Date   

Case for the CQX transceiver possibly commercially available soon #qcx

Klaus Beckers
 

Hi fellows

 I know that a lot of mechanically gifted memebers of this group have already made a number of different cases for the QCX, the pictures of these admirable products can be seen somewhere else in this group. There have been also solutions with 3D-printing and I beleive the required prgrammes could be available from group members. However I am neither mechanically gifted nor do I have a 3D printer and even if I had one, I wouldn't know how to load my PC with those programmes so that the printer would make an useful item.

Therefore it was very interesting to me when I came across a small  note in the recent issue (May 2018) of the  monthly ham radio and electronic magazine "FUNKAMATEUR" (ISSN 0016-2833) that an East German company plans to produce a case for the QCX (dimensions 112 x 35 x 94mm (w/h/d)) which should be available in May 2018, may be towards the end of that month. The URL of that company is

http:// www.shop.bamatech.de

There is also a picture of the case and how it is supposed to look like. Pricing is not yet available.

You may also contact the company for more details under

info@...

By the way, the "FUNKAM;ATEUR" already covered a review of the QCX in its December 2017 issue., page 1191.



Re: Help needed repair of old U3 v 3.09

TrueBlue
 

Apparently there is a redundant thread addressing this situation, so disregard the above.


Re: Help needed repair of old U3 v 3.09

TrueBlue
 

It sounds like at this point you have a perfectly working unit running the wrong (later) version of the firmware.  Correct?  Or is the firmware right and the existing clock just dead?  I'm not clear on this.

If it's the former, I believe the various old versions of the firmware are archived here: https://groups.io/g/QRPLabs/files/Firmware%20for%20U3%20and%20U3S%20kits .  You may have to be a member of the QRP-Labs group to access the files. 

The device most used to program these is the USBASP 2 with a 10/6-pin adapter, which on eBay for me wound up being about US$2.75, total, shipped from China.  You can also use an Arduino, preferably a UNO, which is a little more convenient.  There are files here explaining the process of changing the firmware.


Re: Excellent presentation on Class E Amplifiers and why the QCX finals sometimes can get fried

 

Hans:

Thank you for the excellent explanation.

In many cases, the reports of blown up QCX finals were probably due to static discharge down the antenna feedline :-(

--
73, Bernie, VE3FWF


Re: QCX Odd Behavior #qcx

 

You could also try reloading the firmware.  If you have an Arduino Uno,  you can use it to re-load the firmware.
This process is fairly easy to do and is documented on the QRPLabs site.


--
73, Bernie, VE3FWF


Re: QCX Odd Behavior #qcx

rentwist@...
 

If you have a V2 PCB or earlier, did you do the startup mod?


Re: Excellent presentation on Class E Amplifiers and why the QCX finals sometimes can get fried

Hans Summers
 

Hi Bernie 

Re. your question on voltage and current protection circuits. 

In all my development of QCX I never blew even one single BS170. Not into a dummy load, open load, short, or any random mismatch I had. 

The closest I got to blowing a set of QCX finals was when I was using it in WSPR mode to provide a 5W signal for tuning up an End-Fed Half-Wave antenna. I climbed out onto the roof, fiddled with the tuner (failing to achieve anything). Climbed back in. Several minutes must have passed. I noted the high temperature of the BS170s and smelt the "hot electronics" type of smell... so I abandoned the plan and went to plan B (or was it plan J, K, whatever by that time). But still even those BS170s were fine.

During measurement of the graphs used in the last few pages of the manual I took the output power up to 8, 9 even 10W output, albeit briefly. And still didn't destroy any BS170.

Given the robustness I observed, and the desire to avoid increasing costs, board area, complexity and parts count... I didn't see the need to add protection circuits. 

73 Hans G0UPL 


On Sat, Apr 28, 2018, 20:02 Ham Radio <bernard.murphy@...> wrote:
Hans:

Can you comment on the use of N7VE’s current and voltage protection circuits in his Class E design presentation?

Perhaps not worth the extra effort as the QCX finals are dirt cheap to replace?
--
73, Bernie, VE3FWF


Re: Excellent presentation on Class E Amplifiers and why the QCX finals sometimes can get fried

Alan G3XAQ
 


Those two papers by Paul Harden NA5N come up as “forbidden” on server

From: Hans Summers
Sent: Saturday, April 28, 2018 10:06 AM
To: QRPLabs@groups.io
Subject: Re: [QRPLabs] Excellent presentation on Class E Amplifiers and why
the QCX finals sometimes can get fried

Hi all

I am not an electronics engineer. All is self-taught. I studied physics and my
former career was 22 years in bank IT (software). I know there are some
"proper" engineers here, I am just a guy who loves electronics and radio and
muddles along as best I can, and somehow tries to get somewhere and after a
lot of blood, sweat and tears, eventually manages something at least.

