designing Class C qrp amps

[VA7AAX]

Well, I found an old CB in my junkbox. So pulled it apart and found a prize, a 2SC2075!

This and a previous episode of SolderSmoke led me to think about a simple experiment I want to undertake.
I already have a basic 3.579MHz oscillator running on my bench.

Now I would like to design a 2n2222a stage after this to get 200-300mW. Then I would like to design a 2SC2075 Class C stage to get atleast 3 watts.

I want to know how stuff like how to set emitter resistors and knowing how to do correct impedance transformation.
Can anybody point me in the right direction to approach the task?
Now I know that EMRFD probably has everything that I need, but buying EMRFD is just way over my budget!


Anyways, yeah, any suggestions?

Thanks and best regards.

[KL7AJ]

Well, I found an old CB in my junkbox. So pulled it apart and found a prize, a 2SC2075!

This and a previous episode of SolderSmoke led me to think about a simple experiment I want to undertake.
I already have a basic 3.579MHz oscillator running on my bench.

Now I would like to design a 2n2222a stage after this to get 200-300mW. Then I would like to design a 2SC2075 Class C stage to get atleast 3 watts.

I want to know how stuff like how to set emitter resistors and knowing how to do correct impedance transformation.
Can anybody point me in the right direction to approach the task?
Now I know that EMRFD probably has everything that I need, but buying EMRFD is just way over my budget!


Anyways, yeah, any suggestions?

Thanks and best regards.

The Tuna Tin transmitter has about as straightforward a 2222 final as you can get...it uses a pot for the emitter resistor to adjust the power. By the way....at 300 mW, you WILL need a heat sink on your 2222...which pretty much means you need to use a metal case version....or else bury the thing in a big glob of heat sink lotion.

Eric

[KL7AJ]

http://www.w5usj.com/TxTopperQRPAmp.html

Eric

[WR8Y]

I want to know how stuff like how to set emitter resistors and knowing how to do correct impedance transformation.

Setting up transistor bias wasn't too bad, certainly not for Class C; however, I was in school over a year before we even got started with impedance matching.

THere is an old book from the 80's by Chris Bostwick "RF Circuit Design" that I have at home. I could not understand the math involved, and it sat on my bookshelf for 19 years! Then, 1 1/2 years ago, I went back to school and after going thru "Precalculus" (they used to call that "College Algebra II") I now understood how to do polar - to - rectangular conversions and work the the "j" operator. That math class (along with "College Algebra") gave me the foundation to understand the concepts presented in Bostwick's book.

This won't be a "here's your answer" kind of thing, this will be a long and rewarding road for you. OR, you could just find an existing design...

Anyway, Bostwick's book will be a major source of informatoin as I build my EME station over the next three years. (I already have the L.O and receive mixer stages done!)

[VA7AAX]

Thanks for the replies.
I am going to be looking into a few designs and maybe working around those. The TX Topper looks to be a good design for the irf510's I have. though I might want to save those for a more permanent apps.
I think the PSK 80 Warbler that I just looked up has a good amp design.
Yeah, could never figure that j operator in the impedance

Thanks very much. This is going to be a great learning process

[VK2TIL]

You are at the stage where you need EMRFD; Christmas is coming.

If someone won't buy it for you, buy it for yourself.

[AC0FP]

Thanks for the replies.
I am going to be looking into a few designs and maybe working around those. The TX Topper looks to be a good design for the irf510's I have. though I might want to save those for a more permanent apps.
I think the PSK 80 Warbler that I just looked up has a good amp design.
Yeah, could never figure that j operator in the impedance

Thanks very much. This is going to be a great learning process

Just a little help, just to get you started. If you wish 3 watts from amplifier in class C you need this formula: Vcc squared/ 2 * power out.

Vcc is the voltage the final device can swing. Good transistors can swing from the positive to the negative DC supply rail (if you ask for more than the transistor can deliver then it won't swing to the rails and you will not get the desired power output). An example, if Vcc is 10 volts and you wish 3 watts then: 100/6 = 16.667 ohms which is the impedance you will match to 50 ohms. A low pass L, Pi, or T network can do this. You want the network to match 16.6 + j0 ohms to the 50 ohms load. The "j" is the reactance you need to "tune out" at your operating frequency.

73,

Frank:)

[W8JI]

.

I want to know how stuff like how to set emitter resistors and knowing how to do correct impedance transformation.
Can anybody point me in the right direction to approach the task?
Now I know that EMRFD probably has everything that I need, but buying EMRFD is just way over my budget!


Anyways, yeah, any suggestions?

Thanks and best regards.

Buy a copy of Solid State Design for the Radio Amateur by Doug Demaw.

It not only has everything you need, it is probably the best single book ever written on the subjects you asked about.

73 Tom

[VK2TIL]

SSD is a great book but it's out-of-print and scarce.

The price asked reflects its value as a "collector's item";

http://www.amazon.com/gp/offer-listing/0872590402/ref=ed_oe_p_olp

I still refer to mine but it's not for sale!!

The downside of SSD is that its circuits use ICs that are scarce and are, in some cases, often not in line with present thinking.

I recommended EMRFD earlier; it's more "modern".

Akshay VA7AAX has become a true homebrewer in a short time; his curiosity about how things work is obvious.

If he hasn't got EMRFD by now, he should have!!

[KB9BVN]

Buy a copy of Solid State Design for the Radio Amateur by Doug Demaw.

It not only has everything you need, it is probably the best single book ever written on the subjects you asked about.

73 Tom

That book is "unobtainium" anymore. The ARRL ought to reissue it again, they'd sell hundreds if not thousands.

I have a copy...and I won't be letting it go.

[W8JI]

That book is "unobtainium" anymore. The ARRL ought to reissue it again, they'd sell hundreds if not thousands.

