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CHALLENGE - SS rig for the AM PW (QRP) net.




 
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Author Topic: CHALLENGE - SS rig for the AM PW (QRP) net.  (Read 51020 times)
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W1FVB
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« Reply #50 on: December 03, 2011, 10:34:22 AM »

hi frits. i assembled your driver example. i was hoping i could get away with parts from my junk box. i put the circuit together using a J310 but im not sure if it is working properly.

what kind of output should i expect with 0dBm input?

my output is 1.7V Pk-Pk with a dc offset of about 6.7V. the waveform is heavily clipped as well. i'm not doing any filtering.

Do you use the matching L-Network Sol? ,there's no DC offset if you do and the L-Network is necessary to put a 10 ohm load on the IRF510 while using 50 Ohm on the output terminal.
I'm not sure about the input requirements, but in my QRP transmitter , I get about 3Vpp from my VFO / Frequency Divider section presented to the VN-10.
(At that point probably 10 dBm)
The VN-10 is a small signal amplifier MOSFET and the J310 is a JFET which probably doesn't work as a replacement.
In my setup , I was able to achieve about 8 W output on 3.9 Mhz
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ssbothwell KJ6RSG
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« Reply #51 on: December 03, 2011, 08:48:23 PM »

i did not include the matching network because i also did not use the IRF510 stage. i was planning to use your circuit to drive my irf510 AB amp.

i didnt realize the VN-10 is a mosfet not a jfet. i ordered some from mouser just now (along with the parts i need for your modulator circuit) and will hold off on messing with this circuit until i get the proper components.
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ssbothwell KJ6RSG
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« Reply #52 on: December 08, 2011, 10:30:05 PM »

hi frits,

in your single irf510 design, what value do you use for the source impedance when calculating the L-Network values?
edit: i just noticed in your schematic it says 10ohm to 50ohm.

i tried putting the driver together in spice but it is not working properly. it looks like the problem might be with the bjt push-pull stage. is it biased properly?

also, if i am going to use my own final amp stage (AB IRF510s) rather then your single ended irf510, do i need an L-Network between the bjt driver and the AB irf510 amp?




* driver.jpg (295.01 KB, 1440x874 - viewed 826 times.)

* output.jpg (630.78 KB, 1440x874 - viewed 528 times.)
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W1FVB
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« Reply #53 on: December 09, 2011, 10:15:58 AM »

hi frits,

in your single irf510 design, what value do you use for the source impedance when calculating the L-Network values?
edit: i just noticed in your schematic it says 10ohm to 50ohm.

i tried putting the driver together in spice but it is not working properly. it looks like the problem might be with the bjt push-pull stage. is it biased properly?

also, if i am going to use my own final amp stage (AB IRF510s) rather then your single ended irf510, do i need an L-Network between the bjt driver and the AB irf510 amp?




The 1 K resistor (R2) serves as the bias to the push pull stage. I came to that fixed value after some testing in my QRP transmitter. This value might not work in other setups. It's probably better to drop the 1 K and put a similar bias scheme in as you see for the VN-10
You have R3 as 5K fixed value, that should be set , so you have about 40 mA going through the VN-10

I don't know how your 510 amps input is designed. and the push pull stage might not be able to drive two FETS directly.
It is probably better to just design the drive with the single 510 and treat everything in separate units and proper impedance matching.

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ssbothwell KJ6RSG
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« Reply #54 on: December 09, 2011, 07:22:37 PM »

i got a copy of eagle CAD and some press-n-peel transfer film. i used frits' driver as a test board. it came out pretty nice: http://imgur.com/1ob6p.jpg

in the spirit of this thread, i am gonna try to put together a complete 5W QRP transmitter with pcb art and a parts list. i really like the kitsandparts.com style of modular circuit elements so maybe i will make a set of PCB images for each stage (VFO, amplifier, modulator, and filters). what do you guys think?

edit: i tried to redo the board layout to reduce the size down to 3"x2". i was able to do it but it is a lot more busy and i am not really able to draw a big ground plane on the board. how critical is it to draw a big ground plane?