Now for Class-E... over the years I have made several attempts at it. I
studied the maths. I tried the spreadsheet models. I tried building published
designs. I never was successful. I just could never measure the high
efficiency Class-E is supposed to give, and of course that was also verified
by the temperature of my transistors.

When developing QCX I decided for the sake of low cost (no need for a
heatsink, and no need for big beefy power transistors) I had better try one
more time. I developed what I now call "ghetto" Class-E because it is such a
simplified method of choosing the components... yet, it does seem to work very
well...

This is a short extract from some text I wrote on the topic of Class-E for
part of my presentation next month at Dayton FDIM:

"Some excellent background reading are two papers by Paul Harden NA5N:


http://www.aoc.nrao.edu/~pharden/hobby/_ClassDEF1.pdf and
http://www.aoc.nrao.edu/~pharden/hobby/_ClassDEF2.pdf


Paul NA5N describes two defining features of Class-E:


1) Use of a square-wave drive to reduce switching losses: the transistors are
either on, or off… no lossy region in between
2) Reducing the effects of the transistor capacitances. Class-E has a resonant
tuned circuit. The capacitance of the transistors, normally an unpleasant
lossy aspect, is now a part of the tuned circuit.


Class-E also has a reputation for being difficult to achieve. All those
intense mathematics Google will help you find, don’t help. In reality, once
you realise the secret – it is not so difficult. My “ghetto” design
process for a Class-E amplifier is simple. Perhaps it is not totally optimal
and a few more percentage points of theoretical efficiency could be squeezed
out by the more advanced mathematical treatment. But for the average ham, my
method produces excellent results with a minimum of fuss! I had previously
attempted more complex methods and had always failed.


Calculation of the impedance of a resonant circuit is simple, and there are
many online calculators which will do the job for you. For example,
http://toroids.info/T50-2.php which allows you to type in the operating
frequency, and the desired resonant circuit impedance. Then the calculator
computes the required inductance, capacitance, and the number of turns
required for a certain toroid (in the QCX, a T37-2 is used).


First choose the output impedance. We usually choose 50-ohms, because this is
the input impedance of the Low Pass Filter we will use. The online calculator
will tell you what inductance is needed, and how many turns to wind on the
toroid. The online calculator also tells you the required capacitance to bring
it to resonance at the operating frequency. Here we resort to experiment,
because it is a little difficult to know what the output capacitance of the
transistor is. The device capacitance varies depending on supply voltage and
whether it is on or off. A simple experiment is required, adding different
small capacitances to the circuit, and measuring the efficiency (measure
supply voltage and supply current to calculate power input; then measure RF
power output. Divide one by the other to get the efficiency). It is easy to
find what additional capacitance is required to peak the efficiency. The
resonance is quite broad and non-critical. "

The component values also come out close to some examples Paul NA5N has in his
documents; so that's comforting and you feel you are on the right track :-)

73 Hans G0UPL
http://qrp-labs.com





On Sat, Apr 28, 2018 at 4:42 PM, Glen Leinweber <leinwebe@mcmaster.ca> wrote:

Alan,
A key difference from the classic Class C PA circuit is the lower value of
inductance that feeds DC power to the MOSfet(s). In the classic circuit, this
inductor is a choke, having high impedance at the operating frequency. For
Class-E, it is a much lower impedance, so that it stores significant energy
while the MOSfet(s) are ON (for half a cycle or less). When the MOSfets switch
off, this energy is available for output power.

The word "flyback" comes to mind. During the half-cycle-or-less that the
MOSfets are ON, current rises continuously in this inductor. After switching
off, this inductor current dumps out in the form of voltage: MOSfet drain
voltage swings far above the +12V DC supply voltage.

The LC low-pass filter feeding the antenna is quite conventional. Because
the MOSfet drain voltage is somewhat pulse-like, harmonics are large - the
filter must work hard to reject these harmonics effectively. This can be done
various ways: higher Q, or an extra stage.




Re: Reference Frequency Instability?

