6500 and SWR meter

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  • Updated 4 years ago
Weird problem, the SSDR 1.38.x SWR meter shows 1.5:1 when tuning the amplifier on
15 & 17 meters. When I speak into the microphone the meter goes wild pinning deep into
the red.

A meter placed inline next to the radio confirms the 1.5:1 when tuning and peaks no
higher when talking or whistling. Granted an analog meter is too slow to follow when
talking but a constant whistle shows a constant reading while the SSDR meter is pinning.

This is the SWR presented to the exciter from the amplifier not the SWR presented
by the antenna. The antenna is a Hexbeam with very flat SWR for the record.

I do not see this behavior on the other bands and QSO reports are fine.

The output measured on the antenna side of the amplifier is in the expected range.
For example, 30 watts of drive provides about 400 watts of output on 17 meters.
If the exciter was folding back I would not expect to see that level of output.
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Barry Comer

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Posted 4 years ago

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Photo of KY6LA - Howard

KY6LA - Howard, Elmer

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Ground Loop into your SWR Meter
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Barry Comer

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Pardon my silly question, should this not also show up with the external meter?

All the equipment in the shack is grounded to a single point.
(Edited)
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WH6HI - Pat

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How long is your ground run for grounding your equipment and is it single point connection. 

Pat
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Jim Gilliam

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Sounds like you have RF on your coax between the exciter and amplifier. I'd change the cable to see if maybe you have a loose or poor connection on your interconnecting coax.

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KY6LA - Howard, Elmer

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Add some toroid's to that cable
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Al / NN4ZZ

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Barry,
Initially I was having a problem with RF feedback on the cable between my 6700 and amplifier.  It affected the SWR on some bands and would even shut down the 6700.   I replaced the cable with one that is intended for this purpose.   See this link for more details:

https://community.flexradio.com/flexradio/topics/rfi_shuts_down_the_6k_fast

Here is a picture of the "wireman" jumper and the extra toroids I added that completely solved the problem.  I special ordered a longer version of the cable you can see in the second picture below.   You could certainly make your own jumper. 




EXTRA added toroids shown here:


Regards, Al / NN4ZZ  
al (at) nn4zz (dot) com
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Steve W6SDM

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If I am looking at it right, those are some heavy duty toroids.  They must way about a pound each.  Is that what's in the bottom left of the picture?
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Al / NN4ZZ

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Steve,
Yes, but not as big as they look.....

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

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KM4CQG

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I get that the Ferrite Toroids are needed what I don't understand is why are you not placing them at the Antenna and stopping the RF at the Source.

Or using a choke balun up at the antenna?

These solutions worked for me.

Ian
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Jim Gilliam

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What type of antenna are you using? RF in the shack can be caused by a poor grounding system as well as feeding a balanced antenna with coax and not using a BALUN.

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Barry Comer

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Some additional information, there is a choke just below the hexbeam base plate and a series of snap-on beads on the feedline before it enters the house.
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Jon - KF2E

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Barry,

Are the ferrites you are using mix 31? If you don't have the right composition ferrites they won't do much to help your problem. www.fair-rite.com is the best source I have found for the correct parts.

Jon...kf2e
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KM4CQG

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Barry

I am building the KIO Beam tomorrow have you ran an SWR analyzer meter on it?

My Rig Expert 600 will give me a SWR and Polar Map I will let you know if I encounter a similar problem.

Ian
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Barry Comer

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The Hexbeam has been up for 18 months and I see no issue with the SSDR SWR
meter when running 100 watts with the amplifier in stand by mode.
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KY6LA - Howard, Elmer

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Barry

You obviously have RF in the shack on the feedline between the rig and the Amp

The toroids at the beam will not fix the feedline between the rig and the Amp

It is also not that severe an issue as it takes power when you are using the AMP to become noticeable

Al's suggestion of a toroid laden feedline will likely fix it..