* new-driver-layout.jpg (779.22 KB, 2110x1366 - viewed 572 times.)
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Ed/KB1HYS
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« Reply #55 on: December 10, 2011, 08:42:15 AM »

I like it!  I especially like the modular approach.  This will allow a new builder to complete a section and troubleshoot it without having to worry about interactions.  Also makes circuit analysis much simpler, for those so inclined.
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73 de Ed/KB1HYS
Happiness is Hot Tubes, Cold 807's, and warm room filling AM Sound.
 "I've spent three quarters of my life trying to figure out how to do a $50 job for $.50, the rest I spent trying to come up with the $0.50" - D. Gingery
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« Reply #56 on: December 10, 2011, 09:25:58 AM »

I like it!  I especially like the modular approach.  This will allow a new builder to complete a section and troubleshoot it without having to worry about interactions.  Also makes circuit analysis much simpler, for those so inclined.

I'm with Ed  Smiley
That board looks nice Sol!
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N4LTA
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« Reply #57 on: December 10, 2011, 04:19:34 PM »

You can't AM modulate a Class AB RF stage with a transformer or series modulator - Must be a non linear stage -  class C, D, or E.

That's what I have always been told anyway?
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W1FVB
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« Reply #58 on: December 11, 2011, 11:21:03 AM »

You can't AM modulate a Class AB RF stage with a transformer or series modulator - Must be a non linear stage -  class C, D, or E.

That's what I have always been told anyway?

hum.. I can't see why not.
The modulation basics are the same, double the voltage to the final = 100% modulation = 4X more output. This is true regardless the class of operation the amplifier stage is working in.
It might be very inefficient , because there's no use to bias the amp in Class AB.
..or am I missing something?
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KF1Z
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Are FETs supposed to glow like that?


« Reply #59 on: December 11, 2011, 12:01:53 PM »

To those who are freely sharing ideas and schematics....

I will send FREE any of the parts below, if you are actually going to use them in a
low power AM rig.

just to keep it fair, and spread them around a bit, there are limits   :-)


I have a large quantity of IRL510 mosfets ( same as IRF510)  limit 10 pcs per person
A smaller quantity of IRFP260n ( limit 2 pcs)
and very limited number of 2N3055 ( limit 1 each)

Not that these are hard to find, or particularly expensive, but I can't use them all...

If you'd like some, let me know and send your address via pm or email....

( If you are outside US, may need a little poostage $)


Thanks for sharing!


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N4LTA
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« Reply #60 on: December 11, 2011, 05:01:24 PM »

Most any older ARRL Handbook will tell you  -  the amp power output " must vary as the square of the instantanious  plate voltage  in order for the modulation to be linear. This will be the case when the amplifier is operating Class C."

It indicates that the modulation will not be linear otherwise.

I have always been told that this is pretty important in properly modulating a transmitter.


BTW - does this "challenge" also cover receiving? I would suggest that that would make things much more interesting and also challenging.

SSbothwell

Your PC board layout will be disapointing I think. The lands are long and narrow. Thin lands will delaminate easily from the substrate when heated during soldering. If you try do use this same  type of layout using RF, you will be guaranteed to have stability problems. You need large copper ground planes and short lead lengths. Believe me, I have been laying out PC boards for 40 years and have discovered all sorts of layout problems. Most of the modern PC layout software assumes you are working on digital circuits . You have to learn the "tricks" that are available.

My favorite PC board software is Express PCB which is free. It will print to a standard printer. I use a laser printer to print the artwork on clear film and use positive resist board exposed in a simple UV frame. I develop it and etch with hydrogen peroxide/muriatic acid solution  - I used to use ammonium persulfate and it works a little cleaner - but the peroxide solution is fast and cheap. Long ago I used  ferric chloride - but  it is nasty and stains and is just messy. I hate the stuff.

