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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 51028 times)
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Ed/KB1HYS
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« on: November 06, 2011, 09:08:13 PM »

HoooKay.

With the idea of getting more folks into building their own rigs, and actually using them on the air, I will issue this challenge.  Design a simple, inexpensive, easy to build AM rig that will be suitable for a first time builder, with minimal experience. Post schematics and parts lists etc here. Board members can review, offer suggestions etc.  Any one wanting to build one will have a great starting point (hopefully) and resource right off the bat.   There's so much experience on this board this should be cake!

Design criteria -

1- LOW COST - Using Solid State, Catalog (DIGIKEY or MOUSER) parts.
2- SIMPLICITY- Bare minimum parts count, Point to point, Squashed Bug, or Manhattan style construction.
3- LOW POWER - from 5-25 watts out put.
4- VFO Coverage of at least the General Phone portion of 75-80 meters.
5- EASY-to-BUILD - in sections or stages. (this way someone new can build a piece, test it, and move on when it works)
7- PERFORMANCE - Output should be reasonably clean and stable. Modulation should be 90-100%.

Here's What I'll be drawing up and building:

Starts with a Clapp Oscillator for a VFO, built around an MPF102 JFET, feeding two 2N3904's in a buffer, varicap tunning using a pair of 1N400X type diodes, about as vanilla as it gets, but simple and proven effective.

This will feed an IRF-510 based RF amplifier, which I think can be drain modulated using a filament type power transformer or perhaps a 12V power transformer (thinking easy to get radio shack type parts).

Audio will be op-amp based preamp, into a higher powered LM-380 variant chip, possibly feeding a couple more IRF510s as modulators or...   



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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
kb3ouk
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« Reply #1 on: November 06, 2011, 09:59:56 PM »

instead of using the IRF 510s to make an amp, do like they did with the retro 75 and use a 10 watt or so audio amp IC, then feed the transformer with that.
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« Reply #2 on: November 06, 2011, 11:03:56 PM »

If you want to make it more simple, get rid of the modulation transformer and use a class A series modulator.  The design just "falls out", and the audio will be much better.  Also, the positive peaks are limited only by the power supply voltage.  Negative peak limiter is also very easy with a series modulator.

If 25 watts output is really desired, a larger MOSFET should be used.

But, such a rig would be fairly easy to build.  My son Michael built a class E transmitter when he was 12 years old that would put out up to 5 watts max.  Used a class A series modulator and a voltage tripler off of a fairly hefty wall wart.
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w1vtp
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« Reply #3 on: November 07, 2011, 07:41:46 PM »

Here ya go.  Already designed and laid out for you

http://mysite.verizon.net/sdp2/id11.html

Al
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KA2DZT
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« Reply #4 on: November 07, 2011, 08:15:32 PM »

Al

Nice job on that xmtr.   Sure the heat sink is big enough?Huh

Fred
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« Reply #5 on: November 08, 2011, 02:38:03 AM »

Al

Nice job on that xmtr.   Sure the heat sink is big enough?Huh

Fred

That's Stu's site - AB2EZ
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« Reply #6 on: November 08, 2011, 09:34:24 AM »

I'm using a single IRFP260. Get's me up to 40 W using an old converted 13.8 power supply as an DC modulator. The 260 can provide more but I was limited to the power supply.
The FET has a dedicated digital drive chip which does a good job even under heavy modulation.

Frits


* SAM_0752.JPG (169.13 KB, 800x600 - viewed 687 times.)
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W3GMS
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« Reply #7 on: November 08, 2011, 01:32:27 PM »

Frits,

I would be interested in seeing what scheme you used to modulate the supply?  Is it a switcher or a linear?   Using the supply as the modulator makes the most sense to me. 

Joe, W3GMS

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« Reply #8 on: November 08, 2011, 02:44:31 PM »

Frits,

I would be interested in seeing what scheme you used to modulate the supply?  Is it a switcher or a linear?   Using the supply as the modulator makes the most sense to me. 

Joe, W3GMS



Hello Joe,
It's an old linear power supply. I just pulled the old electronics and build in a pretty
simple modulator circuit (see attached image..my version is slightly different though)
Very simple analog design, but sound pretty good!