Eric THIRKELL
 

Thanks Arv and to all others who have responded. Maybe I have been lucky with Xtal stability since 1940 but I have yet to meet an unstable example confirmed in the last week by two evenings on the air with rock solid stability, firstly on 7.030 MHz after calibration and checking followed on the second occasion using an unknown frequency which happened to be 7.052 MHz. I tried a heat soak stability check against an IC-7300 and a KX3 for two hours with plenty of drop tests and component wiggling to no avail. Frequency shift clearly happens instantaneously on boot up. I shall check MPU contact integrity but have ordered a new chip as back up because it is a cheaper option to an Arduino based reload.
Many thanks again to all. Eric



On Apr 28, 2018 at 6:23 pm, <Arv Evans> wrote:

If the frequency shift is an exact amount with that amount being repetitive then
it would seem that software might be the culprit.  Reloading the software may
be necessary.

If the frequency shift is not an exact repetition of the prior shift then it may be
due to frequency drift in the 27 MHz crystal.  Try adding a small heat sink to
the 27 MHz crystal. 

Arv  K7HKL
_._


On Sat, Apr 28, 2018 at 5:27 AM, Alan G4ZFQ <alan4alan@...> wrote:
I realised my tx frequency had moved up 22Khz. I switched off/on and tried again and saw the tx frequency had now moved up 44Khz. After recalibration the same result reoccurred. I switched to VFO B and found it had not moved from 7.030 so I switched off/on and found tx now on 7.052. A repeat off/on brought VFO B up to 7.074.
There don't appear to be any dry solder joins but I retouched the 27 Mhz xtal pads to make sure but the QCX performance is unaltered.

Eric,

Presumably the 27MHz Xtal is unstable. Can you confirm that with a RX?
If so there is little you can do except trying a replacement.

If you are really adventurous the Si5351 data sheet says "6.4. External Crystal Load Capacitors
The Si5351 provides the option of using internal and external crystal load capacitors. If internal load capacitance is
insufficient, capacitors of value < 2 pF may be used to increased equivalent load capacitance. If external load
capacitors are used, they should be placed as close to the XA/XB pads as possible. See AN554 for more details."  But maybe that's a daft suggestion and might not work anyway:-)

I had the problem with my U3S 10 27MHz Xtals were 99p on Ebay...

73 Alan G4ZFQ





Re: #clock Total Character Count when programming multiple Sub-Lines? #clock

BrianB
 

Exactly what I needed to know. Thanks...


QLG1 after winter break, yellow LED quick pulsing for 1 hr

Tapio OH2EYY
 

The subject says most of the problem. Took mine Ultimate kit with QLG from winter storage and the QLG yellow LED has been flashing short, maybe 0.5-0.75 s blinks for an hour? The red LED is ok, however no lock. 

Any ideas?


Re: Excellent presentation on Class E Amplifiers and why the QCX finals sometimes can get fried

ajparent1/KB1GMX
 

Alan if you take it personally, sorry.  

The fact they are both driven in a particular way and must conform to a specific set of
rules to attain the class E waveform of zero voltage switching is why they are the same. 
There is no rule that says the circuit must be the same only the reactance to store
energy and extract it have to behave.  At that point the parts used and their quality
can push the efficiency numbers around.

As to efficiency.  Driving two mosfets vs 3 changed the rules as power and impedance
are different.  It takes more drive as well if that does nto increase the switching is slower
and efficiency drops.

As to hans using few parts.  Congrats good on him, that is smart engineering.  What
are the trade offs?

However I've never used that spreadsheet as its not in line with what I've done, nor does it
handle all cases well.   Tonne has a far better modeling tool and it compares well with a
very expensive tool Genesys.  The QCX is nice but the explanation is far too simple.  Yes,
I do have it and look at lots of designs as part of understanding the designers choices. 
Sometimes its informative to get into the designers head a bit and understand his goals.

How a circuit is composed and tuned will vary.  so will difficulty in tuning vs efficiency.

Allison


Re: Excellent presentation on Class E Amplifiers and why the QCX finals sometimes can get fried

Richard Harris <g3otk@...>
 

As has been noted, in Class-E the MOSFET switches off just as the drain voltage approaches zero.  But there is a second condition for it to be a true Class-E PA and that is the slope of the drain voltage also approaches zero.  This means that the instant of switching is not critical.  

