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eHam Forums => RFI / EMI => Topic started by: K3WVU on January 22, 2007, 06:34:23 PM



Title: Transmitted SSB signal distortion
Post by: K3WVU on January 22, 2007, 06:34:23 PM
I'm getting reports of badly distorted audio on my ssb signals on lower frequencies.  I've switched out mics and even used another rig, but it makes no difference.  I was looking at trying RF line isolators like those Radio Works sells.  Anyone had any experience with them?

Thanks

Dwight


Title: Transmitted SSB signal distortion
Post by: K6KAP on January 22, 2007, 08:26:11 PM
Not Knowing what rig or power supply you are using makes diagnosis a little more difficult, but,  many times the distortion is caused by RF getting back into the power supply. Sometimes, just grounding the rig and power supply well will resolve the problem. Also, if your  power supply has meters, see if the voltage drops when you transmit. A well regulated supply, supplying enough current for the radio should not drop at all.
Hope this helps.
73! Mach, K6KAP


Title: Transmitted SSB signal distortion
Post by: W8DPC on January 23, 2007, 11:23:18 AM
If you've changed mics AND rigs, then you have to look at what's left in your shack and go from there.  The power supply seems to be the most logical suggestion.


Title: Transmitted SSB signal distortion
Post by: N3OX on January 23, 2007, 12:01:20 PM
"I was looking at trying RF line isolators like those Radio Works sells. Anyone had any experience with them?
"

They don't work very well, from what I understand.  They're pretty low impedance.

Read this for ideas on keeping RF off the feedlines (which could be what's happening)

http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf

It's a little extreme, but has good tips on making chokes that work.

Dan


Title: Transmitted SSB signal distortion
Post by: K3WVU on January 23, 2007, 05:22:17 PM
Thanks.  I'm using an ICOM 706MKIIG and a Jetstream JTPS28 power supply.  


Title: Transmitted SSB signal distortion
Post by: KC8VWM on January 24, 2007, 08:34:49 PM
I agree the power supply should be the area of concentration.

What happens when you connect to a differnt power source like a car battery etc.?

73


Title: Transmitted SSB signal distortion
Post by: KB9CRY on January 25, 2007, 01:24:16 AM
I believe that's a switching power supply as opposed to a linear power supply.  Fellas, aren't there some problems with switching ps?  

I agree, try a different ps and see if that cures the problem.

Phil


Title: Transmitted SSB signal distortion
Post by: KF7CG on January 25, 2007, 10:28:27 AM
From the ads I have seen that is a switching supply. They are more prone to interference in each direction.

I have found that switchers get "confused" when feeding other switchers or loads with large current swings at higher frequencies. My 12 volt television would knock out the switcher used to charge the batteries in my travel trailer and provide 12 volts when connected to regular power. We had to change models of power converter (supply) to get things to work. Thank goodness for warranty!

You might give the Jetstream folks a call, this might be an interaction of the highly vaying load of an SSB transciever with the regulation logic of a switching supply. Depending on the amount of bypass and otherwise capacitance across the power supply in the rig, you could have the input current varying at an audio if not an rf frequency and this could easily couple into the regulation circuitry through the voltage sensor in the supply.

David
KF7CG


Title: Transmitted SSB signal distortion
Post by: K3WVU on January 25, 2007, 02:51:53 PM
The Jetstream is a switching supply.  It's also a very inexpensive switching supply.  

I put my station together recently after a 12 month hiatus from ham radio.  It's identical in almost all respects to my last station, which was problem-free, with one exception:  the power supply.  At the time, I used a MFJ 4125 'Mighty Lite', which is also a switcher.  MFJ advertises its Mighty Lites as RF hash-free.  Maybe that is the problem.  I'll check it out.
Thanks and 73.

Dwight


Title: Transmitted SSB signal distortion
Post by: KB9CRY on January 25, 2007, 04:54:00 PM
Nothing beats a nice, heavy duty, runs all the time Astron.  Buy one and forget about it.  Phil


Title: Transmitted SSB signal distortion
Post by: K3WVU on January 25, 2007, 05:23:32 PM
Phil,

I've had Astrons and they are good.  I know that some MFJ stuff has a bad reputation, but I can safely say that the MFJ Mighty Lites that I had were just as good, and much lighter.  I used them for about 5 years abd I'm sorry I got rid of them when I was selling all my other stuff.  

Dwight


Title: Transmitted SSB signal distortion
Post by: KB9CRY on January 26, 2007, 05:07:26 PM
I understand you Dwight.  It's just that switching power supplies have some inherently unstable characteristics that linear amps do not have.  And, this poster's problem will probably go away if he switched to a linear amp.


Title: Transmitted SSB signal distortion
Post by: K3WVU on January 26, 2007, 06:27:29 PM
Yeah, but I'm the poster and I didn't have this problem previously with a MFJ switcher.  Now I have it with a Jetstream switcher.  Maybe that's it, maybe it isn't.  I guess it's going to take (another)step by step check out to solve this.
Thanks for the info and advice.

73

Dwight


Title: Transmitted SSB signal distortion
Post by: K6KAP on January 26, 2007, 07:13:15 PM
Hi Dwight,

I think the consensus of opinion is your power supply. One thing I haven't seen though is questions about how your station is grounded. Do you have a good, non resonant station ground and that the power supply is grounded to it also. Your problem is so typical of many complaints I received while managing one of the HRO stores. Nine times out of ten the problem was found involving the supply.  Sometimes just grounding well or even moving the location of the power supply from where it is now, especially if the power supply and the radio are in very close proximity, ie the radio on top of the supply.
Keep us all advised when your resolve the problem and what cured it.

73! Mach K6KAP


Title: Transmitted SSB signal distortion
Post by: K3WVU on January 27, 2007, 06:47:23 PM
Hi Mach,
Today I checked things out running on Gel Cells...same problem.  So much for the power supply theory. I wish it was that easy ;-).
I'm going to go step by step through all of my connections, the ground system, and the antenna.  At this point, it's definitely HF antenna/ground system related.  I had a SSB QSO on 2M with no problems, so it's something screwy with the HF antenna/ground.  The maddening thing is that a year ago, I used an identical setup with no problem.
I'll keep everyone posted.
73

Dwight


Title: Transmitted SSB signal distortion
Post by: WA1RNE on January 29, 2007, 10:27:14 AM

 Sounds like you're getting RF feedback into the shack.

 There are many variables to consider;

 > Which bands do you have trouble with and which are worst offenders?

 > The type of antenna and feedline you are using, including antenna tuners, baluns, etc.

  > Describe the location of the antenna and feed with respect to the shack.

 > Describe the station ground system, including the length of the ground connections.


 WA1RNE