I appreciate you having the mod performed. It would be nice if he could do a before and after vid. I got an email from BellsCB, he doesn't do the mod. He didn't comment either way, just mentioned that he didn't.
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DTB "IF Filter Mod" for RCI 29xx radios?
- Thread starter buickid
- Start date
Maybe it is BS; I don't know. I can understand why there is a need to find out why it has too much noise and seek a remedy for it. If these shops are selling snake oil, would also be interested in knowing that too.
As MS said, jacking up the VCO voltage can make the RX more sensitive and noisier too. Seen that with some Cobra 148's. But this can also cause the PLL to go out of lock if it is raised too high - too.
The 2950 I aligned/own has all of the alignment values set to stock, except for a small upward tweak on both the AM modulation and SSB/ALC. Even at stock VCO voltage, it still has a nasty receive compared to a Uniden chassis radio. The TX is all fine 'n dandy; just the receive is subpar.
Put it on a HP 8656B freq gen and a SINAD meter and adjusted it for maximum signal with the least amount of noise. I might also point out that the total harmonic distortion reading on the SINAD meter clearly pointed out this radio is a real stinker. Not the first 2950 I have tweaked with either; they all had a less than desirable noise figure. Perhaps the audio circuit is to blame; who knows unless it can be qualified.
If a shop really wanted to find out the problem area, they would put their best tech on it with a O-scope and find the offending circuit or part(s). Then let the chips fall where they may. Of course, that someone should be skilled enough to do just that and be very handy with their scope and then see if they can find a useful remedy. If Bob's CB Shop has/hasn't done that; I have no way knowing their claim is true. Until then, I will not say that it is BS until proven one way or another . . .
As MS said, jacking up the VCO voltage can make the RX more sensitive and noisier too. Seen that with some Cobra 148's. But this can also cause the PLL to go out of lock if it is raised too high - too.
The 2950 I aligned/own has all of the alignment values set to stock, except for a small upward tweak on both the AM modulation and SSB/ALC. Even at stock VCO voltage, it still has a nasty receive compared to a Uniden chassis radio. The TX is all fine 'n dandy; just the receive is subpar.
Put it on a HP 8656B freq gen and a SINAD meter and adjusted it for maximum signal with the least amount of noise. I might also point out that the total harmonic distortion reading on the SINAD meter clearly pointed out this radio is a real stinker. Not the first 2950 I have tweaked with either; they all had a less than desirable noise figure. Perhaps the audio circuit is to blame; who knows unless it can be qualified.
If a shop really wanted to find out the problem area, they would put their best tech on it with a O-scope and find the offending circuit or part(s). Then let the chips fall where they may. Of course, that someone should be skilled enough to do just that and be very handy with their scope and then see if they can find a useful remedy. If Bob's CB Shop has/hasn't done that; I have no way knowing their claim is true. Until then, I will not say that it is BS until proven one way or another . . .
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I might be a little harsh in my initial assessment. Thousands of these rigs are out there. Thousands of dudes are always wanting crap done to them. I find it highly irregular that the net is void of any anecdotal evidence on this mod.
It just ain't right...
It just ain't right...
"The 2950 I aligned/own has all of the alignment values set to stock, except for a small upward tweak on both the AM modulation and SSB/ALC. Even at stock VCO voltage, it still has a nasty receive compared to a Uniden chassis radio. The TX is all fine 'n dandy; just the receive is subpar"
Is this a 1st generation orage backlit model, Or is a "DX" version? I can remember going over alot of what was posted on the net at that time concerning the first generation models. They had a laundry list of issues. I agree that the uniden chasis has a far better RX, But remembering the RX on the Jackson I had long ago the "DX" model I have now seems close, Not perfect...But close.
Is this a 1st generation orage backlit model, Or is a "DX" version? I can remember going over alot of what was posted on the net at that time concerning the first generation models. They had a laundry list of issues. I agree that the uniden chasis has a far better RX, But remembering the RX on the Jackson I had long ago the "DX" model I have now seems close, Not perfect...But close.
Got my 2950DX back yesterday, hooked it up last night and used it until about midnight. I can't do a vid as Duster would like but I will say I personally feel the noise floor is actually lower. Lower meaning less background noise. As the night went on and the conditions got quieter I could tell quite a bit of difference after all the garbage stopped. So for 25 dollars plus shipping I am a happy camper and again Dave at DTB Radio has a happy customer as usual.
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M42Duster
Duster there is a video how to do this mod if your solder and unsolder skills are ok you really need to do this mod. Tonight with skip not crazy but not quiet it's like having a completely different radio, the noise is not enough to cover up the audio it really works great. I would not steer you the wrong way but you can be rest assured I will try it myself on the next 2950DX I buy it really is a big difference in certain issues and tonight was one of them
Duster there is a video how to do this mod if your solder and unsolder skills are ok you really need to do this mod. Tonight with skip not crazy but not quiet it's like having a completely different radio, the noise is not enough to cover up the audio it really works great. I would not steer you the wrong way but you can be rest assured I will try it myself on the next 2950DX I buy it really is a big difference in certain issues and tonight was one of them
Guys, Let's hold up a sec. We need to understand something here. "image rejection" and "white noise" are two different issues. I am with m42duster on this one. This modification was done for a random issue with image rejection with the early model second generation radios.
I have no dought that you are experencing a Quiter front end, but I garenty you it has nothing to do with that modification, But rather a quality, propper, RX tuning.
I have no dought that you are experencing a Quiter front end, but I garenty you it has nothing to do with that modification, But rather a quality, propper, RX tuning.
Update: I received the radio I ordered and have been using it with good result, but I recently discovered the IF mod has not been done, upon looking at the warranty sticker (intact). Dave did offer a refund, but I want the mod done, so I'm sending it back. This offers a chance for me to make a before and after video, to see if it makes a difference. I'll take a before video of the radio listening to a dead channel, then have a short QSO with a local, then when the radio comes back, do it again under similar conditions.
It's ashame you have to go through so much trouble only to find out there is no difference in the before and after. But if it will help people to understand the difference between image rejection and "noise" reduction then it's all good.
Two completely different animals.
Just make sure you make an identical baseline for comparasin as best you can.
Two completely different animals.
Just make sure you make an identical baseline for comparasin as best you can.
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