Topics

QRP kit amplifiers

Laurence Oberman
 

So I was planning to retrofit build the old V4 into a new case etc. I
ordered the agc board and built the nano S meter circuit last night.

Looking at the latest Spec An tests I was thinking about getting the
10 Watt Amplifier board from qrp kits, and setting the ubitx to only
transmit at about 2w maximum into the 10W amplifer.
This would avoid the weird 20M issue I have on that board due to the
heating issue and have 10W on all bands.

Has anybody used the qrp kits amp.

Thanks
Laurence
KB1HKO

barry halterman
 

I have not used this particular amp but I have attempted to run another amp externally.  I had an issue with the ubitx going into oscillation once the carrier dropped, just before the tx/rx change over. My power meter on the amp would show about 15 watts output during key down and around 5 watts key up before the relay would go to the tx/rx change over. Scrapped that idea very quickly, but you might not have that issue.
The amp works perfectly with my elecraft kx3 as I can push it to 50watts.
Barry

Laurence Oberman
 

Hello Barry
Thank you for your email.
I think I will test this and report back to the group.

The V4, even with the Axicoms has the heating issue but at 2w all
bands are clean on my old Agilent SPEC An.
So it could be a way to get fully compliant assuming of course the AMP
does not create its own non compliant harmonics.

Thanks
Laurence

On Wed, Mar 20, 2019 at 12:14 PM barry halterman <kthreebo@...> wrote:

I have not used this particular amp but I have attempted to run another amp externally. I had an issue with the ubitx going into oscillation once the carrier dropped, just before the tx/rx change over. My power meter on the amp would show about 15 watts output during key down and around 5 watts key up before the relay would go to the tx/rx change over. Scrapped that idea very quickly, but you might not have that issue.
The amp works perfectly with my elecraft kx3 as I can push it to 50watts.
Barry

Curt
 

Laurence

It is a nice design, if you are referring to the QRP-Labs design?   Funny thing the designer is on our list (she is quite active here), and its merchant and co-designer may have helped start this group!  [if indeed you reference someone else - do compare it carefully to what QRP-Labs is offering]. 

Feeding it with the existing uBITX PA, even dialed back, sounds like madness.  One should remove the uBITX PA to properly feed it.  While it is clearly a better PA, it sounds to be to be a lot of effort for a fraction of an S-unit it output.  But since it could simultaneously cure the relay-related spurious - you may be onto something. 

Curt

Laurence Oberman
 

Yep, for me its about the weird 20M spur thing I have.
In general the QRP labs Amp (Thanks Allison :)) seems it can run hot
for a long periods so maybe its a good way to deal with this.
I am indeed talking about the 10 W QRP labs amplifier
The test to feed with 2W was just a start, I agree if its clean and
works IT may be a way to cure the spurs.
Thanks
Laurence



On Wed, Mar 20, 2019 at 12:25 PM Curt via Groups.Io
<wb8yyy=yahoo.com@groups.io> wrote:

Laurence

It is a nice design, if you are referring to the QRP-Labs design? Funny thing the designer is on our list (she is quite active here), and its merchant and co-designer may have helped start this group! [if indeed you reference someone else - do compare it carefully to what QRP-Labs is offering].

Feeding it with the existing uBITX PA, even dialed back, sounds like madness. One should remove the uBITX PA to properly feed it. While it is clearly a better PA, it sounds to be to be a lot of effort for a fraction of an S-unit it output. But since it could simultaneously cure the relay-related spurious - you may be onto something.

Curt

ajparent1/KB1GMX
 

Feed the QRPl 10W amp with 2W????  Let me know if it survives!
IT only needs 25-30milliwatts drive.  Any more than that and your in
overdrive territory.  That will make lots of harmonics.

It will run hot at full power for sustained period of time.  SSB peaks
will not make that warm much at all..

Allison

Jerry Gaffke
 

That QRP Labs amp has about 26dB of gain at an input impedance of around 200 ohms,
feeding it from a 50 ohm terminated amp would mean around 20dB of voltage gain.
    https://groups.io/g/QRPLabs/message/30760

Feeding the amp 2 Watts would blow holes in the BS170's.
10W=40dB, so you would want a roughly 13 dB 50 ohm attenuator
to throttle your 2W=33dBm down to the 40dBm-20dB=20dBm that the amp expects.