If you are serious about making PC Boards, I suggest that you use the photo expose method. The iron on stuff works but the quality of the boards is not great. I can etch a .01" wide  strip using the photo process. From my experience, the iron on process, can't come close to that.

I have been working on a Vacker VFO today that I layed out out and etched this morning and may post some photos of the board later.

Have fun with your projects.

Pat
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N4LTA
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« Reply #61 on: December 11, 2011, 06:28:54 PM »

Here is a Vacker VFO board that I built today. Works very well and stayed put better than I expected. Right now it is running at 5.0 Mhz. The unbuilt area on the right is a 5 pole lowpass filter and resistive attentuator.



 Here is the board after being developed



Board after stripping resist with steel wool




Board after plating with MG Chemicals Liquid Tin





Completed and tested Vacker VFO. It currently is running at 5.0 Mhz and I am happy with the stability




Below is a prototype 75 Meter high fidelity am tuner and audio amp. It was made to monitor the local net frequency. The front end uses a NE602 which is not known for high dynamic range so it has a very narrow bandpass filter. A different filter would be required to cover more than 50 Khz of the band. The IF amp uses two conventional IF transformers. The AGC is somewhat unconventional and works very well. The IF feeds a High Fi AM detector as described by G3YNH. It has a Sallen Key bandpass filter after the signal is detected Sounds very good. Bandwidth is about 10 Khz. The audio amp uses a couple of complimentary output transistors and is very clean at about 1.2 watts. It drives an 8" speaker easily without distortion.

Audio Amplifier




High fidelity 75 meter tuner





Pat



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ssbothwell KJ6RSG
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« Reply #62 on: December 12, 2011, 01:29:02 AM »

wow pat, those boards look really amazing!

how do you tin the board?

that first board i etched was using the default copper trace sizes. i am trying to put together a better one with larger traces. i'll post that soon.

i dont think have the resources to setup a dark room for film development, maybe someday.

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« Reply #63 on: December 12, 2011, 10:13:49 AM »

Solomon,

You don't need a darkroom. The board is sensitive to UV light only. You can use a florescent bulb but the best way is to buy a low cost UV tube and build a wood frame with a glass top. Then you lay down the printed positive, lay the sensitive board on top and  put a cover on top (or build a hinged lid like I did)

Turn on the light for about one minute and thats it. You develop the board in normal room light. I can go from printer to finished, plated board in 15 minutes. I drill it after plating on a low cost drill press using resharped carbide drills - They are cheap  - use a #65 for IC and parts and a #60 or larger leads - like TO220 etc and a #55 and #50 is also nice for larger holes..

The exposure frame takes a few hours to build and then it's finished for a lifetime. It really is worth it if you plan to do IC type boards single sided. You can make traces thin enough to run between the IC pins easily.
This is useful when making microprocessor boards etc. Thin traces are not real useful for RF.

The plating is done with MG Chemicals Liquid Tin - It cost about $35 per quart but can do lots of boards. It is necessary when doing SM type work. I clean the board with steel wool (brillo) and that also does a good job of degreasing the copper and then immerse in the Liquid Tin for a couple of minutes. Then I take out the board and lightly clean (lightly or you will remove the tin) with brillo again. Then solder away.

The chemicals required are the positive developer (about $10 for enough for lots of boards) - Don't try to make your own with sodium hydroxide as described on the net (unless you get a formula for one with a buffer) - without the buffer - you will screw up many boards.  You need an etchant that can be made with two parts hydrogen peroxide (drugstore peroxide) and one part muriatic acid ( you can buy a gallon at Lowes for $6 - don't get the low fume version  - it has less concentration - you need about 30%. Pour the acid carefully into the peroxide - not the opposite. It is very cheap and works great - way better than that nasty ferric chloride - not quite as good as ammonium persulfate - but that has to be heated - (I used it in a pyrex dish on the range for 30 years.)

