Solid state 20M with VFO and CW/AM

[ve3lyx]

I am working on a solid state transmitter project. A freehand build (no schematic)
I have the MPS102 osc built , a classic Hartley, permeably tuned, fixed capacitance. I have the NPN buffer built and am trying to come up with a non toroidal broadband deal to couple it to my C1760 driver transistor . I need the coil there to install my loop modulator for AM as is in my Crystal controlled 80M rig. I have it covering the entire 20M band so CW and AM should be good. Havent picked a final amp yet. This is a spare time project but seems to be marching along anyway.
Don

[ve3lyx]

Starting to come together. Slug tuned osc coil with its fixed cap is in front. Green coil for coupling the buffer to the driver stage is mounted and is  low Q deal which will hopefully allow sufficient wiggle that set will work well. It has a link coil right next to the main coil which feeds the driver  hopefully resonbly well. Outboard of that is the Absorption coil (twisted wires feeding out) which will provide the AM function when desired.  The PA will probably wind up on another board.
Don

[ve3lyx]

Been working on it a few parts per day. I changed my mind and put my final amp on the same board. and it is almost wired in completely. Emm resistors are in and bypassed for both the driver and final. Emm resistors are an old trick , (Christmas bulb) as the value works well and I have a couple of hundred "in stock".  I have decided to shunt feed an outboard PI network for the final and that will be a separate board. (or simply mounted to the project case. ) Soon will come the hard part trouble shooting the design and getting it to run. Should be able to get close to 5 watts out and on 20M that is like a KW on 80M.
Don   
I should mention I found a C2029 transistor for my final. 

[ve3lyx]

Been tempted to pair as set of finals but keep telling myself. "Discipline son. Don't get carried away. This is QRP after all." My friend Geoff VE3XFE has been working long distances on SSB at 500 Milliwatts on his Icom. It is his success that has spurred me on in this project. He wont even try 5 watts. Says "Nope, only 500 mils or it doesn't count."
Don

[ve3lyx]

Did some more today. Getting close to the smoke test.
I need to go over the whole circuit and find and fix all my errors. Probably should draw the schematic first now that the design is established.
Don

[ve3lyx]

did a bit more today. Getting nearer the sink or swim moment
Don

[ve3lyx]

Its alive!
Fired up the osc and buffer today. Seems good. Have to make the output circuit bfore \I power the driver and PA.
Don

[HA5DI]

Don

is AM allowed on 20m? In Hungary (and I think in many other countries including EU) bandwith is limited to 2.4 kHz on HF, so both AM and DSB are ligally prohibited

Regards... Béla

[ve3lyx]

Yes any form of phone is permitted with us here in Canada. I did a good search. Bandwith must be within normal limits. Us AMers try to stay in our own AM window if at all possible so as to allow others equal enjoyment. I am sorry to hear 20AM is not allowed in Hungary. What bands is it allowed?
AM gets a bad rap. If you operate AM much you soon discover it is not Am that is using huge portions of bandwith. You can park two nets with in 5 KHz (good example is the 7290 7295 spots on 40m) The two will carry on round table groups simultaneously and never hear or bother each other.
I have been exploring a type of AM from about 1917. It works well and is easy to implement. It would be the go to system in an emergency and it can be rigged in a few minutes. It appears to me to have a very narrow space. It looks different on MY monitor scope then my normal AM transmitter. You have to be right on top of it to hear it.
However this rig will also do CW so we can still work! I also work a fair amount of SSB however I don't have a QRP friendly SSB rig
don
Further to todays success. I need to install at least one RF choke. I made the final LC circuit today. it may not work but I saw something similar on a old Collins transmitter so for the extra hour or so it took to make it I figure it is worth the shot. I want it to be broad enuf no tuning is required but narrow enuf no harmonics escape. I used my GDO to establish the coils. now I need too find the c needed to pull them into range which will also bring impedance in the ballpark. When I have it all sorted out the schematic will be here. I find it fun jumping into a project like this and digging my way back out. As always one learns a lot in  a hurry.
UPDATE
Powered up the last stages. Seems good. Used a poly vary cap to tune my T network but it appears to work and tune smoothly. Need to wire up a CW key for the driver. May leave the driver with some voltage on but not enuf to run so the hit isn't so big. Need to decide on a project case. I am leaning towards a metal recipe box.
Ran the PAs on a 9 volt. They killed it in minutes but output to that point (battery death)was decent .
I am encouraged so far. Time to clean up, mount, etc. I will leave the AM jack till I have it mounted.
I made a T network for output and put a single cap to ground at the centre connection to tune it. Appears to work as I had hoped. Time will tell.