The QSX Amp design is primarily by Hans, but with lots of help and advice from Allison.
She's had a career in RF design, can do this stuff in her sleep.

The uBitx has 10 Watts of RF about an inch away from an IF amp with signal levels
well under a milliWatt, and we are worried about spurs that are 40 or 50 dB down from that milliWatt.
Amazing it works as well as it does.
Having the power amp separated physically from the low level IF amps on the uBitx
may well be what's needed to cure some of the spurs.

Jerry, KE7ER



On Wed, Mar 20, 2019 at 09:48 AM, Laurence Oberman wrote:
Yep, for me its about the weird 20M spur thing I have.
In general the QRP labs Amp (Thanks Allison :)) seems it can run hot
for a long periods so maybe its a good way to deal with this.
I am indeed talking about the 10 W QRP labs amplifier
The test to feed with 2W was just a start, I agree if its clean and
works IT may be a way to cure the spurs.
Thanks
Laurence

ajparent1/KB1GMX
 

Curt,

It is Hans design, I only offered assist and comments plus a bit of hard core testing.
He did a fabulous design that proves what the devices can do.

My .02$ is its so rare that people put the effort to do it right that everyone expects
poor results form IRF510. Yet I (and others) use them at 6M.

Your right on the drive 2W is really trying to fry the BS170s considering
25-30 milliwatts re all that needed for full power.  The ubitx predriver should
be able to supply that much RF.

Additionally tail ending the ubitx amp with that amp will NOT improve the
spurs or harmonics as it will just do what its is supposed to do, that being
amplify all the signals applied to its input through and beyond 6M.

If you do not filter the input expecting the output to be "better" is a
dream not reality.

Allison

Laurence Oberman
 

Allison, OK
Makes sense
Trying to cheat to see quickly clearly would have got me into trouble

Too used to linears at HF where you can feed it a chunk of Watts to
get the much higher power

On Wed, Mar 20, 2019 at 1:14 PM ajparent1/KB1GMX <kb1gmx@...> wrote:

Feed the QRPl 10W amp with 2W???? Let me know if it survives!
IT only needs 25-30milliwatts drive. Any more than that and your in
overdrive territory. That will make lots of harmonics.

It will run hot at full power for sustained period of time. SSB peaks
will not make that warm much at all..

Allison

Laurence Oberman
 

Hi Jerry
Yes, I had in mind a 10db , I also have a 20db to use

On Wed, Mar 20, 2019 at 1:18 PM Jerry Gaffke via Groups.Io
<jgaffke=yahoo.com@groups.io> wrote:

That QRP Labs amp has about 26dB of gain at an input impedance of around 200 ohms,
feeding it from a 50 ohm terminated amp would mean around 20dB of voltage gain.
https://groups.io/g/QRPLabs/message/30760

Feeding the amp 2 Watts would blow holes in the BS170's.
10W=40dB, so you would want a roughly 13 dB 50 ohm attenuator
to throttle your 2W=33dBm down to the 40dBm-20dB=20dBm that the amp expects.

The QSX Amp design is primarily by Hans, but with lots of help and advice from Allison.
She's had a career in RF design, can do this stuff in her sleep.

The uBitx has 10 Watts of RF about an inch away from an IF amp with signal levels
well under a milliWatt, and we are worried about spurs that are 40 or 50 dB down from that milliWatt.
Amazing it works as well as it does.
Having the power amp separated physically from the low level IF amps on the uBitx
may well be what's needed to cure some of the spurs.

Jerry, KE7ER



On Wed, Mar 20, 2019 at 09:48 AM, Laurence Oberman wrote:

Yep, for me its about the weird 20M spur thing I have.
In general the QRP labs Amp (Thanks Allison :)) seems it can run hot
for a long periods so maybe its a good way to deal with this.
I am indeed talking about the 10 W QRP labs amplifier
The test to feed with 2W was just a start, I agree if its clean and
works IT may be a way to cure the spurs.
Thanks
Laurence

Laurence Oberman
 

Using my Spec An at 2w on the V4 I dont see the heating or the spurs
on CW, hence why I was interested in trying it.
Its an easy test now, as I can cap the Ubitx at 1W, use a 10Db
attenuator and go into Hans's / Allisons Amp and into the Spec Ann
again via the coupled minicircuits output like before.

