RCI 2995 not quite right on USB issue

[SteveSteve]

Bought new 2995 dxcf. Works fine on am/fm and lsb. About 140 watts pep and great audio. But, usb, not so great audio and power more around 100 watts. The audio isn't muffled or dirty sounding, its more like its transmitting at a far narrower band width than the other modes. It has that very tight, lacking real quality to its audio, maybe like its only transmitting a 1 or 1.5 kc wide signal. It just doesn't sound good at all, nothing like its lsb sound. Its no longer under warranty, so either if someone gives me some good advice as to what might be wrong maybe I can fix, or a trip from here to a mail in repair shop is gonna be super pricey. Love the radio, but this usb issue is killing me. Thanks

 

[brandon7861]

post # 58 and 59 are coming to mind here

Galaxy 99V Bad sounding SSB

It is hard for me to even find a thread anymore because all titles run up and down, Not lengthwise. Everything checks out good on this radio. I borrowed the upper shield off of another radio. The shield that covers the PLL on the solder side of the board and I am told the radio sounds better but...

www.worldwidedx.com

 

[SteveSteve]

Yeah, thats an interesting couple of posts.

 

[Handy Andy]

its more like its transmitting at a far narrower band width than the other modes. It has that very tight, lacking real quality to its audio, maybe like its only transmitting a 1 or 1.5 kc wide signal. It just doesn't sound good at all, nothing like its lsb sound.

Per the "Post 58 and 59 reference...

Too many people tend to focus of frequencies - and not the audio passband - in this case when the "audio quality" seems to be lacking - the issue aroudn that is what was mentioned as well as every time someone tries to tune in an older radio that the SSB seems to lack fidelity on one band yet it sounds dynamite on the other...

Ok, grab some paper and draw out what you're doing...

When the Audio on one mode seems to be just fine, yet the other side isn't - what is happening?

What Post 59 says - the crystal lattice in the RF-tight IF-filter box is drifting and it looks like it's drifting "south" - you can fix that somewhat by tweaking the center IF to more closely match the better passing range of IF frequencies the SSB signal generates - to a point.

Had to do this on PC-122/Pro-810e due to the tight IF pass filter - so you had to shift the IF of the Audio SSB signal to let it pass thru with less attenuation - it is a game you can play with the radio - for then the other IF side - that mixes with it to make the 27MHz (at the PLL) has to make up the offset - those changes in the Audio side - change the frequency range - makes the SSB signal drift to the "South" direction just to hear it better - so you tweak that SSB offset from the PLL side to raise up the SSB mixed frequency back to make it more center slot with the others.

 

[nomadradio]

This is going to be a lot like trying to set a distributor's spark advance without a timing light.

The crystal that sets the radio's internal carrier frequency has three trimmer coils. One at a time is selected for the mode that's active. If the trimmer coil L20 is set wrong, it can have this effect. But without a way to read the frequency coming out of Q58, this can't be pinned down easily.

And as Andy says, the sideband filter itself sometimes drifts away from the design frequency and clobbers one sideband. Likewise not something that can be measured easily.

Does the channel noise sound vastly different when switching from LSB to USB? They should have roughly the same pitch, switching between sidebands.

73

 

[SteveSteve]

The difference in rx overall sound between usb and lsb is about normal, what Id expect. Also, to mention rx on usb in how other stations sound is normal as well. Its just the tx Audio quality on usb thats off. I do want to thank everyone that took the time to try and help, it is appreciated.
I'm think at this point it's probably gonna need a proper tech look at it.
Steve