Uneaven sidebands on my Johnson Ranger ll.

[Knightt150]

Hello: I have been told that my sidebands are uneven on my JOHNSON RANGER ll, the vfo case is well grounded but RF is somehow getting into the vfo. I have been told the final plate tune needs to be grounded, and several other stories on what needs to be grounded to fix this problem.

Has anyone solved this issue, tell me what I need to do to fix it.

John W9BFO

[Steve - K4HX]

This is not uncommon. Likely due to a slight amount of FM/PM. If your audio is not fuzzy or distorted, I'd not worry about it.

[WD5JKO]

John,

   The problem you describe is common with many vintage AM transmitters. This is particularly true when the VFO is running at the same frequency being transmitted. If the VFO is on 7 Mhz when you are transmitting on 7 Mhz, there will be some simultaneous AM and FM. This leads to one sideband being stronger than another. See the following link, and go to the bottom:
  
   http://www.cliftonlaboratories.com/am_modulation.htm

   On my Gonset G-76, when on 15m, and the VFO on 40m, I only had one sideband! Switch to a crystal, and the sidebands were identical. I now use an external VFO for that rig that always runs on 160m. The quickest way to verify this issue in your Ranger is to switch to a crystal instead of the VFO.

Jim
Wd5JKO

[Knightt150]

When I go to the crystal osc the problem is not there.

John W9BFO

[steve_qix]

On what band does this happen?

As others in this thread have mentioned, the oscillator is being "pulled", causing FM or PM (Phase Modulation).  There are many possibilities.  Could be some RF leaking in from the final RF amplifier back into the oscillator.  This is the most common case.  Is the shielding intact?  RF bypass caps going to the oscillator housing OK?  Less possible, but still a chance - audio getting back into the oscillator power feed, which can cause a similar effect.

The ranger oscillators have a dropping resistor and a VR tube within the oscillator housing.  Over time the resistor drops in value, and this can burn out the regulator or render it ineffective.  This resistor should be moved outside of the oscillator housing to beneath the chassis.  This will also keep heat out of the oscillator compartment.  Without the regulator (if this is what happened), audio could find its way into the oscillator.

No matter what the cause, the oscillator is being pulled, which will cause incidental FM.  The sidebands produced by the FM (or phase modulation) will cancel / augment the sidebands present in the AM signal, and you will get non-symmetrical sidebands.  It also generates some level of distortion.

[W7TFO]

Quote: I have been told that my sidebands are uneven on my JOHNSON RANGER ll

Some people pay extra for that...

73DG

[Knightt150]

Thanks for the comeback from everyone, the shielding is good I have grounded the vfo case to the front panel, the resistor on the VR tube has been replaced with a new one, and I only know of this happing on 40m. It may be happing on other band I don't know.

I was told this could happen if the final plate tune was not grounded I don't know.

This problem dose not happen on my old ranger, I don't know what the difference is.

John W9BFO

[W3GMS]

John,

Tom-W8JI spent quite some time developing a solution for some VFO jumping problems.  Here is a link to his web site.  I do realize that yours may not be jumping, but it appears related to your non-symmetrical side bands.

RF feedback from Ranger to Ranger can vary due to many grounding factors.  So just because they look the same, in reality they are different from a ground integrity standpoint.    

If you did not want to dig into the Ranger, a low coast DDS solution would solve your problem.  

http://www.w8ji.com/johnson_vfo_chirp_jump.htm

Joe-W3GMS

[WD5JKO]

That is good stuff from W8JI

Look at what Johnson says about their 122 VFO on page 17, section 1, e:

http://wireless-girl.com/Projects/AMTransmitters/JohnsonVFOkeyingMod.pdf

I attach image below.

I would wager that the frequency pulling would get better if the 6146 RF PA tube in the ranger were neutralized.

Jim
Wd5JKO

[W3GMS]

That is good stuff from W8JI

Look at what Johnson says about their 122 VFO on page 17, section 1, e:

http://wireless-girl.com/Projects/AMTransmitters/JohnsonVFOkeyingMod.pdf

I attach image below.

I would wager that the frequency pulling would get better if the 6146 RF PA tube in the ranger were neutralized.

Jim
Wd5JKO

Great find Jim on the section about RF fields and the VFO.  Had not seen that before. 

I would wager, a lot of rigs of that era have the same issue.  For those familiar with the Vernon Chambers 813 rig which uses a self contained VFO, problems have been noticed with that transmitter as well.   Most of the rigs that have the tendency to have slightly asymmetrical side-bands, I have never notice by ear any of the distortion that they produce.  Then again, many are stock audio and they are what they were designed to be.  I have a Ranger but its highly modified and I have never had any reports of asymmetrical side-bands, but I may.  If I do have that issue, I would fix it but that's just me.       

Joe-GMS   

[w1vtp]

Agilent (the old HP test instruments) puts out a nice article "Agilent: Spectrum Analysis Amplitude and Frequency Modulation" (Application Note 150-1).  It would be worth your while to download it for your resource library.

I have extracted one page from it that might be helpful.  We have visited this subject several times on this forum.  Yes, it's a common problem with the older rigs. 

Asymmetrical AM sidebands occur when there is some FM component (incidental FM)  that occurs at the same time at the AM modulation component.  It is not the same thing as the so-called "pulling" that can happen with not quite adequate voltage regulation.  Pulling can be heard if you put on your BFO and listen to  a transmitter.  The subject at hand may not be heard this way depending on the severity of the FM.  Here's a portion from that page:

"Pure AM or FM signals always have equal sidebands, but when
the two are present together, the modulation vectors usually add in one
sideband and subtract in the other. Thus, unequal sidebands indicate
simultaneous AM and FM."

