JP32 works too, it comes off of the secondary trace that JP29 feeds. I used to replace JP32 with my adjustable low carrier audio fed high swing mod.
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Palomar RFX95HD
- Thread starter grimace
- Start date
This little device is indeed impressive.
So I did a wire connection test before full blown installing the rfx just in case I didn't like it and could easily return all to stock before drilling the radio.
So before testing, the Bell's cb 29 dead key was just shy of 1 watt and pep right around 20.
Tested through the rfx with amp off first to see if everything remained the same and it did. Powered up the rfx, key up, hear the relay click and modulates to 100 pep +/-.
Heck yeah that's pretty freaking cool!
I get hellacious voltage and current drop so the radio power jack needs upgraded because the teeny wires aren't cutting it. Upgrading that and a heavy power cord might mitigate that issue.
So I did a wire connection test before full blown installing the rfx just in case I didn't like it and could easily return all to stock before drilling the radio.
So before testing, the Bell's cb 29 dead key was just shy of 1 watt and pep right around 20.
Tested through the rfx with amp off first to see if everything remained the same and it did. Powered up the rfx, key up, hear the relay click and modulates to 100 pep +/-.
Heck yeah that's pretty freaking cool!
I get hellacious voltage and current drop so the radio power jack needs upgraded because the teeny wires aren't cutting it. Upgrading that and a heavy power cord might mitigate that issue.
Shadetree Mechanic
Delaware Base Station 808
I have always wondered if a power pole connector could be made to fit in the stock power socket hole? I am going to get one of these little amps after we get the holidays out of the way. Thanks for sharing this.
Shadetree Mechanic
Delaware Base Station 808
Audio fed high swing mod? Sounds exactly like what the RFX95 needs. Care to share any details?
The premise is that the Pre-Driver power feed jumper (JP32) is removed, and a diode samples the positive going TX audio voltage, the added electrolytic capacitor (negative side grounded to the can of L17), this stores the TX voltage, it "idles" at 12v (from the transformer and blocking diode), then charges up to 24v or more on positive audio peaks. It only reacts to the positive peaks, as negative peaks are blocked by the added 1N4148 diode. It does not have to be a higher current diode, as the TX Pre-Driver circuit is low current.
The 1k (or was it the 20k Delta Tune?) potentiometer (or any) can set the low carrier setting, there is/should be a resister (1k? 100 Ohms?) from the low side of the pot to ground, this sets your lowest carrier level from the potentiometer. When the added capacitor charges up on positive going audio peaks, the carrier comes up to full, and drops back in between words. This causes the meter to swing wildly, on the TX side, and on the receiving side.
Imagine having a 100mW carrier (1/10 of a Watt) (even through the amplifier) swinging up to the max that the amp can deliver.
I did a similar setup in one of my previous RCI2970 (1st gen) radios, 100mW swinging up to 150W.
You can experiment with different size capacitors, need to be 50v or more, though, a bigger capacitor value will hold the signal longer, a smaller capacitor will drop out faster.
Also, this has no effect on the AMC (if (preferably) intact).
This is also way better on the Oscilloscope pattern than the Resistor/Cap mod to JP36, which has dropouts on negative peaks.
I hadn't done one of these since before 2000, when I moved to the Clearwater area then. I moved to Tampa in 2012. So the specifics are kind of "fuzzy".
Got my little installation to a stopping point and am impressed with the rfx add on. Make yourself a stencil because it does NOT come with one and if you're ocd like me and want things squared up, it's a must. FYI The radio power jack had to be upgraded because the oe jack just doesn’t cut it for the juice the rfx requires. I put the amp on/off on the channel 9/19 switch which is nice for when the powa is needed.
On the rear the rfx will add on about 2-1/4" which is quite a bit for an overhead cubby or depth restrictions (something to consider). Also with the amp installed, you still have plenty of room to connect your pl259.
Without tweaking dead keys or modulation from what Bell's had done to the radio, it achieves approx 85 to 100 on the peaks. I purposely drove it pretty hard into the dummy load and never got much past warm. Figured I'd spice up the channel display and meter light while I was in the neighborhood just because.
Pictures for reference below in case any of you fellers are doing one of these.
On the rear the rfx will add on about 2-1/4" which is quite a bit for an overhead cubby or depth restrictions (something to consider). Also with the amp installed, you still have plenty of room to connect your pl259.
Without tweaking dead keys or modulation from what Bell's had done to the radio, it achieves approx 85 to 100 on the peaks. I purposely drove it pretty hard into the dummy load and never got much past warm. Figured I'd spice up the channel display and meter light while I was in the neighborhood just because.
Pictures for reference below in case any of you fellers are doing one of these.
Nice job Ed ! I have one sitting next to a Galaxy 2100 that has no output, probably send them to Denny soon.
Happy new year my friend !
Todd
Thank you sir, hopefully it'll turn out well with that rig too. Please do report the results.
Happy new year to you as well!
Shadetree Mechanic
Delaware Base Station 808
I have installed one of these on my Galaxy 86v, and it sounds great on AM. On sideband, not good at all. Has anyone put one on a sideband radio, and did it sound ok? Does anyone know if the trim pot is the bias? It appears to be, just want to make sure.
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How does the radio sound by itself on SSB? The RFX is no doubt being driven too hard for clean sideband. Try turning the mike gain down until the RFX power is roughly equal to the barefoot radio. If this clears it up, that's the cause.
If turning the mike gain way down makes it sound worse, this points to a problem with insufficient bias current.
Maybe
73
If turning the mike gain way down makes it sound worse, this points to a problem with insufficient bias current.
Maybe
73
The installation looks good though, hopeful you can iron out the ssb. I've only done the Cobra 29 so can't be of any help to you.
Did the existing heatsink holes match the rfx mounting holes?
Shadetree Mechanic
Delaware Base Station 808
The radio by itself sounds great on ssb. It almost sounds choppy, and reducing the mic level makes it worse. With the mic level up all the way, eating the mic loudly will keep it from chopping. But still sounds bad.
Any idea what an acceptable bias current would be? Maybe I can measure bias current on the power wire, I will report back what it is.
Shadetree Mechanic
Delaware Base Station 808
Thanks, the heat sink holes were a perfect match. Just had to drill them out a little.
That chopping usually tells me there is NO bias supplied - the D4 R4 R5 (CB Tricks ERF 1230 methods) are powering the Gate region.
So remember that when you turn on bias into these amps - the input power associated with the radio - HAS GOT TO BE TURNED DOWN - else the amp will not only clip and distort (that 28V Zener clamp is only going to work for so long) but will cook the amp - so when you add bias, the radios own output power needs to be cut down nearly by 75% - that means a 12W carrier? 4W out now... sort of thing - you literally make the radio a "duck" to keep the amp working and not blowing up.
So remember that when you turn on bias into these amps - the input power associated with the radio - HAS GOT TO BE TURNED DOWN - else the amp will not only clip and distort (that 28V Zener clamp is only going to work for so long) but will cook the amp - so when you add bias, the radios own output power needs to be cut down nearly by 75% - that means a 12W carrier? 4W out now... sort of thing - you literally make the radio a "duck" to keep the amp working and not blowing up.
My educated guess would be 25 to 50 mA. Just the same, turn the mike gain down to a half Watt PEP and then carefully crack VR1 upwards. Stop when you hear the 'rasp' clear up. This is not exact, but should reduce the complaints without burning up the amplifier.
Distortion that gets worse the lower you turn the mike audio is what the eggheads call "crossover distortion", or "zero-crossing" distortion.
73