That way I can characterize it with the amp in circuit

On Wed, Mar 20, 2019 at 1:23 PM ajparent1/KB1GMX <kb1gmx@...> wrote:

Curt,

It is Hans design, I only offered assist and comments plus a bit of hard core testing.
He did a fabulous design that proves what the devices can do.

My .02$ is its so rare that people put the effort to do it right that everyone expects
poor results form IRF510. Yet I (and others) use them at 6M.

Your right on the drive 2W is really trying to fry the BS170s considering
25-30 milliwatts re all that needed for full power. The ubitx predriver should
be able to supply that much RF.

Additionally tail ending the ubitx amp with that amp will NOT improve the
spurs or harmonics as it will just do what its is supposed to do, that being
amplify all the signals applied to its input through and beyond 6M.

If you do not filter the input expecting the output to be "better" is a
dream not reality.

Allison

ajparent1/KB1GMX
 

Repost to fix editing lag.

Jerry,

You are wrong.   The voltage gain is still the same and the 26 DB is power gain.
Going from 50 ohms to 200 will not cost 6db as the amp still still see voltage 
(uses mosfets) and 4:1 is not as bad as it seems.

However the attenuator to get to 25-30 Mw of drive is half the battle as the 
ubitx amp set to 2W at 80m would barely make a few milliwatts at 10M.
All the problems identified nearly a year ago would remain and you would 
be wasting power.

The best possible case is remove the finals, the drivers, and even the predrivers.
Build a real predriver using the 2n3866 or 5109 in a wideband amp format.  Replace Q90
with a decent device or dial its gain to about 10. from RV1  feed the RF to the off board 
predriver and QRPl amp to off board LPF and TR switching.   I would make the TR
switching and LPF an off board addition as well to try and eliminate  the board level
issues.  Since it would be needed at that point to add an input BPF before the
external predriver and really clean up the mess.  Why? the QRPL amp has useful
gain to beyond 70mhz so if you feed it crap (harmonics and spurs) it will do its
very best to amplify it.

I'd expect that to be a bit better but still not a full and complete cure for many of 
the issues.  Its also untested.  I can hear the moaning now for I need a kit for that,
it won't fit in my box, does that mean I need new software for the LPF and BPF
filter boards?    

Allison

ajparent1/KB1GMX
 

Laurence Oberman
10:43am   
Using my Spec An at 2w on the V4 I dont see the heating or the spurs
on CW, hence why I was interested in trying it.

Based on what I said many times in the last year.... CW had no spur issue only harmonic issues.
SSB has serious spur issues.

And generally V3 and V4 had no (none) significant changes in the RF generation and it was
only an attempt to fix pop/click and the audio amp chip issue.

Allison

ajparent1/KB1GMX
 

Laurence Oberman,

The QRPL 10w amp is not your usual tail end linear amp its a two stage driver and linear.
Many of the high end LDmosfet pallet amps (not the cheap Epay crap) are single stage
using current generation with gains in the 20-24db region and 2W for many is still too much.

So the only amps that behave like that are you run on the mill Ham linear design to
take the power of 100W radio or maybe the more specialized ones for FT817 class
radios.  Most all either use tubes, older bipolar designs, or if mosfets with input
attenuators to tolerate that.

Allison







Laurence Oberman
 

Hello Allison

I was focused on the CW issue I had shared before with the example at 20m
After a cabling/mic socket issue had crept in I had not tested SSB but
I can now.

What I am getting from all of this though is that you feel none of
this now worthwhile to try.
If you recall. I was going to chase the 20m spur I saw saying maybe
its a fault on my board, but then others said they
have seen it too and you confirmed what it was the heating issue.

Anyway, its awesome to have you on this list and I am sure you get
frustrated by all our crazy suggestions so I am thankful for your
time.