* series_modulator.jpg (54.33 KB, 750x525 - viewed 1360 times.)
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« Reply #9 on: November 08, 2011, 04:04:09 PM »

Frits,

Looks good.  Just essentially modulating the reference voltage.  I bet it sounds just fine.  A very similar scheme works for getting audio onto the screen grid of the final tube.  The beauty is, you can dial in the amount of audio you want while keeping the resting or steady state voltage the same.

I bet it sounds good  as well.

Joe, W3GMS   
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« Reply #10 on: November 08, 2011, 04:16:25 PM »

If anybody is interested , last year I have build a 2W AM rig. This guy is a "standalone" with build in VFO but still using digital drive and series modulation.
Here's a download link to the schematics:
http://files.myopera.com/Frister/projects/80MPW.zip

Thanks to guys like Steve WA1QIX , running the Class E website with tons of info  Cool

Frits
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« Reply #11 on: November 08, 2011, 06:26:03 PM »

Fritz,
Great little PW rig!  Nice job.
Joe, W3GMS
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Ed/KB1HYS
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« Reply #12 on: November 09, 2011, 11:13:15 PM »

Frits, that lil rig is da bomb.
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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 #13 on: November 10, 2011, 09:26:36 AM »

Frits, that lil rig is da bomb.

Grin Thanks guys. At some point in the QRP net last season, Timtron called me the channelmaster  Cool
seriously, good luck on building your transmitter Ed. I'm curious to see what you cook up.
I first started by trying to modulate in a earlier stage with 2 transistor in push pull , and they were driving the Gate of a IRF510. I had a hard time getting clean audio out of it, at same point is was half way decent, but still not satisfying. That's when I ended up with the digital drive and modulating the Drain of the FET.
A whole handful of components made place for a single chip and no more worries about linearity of earlier drive stages.

Frits
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w3jn
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« Reply #14 on: November 10, 2011, 11:09:13 AM »



Starts with a Clapp Oscillator for a VFO, built around an MPF102 JFET, feeding two 2N3904's in a buffer, varicap tunning using a pair of 1N400X type diodes, about as vanilla as it gets, but simple and proven effective.






Ed, having been there and done that with voltage tuned oscillators, I highly recommend you use a variable capacitor instead of varicap tuning.  There are many, many potential pitfalls with varicap tuning that are easy to avoid if you use a good variable capacitor.   FMing, unwanted RF feedback causing FMing and drift, FMing due to dirty spots in the tuning potentiometer, non-linear tuning, drift from minute changes in Vref, drift and low Q (causing sluggish oscillation) due to 1N4xxx diodes being pressed into varicap service, phase noise, and I could go on. 

Better is to use as high-Q an inductor, variable cap, and any other caps in the tank as possible.  Use as light a coupling as you can to the tank and still maintain reliable oscillation.

A decent quicky oscillator is a NE602.  It includes a voltage regulator, a buffer, and balanced outputs.  Needs one transistor to amplify the outputs to drive a TTL load.  The nice thing about this is most of the components are on the chip and therefore rigidly mounted.  Using SMD caps and a robust tank assembly and you can hit it with a hammer and it won't budge.
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« Reply #15 on: November 12, 2011, 07:41:39 PM »

Quote
Very simple analog design, but sound pretty good!

Hi Frits,

Just curious why C4 and C5 are in series, or was C4 supposed to go to ground?


Thanks

Phil - AC0OB
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Ed/KB1HYS
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« Reply #16 on: November 12, 2011, 11:17:55 PM »

Went with a Air-variable cap in an MPF102 based armstrong oscillator (tickler type) very easy to build. Feeds a couple of 2N3904s (I think, the dang things seem to shrink more each year) as a buffer.  Works good on the breadboard setup, and is pretty stable for not having been soldered together yet.   Going to get a perf board and assemble it permanently.

Next will be the IRF-510 PA.  Should be good for 5 watts or so.   
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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 #17 on: November 12, 2011, 11:23:07 PM »

Quote
Very simple analog design, but sound pretty good!

Hi Frits,

Just curious why C4 and C5 are in series, or was C4 supposed to go to ground?


Thanks

Phil - AC0OB

Hi Phil,
Yeah, that wasn't really an up to date schematic. The first thing that I changed on it , was dropping C5 and
C4 is just an audio coupling capacitor. I made a few other changes, like dropping R1 all together.

