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Message |
    
Resistor
Junior Member
Username: Resistor
Post Number: 15
Registered: 7-2004
| | Posted on Tuesday, August 17, 2004 - 8:56 am: | 
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I have and old 2980 and was wondering if its possible to replace the variable resistors like VR-14 (AM mod) with a larger type knob mounted to the front or side of the radio. IF so is there anything I should know as far as values or where I could find one. Is a potentiometer a variable resistor? Would the longer wires from the board give my any problems?
Thanks
Resistor™ CEF-366® / Marc |
Tech808
Moderator
Username: Tech808
Post Number: 3318
Registered: 8-2002
| | Posted on Tuesday, August 17, 2004 - 10:00 am: |
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Marc,
Yes it could be Done but the question I have is WHY?
VR-14 was Not designed to be constantly adjusted.
You only Adjust / Set it Once and never touch it again unless something goes wrong with the radio or it needs to be re-aligned.
The radio already has a Mic Gain Control to use.
On my radios I adjust / set it to 85-90% Modulation and have never had to re-adjust it again.
And it would completey ruin the looks of the radio to start drilling holes and adding knobs / controls that are completely un-needed.
Just my personal thoughts.
Lon
Tech808 |
Resistor
Junior Member
Username: Resistor
Post Number: 16
Registered: 7-2004
| | Posted on Tuesday, August 17, 2004 - 11:34 am: |
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I guess your right Lon. I've been adjusting it allot lately more from confusion from my meter than anything else. Maybe you can help set me straight on my PDC 600LP Meter. Whats the proper point to set the mod level on the meters mod scale. What i'm trying to say is that the meter has a "Set" and "Mod" switch for the mod meter, but it doesn't specify where to set it to calibrate it on the "Set" Position. Does it get set to the fullest right position at the +3 reading or at the 0 position on the scale. Until I know this I can't be certain i'm reading my mod level correctly.
I like to keep a nice clean mod setting and will take your advice on setting it to the 85-90% level. Once I can set my meter correctly that is.
Thanks for your advice. Nice to have someone to turn to...
Resistor™ CEF-366® / Marc |
Tech808
Moderator
Username: Tech808
Post Number: 3320
Registered: 8-2002
| | Posted on Tuesday, August 17, 2004 - 5:48 pm: |
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Marc,
Sorry never used the PDC 600LP but they are all pretty much the same.
Turn your Knob on the meter to "SET" for Mod/SWR and then Key the Mic on AM and say Nothing and Set / Adjust the needle to "3"
Then turn the Knob back to SWR/MOD and it should give you the reading. |
Hollowpoint445
Intermediate Member
Username: Hollowpoint445
Post Number: 261
Registered: 6-2004
| | Posted on Wednesday, August 18, 2004 - 12:46 pm: |
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Resistor - modulation meters are not capable of accurate modulation readings. There is no way a mechanical movement is capable of moving at an audio rate. They'll give you a ballpark reading, but nothing very accurate. They are basically something to watch when you're chatting. The only device that is capable of accurate modulation readings is an oscilloscope - preferably showing a trapezoidal pattern to show modulation and linearity.
If you want to adjust your modulation without an oscilloscope there is a way to do it and make sure you aren't causing bleedover.
Get a friend to act as your assistant. The better his radio is with adjacent channel rejection, the easier his job will be. Choose 2 adjacent channels that are pretty quiet - no skip or backround noise. The channels need to be right next to each other - no "A" channel gaps. Your assistant should have a good copy on you when chatting on the same channel. He should adjust his RF gain control so you are mid scale at the most on his S-meter. Your signal shouldn't be so strong that he'll think you're bleeding over when it's just a strong signal making his receiver misbehave. When this has been accomplished you should change to the adjacent channel, make a small modulation adjustment, and then talk loudly or whistle for a few seconds. Then change back to the channel he's listening on to see if he heard any bleedover. What he's listening for is just scratchy noise on the frequency that only happens when you're talking - bleedover. It should happen the entire time you're talking, not just when you first start talking. There is a brief period of time that the limiter circut takes to work and "limit" the signal. If he didn't hear any bleedover then you should repeat the proceedure until he does. Once he hears bleedover you should back down the adjustment slightly until he doesn't hear it anymore. When he stops hearing bleedover you are as close to 100% modulation as you can be without an oscilloscope and tone generator. You're also sure that you aren't causing bleedover.
Good luck! |
Resistor
Junior Member
Username: Resistor
Post Number: 18
Registered: 7-2004
| | Posted on Tuesday, August 24, 2004 - 4:57 pm: |
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Thanks Hollowpoint
Makes good sense to me. I'll try that method with the wife... (Wish me luck) I'll need it..
Resistor™ CEF-366® / Marc |
Hollowpoint445
Intermediate Member
Username: Hollowpoint445
Post Number: 281
Registered: 6-2004
| | Posted on Wednesday, August 25, 2004 - 5:17 am: |
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Let us know how it works out. |