You can never have too many toroids when you are dealing with RF
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Al / NN4ZZ

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Like Howard said

"You can never have too many toroids when you are dealing with RF"

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

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Using torroids and beads is like putting a band aid on the problem. There are too many installations that don't require such drastic actions. It would seem that a good single point grounding system and care of using a balun or choke at the feed point would cure the problem rather than mask it.
(Edited)
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WH6HI - Pat

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One thing that is hardly ever talked about is the length of the ground run.  At RF, just attaching to a ground point is not enough.You need to know the length of that ground.  If the distance to actual earth ground is greater then 1/4 wave length or greater at the offending Frequencies.  There will be a hot spot of RF Voltage on the station ground.  Of course it all starts at the antenna, in that the antenna sees the ground side as just another antenna all the way through the station to your earth ground point.  So first things first.  check you ground length to the earth ground.  This could be a ground rode out the window X distance from the station or a Water Pipe X distance to earth ground.
This part of the equation has to be solved first and may take care of all you problems.  If you are using antennas that are unbalanced, there is a good chance that RF is coming on the outside of the Shield.  G5RV antennas, common coax fed dipoles, some types of veticals.  All can do this and are next on your RF hit list.  RF chocks of various kinds can help.  Next is plain old interference to the circuitry of the equipment. This is mostly on the exposed Audio devices of the radio, speakers powered speakers computer audio out etc.  This is a good place tho check the grounds. If the grounds are OK and you have done the previous exercises then it is time for some Ferrite.  I use both 31 and 43 formulations and try each one to see how effective they are.   I love RF, but the most important thing to remember is think wave length first to solve RF problems and ground is not necessarily a ground if it to far from where you don't want RF.

Pat    WR1Z
(Edited)
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Barry Comer

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I disconnected the external ground wire at the single ground point point with no change. Thanks for the suggestion.
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WH6HI - Pat

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Next step is RF chock at the antenna end.  Make sure to reconnect your ground system.  Don't want to have to many variables going at once.   My last step was to put chokes at both of my antennas, that removed all RF from my present Shack....GL

Pat
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Al / NN4ZZ

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Hi Pat,
There can be another factor when an amplifier is also involved.  The radio output is driving the amplifier input and not the antenna directly.  While the goal is for the amplifier to present a perfect 50 ohm load on all bands this is not always the case.   And the length of the jumper coax between the radio and amplifier can impact the mismatch more at certain frequencies.  

Even if the antenna is perfectly matched and/or a choke balun is used on the antenna or  output side of the amplifier, there can still be a problem.  You can still get some common mode RF from the input side of the amplifier back to the radio.  Note, I'm not discounting the importance of proper grounding, just saying it is not always the solution to this particular problem 
 
Sometimes the problem between the radio and amplifier can be solved by just changing the length of the coax jumper.  But you may just move the issue to another band.  Another solution is to use a jumper cables with toroids.  That seems to work better for all bands.  At least it has worked for me with several different radios.  .
 
Regards, Al / NN4ZZ  
al (at) nn4zz (dot) com
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WH6HI - Pat

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Hi Al,  Yes, you are perfectly correct as far as matching is concerned, but SWR between components like the Tuner to radio with 1.5 SWR or less does not mean a lot.   And of course wave length is still part of the Equation there also.  Most common mode radiation is usually riding on the outside of the shield and is what causes the hot RF situation in the shack.  So one has to include all physical aspects, end to end, when dealing with this type of situation.  A long time ago, I had a shack that was on the second floor of my house.  I installed a nice ground rod, actually there were five and inch and half  wide ribbon cable from the shack the the bonded ground rods.  I even soldered all this together.   Well first time I tried to operate my new shack I had a very Hot RF situation in the shack.  Well I had to stand back and scratch my head and that with the nice job I did grounding why did it not work correctly?   After a little testing band by band.  I found that the problem was just on 20, 15 and 10 meters.  At that point I started thinking about the wave length.  The solution was actually easy and in about an hour I had it fixed.  No ferrites needed.  What I did was put a radial system for each band using 1⁄4 wavelength runners out the window attached to the ground cable at the connection point in the shack.  Doing this moved the Voltage out of the shack to the ends of the 1⁄4 wave radials.  No more RF in the Shack.    There are many solutions to RF problems,  but they all start with analyzing everything from the point of view of wavelength.  


Pat  
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Barry Comer

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What puzzles me is why the SSDR meter shows the same reading as the external meter for a number of constant tones but goes nuts when a voice is applied. The tones are generated using an external tone box (e.g. 1000hz, 2200 hz etc.) For all the tones both meters are the exact same reading.