If attached a more update version of the modulator, which all so includes the final stage.
(the rest of the files are in the zip file in one of my previous posts)

Frits


* 4_22_2011-Update.jpg (128.62 KB, 1596x765 - viewed 798 times.)
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« Reply #18 on: November 13, 2011, 09:44:12 AM »

I am thinking a a simple one transistor mosfet oscillator in an Armstrong tuned Drain circuit with a link coupled output into a two section PI filter. A big mosfet with 28VDC on it should make some noise on 75M. Might take some fooling with the biasing and tapping of the coil but it should put up a big signal with a serious Mosfet like one from an old ATX power supply.
Hook this up to your 3055 modulator.

Mike WU2D


* MosfetOscillator.jpg (53.59 KB, 891x699 - viewed 715 times.)
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w3jn
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« Reply #19 on: November 13, 2011, 09:45:48 AM »

Modulated oscillators are great if you wanna piss off everyone else on the band...
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« Reply #20 on: November 13, 2011, 10:00:29 AM »

be just like a PW solid state version of timtron's SBE rig.
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Ed/KB1HYS
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« Reply #21 on: November 14, 2011, 12:31:40 PM »

Mike -  I like the modulated self-excited oscillator idea (I built a tube QRP version for the Net) but one needs a well regulated power supply and there are other issues to tame before it's ready for routine use. They are sensitive to layout and mechanical rigidity (I heard of one you could modulate by yelling at it!) so heavy buss wire and good solid constrution throughout are required.  Also, they can be tough to tune on frequency due to hand/body capacity. 
 
Still, it can be done, and done well, if you want to work a bit at it.  Personally, I think HLRs example is optimised for a different set of design criteria, there are others who run them using 811 tubes and you'd not notice unless you ran your BFO and heard a bit of "wobulation" or if you were running a flex type rig and were watching the screen.

I'd go for it.  With low power on 80 meters, you're not going to bug too many folks while you work out the issues.
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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
ssbothwell KJ6RSG
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« Reply #22 on: November 14, 2011, 10:48:47 PM »

i have to study this thread very carefully. in the mean time, i just want to say that ALL my previous posts have been oriented towards building a rig with similar design specs as Ed's first post. I AM the newbie builder that wants to construct a flea power rig from scratch as an educational project. Smiley

i'm dead in the water on my IRF510 amp but i have i have several working oscillators and small signal amps for 80m and 40m. i really need to troubleshoot my IRF510 design and figure out how to get it producing a clean signal and then learn how to modulate it.

i look forward to digging through and closely studying this thread.

THANK YOU.

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« Reply #23 on: November 15, 2011, 08:35:32 AM »

I have worked Bob, W2ZM many times on 160 with his old buzzard Heising modulated Hartley oscillator.  As long as he kept the audio level down a bit it was amazingly stable and sounded quite good. 

Joe, W3GMS 
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« Reply #24 on: November 15, 2011, 09:26:18 AM »

i have to study this thread very carefully. in the mean time, i just want to say that ALL my previous posts have been oriented towards building a rig with similar design specs as Ed's first post. I AM the newbie builder that wants to construct a flea power rig from scratch as an educational project. Smiley

i'm dead in the water on my IRF510 amp but i have i have several working oscillators and small signal amps for 80m and 40m. i really need to troubleshoot my IRF510 design and figure out how to get it producing a clean signal and then learn how to modulate it.

i look forward to digging through and closely studying this thread.

THANK YOU.



Hi Solomon,
I recommend trying my setup , to drive the Gate of the IRF510 with a single chip.
Before I came to that conclusion , I've played around with driving the IRF510 the analog way with 2 transistors in a so called "push pull" configuration. No problem getting power out of the 510. In the schematic you'll see my attempt to modulate the push pull transistors, but I never got it sounding OK. The trick is to make sure everything is perfectly linear. And dealing with bias potmeters can be tricky to.

Anyway, maybe you can use the idea of the the 2 push pull transistors to drive the gate of the 510.
*Please note that this schematic is without any low pass output filtering*

Frits


* mm2.jpg (105.37 KB, 1141x678 - viewed 811 times.)
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