Sincerely
Laurence

On Wed, Mar 20, 2019 at 1:54 PM ajparent1/KB1GMX <kb1gmx@...> wrote:

Laurence Oberman
10:43am #66868
Using my Spec An at 2w on the V4 I dont see the heating or the spurs
on CW, hence why I was interested in trying it.

Based on what I said many times in the last year.... CW had no spur issue only harmonic issues.
SSB has serious spur issues.

And generally V3 and V4 had no (none) significant changes in the RF generation and it was
only an attempt to fix pop/click and the audio amp chip issue.

Allison

ajparent1/KB1GMX
 

Laurence,

It why I gave up last year with it.  For the time and effort I had invested it could (and did) build
something clean from the ground up.

V5 fixes a few issues but some cases yes, some no, most at least somewhat better.

The power amp issues are as they were last year and no improvements applied.
Everything any one would ant to know about that is in the wiki.

Everyone wants a single pill fix.  There are three areas that need to be fixes, band pass
into the TX, the whole TX and output switching was a bandaid to keep the board the
same size and form factor.  IT goes to prove that compared to a monoband radio 
multiband has a far greater set of challenges and shortcuts will extract pain.

Allison

Laurence Oberman
 

Great insight,
I want to state once again, while some have bemoaned the Ubitx, I have
never and I fully appreciate everybody's efforts, I watched you spend
a huge amount of time on it and we all benefited from it.
So again to Ashar, to you!!(ajparent) to Jerry, Curt, Jack and too
many others too mention (you all know who you are), while it may seem
like the moans from some, I need all of you to know its appreciated by
all of us here.

So Thank You!!!

Kindly
Laurence Oberman
KB1HKO (a digital guy who wishes he had stayed in analog :))

On Wed, Mar 20, 2019 at 2:19 PM ajparent1/KB1GMX <kb1gmx@...> wrote:

Laurence,

It why I gave up last year with it. For the time and effort I had invested it could (and did) build
something clean from the ground up.

V5 fixes a few issues but some cases yes, some no, most at least somewhat better.

The power amp issues are as they were last year and no improvements applied.
Everything any one would ant to know about that is in the wiki.

Everyone wants a single pill fix. There are three areas that need to be fixes, band pass
into the TX, the whole TX and output switching was a bandaid to keep the board the
same size and form factor. IT goes to prove that compared to a monoband radio
multiband has a far greater set of challenges and shortcuts will extract pain.

Allison

Laurence Oberman
 

I should add:

RF is wizardry, now the new mm Wave is witchcraft, however even
digital at high frequencies is RF as folks have found it.
Nevertheless, my day job is a Principal software maintenance engineer
at Red Hat where mostl all I worry about are Linux kernels Storage
hardware and data structures with 1's and 0's.

I have it easy to you Allison

On Wed, Mar 20, 2019 at 2:26 PM Laurence Oberman via Groups.Io
<oberman.l=gmail.com@groups.io> wrote:

Great insight,
I want to state once again, while some have bemoaned the Ubitx, I have
never and I fully appreciate everybody's efforts, I watched you spend
a huge amount of time on it and we all benefited from it.
So again to Ashar, to you!!(ajparent) to Jerry, Curt, Jack and too
many others too mention (you all know who you are), while it may seem
like the moans from some, I need all of you to know its appreciated by
all of us here.

So Thank You!!!

Kindly
Laurence Oberman
KB1HKO (a digital guy who wishes he had stayed in analog :))

On Wed, Mar 20, 2019 at 2:19 PM ajparent1/KB1GMX <kb1gmx@...> wrote:

Laurence,

It why I gave up last year with it. For the time and effort I had invested it could (and did) build
something clean from the ground up.

V5 fixes a few issues but some cases yes, some no, most at least somewhat better.

The power amp issues are as they were last year and no improvements applied.
Everything any one would ant to know about that is in the wiki.

Everyone wants a single pill fix. There are three areas that need to be fixes, band pass
into the TX, the whole TX and output switching was a bandaid to keep the board the
same size and form factor. IT goes to prove that compared to a monoband radio
multiband has a far greater set of challenges and shortcuts will extract pain.

Allison

Arv Evans
 

I'm probably wrong...that is a chronic situation...but might it be possible to turn down the
drive level on SSB until the signal is cleaner if driving an outboard amplifier?

