Date   

Re: QCX-SSB: SSB with your QCX transceiver

Jerry Gaffke
 


They are quite different.
I suggest you read the circuit descriptions in the assembly manuals up on qrp-labs.com

Both are non-linear, so suitable for CW or FM.
The QCX amp is class E so more efficient but covers a single band, envelope shaping through the Q6 integrator, final is three BS170's
The 5W amp is class C, covers all of HF, includes a novel circuit for envelope shaping under the control of the uP, final is one IRF510.
Very different!

Jerry


On Thu, Jan 31, 2019 at 10:08 AM, <freefuel@...> wrote:
Hi Hans, how close is the circuit in your 5W HF PA kit to the circuit in the QCX? 


Re: QCX-SSB: SSB with your QCX transceiver

John VA7JBE
 

Great discussion so far.  From what I can understand at least some of the issues raised might be addressed by swapping in a $12 TeensyLC board, which has a cortex-M0+ processor and would provide 12bit ADC/DAC as well as a 48 MHz clock speed.  Though I'm still interested to see some performance measurements from the atmega328.

https://www.pjrc.com/teensy/teensyLC.html

Cheers,
John VA7JBE


Re: QCX-SSB: SSB with your QCX transceiver

Kārlis Goba
 

Actually if think about the envelope generation, it becomes clear that driving Q6 in a linear fashion (from a DAC or integrator) wastes any gain of efficiency there was from using the FETs in switch mode whatsoever. Pretty likely the Q6 will need heatsink due to linear mode. In order to retain efficiency, Q6 needs to work in switch mode as well with a PWM signal. The current can be filtered with an inductor (Buck converter stage).

--
Karlis YL3JG


Re: QCX-SSB: SSB with your QCX transceiver

Jerry Gaffke
 

> The process of updating the 5351 has its own cost to the signal  quality
> as every time you change the frequency its a small jump and you get
> non-coherent spikes and that is a form of noise modulation.
I looked hard at the si5351 output when driven with the si5351bx code
while updating every 100ms with 1hz increments in output frequency.
Unexpectedly smooth, no runt pulses, no dirt visible at all on the scope
at the time of the transition, a pure tone as it slowly crept through the
audio bandwidth of a receiver.


Any discontinuities could be reduced by using burst mode writes
(with auto-increment on the register address)
and upping the i2c clock rate if possible.

There might be a bit of noise injected by the i2c bus activity,
but I didn't hear it.

Yes, the ATMega328P ADC is 10 bits, I was wrong to suggest it was 8. 

>  what about with the key shaping amp and the DSP/PWM firmware?

That is what Guido is successfully doing, though I suspect it is not ideal.
For one, Q6 is fundamentally an integrator.  So the new state you put it into 
will depend on the previous state.  Listening to the current state with an ADC
might help considerably.  I'd be a lot happier just driving it with a 12bit DAC
if that was available.

Jerry, KE7ER


Re: Any one monitoring the QRP GUYS website

jjpurdum
 

I can assure you that's not their normal behavior. I have written to the owners and told them what's going on.

Jack, W8TEE

On Thursday, January 31, 2019, 10:18:37 AM EST, Charles W. Powell via Groups.Io <doctorcwp@...> wrote:


I just got a noise bridge kit from them.  It was sent out promptly.  But that’s not a good way to generate business by not responding to problems.

73,

Charles - NK8O

On Jan 31, 2019, at 7:08 AM, Ken Bell <kn4dgr@...> wrote:

Does anyone know the QRP guys?  I've bought  a few thing from them over the past couple of years and am happy with their kits.  I recently bought an antenna with tuner and it was missing parts.  I've emailed them a couple of time on a couple of different email addresses over a few days and haven't heard anything from them.  Does anyone know if they are still active?   

Best regards, 

Ken
KN4DGR


Re: Any one monitoring the QRP GUYS website

jjpurdum
 

Yes they are still active. I'll forward this to one of the owners.

Jack, W8TEE

On Thursday, January 31, 2019, 10:08:43 AM EST, Ken Bell <kn4dgr@...> wrote:


Does anyone know the QRP guys?  I've bought  a few thing from them over the past couple of years and am happy with their kits.  I recently bought an antenna with tuner and it was missing parts.  I've emailed them a couple of time on a couple of different email addresses over a few days and haven't heard anything from them.  Does anyone know if they are still active?   