I have a copy...and I won't be letting it go.

It may be past protection now, so someone might grab it.

I'll suggest to MFJ they look into priniting and selling it. They did "Antennas and Transmission Lines" by Kuecken that way. That's one of the best moderately advanced antenna handbooks ever made.

[K5UOS]

I remember when I was making the transition from homebrew tube to homebrew solid state. I received a gift copy of Solid State Design from my dad, W1KPS (SK). As Tom infers, certain principles don't change. There are two notable sections that I personally believe are timeless and useful today. There are other sections that are useful but a couple pertain to this thread.

Chapter 4 in SSD has straight forward information and design formulae for Matching Sections which I have adapted to circuits in both solid state and tube gear. This thread was about designing Class C amps. I have a comfort zone using L-C-C networks to match lower level stages to a PA gate or base input and for the low impendance drain or collecter to 50 Ohm low pass filters for power amps in the 10 to 50W range. I also use the Pi Network formulas for filters from 25 ohm to 500 ohms with the latest being 500 ohm filters for 3 discrete solid state oscillators for use in a hybrid homebrew tube receiver front end. The L-C networks have been useful for terminating crystal filters.

I set up most of the SSD formulas in an Excel sheet that I have been using for 20+ years.

Another classic circuit in Chapter 2 shows the Universal QRP Transmitter. This was interesting to me back in the late seventies when transitioning to SS because it was essentially a solid state example of the old 6AG7/6L6 MOPA. I can't think of a better 1st project than this...well, maybe a 6AG7/6L6...but a different thread.

Lastly, the receiver in Chapter 5, P102, was an early favorite of mine as it resembled the tube 40/80 meter Handbook receivers I built in my early homebrew tube days. The dual gate mosfet may be a bit harder to find but remains a reasonably popular device for homebrewers even today.

Note: On page 104 there is a receiver that uses the same IF amp (MC1350P) that the much heralded K2 uses decades later.

All this said and second hand prices for SSD being what they are, the more modern EMRFD is a great buy for the price. Much of the same timeless information and certainly a rich collection of circuits to keep any serious homebrewer/experimenter busy. Both books were written for the ham who was not a graduate engineer but made the decision to build some or all of his /her gear. I believe buying either is an investment not an expense.

One thing I like about EMRFD is that it often avoids absolutes. A section on IF amplifiers may progress through many device types and configurations without stating which is the best but relating the various strengths and weaknesses and leaving the choice up to the reader.

K5UOS

[W4HAY]

I don't know if it's still available, but the Sam's Publications RF Circuit Design by Chris Bowick is also good. CAUTION: If you're queasy about Smith Charts and S-parameters, this one will positively terrify you!

[VA7AAX]

HAY, I think i want to stay away from Smith Charts!(though, n0ax has 3 columns about it in his Hands0n radio column,might read up on that)

Well, yeah, I have heard of SSDRA. but yeah, they sell for collector's prices.;)

Christmas is coming so let's keep our fingers crossed.

A homebrewer without EMRFD is like a HAM without radios!

Recently, I was given the SPRAT CD v2 on "permanent loan" basis. It has issues 1-109 and I have been enjoying that too . A very cool read indeed!

[VA7AAX]

The RF Circuit Design by Chris Bowick is available (2nd edition) through amazon for $40

[KL7AJ]

Buy a copy of Solid State Design for the Radio Amateur by Doug Demaw.

It not only has everything you need, it is probably the best single book ever written on the subjects you asked about.

73 Tom

Yes...and you'll have to pry my copy from my cold dead bony hands. :)

[KL7AJ]

Just realized that "Fine Business" has been a silent key for over a decade. I must be getting old. :)

[KA5LQJ]

Ok,

Please indulge and old man. As best I can remember, "Class C" amps, "swung" something like 80 to 90% of the "duty cycle" and were used to amplify AM transmitters back-in-the-day before less scrupulous Class D "operators" started using them, ruining it for everyone else. :mad:

I happen to be the happy recipient of a 1950 edition of Editor's & Engineer's Handbook. :D Sadly though, due to my disability check, I can only dream of getting the parts together to build one of those AM amps. :(

Respectfully,
73,

Don/KA5LQJ

[KB1LQD]

You are at the stage where you need EMRFD; Christmas is coming.

If someone won't buy it for you, buy it for yourself.

Best book I ever bought for a Xmas present for my twin.... Ya we share :)

Also, Find your way around these websites...

http://www.electronics-tutorials.com/
http://my.integritynet.com.au/purdic/
(This ones pretty good)

[W4CBJ]

Yep, I find that some of the older books have 'good stuff' that the newer ones don't. One of mine has a simple explanation of the " J" operand. If I can find it....I will post it on the QRZ forum. How many people would be interested or could even understand this ? In the event that you may need funds for republishing an old radio text....you can find me at the nearest homeless shelter. 73 Joe W4CBJ

[AC0FP]

I will add additional information to my post #7. Google AN267, this is a Freescale (Motorola) application note on matching networks, its as interesting as it is practical! Hint, go with the T-match (D)! ;)

http://www.lansdale.com/Articles/an267.pdf

73,

Frank:)

[VA7AAX]

Thanks very much

Will definitely keep the articles and suggestions on hand.
yeah, I am still going to be building a 2SC2075 amp based on the PSK-Warbler.

Check my new project.!
73 de va7aax

[AC0FP]

Thanks very much

Will definitely keep the articles and suggestions on hand.
yeah, I am still going to be building a 2SC2075 amp based on the PSK-Warbler.

Check my new project.!
73 de va7aax


You are welcome. The 2SC2075 should work very well.

If you have any additional questions post here, or send a PM!

73,

Frank:)