Nathan and Alan Sokal filed a Patent (US 3,919,656) in 1973 for a Class-E PA, although it transpires that the basic circuit was the subject of a Ph.D thesis by Gerald Ewing at the Oregon State University in 1965.   Nathan Sokal (WA1HQC) described this circuit together with design formulae in the Jan/Feb 2001 issue of QEX magazine.  I found all of the above on the internet.  Sokal's formulae appear to have been used in Tonne Software's Class-E design software, which can be downloaded for free.  I have used this software with success and achieved high efficiencies - often 85 to 90%, although such high efficiencies are sensitive to measurement error.

Sokal's circuit uses an RF choke between the drain and the supply and there is a series inductor and capacitor between the drain and the output and it is tempting to assume that this is tuned to the transmit frequency.  It isn't - the resonant frequency is below the transmit frequency.  There needs to be an inductive component between the drain and load.  Tonne's software also includes an option for an L-match, so that load resistance and power output can be specified independently, rather than one determining the other.

There is another version of this Class-E topology which uses an inductance between the drain and the supply, rather than a much higher inductance that acts as a choke.  This was the subject of a paper by Kumar et al - " High-Efficiency Broadband Parallel-Circuit Class E RF Power Amplifier With Reactance-Compensation Technique " IEEE Transcations on Microwave Theory and Techniques, March 2008 - I found a copy on Researchgate.  The formulae are much simpler than Sokal's and I put together a spreadsheet to make the calculations.  

I have used both Sokal and Kumar variants, including push-pull (not described in their papers) up to 50W using  a pair of IRF510.  Push-pull is very attractive because even order harmonics cancel and so filtering is much easier. 

I hope this background information is of interest.

Richard G3OTK


Re: Reference Frequency Instability?

Arv Evans <arvid.evans@...>
 

If the frequency shift is an exact amount with that amount being repetitive then
it would seem that software might be the culprit.  Reloading the software may
be necessary.

If the frequency shift is not an exact repetition of the prior shift then it may be
due to frequency drift in the 27 MHz crystal.  Try adding a small heat sink to
the 27 MHz crystal. 

Arv  K7HKL
_._


On Sat, Apr 28, 2018 at 5:27 AM, Alan G4ZFQ <alan4alan@...> wrote:
I realised my tx frequency had moved up 22Khz. I switched off/on and tried again and saw the tx frequency had now moved up 44Khz. After recalibration the same result reoccurred. I switched to VFO B and found it had not moved from 7.030 so I switched off/on and found tx now on 7.052. A repeat off/on brought VFO B up to 7.074.
There don't appear to be any dry solder joins but I retouched the 27 Mhz xtal pads to make sure but the QCX performance is unaltered.

Eric,

Presumably the 27MHz Xtal is unstable. Can you confirm that with a RX?
If so there is little you can do except trying a replacement.

If you are really adventurous the Si5351 data sheet says "6.4. External Crystal Load Capacitors
The Si5351 provides the option of using internal and external crystal load capacitors. If internal load capacitance is
insufficient, capacitors of value < 2 pF may be used to increased equivalent load capacitance. If external load
capacitors are used, they should be placed as close to the XA/XB pads as possible. See AN554 for more details."  But maybe that's a daft suggestion and might not work anyway:-)

I had the problem with my U3S 10 27MHz Xtals were 99p on Ebay...

73 Alan G4ZFQ





Re: QCX Odd Behavior #qcx

 

Double check that all the pins on the micro-controller are properly seated in the socket and are making a good connection.

Next, I would try another micro-controller ...
--
73, Bernie, VE3FWF


Re: Excellent presentation on Class E Amplifiers and why the QCX finals sometimes can get fried

 

Hans:

Can you comment on the use of N7VE’s current and voltage protection circuits in his Class E design presentation?

Perhaps not worth the extra effort as the QCX finals are dirt cheap to replace?
--
73, Bernie, VE3FWF


Re: Excellent presentation on Class E Amplifiers and why the QCX finals sometimes can get fried

Steven Dick
 

Those two papers by Paul Harden NA5N come up as “forbidden” on server
 

Sent: Saturday, April 28, 2018 10:06 AM
Subject: Re: [QRPLabs] Excellent presentation on Class E Amplifiers and why the QCX finals sometimes can get fried
 
Hi all
 
I am not an electronics engineer. All is self-taught. I studied physics and my former career was 22 years in bank IT (software). I know there are some "proper" engineers here, I am just a guy who loves electronics and radio and muddles along as best I can, and somehow tries to get somewhere and after a lot of blood, sweat and tears, eventually manages something at least.
 