Best regards, 

Ken
KN4DGR


Re: QCX-SSB: SSB with your QCX transceiver

freefuel@...
 

Hi Hans, how close is the circuit in your 5W HF PA kit to the circuit in the QCX? 

-Justin N2TOH 


Re: QCX-SSB: SSB with your QCX transceiver

ajparent1/KB1GMX
 

part B
>>>I assume most errors will result from how fast Guido can update the si5351, and how accurately
and quickly he can adjust voltage into the final.<<<

The process of updating the 5351 has its own cost to the signal  quality as every time you change
the frequency its a small jump and you get non-coherent spikes and that is a form of noise
modulation. Some could likely well out of band.  One source of error, the other is the coarseness
of the change and the more coarse the greater the discontinuities.

>>>Whether the power FET's can remain linear enough at low supply voltages, I don't really know.
Though doesn't seem to be a problem when key shaping on CW rigs.<<<

Cw keying is fairly simple as your rise time and fall times need to be controlled to avoid
creating clicks or instantaneous modulation but not all that hard as its a milliseconds
level event (ie fairly slow).

First linearity for that is, power out vs Drain voltage as they are operating as switch.  If
the gate is driven sufficiently hard it is quite linear.  Since its easy to plot the V-P curve 
you can correct any errors my measuring the output.  That allows one to "predistort"
to get a linear output.  However, power mosfets being designed for switching use
are ideal as we can get.  There are GaN,  mosfets using Galium nitride that are both
fast and efficient switches with on resistance in the sub 70 milliohm on range.
I've used them and the do perform, but for practical hams power mosfets are good.

>>My guess is that IMD and such gets worse as a percentage of the instantaneously emitted signal,
but remains acceptable as a percentage of the peak emitted signal.<<

There are many contributors, like rounding and truncation of the input signal in the CPU being
an 8bitter.   The input DAC is at best 10 bits and likely only 8-9 bits used.  To get this to work
we need to extract two components of voice one being simply frequency and the other is
amplitude the former is a bit math intensive the, latter is fairly simple. The  relationship of
amplitude to phase of the RF for faithful reproduction.  The greater the processing delay
the more difficult to get a near real time result.  Also if the processing delay is too great
the sampling may be corrupted.  There are other factors like time to update the 5351,
granularity of the update, power setting delay (Q6 driving the class E amp) and the
granularity of the update ( current is maybe 64 steps or 5bits) and that has its effects
both in the frequency domain and in the amplitude domain. Minimally it would make
the signal sound like the radios compression is turned to max.  Also the amplitude has
the limitation of rate of change as you can create side bands and too slow you
have phase errors.  To say there are a lot of interrelated factors is an understatement.
It is in the place I've called hoary complex math required.

Allison


Re: QCX-SSB: SSB with your QCX transceiver

Jerry Gaffke
 

>  The IQ quadrature still can't go below 3 or was it 3.5 mhz

The Si5351 "Phase Offset" registers as described in SiLabs AN619 
are 7 bits, one for each of the three clocks, step size of 1/4 of a VCO period
VCO goes down to 600 mhz, so max phase offset is  (2**7)/(4*600e6) = 53.333333 ns.
For quadrature clocks, we need to delay one clock by 1/4 of the period of the target freq,
so minimum freq for quadrature clocks using an Si5351 phase offset register is
    1/(4*53.333333e-9) = 4.687500mhz
But Hans has found that the VCO's in the Si5351 can reliably go well below the spec'd 600mhz,
low enough to cover all of 80 meters.

Guido is able to transmit on 160 meters. 
A 74AC74 as used on the SoftRock to create quadrature clocks is trivial enough,
and costs $0.10 in quantity.  Use that if you wish quadrature clocks for 160 meters.
Current QCX code is easily hacked a wee bit further, that would be
the least of my worries if implementing SSB with Guido's method.

Guido's code is there to demonstrate SSB on a QCX.
It is not an attempt to finalize production firmware that also supports CW.

