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Tnx,
Arv your right. No longer have the knowledge handy to draw upon. But thanks for the great advice. I will guess my way along.
Just thought someone could hold my hand a little.
Chip

Allison,

I assume this was in response to my question about swapping out Q10,11,12 for BFR106's
for better receive performance on the high bands.
? >? It would at 20mhz and up but not worth the effort for 80 though 20M.

Sounds like those spurs when transmitting on the high bands will not get solved by just piddling around.
Maybe v5 of the uBitx could have pads on the board for the 86.85mhz PX1002 SAW as an alternate:
??/g/BITX20/message/51172?
For v3 and v4, a daughterboard for the PX1002 could mount into the 3 holes meant for the 45mhz filter.

Those wishing to stick with the cheaper 45mhz filter can dumb the uBitx down to an 80m-17m rig.
Or deal with plug-in filters or the considerable complication of switched filters to replace the current 30mhz LPF at L1,2,3,4
Or knowingly choose to send their spurs off into the ether, flouting the law on a 10W QRP rig.
? ?
If the PX1002 works here, seems well worth the $6 quantity 1000 price, $12 single piece from Mouser.
Easier, simpler, more compact, and perhaps cheaper than switching a bunch of filters.

Jerry, KE7ER

I am going to try this with my V4 -? help my understanding of a variable Pot -? is your slider (center pin) hooked to the same pin on D16?? what effect does this have on total resistance -? could you just hook the 12 ohm resisitor in parallel between pin 1 and pin 2 of the pot???? then you would just be adding 125 + (pot value) / 2 for the total resistance??

--
Richard
KC7DDW

Hi,

I travel a great deal, and always take the radio. I’m away from the ubitx at the moment, and can’t measure it.?

I’ve had an idea for a “tablet-like” rig using the Nextion display to make this suitcase friendly.?

Anyone have any ideas about enclosure size, shape, manufacturer?

Wow! Working 10& 15 FT8 with 3 watts, using my new ubitx and a raspberry pi with 7" screen! ?Working great.

Wondering about drive levels from the USB sound card I bought the DS203 mini scope. I found it half price from its $250 retail price.

Note the signal, after I turned the audio level from the pi down to eliminate fkattopping.

Wow! Working 10& 15 FT8 with 3 watts, using my new ubitx and a raspberry pi with 7" screen! ?Working great.

Wondering about drive levels from the USB sound card I bought the DS203 mini scope. I found it half price from its $250 retail price.

Note the signal, after I turned the audio level from the pi down to eliminate fkattopping.

On Tue, Jun 19, 2018 at 10:51 am, Jerry Gaffke wrote:

I assume that this is a very good idea for those who wish to avoid spurs
greater than the legal limit of -43 dBc on the 15m, 12m and 10m bands,
though if you keep the mike gain down and monitor the output closely it is
possible to operate legally.?

Its critical to battery operation for stable operating point.? Does not help the spur
issue much at all.??

Generally the spurs are there, we can argue how bad.? The one on my bench?
cannot go to above 20MHz without band specific (bandpass) filters before the amp.

Allison

Yes Sir,
Been at this a few weeks now. It has got to be a relay or something that is just not engaging all the test measurements from the document listed in the beginning were so very close. I am just not sure where or how to proceed to the next step
Thanks for responding
Chip

It would at 20mhz and up but not worth the effort for 80 though 20M.


Allison

The issue is not so much the stacked outputs (3904 and 3906) or the 2.2ohm emitter resistors.

That amp can easily put several hundred milliwatts into the speaker.

The bias arrangement is fair but some resistance in series with the diodes will move
the quiescent current to about a milliamp or two in the stack is helps.

The output is an emitter follower with mirror and by nature fairly linear.? The driver is
where the havoc begins.

The problem is in the driver Q71 as there is limited at best guarantee it will bias to half the Vcc.
The lack of DC feedback there is a problem. IF anything I'd take the 10K and spit it into 2 2.7K
with one end connected to the emitters the other of the series pair to the base and in the center 10uf to ground.
Without that "servo loop" the amp may be improperly biased.

What can happen:?
If the transistor Q71 has low Hfe the collector will be higher than about 6V
and the bias current though the output stack will be low.? The voltage swing
will be limited to less than half the power supply voltage before clipping sets in.

If the transistor Q71 has high Hfe the collector will be lower than about 6V
and the bias current though the output stack will be high.? The voltage swing
will be limited to?less than half the power supply voltage before clipping sets in.

In both cases there is limited feedback (R74 helps a little) to insure the bias?
for Q71 is at the correct point to set the output up.

If we bias Q71 off the output or even its own collector it will tend to self center
and things should behave correctly.? However if the bias resistor is not spilt
and bypassed for audio the stage gain will be reduced.

All the tricks used in chip amps are so the designer avoids capacitors as they are bulky
and impossible to put in the chip so it requires pins to connect to.? Less pins, less cost.
To do that they use tricks like current mirrors and differential amps.

FYI back in my past I worked for a company that built custom audio consoles to 32 channels
and my pet project was a 500W/channel stereo amp that could be bridged for 1000W mono.?
It was fun heating up huge heatsunk 1 ohm resistors.? Performance had to meet audiophile
and studio levels.?

Allison

Take a look at this project for enough good ideas to get you started. Uses the 8307 and the 3914



Years ago I built something similar (not using the 8307)
The 3914 is a ratiometric device, so if you feed in a forward power signal as its reference, and a reflected power signal as the measured quantity you'll get a rudimentary SWR display

N5IB

Let me know when this is available.. may need 3 or 4..
--
72 and God bless
KD4EPG

Dumb question; have you verified 12 volts to the final. I'll be testing while hooked via USB to my computer and forget to turn on the power supply. A mind is a terrible thing to lose but I'm becoming accustomed to it.

I'm off looking at a very inexpensive standalone LED bargraph mWattmeter with a 25W to 25mW (30dB) range using the cheap AD8307s, but there are apparently MANY MANY different implementations and desires out there. Might be worth another "Topic" ......hard to tell from this huge list of "Topics" ;o).....heck, here is yet another "Topic". Useful and focussed on the uBITX or BITX40.

Lets try no microcontroller (and firmware) and just a basic LED bargraph display ......first.

Comments ? input ? suggestions ?

73 Kees K5BCQ

Thank you?

Thank you?