWR readings off. 

Lloyd
VE3ERQ

AA0KM

What I have found on the Flex it is extremely sensitive to 50 ohm load. Using an antenna and plotting swr  with mfj-analyzer going over 50 ohms just a little and the flex smartsdr SWR goes up really fast.

But bellow 50 to 45ohms or so it matched mfj and the software meter.

I was trying to adjust an antenna with just the Flex and it was giving me fits until I watched the OHM's with the mfj-analyzer.

Lowest I could get to match was 1.4 on smart sdr and 1.0 on the mfj-analyzer but at 45 ohms. 

About 1.3 or 1.4 in smart sdr was as low as it would go but analyzer would show lower. 

73 Jeff

Walt - KZ1F

I did not catch that other thread Al, I like that suggestion. As I am doing the UI widgets for S(er)SDR I will incorporate them.

Thanks!!