Jerry, KE7ER



On Wed, Jan 30, 2019 at 01:39 PM, ajparent1/KB1GMX wrote:

The IQ quadrature still can't go below 3 or was it 3.5 mhz.  I'm puzzled by Guidos
comments on that.  If the IQ VFO is not 90 degrees then the  RX still works but
as a simple DCRX without image rejection.  There are ways around that but
none trivial or compatible with current QCX code.


Re: Any one monitoring the QRP GUYS website

Michael Sharp
 

I had exactly the same thing happen with the UnUnTenna Plus kit. It was missing the mounting hardware for the polyvaricons. I’ve contacted them twice, and even ordered a couple of more kits from them with absolutely no response.

I did a little research on the polyvaricons. It turns out there are only a few people on the planet who make these things. Mitsubishi is one, and the other company is FX. Mitsubishi uses the oddball thread size and pitch... something like M1.4 x .73 if I remember correctly. FX uses standard M2.5 screws. Just be careful about the length for the mounting. Too long of a screw, and you will damage the polyvaricons plates. I ended up using M2.5 x 3 nylon screws which seem to work just fine for my situation.

I agree, they need to take care of the customer a little bit better, even if it was with a standard reply. But to have nothing, and having to do research and additional travel for something you *paid* for isn’t helping their business or reputation.

-Michael
KD9MED


Re: U3S and Receiver will it work for SSB voice

freefuel@...
 

what about with the key shaping amp and the DSP/PWM firmware?

-Justin N2TOH  


Re: QCX and LiFePo Batterys all enclosed into an old ammo can...ever done before? #40m #case #enclosure

N3MNT
 

  • I mounted my QCX and a paddle to a piece of lexan that is sized for the survivor box . I also have room for a 3S LiPo 1600MaH  ( already have several).  I simple remove the lexan base with radio and paddle and I am ready to go.  Headphones also fit. I have a second identical survivor case that houses my Elecraft antenna tuner GPS board and cables.  Wire antenna,coax and a throw line are in a small nylon bag. 
On Thu, Jan 31, 2019 at 12:21 PM, KE0GYC wrote:

https://www.amazon.com/MTM-Survivor-Ring-Seal-Small/dp/B00SUUN05Y


Re: QCX and LiFePo Batterys all enclosed into an old ammo can...ever done before? #40m #case #enclosure

N1EDC
 

Seems to me that an ammo can is larger than needed for a super-efficient transceiver smaller than a paperback.

My current QCX is in it's own enclosure, but I did plan on building a 30m one into a small MTM Survivor drybox.  I figure you should be able to fit 3x 18650 cells for a 2.5-3.5AH battery.

https://www.amazon.com/MTM-Survivor-Ring-Seal-Small/dp/B00SUUN05Y


Re: QCX-SSB: SSB with your QCX transceiver

ajparent1/KB1GMX
 

On Thu, Jan 31, 2019 at 08:44 AM, Jerry Gaffke wrote:
But Guido's method does away with the dual mixers of the SDR approach, and requires only one DAC.

Actually SDR only requires 1 DAC.  If the DAC is fast enough you can do direct synthesis
without frequency change. If you cannot do it super fast then at some lower frequency like
30 or 100khz and do a simple up-conversion like many of the current DSP SSB radios. 
FYI Guido uses two a PWM to simulate a DAC so it has its limitations (about 5-6bit resolution).
A real DAC even 8bit would likely improve the result but it has to be reasonably fast.

The problems with MOSFets at low power is driving them, the gate is very capacitive and 
eats current on transitions.  But I've run small mosfets at 13.56 mhz with 90% PAE to 5W out.
The drive in that case was the TI 5111 chip and power cost was 200mW to drive the mosfets.
Class e is switch mode so there is no IMD, only harmonics. Once you modulate the amp
you can get trash from the modulator but that is controllable too. so they tend to be unusually
clean.  The big economy is when you shoot for 100 or 300W full carrier!

As to class E (and class D) most of the efficient AM transmitters are one or the other
and usually use class D for the modulator as well.    Hams around here have had that
for years and There was at least one kit (Retro-75 from Small Wonder Labs in 2010)
that did QRP power class E on 75M.

So doing AM with a QCX would be dirt simple the the power level would be in the 
1.25W to 2.5W (carrier) range for 5W PEP.

