RCI 2970DX Receive Help Needed

[Dmans]

All,
I have recently aquired an RCI 2970DX in a trade for some work I did. It was "Truckerized" with the bias VR's max'd out, mod limiter cut and strangest of all-the wiring from the power plug (internal to the chassis) to the amplifier section pulled out of the Molex connector. As you can imagine the transmit pattern on the scope was the ugliest thing you have ever seen. Suffice to say, all of these items have been corrected and I performed a full alignment (2 times to be sure all was well).

Today, I had a little time and compared the receive to a recently refurbbed 148GTL (aka "the Turd"-a made in the Malaysia version) and my trusty Kenwood TS440. I found the 2970 very hard to listen to. In comparison to the other 2 radios, it had a lot of white or hash noise in the receive.

Both the 148 and the 2970 were using an external speaker rescued from a throw away "surround sound" system.(Red arrows)
The TS440 was using an SP 430 external speaker.

The 148 and the TS440 were on the same power supply (yellow arrow below the bench) set to 14.3Vdc.
The 2970 was on the MFJ 30a Switching power supply (yellow arrow next to the 2970) set to 14.3Vdc.
All 3 receivers were switched with a coax switch(blue arrow)while tuned to the same frequency.

The TS440 had the best receive with the 148 a very close 2nd. The 2970 gave me a headache trying to listen to it.

If I had the ability to make and post a video of this "non-scientific" test I would.

So the question is, Has anybody found a way to tame the white/hash noise on the RCI chassis? Is it worth messing with or should I pass this on to the next guy?

73
David

 

[sp5it]

Get RF generator, SINAD meter and make rx alignment again.

 

[Handy Andy]

Go get that radios covers off and let's take a look inside - the most likely issue is around Q19 (RF Amp) and look for work - they may have put in the 2SC2999 and removed the 2714 or 1674 low-power RF amp part to replace it

Else L5/L6 just may need a re-tweaking to reduce the "Quadrature" white noise the RF amps own junctions add to this.

Thats the simple stuff, but to make the dual-FET gates quieter, you'll have to do some more work - in and around C65 and C66 - and their 1K5 (R79 and R80) "working load" resistors to clean up an otherwise noisy PLL out at L17.

The Mod is similar to what Uniden does to their PC68 and PC66 series radios - they parallel a cap resistor (R10 / C6) to that FET - but send some of the signal off - tied to ground at their output as C161 under the board - as the means to "dampen" the output (before it hits that "Source/Drain" junction) as a means to tame down a white noise distortion caused by the other white noise the PLL VCO loops make that can affect the quality of the image gleaned off of it.

To help, @kaos513, I and many others - we had a thread about the PC66 he was working on and nearly rebuilt the whole thing while posting on the thread the various issues he had with it. One instance he was having problems with the Receive - so one of the many things I've found to help with taming down receiver issues is by deadening a noisy or "reflective" PLL IF Image tap by alterig C161's value to help with noise levels and improve the RX noise level.

It's Post #110 in the thread - it got kinda' lively and with many members we don't hear too much from anymore - but I had fun during the time this was going on.

uniden pc 66 XL no power

strange issue now im off frequency reading : 27.1847 Nobody will ever know!

www.worldwidedx.com

 

[Dmans]

I did that twice Mike. But thanks for the suggestion.
I believe the SSB receive came in at -112dbm at 12 dB/SN. I performed the procedure 2 times just to be sure.
It just seems to have a greater amount of hash in the receive than the others. I know this unit is not a Kenwood but it is irritating to listen to. The receive is very high pitched as well. Maybe a capacitor to the speaker circuit would cut some of the "high's" out of it??

73
David

 

[Dmans]

Go get that radios covers off and let's take a look inside - the most likely issue is around Q19 (RF Amp) and look for work

Thanks Andy. I will give that a try next time Ii get some free time. If that doesn't solve it, down the road it goes.

73
David

 

[undertaker]

DMANS all of my rangers have that white noise.. guess they always will ..

 

[Dmans]

I thought it may be something I could use as a back-up (as if I need another).
I will give it another pass and if it still has the "white noise" down the road it goes.

73
David

 

[DXman]

I have a 2970N2, got it about 5 mo's after they 1st came out. I have notice the "white noise" is less on this radio than all my other 29750's/2970's dx models.
Buy using a "clear speech" speaker from West Mountain Radio, the "white noise" is more tolerable.

 

[Dmans]

This one is a 2970DX. It has the Bi-polar driver and final transistors (2166 & 2312) and the amp board has 2x2290 Toshibas. The bulk of the main board is SMD. This radio is a bit of everything-mostly white noise!
I have the tools to work on SMD boards but do not have an inventory of parts for them. I don't think the juice is worth the squeeze on this one and will probably pass it on.

73
David

 

[Holydvr]

I have had the same issue with Ranger built stuff. I did end up sending it down the road.

 

[Shadetree Mechanic]

On the Galaxy radios, L8 adjusts the double transistor stage. Detuning L8 will get rid of most of the static sound without killing too much of the signal. Does the 2970 have this?

 

[Dmans]

Does the 2970 have this?

The schematic shows L8 connected to 2 FET's.

I will give this a shot next chance I get.

Thanks

73
David

 

[Shadetree Mechanic]

The schematic shows L8 connected to 2 FET's.

I will give this a shot next chance I get.

Thanks

73
David

I found this information when I was working on an 86v. I do this to all my radios now.

Galaxy DX86V mods

Just put a 10k across C158, initial testing sounds great. Getting ready to put it on the scope in the shack. Curious, did you restore r176 back to stock or did you leave it with your trimmer?

www.worldwidedx.com

 

[peabody830]

Ranger radios have alway had problems with white noise. Gets a little better in ssb mode . And if it had been truckerized, it didn't help it

 

[nomadradio]

There was a trick we used on the older through-the-hole circuit board 2950 radios. We pulled R75 and substituted a 2k, or maybe a 5k trimmer pot. Increasing the resistance of R75 would reduce the collector current of Q18, the receiver's first RF amplifier stage.

Would also reduce noise.

And signal gain. The trick was to guess how high the customer's antenna noise level would be and set the trimpot so sensitivity wasn't reduced enough for the customer to care about.

A crude hack, but better than nothing.

Well, sometimes it was. Never have tried to do this on a SMT 'DX' radio.

73