BTW - I layed out a board last week for the modulator - I want to give it a try. I have always heard that it is a good idea to modulate both the driver and final with a SS transmitter.  It is easier to get 100% modulation.


Pat

Again - Have fun
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ssbothwell KJ6RSG
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« Reply #64 on: December 13, 2011, 04:55:47 PM »

oh wow. i didnt realize the exposures are so simple. perhaps i'll put together a uv light setup in the future, but for now i have a bunch of untreated copper and press-n-peel paper to work through.

i'm attaching a pcb layout for frits' driver board. this one uses larger traces and a giant ground plane. is this a better layout style?

edit: i changed the design rules a bit and beefed up the traces. i've got both versions attached to this post now.
edit2: i just noticed the newer layout is missing a trace. i have to work on this board some more. pcb layouts are tricky!


* driver-layout.jpg (921.11 KB, 2710x1213 - viewed 571 times.)

* driver-layout2.jpg (1084.11 KB, 2710x1213 - viewed 550 times.)
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N4LTA
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« Reply #65 on: December 13, 2011, 08:43:20 PM »

Looks good. Build one and see how it works


PC Layout is somewhat an art. You learn a lot of tricks as you go. I enjoy doing it almost like working a puzzle. I like to see how compact I can squeeze thing in.

You can check and double check and then an error pops up right in the middle of building it. I'd be embarrased to show you my box of boards that one day I hope to salvage the parts out of. The monitor receiver that I show in the photos is an expansion of a compact board I made last week. It had a high frequency oscillation that I could not track down. I ended up doing a new layout with a little more wasted space.

Pat
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Steve - K4HX
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« Reply #66 on: December 13, 2011, 08:50:43 PM »

Nice boards!

What is the local net freq?

Did you ever get your log periodic up?




Below is a prototype 75 Meter high fidelity am tuner and audio amp. It was made to monitor the local net frequency.
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ssbothwell KJ6RSG
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« Reply #67 on: December 14, 2011, 05:13:26 AM »

here is a type3 mixer i put together. i plan to use this in a superhet receiver to go along with my 35w transmitter. Smiley

i am etching a driver circuit now for my irf510 amp.

edit: and now the driver board is attached. i dont have the proper dril bits to finish these boards but i should have them in a day or two.


* type3mixer.jpg (165.85 KB, 1280x960 - viewed 550 times.)

* driver-board.jpg (204.07 KB, 1280x960 - viewed 542 times.)
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N4LTA
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« Reply #68 on: December 14, 2011, 02:39:23 PM »

The local AM net (OF Net) is on 3715 Khz on Sunday afternoon at 3:00 pm EST and at 9:00 am on Tuesday mornings. Most of the guys run 100 watts or less.

Negative on the log antenna - It's still standing in the garage corner in the box. I have had trouble getting someone to put it up for me. The local club used to be a good source but the members as myself are suffering from gray hair itis - After falling off a ladder up 17 feet 2 years ago while putting up a dipole - I no longer climb. I will probably have to pay a professional to put it up. I  back burnered it when the upper bands were slow. Now I need it. Someone said there were 2  guys in Columbia, SC who would work for $100/hour together and I may have to go that route.
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« Reply #69 on: December 14, 2011, 08:33:15 PM »

Sol,

I like those boards a lot. Plenty of ground plane. I think they will really work well. My software won't do that. I may have to look at yours.

Pat
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Steve - K4HX
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« Reply #70 on: December 14, 2011, 08:39:20 PM »

OK. I've checked into the OF Net once or twice. IIRC, Terry, N4RQ is a semi-regular. He used live about 40 miles from here.

I might be convinced to give you a hand with the log antenna. I won't volunteer a certain AMer in NC, but he might help too. You can drop me a PM to speak further.