[ve3lyx]

Did some biasing and then some testing. Seems pretty strong. Driver keys well but needs some RF choking in its trigger line. Still a few questions to sort out. Testing of PA was done with a nine volt which quickly became a 5 volt however was still working. Rig is intended to run on 12 Volts. It is at the ugly stage now. Needs a strong well shielded cabinet. It has  strong carrier on this voltage. Almost afraid to give it 12v with sufficient amps.
don

[ve3lyx]

XYL came up with a cabinet. A recipe box from the $ store. (metal.)
I started fitting it in. Black knob is for tank final tank tuning. Stub from slug tuned coil on the other side which will get a custom made knob. Top hole will be for microphone bottom for CW key. Time to quit for the day. I use the cabbage rule here when building. "Quit while you're ahead"
don

[HA5DI]

It is allowed on 29MHz and up

I am sorry to hear 20AM is not allowed in Hungary. What bands is it allowed?
AM gets a bad rap. If you operate AM much you soon discover it is not Am that is using huge portions of bandwith. You can park two nets with in 5 KHz (good example is the 7290 7295 spots on 40m) The two will carry on round table groups simultaneously and never hear or bother each other.

[ve3lyx]

Aside from the transmitter section I designed and built a receiver for use with this style of transmitter. It was featured on DX Unlimited from RHC in January. It started out as an experiment just to test absorption loop control of regeneration in a regen receiver which was a natural outgrowth of the loop modulation experiments. The design was patented in the UK about 1926 by WA Clough and was off course a tube type regen. Not wanting to shell out any gold I built an Armstrong circuit regen using a MPS102 Jfet. I added a NPN audio amp , a very simple device , three resistors and two caps. Not having a spare variable cap I used a ceramic slug tuned coil and used a 221pf cap to bring it in freq which at this time was 80M. The combo of the passive control of regeneration and the permeability tuning produced a real good receiver from the git go. two transistors but it copies SSB with unbelievable ease and tunes nicely. Once the 25K pot that absorbs excessive feedback to control regeneration is set it almost never requires touch up across the whole and.  This is just my initial excursion into this so I am sure there is lots to be learned.  It will copy anything my TS830s copies and was much easier to tune SSB signals in.  Drawbacks? I live near a MW broadcast transmitter that recently modified their guy wire filtering (cheaper) and the station is sometimes overpowering here. A solution was to use a separate listening antenna since I don't the whole inverted Vee to hear and to short the tx antenna during receive with the bottom section of the rx tx DPDT switch. I will be brutally honest. This was an unplanned and accidental success. I was merely exploring all venues of absorption loop use to be sure I had it covered.
don

[ve3lyx]

 I had it on air just now. No takers but it tunes well and loads . The final tunes about centre of the control for 14056 where I tried it with a well defined peak. It drifts a bit as it warms up but I think I can deal with that to minimize it.
I may remove the Am part as it would take a minute. I have yet to hear any AM on 20m QRP or QRO.
I will give it a week and then decide. I have to find the 20M CW hotspots for QRP.
don

[ve3lyx]

Its done. Haven't had a QSO yet but it is working, puting out decent power and I have the AM function working. That is a side deal and not the radios main function. Just something I can do if need be. Rig still drifts on warm up but not bad now. Decent caps will probably cure most of that as I have dealt with all the other issues I know how to fix including letting the OSC loaf which keeps it reasonable temp wise.
Circuit is a Hartley osc with a MPS102 Fet. Cerrmic slug tuned coil wound for 20m and a fixed cap used to bring it on freq. After that all tuning is with the slug screw which protrudes from the front with its own knob. The osc drives a 2n3725 NPN transistor through a 56pf cap. It is biased on the base by a 68k over a 22k resistor connected in normal fashion. The Collector feeds a broadbanded coil which is mostly just coil and needed only a wee tiny cap to bring it in range. (10pfs). It moves nicely as the rig is tuned from osc. It drives a C1760  driver NPN through a 10 turn link wound on the end of the broadband coil.
A Christmas light bulb provides it protection and also functions nicely as a visable code indicator when keying. This stage is keyed (osc runs all the time when tx is on. ) A carbon mic plugged into the key circuit provides emergency AM if desired. The driver drives a C2029 transistor thru a 100pf cap . That drives a T network tuned in  its centre by a poly cap from a junked transistor radio. It works quite well. I never tried it before but saw it on an old Collins transmitter so tried it. Works like a PI but need only one cap.
Hope to work some of you on air. Am hanging around 14050 to 14060 when time permits.
 
don