Allison


OCXO SYNTH

m0bmn
 

Hi all

Just got my OCXO Synth module kit this morning . A question … Is it a good or bad idea to use cotton wool inside the main oven box ? (and the lower and outer boxes too).

The U3S will be in a outbuilding  at the end of the garden (Basically a wood shed) so want to give it as much chance as I can.

Thanks

73 Paul M0BMN

 

 

 


Re: QCX-SSB: SSB with your QCX transceiver

Jerry Gaffke
 

I assume most errors will result from how fast Guido can update the si5351, and how accurately
and quickly he can adjust voltage into the final.  Those errors could be improved upon
considerably at little cost, as suggested in post 30871.

Whether the power FET's can remain linear enough at low supply voltages, I don't really know.
Though doesn't seem to be a problem when key shaping on CW rigs.
My guess is that IMD and such gets worse as a percentage of the instantaneously emitted signal,
but remains acceptable as a percentage of the peak emitted signal.

Jery



On Thu, Jan 31, 2019 at 08:18 AM, Kārlis Goba wrote:
Guido's method is not much simpler in terms of generation (due to probable source of many errors that might jeopardize TX quality beyond what is allowed for a SSB signal on air), but rather a neat hack of existing hardware. What it stands out is that it allows for a simple and efficient amplification.


Re: Any one monitoring the QRP GUYS website

Michael N6MST
 

You don't actually say that you ordered it from QRPGuys, did you buy it second-hand? What parts are missing? You could try over at the CalQRP group, at least one of the QRPGuys is a regular.


Re: QCX-SSB: SSB with your QCX transceiver

Jerry Gaffke
 

Perhaps. 
But Guido's method does away with the dual mixers of the SDR approach, and requires only one DAC.
Any of them require an si5351 or something else more expensive to generate the carrier.
Unless you're fabbing your own chips, Guido's approach might get by with cheaper hardware.

Yes, filter rigs are "traditional". 
But they are how most of us understand what an SSB signal is.

You're right, the fundamental advantage of this approach is that it allows the use of
a non-linear RF amp, powering it from a switch mode power supply.  More efficient.
Though FET's are not as clean when powered from lower voltages than they are designed for,
that may limit how well this can work.

You can build an efficient AM transmitter by modulating a final non-linear amp in a similar manner,
driving that amp with a constant frequency carrier.  As has been done for 100 years.
The trick here is that the carrier is now not a constant frequency, but jumps around a little bit.
The notion that this little trick can somehow suppress the carrier and opposite sideband is still
bending my head some.  

Jerry, KE7ER


On Thu, Jan 31, 2019 at 08:18 AM, Kārlis Goba wrote:
This isn't really a contender in means of _generating_ a SSB signal. There are much easier methods to do that, e.g. with a quadrature modulator with two (I and Q) audio signals generated by a MCU. I'm pretty sure that's what QSX will do, and what modern transmitting SDRs do (except for the ones that can run their DACs directly in the RF band).

There is no need to filter sidebands anymore with crystal filters etc. Those days are gone.

Guido's method is not much simpler in terms of generation (due to probable source of many errors that might jeopardize TX quality beyond what is allowed for a SSB signal on air), but rather a neat hack of existing hardware. What it stands out is that it allows for a simple and efficient amplification.


Re: QCX-SSB: SSB with your QCX transceiver

Kārlis Goba
 

This isn't really a contender in means of _generating_ a SSB signal. There are much easier methods to do that, e.g. with a quadrature modulator with two (I and Q) audio signals generated by a MCU. I'm pretty sure that's what QSX will do, and what modern transmitting SDRs do (except for the ones that can run their DACs directly in the RF band).

There is no need to filter sidebands anymore with crystal filters etc. Those days are gone.

Guido's method is not much simpler in terms of generation (due to probable source of many errors that might jeopardize TX quality beyond what is allowed for a SSB signal on air), but rather a neat hack of existing hardware. What it stands out is that it allows for a simple and efficient amplification.

--
Karlis YL3JG


Re: Any one monitoring the QRP GUYS website

Armin, DJ2AG
 

on 16th of January I emailed a technical question regarding a  tuner kit I bought from them and received an answer within 20 minutes.

73 Armin, DJ2AG