It is hardly ever a real concern unless the problem is severe

Al

[Steve - K4HX]

and I only know of this happing on 40m.

Makes sense. RF feedback is more likely to occur on bands where the VFO is at the operating frequency. This occurs on 160 and 40 meters for many transmitters of the 50s/60s era.

[W2JBL]

I have that problem with the WW-II surplus ARC-5 transmitters (I have two stations that use them now) and before people had SDR radios I NEVER got a complaint about it. In my case it's because the little rigs are MOPA
(master oscillator power amplifier designs for you folks in Rio Linda) and naturally pull the oscillator under modulation or changes in load. These were designed in the mid 1930's. Most people can not hear the difference, so as far as I'm concerned SCREW THE SDR crowd. If they want to listen to tube radios then they should use a F@#$ing tube receiver. Otherwise just don't look at the display. Good luck with your Ranger. Some people with panadapators have become the modern day Kilocycle Cops and need to get a life. That said bypass every lead in and out of the Ranger VFO box (except the RF out of course) and things will get better. It worked on my Ranger many years ago.

[kb2vxa]

"This resistor should be moved outside of the oscillator housing to beneath the chassis."

That's what I did to every Ranger and Valiant I repaired and/or audio de-yellowfied, but I also changed it to a wirewound resistor so its value wouldn't change. In all cases the original was WAY out of spec. Speaking of AM & FM, check out Timtron's SBE, the infamous slop bucket eliminator.

[WD5JKO]

I have that problem with the WW-II surplus ARC-5 transmitters

   I was reading an old ER the other day concerning a 1920's MOPA design. The neutralizing adjustment was "perfect" when there was no chirp from CW keying. With the ARC-5 it too is a MOPA, and there is a "fixed" neutralizing adjustment. I don't know how well it works, but I can say with the BC-458 converted to a VFO for Central Electronics, there is only one 1625 used. Varying the antenna coupling knob does indeed shift the VFO. Here the neutralization is not even close (one 1625 removed).

  Back to point, would the issue at hand here (this thread) be improved if the ranger 6146 PA were to be neutralized?

Jim
Wd5JKO

[w1vtp]

I have that problem with the WW-II surplus ARC-5 transmitters (I have two stations that use them now) and before people had SDR radios I NEVER got a complaint about it. In my case it's because the little rigs are MOPA
(master oscillator power amplifier designs for you folks in Rio Linda) and naturally pull the oscillator under modulation or changes in load. These were designed in the mid 1930's. Most people can not hear the difference, so as far as I'm concerned SCREW THE SDR crowd. If they want to listen to tube radios then they should use a F@#$ing tube receiver. Otherwise just don't look at the display. Good luck with your Ranger. Some people with panadapators have become the modern day Kilocycle Cops and need to get a life. That said bypass every lead in and out of the Ranger VFO box (except the RF out of course) and things will get better. It worked on my Ranger many years ago.

Couldn't agree with you more Chris...  I am using two Flex radios and see asymmetrical sidebands from time to time.  As long as I can copy the guy I'm fine - even the "Errr you sound like you have a sock in your mouth..."     stations I'm fine with.  In that case, I have a receiver EQ that I can employ and it solves most limited bandwidth issues.

Spectrum Analyzers can be a great tool as well as Time Domain Displays but  we shouldn't turn into spectrum management cops.  True, we hear occasional "I think your phase is inverted" reports  but in that case, it's helpful for the guy at the other end to get more talk power at his disposal.  The other report is the "dipping carrier" report but even that report should be given only in the case of severe ALC action I think.

Anyway, this has been an interesting thread.  Asymmetrical sidebands in the scheme of things is the least important issues - it's just a finesse thing of wanting to have a transmitter that puts out a good AM signal.

73, Al

[Dave K6XYZ]

I heard an asymmetrical AM signal and mentioned it to the gent....then later I was tuning around and found there were a LOT of these AM stations out there with unequal sidebands....
Then I stagger tuned my receiver IF and magically....those darn AM stations cleaned up their act immediately!!!

[Knightt150]

Thanks again for all the input, I will say this when I look at my scope with 100% mod and injecting a 1Kc tone into the mike input both side bands look identically the same.
It seems funny to me after they leave the antenna and are received some where one side band is less than the other.

John W9BFO

[Steve - K4HX]

You cannot see the sidebands on an oscilloscope.

[kb2vxa]

"Then I stagger tuned my receiver IF and magically....those darn AM stations cleaned up their act immediately!!!"

Widening the passband to allow both sidebands to reach the detector equally will do it, but so will aligning the cans to the correct frequency. You had the carrier center frequency offset thus attenuating one sideband, when the carrier is centered you'll not have that effect.

I discovered that misalignment some years ago when the crystal filter in my National Radio NC-173 didn't work worth a poop. The 455KHz IF cans drifted out of alignment and/or the crystal drifted. When all were tuned to the 455KHz crystal the filter worked as intended.

[Knightt150]

Hello: thanks for all the help, I think I have the fix thanks to W8JI there is RF getting back into the front panel and on to the VFO shaft from the plate tuning capacitor.

The fix is easy (just put a insulated coupler in place of the bronze coupler on the plate tuning capacitor shaft) no RF is going to go get through that coupler.

If you look close at the rods going through the front panel there is a lug pressing on the shaft to ground it and put some pressure on the rod, this wares over time and loses contact.

John W9BFO

[KX5JT]

Makes sense!  XTAL was fine.  Glad you have that solved John and now it's documented for posterity!!

[flintstone mop]

Quote: I have been told that my sidebands are uneven on my JOHNSON RANGER ll

Some people pay extra for that...

73DG

Prolly someone using an SDR 'scope and sees his sidebands modulating on his 'puter

Fred