The local AM net (OF Net) is on 3715 Khz on Sunday afternoon at 3:00 pm EST and at 9:00 am on Tuesday mornings. Most of the guys run 100 watts or less.

Negative on the log antenna - It's still standing in the garage corner in the box. I have had trouble getting someone to put it up for me. The local club used to be a good source but the members as myself are suffering from gray hair itis - After falling off a ladder up 17 feet 2 years ago while putting up a dipole - I no longer climb. I will probably have to pay a professional to put it up. I  back burnered it when the upper bands were slow. Now I need it. Someone said there were 2  guys in Columbia, SC who would work for $100/hour together and I may have to go that route.
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ssbothwell KJ6RSG
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« Reply #71 on: December 15, 2011, 11:35:34 PM »

frits, i put together the driver. it seemed to be working great. using a 12V/1.5A power supply i was getting ~4w out from 100mW input, but then i decided to try connecting it to a 13.8V/3A power supply and i think i burnt out the irf510. oops.

i am using a completely inadequate heatsink on the irf510 and i positioned the irf510 poorly so the heatsink is bumping against the l-network capacitor.

how big of a power supply should i be using?

edit: i replaced the irf510 and hooked it into a 12V/750mA power supply. now i am getting perfect  7.5VRMS output from a 1.1VRMS input. the waveform looks perfect.

this will be perfect to drive my push/pull irf510 amp.  Smiley



* image (25).jpg (156 KB, 1280x960 - viewed 523 times.)

* 1215112022.jpg (305.71 KB, 1280x960 - viewed 543 times.)
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W1FVB
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« Reply #72 on: December 16, 2011, 08:21:00 AM »

frits, i put together the driver. it seemed to be working great. using a 12V/1.5A power supply i was getting ~4w out from 100mW input, but then i decided to try connecting it to a 13.8V/3A power supply and i think i burnt out the irf510. oops.

i am using a completely inadequate heatsink on the irf510 and i positioned the irf510 poorly so the heatsink is bumping against the l-network capacitor.

how big of a power supply should i be using?

edit: i replaced the irf510 and hooked it into a 12V/750mA power supply. now i am getting perfect  7.5VRMS output from a 1.1VRMS input. the waveform looks perfect.

this will be perfect to drive my push/pull irf510 amp.  Smiley



Nice work Sol!
The FETS Drain is connected to the casing, better to isolate the heatsink, you don't want DC and RF flowing over it  Wink
The FETS current depends on the load from the L-Network and the level of bias,
in your case 750 mA should be OK, but better to not max out your power supply.

Great progress!
Frits
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« Reply #73 on: December 16, 2011, 08:59:20 AM »

Steve,

Did you get my pm? I sent it (I thought) but it isn't shown in my sent messages.

Sol.  Good work on the amp driver. When you modulate it  - I'd run it in class C as most of the literature states that you need a nonlinear final (square law) to get linear am modulation. That should make it a little harder to drive, but it will run much cooler and be easier on the output devices. You may want to consider modulating the driver also. Running class C will be more stable also, and will do away will the bias circuit and thermal problems there.

You need a power supply that can deliver the current that is needed and not "squat down" when the amp is driven for lond periods - the heat sink needs to be big enough to keep the device from getting smoking hot when the key is down for a minute or so since it is goind to be AM. This is with the amp fully modulated and it may be a challenge to keep the device cool at full rf power and fully modulated.

Have you blistered you index finger tip yet? You probably will. I have branded myself with a TO39 circle many times testing how hot a device is.



Pat
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ssbothwell KJ6RSG
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« Reply #74 on: December 16, 2011, 04:52:14 PM »

thanks for the kind words. i've got the modulator circuit built but i used the wrong package size for the pots. i need to go find some 16mm pots from the electronics shop. i'm heading over there in a minute.

how do i determine when the circuit is running in class C?

in class C, the driver shouldn't draw any current when their is no input signal, right?
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