Now for Class-E... over the years I have made several attempts at it. I studied the maths. I tried the spreadsheet models. I tried building published designs. I never was successful. I just could never measure the high efficiency Class-E is supposed to give, and of course that was also verified by the temperature of my transistors.
 
When developing QCX I decided for the sake of low cost (no need for a heatsink, and no need for big beefy power transistors) I had better try one more time. I developed what I now call "ghetto" Class-E because it is such a simplified method of choosing the components... yet, it does seem to work very well...
 
This is a short extract from some text I wrote on the topic of Class-E for part of my presentation next month at Dayton FDIM:
 
"Some excellent background reading are two papers by Paul Harden NA5N:


Paul NA5N describes two defining features of Class-E:

1) Use of a square-wave drive to reduce switching losses: the transistors are either on, or off… no lossy region in between
2) Reducing the effects of the transistor capacitances. Class-E has a resonant tuned circuit. The capacitance of the transistors, normally an unpleasant lossy aspect, is now a part of the tuned circuit.

Class-E also has a reputation for being difficult to achieve. All those intense mathematics Google will help you find, don’t help. In reality, once you realise the secret – it is not so difficult. My “ghetto” design process for a Class-E amplifier is simple. Perhaps it is not totally optimal and a few more percentage points of theoretical efficiency could be squeezed out by the more advanced mathematical treatment. But for the average ham, my method produces excellent results with a minimum of fuss! I had previously attempted more complex methods and had always failed.

Calculation of the impedance of a resonant circuit is simple, and there are many online calculators which will do the job for you. For example, http://toroids.info/T50-2.php which allows you to type in the operating frequency, and the desired resonant circuit impedance. Then the calculator computes the required inductance, capacitance, and the number of turns required for a certain toroid (in the QCX, a T37-2 is used).

First choose the output impedance. We usually choose 50-ohms, because this is the input impedance of the Low Pass Filter we will use. The online calculator will tell you what inductance is needed, and how many turns to wind on the toroid. The online calculator also tells you the required capacitance to bring it to resonance at the operating frequency. Here we resort to experiment, because it is a little difficult to know what the output capacitance of the transistor is. The device capacitance varies depending on supply voltage and whether it is on or off. A simple experiment is required, adding different small capacitances to the circuit, and measuring the efficiency (measure supply voltage and supply current to calculate power input; then measure RF power output. Divide one by the other to get the efficiency). It is easy to find what additional capacitance is required to peak the efficiency. The resonance is quite broad and non-critical. "
 
The component values also come out close to some examples Paul NA5N has in his documents; so that's comforting and you feel you are on the right track :-)
 
73 Hans G0UPL
 
 
 
 
 
On Sat, Apr 28, 2018 at 4:42 PM, Glen Leinweber <leinwebe@...> wrote:
Alan,
A key difference from the classic Class C PA circuit is the lower value of inductance that feeds DC power to the MOSfet(s). In the classic circuit, this inductor is a choke, having high impedance at the operating frequency. For Class-E, it is a much lower impedance, so that it stores significant energy while the MOSfet(s) are ON (for half a cycle or less). When the MOSfets switch off, this energy is available for output power.

The word "flyback" comes to mind. During the half-cycle-or-less that the MOSfets are ON, current rises continuously in this inductor. After switching off, this inductor current dumps out in the form of voltage: MOSfet drain voltage swings far above the +12V DC supply voltage.

The LC low-pass filter feeding the antenna is quite conventional. Because the MOSfet drain voltage is somewhat pulse-like, harmonics are large - the filter must work hard to reject these harmonics effectively. This can be done various ways: higher Q, or an extra stage.
 



Re: Excellent presentation on Class E Amplifiers and why the QCX finals sometimes can get fried

jjpurdum
 

Hans:

I knew there had to be some serious software development in your background to squeeze all of those features into a Nano. I'm sure the physics training helped in your engineering efforts, but the QCX represents a very rare merging of the two disciplines...well done! My understanding is that we don't see more Class-E amplifiers because it's difficult to "get'er done". Cleary, the QCX got it right.

Can't wait to see what's next...!

