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2995dx modulation on a scope
- Thread starter GnG8d
- Start date
Yeah, I've got a mess on my hands, lol.
I have 25 IRF520's coming and a couple handfuls of other SMD transistors, resistors and capacitors. I know that I fried at least 3 520's in the final PA and at least the driver in the 2970. I think what happened was that test board had leads that were to short and too stiff. It stressed the delicate board when ever I handled it to turn the trimmers. So when I made the leads longer it picked up RF and took off on me. Once I lost at least one 520 it set off a chain of events because I think they tend to short rather than open like a bipolar.
On the 2995, I've got some new ceramic and plastic tuning tools coming. The cheap radio shack tools weren't getting it. I think after removing the diode and putting the transistor back in the modulation circuit, it just needs retuned.
The biggest fear is that the parts I have coming aren't going to be correct. The schematics are not for the latest board revision and some of the listed transistors are obsolete already. So I spent literally hours on different sites tracking down what should be compatible replacements.
I'm not happy about this mess, but I'm knee deep in it now even though this is not what I expected after buying 2 brand new RCI radios from somebody I trusted.
I'm going to claim a small victory on the 2995. I got it back to stock form last night, along with modulation control, variable power and symmetrical modulation at +95%/-95%. I then added a 220ohm/1N4148 in series on R292 leaving the 560ohm there. I did it this way because it worked to some degree on the 2970 and I just needed something back on the air. With this I got +125/-95% modulation keying 35w peaking 160w. That's a far cry from the pinched up 40% negative modulation I started with trying to run any kind of carrier. To peak 100w, I have to drop my carrier to something like 15w and the positive peaks jump to around 180%, so it still needs fine tuning so the carrier doesn't need dropped so low.
So, as soon as UPS gets here, I'll start on the 2970 by replacing all 11 FETs to start. I want to get it back to stock form and then experiment a little. I'm thinking of having a couple boards made up at Pad2Pad. I designed a couple with pads for trimmers, diodes and DIPs that are less than an inch square, but I need to submit one and see what they want $$ first
So, as soon as UPS gets here, I'll start on the 2970 by replacing all 11 FETs to start. I want to get it back to stock form and then experiment a little. I'm thinking of having a couple boards made up at Pad2Pad. I designed a couple with pads for trimmers, diodes and DIPs that are less than an inch square, but I need to submit one and see what they want $$ first
That 35/160 figure sounds right on the money. With my TS-950SDX at 100% modulation, I get about 35/150. I can't really do the same kind of NPC tricks with it though since it's low-level modulated, so that's about as good as it gets.
I'm curious to know how the rig sounds on SSB, with and without the NPC mods. There's a guy locally that has a 2995, and it sounds okay on AM, but on SSB the audio is poop. I've always suspected this to be a side effect of some kind of AM modulation tweak but I've never seen inside the radio so I can't be sure.
-Bill
I'm curious to know how the rig sounds on SSB, with and without the NPC mods. There's a guy locally that has a 2995, and it sounds okay on AM, but on SSB the audio is poop. I've always suspected this to be a side effect of some kind of AM modulation tweak but I've never seen inside the radio so I can't be sure.
-Bill
This might sound like an odd question but why even bother with this if you do not have too???
An SP1-A or something like it would have all the clipping and filtering and gain sorted out so that all you need do is install it and adjust it in under 10 minutes. If you want turn it off when you want normal swing turn it off when you want to make better use of your average talk power. Massive amounts of swing generally do not do that much for you outside for making you like like skipp rolling in!
An SP1-A or something like it would have all the clipping and filtering and gain sorted out so that all you need do is install it and adjust it in under 10 minutes. If you want turn it off when you want normal swing turn it off when you want to make better use of your average talk power. Massive amounts of swing generally do not do that much for you outside for making you like like skipp rolling in!
Why not?
But seriously, the radios were already hacked up, why not experiment a little?
I don't know anything about it. But a couple of those speech processors have been hit or miss on approval ratings. And the 10 minute install can be tangled with issues I've read.
I'm looking to eliminate massive amounts of swing, that's what started all of this. When I started, these radios pinched up the negative peaks with normal carrier levels. I had to run 5w peaking 200 to get a decent looking wave form and they ran full power at any carrier setting as well. I want variable power, normal carrier levels and some degree of asymmetrical modulation.
Me too, the RCIs are supposed to be great sounding SSB rigs, so we will see. The other morning after I got the 2995 back up and running, I made a few contacts in California. I got several unsolicited comments about the audio that morning ....... on AM anyway.
I've read posts from Stacy Adams on other forums for a couple of years, and he seems straight up, so I'll take his comment on another forum as a positive note ........
Stacy Adams said:
One thing I've noticed is the average power has dropped off considerably. But I remember Shockwave and a few others saying that the carrier should be the same as the average power, or at least minimal forward average swing. I'm going to guess that an improperly modulated signal creates a lot of artifacts which increase average power readings.
Okay, I'm good. Carrier x 1.5 for average power and carrier x 4 for peaks. Peak x .25 for carrier and peak x .375 for average power.
I'm trying to run closer to peak x .2/.22 because of the amp I'm using, but other than that it's all good. The big average numbers were obviously coming from the 40% negative peaks.
I'm trying to run closer to peak x .2/.22 because of the amp I'm using, but other than that it's all good. The big average numbers were obviously coming from the 40% negative peaks.
Hey, I know Stacy Adams. We're local to each other, and I've met him at couple of breaks. He's a nice guy.
The fellow who runs the 2995 locally usually keeps his mic gain turned down to keep his audio sounding clean. The AM gain levels don't work well on SSB though.. The audio is too low and sounds grainy and choppy. Turning the gain up helps (I have to keep reminding him to adjust it), but it still sounds distorted to me.
The radio was supposedly new in the box when he got it, but I guess there's no way to be sure how stock it is without cracking it open.
-Bill
The fellow who runs the 2995 locally usually keeps his mic gain turned down to keep his audio sounding clean. The AM gain levels don't work well on SSB though.. The audio is too low and sounds grainy and choppy. Turning the gain up helps (I have to keep reminding him to adjust it), but it still sounds distorted to me.
The radio was supposedly new in the box when he got it, but I guess there's no way to be sure how stock it is without cracking it open.
-Bill
Yeah, the RCI is generally pretty tame on AM and that is what helps it on SSB I believe, they are not known to be Galaxy loud. If he needs to turn the gain down on AM, my guess is that he got some sort of a tune up when he bought it, knowingly or not, lol.
Sorry to dig this up but I just recently acquired a 2995 DX and am looking to lower the deadkey and drive a 6 pill. I used the Topgun MD-1 and CP-1 on my 2970dx and it works rather well. So after reading through this thread im still a bit confused about the best results. Do i put 250 ohms in series a 1n4001 and run it parallel with r292 and call it a day?
Let me rephrase the question. Is this the correct method people are currently using the NPC mod these radios. Im looking to deadkey about 5 to 30 watts with full swing pep and good average
UPDATE
I put 250 ohms in series with a 1n4001 and ran it parallel with r292 radio is now providing good average swing and a very good adjustable dead key range.
I also removed the two resistors on pin 1 and 2 on the audio IC added the cp-1 compressor on the audio IC.
Thank you for this useful thread
UPDATE:
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