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Royce 1-642 Modulation Help Please

3pinplug

Member
Jul 23, 2016
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Hi all

After some help to solve a recent problem that has come to light, I have been getting reports of poor modulation from users both local and long distance when I am DX'ing. Set up a radio near by and my mod sounds gritty / distorted on SSB.

I tried adjusting VR11 (SSB ALC) and although it made it a tiny bit less gritty / distored, it didn't really make it much better.

Since the problem, I brought a new stock mic and have also tried a couple of other mics and no difference, I have good swr and have cut / resoldered the connections on both ends of my aerial lead and checked the coax just in case - no short which is good.

What is the best way to track the mod though the radio from the mic to find out what is causing the distortion or is there a known fault i should look at with these?

Thanks

Mark
 

AudioShockwav

Extraterrestrial
Staff member
Apr 6, 2005
7,369
4,978
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Sierras Near Yosemite National Park
Can you post some clear pictures of the main board?

I have to disagree that all Royce Radios are trash dumpster material, I used to run a 643 base station that quite worked well and a few mobiles that were decent radios.
If the SSB sounds " Gritty" someone may have defeated the ALC.

73
Jeff
 
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nomadradio

Analog Retentive
Apr 3, 2005
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You really need to be able to hear it for yourself.

There are two flavors of "gritty" that are most common.

First would be a harsh should when the mike gain is turned up, but clears up with the mike gain turned down to one-half power or less. This would be the ALC setting.

Second is called "zero-crossing" distortion. You can identify this by turning the mike gain down until the wattmeter barely flickers above one Watt. If the audio is gritty this way, and gets clearer with the mike gain turned back up, the driver and final-transistor bias adjustments deserve a close look.

73
 

Smokinone

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Jun 24, 2020
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3pinplug

Member
Jul 23, 2016
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3
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Hi all

Sorry for the delay in replying to all your comments I hadn't been well over the past few days.

Firstly, Staybolt for a forum where like minded radio users come together to help each other, thank you for your extremely valuable input to help resolve my issue.

I will answer some of the very helpful comments now, unfortunately I do not have a Mic gain Control on the radio only the ALC horseshoe control. If I adjust the horseshoe for AM Mod can I ask if that makes any difference tothe SSB mod at all?

I attach some photos of the main board as requested, you will notice the CCI3001 PLL is no longer in it as it has had a Maurer module fitted to to give Low, Mid and Hi channels.

It has performed well with regular contacts all overthe place until recently and no reported mod issues, i have a gritty / raspy sound round my voice when i speak whenmonitored on another radio, turning the alc down (currently set half way) makes a very minimal difference but even at min its still not right at all.
 

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3pinplug

Member
Jul 23, 2016
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Just tried radio in PA mode and it sound lovely so may just be limited to SSB. I willtry transmitting tomorrow eve yo another radio on AM and see if it is diatorted.
 

nomadradio

Analog Retentive
Apr 3, 2005
5,325
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Louisville, KY
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The "AM Mod" adjustment almost never serves to set the sideband audio limit. The ALC adjustment should be the sideband-only way to keep the power level below the distortion level.

About that "worst when soft" or "worst when loud" comparison. How does that stack up? That can be a trickier comparison to make without causing acoustic feedback. A pair of headphones is your friend when there is no mike gain control.


73
 
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3pinplug

Member
Jul 23, 2016
21
3
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54
Hi
Yes double checked onanother radio i have and the reports i was getting are valud it doesn’t sound right. I will try and record a wav file of it set to min and max on the ALC and see if i can upload those instead of jpegs, hopefully if you guys can hear it, that may point me in the right direction. Just off to work now so will see what i can do this evening when i get in.
 

3pinplug

Member
Jul 23, 2016
21
3
13
54
Hi all
Am I barking up the wrong tree here?
I set up to record the radio mod and it sounded off frequency to me tonight so I set up my oscilloscope and two generator and include the images below, now I am still trying to lean so no expert but the ALC (VR11) from the modulation envelopes appears to be working and the top envelope i set the radio to looks ok, can someone with more knowledge confirm but from what I can see on net thats the shape you want.
I then turned to channel 12 high (27.55mhz) and took frequency readings on AM, USB and LSB. AM is ok, but USB which iu have been transmitting the gritty sound on is further away from 27.555 than LSB is that correct and of not which one LSB or USB is off, assuming they should be the same distance up or down from the center frequency 27.555?
Fingers crossed I am moving in the right direction want to get back on the air as really like operating on the 1978 royce.
 

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3pinplug

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Jul 23, 2016
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This took some doing on the recording front but hopefully you can hear the files, recorded them with SSB ALC on Max and Min. Its the distorted buzz around the edges that is the problem / reports I am getting, if i then run a linear its even worse. Its not a clean sounding mod and its a brand new stanadrd microphone that i brought to see if that resolved the problem but it didn't, thanks for the help very much appreciated. Let me know the files are accessible, if not i will try again.
 

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3pinplug

Member
Jul 23, 2016
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I would like to double check the driver and final bias values as I did attempt to set them some time back and I an wondering if maybe I haven't done it correctly. Originally I was working of the Pace 8193 service manual which when you cut the wire link shown in the photos (putting an ammeter across the cut wire link) thenit said to adjust VR13 which I did. Locatin g a copy of the correct Royce 1-642 schematic (section below) that actually has " 2 x VR's for bias setting" (VR13 & VR14) so I don;t think I have done this correctly. The only problem is when you cut the wire and put the ammeter across and adjust VR13 you can set it for 80ma ?(as per the Pace 8193 says to) but then how do you then isolate the other sectionof the circuit to set the bias vias VR14? Where do I connect too / what do I have to disconnet?
 

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