72,
Jack, W8TEE


On Saturday, April 28, 2018, 10:06:33 AM EDT, Hans Summers <hans.summers@...> wrote:


Hi all

I am not an electronics engineer. All is self-taught. I studied physics and my former career was 22 years in bank IT (software). I know there are some "proper" engineers here, I am just a guy who loves electronics and radio and muddles along as best I can, and somehow tries to get somewhere and after a lot of blood, sweat and tears, eventually manages something at least. 

Now for Class-E... over the years I have made several attempts at it. I studied the maths. I tried the spreadsheet models. I tried building published designs. I never was successful. I just could never measure the high efficiency Class-E is supposed to give, and of course that was also verified by the temperature of my transistors. 

When developing QCX I decided for the sake of low cost (no need for a heatsink, and no need for big beefy power transistors) I had better try one more time. I developed what I now call "ghetto" Class-E because it is such a simplified method of choosing the components... yet, it does seem to work very well... 

This is a short extract from some text I wrote on the topic of Class-E for part of my presentation next month at Dayton FDIM:

"Some excellent background reading are two papers by Paul Harden NA5N:


Paul NA5N describes two defining features of Class-E:

1) Use of a square-wave drive to reduce switching losses: the transistors are either on, or off… no lossy region in between
2) Reducing the effects of the transistor capacitances. Class-E has a resonant tuned circuit. The capacitance of the transistors, normally an unpleasant lossy aspect, is now a part of the tuned circuit. 

Class-E also has a reputation for being difficult to achieve. All those intense mathematics Google will help you find, don’t help. In reality, once you realise the secret – it is not so difficult. My “ghetto” design process for a Class-E amplifier is simple. Perhaps it is not totally optimal and a few more percentage points of theoretical efficiency could be squeezed out by the more advanced mathematical treatment. But for the average ham, my method produces excellent results with a minimum of fuss! I had previously attempted more complex methods and had always failed. 

Calculation of the impedance of a resonant circuit is simple, and there are many online calculators which will do the job for you. For example, http://toroids.info/T50-2.php which allows you to type in the operating frequency, and the desired resonant circuit impedance. Then the calculator computes the required inductance, capacitance, and the number of turns required for a certain toroid (in the QCX, a T37-2 is used). 

First choose the output impedance. We usually choose 50-ohms, because this is the input impedance of the Low Pass Filter we will use. The online calculator will tell you what inductance is needed, and how many turns to wind on the toroid. The online calculator also tells you the required capacitance to bring it to resonance at the operating frequency. Here we resort to experiment, because it is a little difficult to know what the output capacitance of the transistor is. The device capacitance varies depending on supply voltage and whether it is on or off. A simple experiment is required, adding different small capacitances to the circuit, and measuring the efficiency (measure supply voltage and supply current to calculate power input; then measure RF power output. Divide one by the other to get the efficiency). It is easy to find what additional capacitance is required to peak the efficiency. The resonance is quite broad and non-critical. "

The component values also come out close to some examples Paul NA5N has in his documents; so that's comforting and you feel you are on the right track :-) 

73 Hans G0UPL





On Sat, Apr 28, 2018 at 4:42 PM, Glen Leinweber <leinwebe@...> wrote:
Alan,
A key difference from the classic Class C PA circuit is the lower value of inductance that feeds DC power to the MOSfet(s). In the classic circuit, this inductor is a choke, having high impedance at the operating frequency. For Class-E, it is a much lower impedance, so that it stores significant energy while the MOSfet(s) are ON (for half a cycle or less). When the MOSfets switch off, this energy is available for output power.

The word "flyback" comes to mind. During the half-cycle-or-less that the MOSfets are ON, current rises continuously in this inductor. After switching off, this inductor current dumps out in the form of voltage: MOSfet drain voltage swings far above the +12V DC supply voltage.

The LC low-pass filter feeding the antenna is quite conventional. Because the MOSfet drain voltage is somewhat pulse-like, harmonics are large - the filter must work hard to reject these harmonics effectively. This can be done various ways: higher Q, or an extra stage.



Re: Excellent presentation on Class E Amplifiers and why the QCX finals sometimes can get fried

Hans Summers
 

Hi all

I am not an electronics engineer. All is self-taught. I studied physics and my former career was 22 years in bank IT (software). I know there are some "proper" engineers here, I am just a guy who loves electronics and radio and muddles along as best I can, and somehow tries to get somewhere and after a lot of blood, sweat and tears, eventually manages something at least. 

Now for Class-E... over the years I have made several attempts at it. I studied the maths. I tried the spreadsheet models. I tried building published designs. I never was successful. I just could never measure the high efficiency Class-E is supposed to give, and of course that was also verified by the temperature of my transistors. 