Arv
_._


On Wed, Mar 20, 2019 at 11:50 AM ajparent1/KB1GMX <kb1gmx@...> wrote:
Repost to fix editing lag.

Jerry,

You are wrong.   The voltage gain is still the same and the 26 DB is power gain.
Going from 50 ohms to 200 will not cost 6db as the amp still still see voltage 
(uses mosfets) and 4:1 is not as bad as it seems.

However the attenuator to get to 25-30 Mw of drive is half the battle as the 
ubitx amp set to 2W at 80m would barely make a few milliwatts at 10M.
All the problems identified nearly a year ago would remain and you would 
be wasting power.

The best possible case is remove the finals, the drivers, and even the predrivers.
Build a real predriver using the 2n3866 or 5109 in a wideband amp format.  Replace Q90
with a decent device or dial its gain to about 10. from RV1  feed the RF to the off board 
predriver and QRPl amp to off board LPF and TR switching.   I would make the TR
switching and LPF an off board addition as well to try and eliminate  the board level
issues.  Since it would be needed at that point to add an input BPF before the
external predriver and really clean up the mess.  Why? the QRPL amp has useful
gain to beyond 70mhz so if you feed it crap (harmonics and spurs) it will do its
very best to amplify it.

I'd expect that to be a bit better but still not a full and complete cure for many of 
the issues.  Its also untested.  I can hear the moaning now for I need a kit for that,
it won't fit in my box, does that mean I need new software for the LPF and BPF
filter boards?    

Allison

Jerry Gaffke
 

Allison, not sure I follow.

I believe that when efficiently driving the 200 ohm QSX amp through a 1:4 transformer
from a 50 ohm source, the QSX amp has a power gain of around 26 dB.
But driving the QSX amp directly (with some parallel resistance so the driver
sees 50 ohms), the voltage to the QSX gates will be reduced by half,
and power by a factor of 4, which is 6dB.

Perhaps you assume we let the source just go ahead and drive the QSX amp
at 200 ohms or so, forget about the 50 ohms thing.  Which may be fair enough,
depending on what we drive it with.

I agree that if the QSX Amp is used, the uBitx driver and final stages should be disabled.
All that power so near the IF amps is likely causing some of the spurs. 

The v5 uBitx is very close to fully compliant with FCC specs on all bands.
Few in the forum will bother with the complication of switchable
bandpass filters in front of the PA, and I'm OK with that on a QRP rig.
If going to 100W or more (or if having higher standards than the FCC)
then spurs, harmonics, IMD, residual carrier, opposite sideband,
and transmit pops should all be addressed.
Perhaps best off just moving to a different rig, unless in it for the challenge.

Jerry, KE7ER


On Wed, Mar 20, 2019 at 10:50 AM, ajparent1/KB1GMX wrote:
You are wrong.   The voltage gain is still the same and the 26 DB is power gain.
Going from 50 ohms to 200 will not cost 6db as the amp still still see voltage 
(uses mosfets) and 4:1 is not as bad as it seems.

However the attenuator to get to 25-30 Mw of drive is half the battle as the 
ubitx amp set to 2W at 80m would barely make a few milliwatts at 10M.
All the problems identified nearly a year ago would remain and you would 
be wasting power.

The best possible case is remove the finals, the drivers, and even the predrivers.
Build a real predriver using the 2n3866 or 5109 in a wideband amp format.  Replace Q90
with a decent device or dial its gain to about 10. from RV1  feed the RF to the off board 
predriver and QRPl amp to off board LPF and TR switching.   I would make the TR
switching and LPF an off board addition as well to try and eliminate  the board level
issues.  Since it would be needed at that point to add an input BPF before the
external predriver and really clean up the mess.  Why? the QRPL amp has useful
gain to beyond 70mhz so if you feed it crap (harmonics and spurs) it will do its
very best to amplify it.

I'd expect that to be a bit better but still not a full and complete cure for many of 
the issues.  Its also untested.  I can hear the moaning now for I need a kit for that,
it won't fit in my box, does that mean I need new software for the LPF and BPF
filter boards?