When developing QCX I decided for the sake of low cost (no need for a heatsink, and no need for big beefy power transistors) I had better try one more time. I developed what I now call "ghetto" Class-E because it is such a simplified method of choosing the components... yet, it does seem to work very well... 

This is a short extract from some text I wrote on the topic of Class-E for part of my presentation next month at Dayton FDIM:

"Some excellent background reading are two papers by Paul Harden NA5N:


Paul NA5N describes two defining features of Class-E:

1) Use of a square-wave drive to reduce switching losses: the transistors are either on, or off… no lossy region in between
2) Reducing the effects of the transistor capacitances. Class-E has a resonant tuned circuit. The capacitance of the transistors, normally an unpleasant lossy aspect, is now a part of the tuned circuit. 

Class-E also has a reputation for being difficult to achieve. All those intense mathematics Google will help you find, don’t help. In reality, once you realise the secret – it is not so difficult. My “ghetto” design process for a Class-E amplifier is simple. Perhaps it is not totally optimal and a few more percentage points of theoretical efficiency could be squeezed out by the more advanced mathematical treatment. But for the average ham, my method produces excellent results with a minimum of fuss! I had previously attempted more complex methods and had always failed. 

Calculation of the impedance of a resonant circuit is simple, and there are many online calculators which will do the job for you. For example, http://toroids.info/T50-2.php which allows you to type in the operating frequency, and the desired resonant circuit impedance. Then the calculator computes the required inductance, capacitance, and the number of turns required for a certain toroid (in the QCX, a T37-2 is used). 

First choose the output impedance. We usually choose 50-ohms, because this is the input impedance of the Low Pass Filter we will use. The online calculator will tell you what inductance is needed, and how many turns to wind on the toroid. The online calculator also tells you the required capacitance to bring it to resonance at the operating frequency. Here we resort to experiment, because it is a little difficult to know what the output capacitance of the transistor is. The device capacitance varies depending on supply voltage and whether it is on or off. A simple experiment is required, adding different small capacitances to the circuit, and measuring the efficiency (measure supply voltage and supply current to calculate power input; then measure RF power output. Divide one by the other to get the efficiency). It is easy to find what additional capacitance is required to peak the efficiency. The resonance is quite broad and non-critical. "

The component values also come out close to some examples Paul NA5N has in his documents; so that's comforting and you feel you are on the right track :-) 

73 Hans G0UPL





On Sat, Apr 28, 2018 at 4:42 PM, Glen Leinweber <leinwebe@...> wrote:
Alan,
A key difference from the classic Class C PA circuit is the lower value of inductance that feeds DC power to the MOSfet(s). In the classic circuit, this inductor is a choke, having high impedance at the operating frequency. For Class-E, it is a much lower impedance, so that it stores significant energy while the MOSfet(s) are ON (for half a cycle or less). When the MOSfets switch off, this energy is available for output power.

The word "flyback" comes to mind. During the half-cycle-or-less that the MOSfets are ON, current rises continuously in this inductor. After switching off, this inductor current dumps out in the form of voltage: MOSfet drain voltage swings far above the +12V DC supply voltage.

The LC low-pass filter feeding the antenna is quite conventional. Because the MOSfet drain voltage is somewhat pulse-like, harmonics are large - the filter must work hard to reject these harmonics effectively. This can be done various ways: higher Q, or an extra stage.



Re: Excellent presentation on Class E Amplifiers and why the QCX finals sometimes can get fried

Glen Leinweber
 

Alan,
A key difference from the classic Class C PA circuit is the lower value of inductance that feeds DC power to the MOSfet(s). In the classic circuit, this inductor is a choke, having high impedance at the operating frequency. For Class-E, it is a much lower impedance, so that it stores significant energy while the MOSfet(s) are ON (for half a cycle or less). When the MOSfets switch off, this energy is available for output power.

The word "flyback" comes to mind. During the half-cycle-or-less that the MOSfets are ON, current rises continuously in this inductor. After switching off, this inductor current dumps out in the form of voltage: MOSfet drain voltage swings far above the +12V DC supply voltage.

The LC low-pass filter feeding the antenna is quite conventional. Because the MOSfet drain voltage is somewhat pulse-like, harmonics are large - the filter must work hard to reject these harmonics effectively. This can be done various ways: higher Q, or an extra stage.