HFU HF Underground
Technical Topics => The RF Workbench => Topic started by: makeRF on August 27, 2013, 2130 UTC
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Hello all,
I recently joined the forums after being a long time lurker (probably a few years now), and am mainly interested in the electronics / homebrew aspect of radio, but do a fair amount of SWL and general ham activities as well. My favorite past time is building simple transmitters and want to share some of my builds to get feedback and encourage others to pick up a soldering iron and have some fun.
I recently posted on my website an article that would be of particular interest to the community here.
So You Want to Be a Shortwave Pirate
http://makerf.com/posts/so_you_want_to_be_a_shortwave_pirate (http://makerf.com/posts/so_you_want_to_be_a_shortwave_pirate)
Essentially this takes the Michigan Mighty Mite transmitter build and adds on an audio modulator and low pass filter to create a very basic shortwave pirate transmitter that puts out about 1/2 watt. Of course, this should only be used while hooked up to a dummy load!
The circuit is simple enough for novices to build, and is pretty fun to experiment with. Feedback and discussion are welcome!
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I burn wire and scrape with xacto knife too! A simple approximate dipole ought to get over 100 miles with good conditions but will be weak. Then if that works, step up to a 10 watt design which is no more difficult just more parts. And no you won't get a full 10 but it will be over 10x more power.
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Cool.
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@moof Yes, I plan to post a circuit that has additional power at some point. I have a few ideas for posts queued up that I want to cover first. I've built one 10 watt transmitter so far, using the designs posted on the Radio Anarchy angelfire site, which work quite well and has quite a larger signal. That was a good learning experience, as it was my first non-kit transmitter build.
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Me too! Radioanarchy guerrilla was my first try and he was very helpful with my newbie questions years ago. Mine does 3 watts into improvised dipole which to me was unexpectedly low but it runs cool and doesn't need an extra fan. I really like the channel Z design on the yahoo pirate group. Very clear instructions. It does have 1 obscure choke part and some ferrite rods that you can find on hosfelt.com or overseas on amazon. It needs a fan but worked great first time for me every build. Does 6 watts minimum for me. Maybe 8. Maybe 10 on dummy load.
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My first go around with the Guerrilla worked, except it was only putting out 0.5 watts. I put it aside for a couple years, and revisited it again several months ago. Turns out I was using torrids that I thought would work, but had completely different inductance values (whoops!). I swapped out the inductors with the correct values, and had 10 watts into a dummy load. Live and learn.
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Turns out I was using torrids that I thought would work, but had completely different inductance values (whoops!). I swapped out the inductors with the correct values, and had 10 watts into a dummy load. Live and learn.
I feel your pain. I once used what LOOKED like T50-2s from a hamfest table in a build and the same thing happened to me. After checking with an inductance meter and working backward from the calculations, they turned out to have an AL value of 175 rather than 49, indicating #3 material. These toroids were red just like #2s, but should have been gray. "Somehow" these fails from the factory found their way onto that table. I wonder how many other people ended up with non working projects. I'll always love hamfests, but I now pass on buying my toroids there.
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cool new topic - "Black Arts"
- (with a beer in hand) this is me ! !
A few weeks ago I thought of getting back into it, to change
The Guerrilla tx to be a little more simple and reliable to make,
and easier to get parts, by walking into a Radio Shack.
- to make the oscillator with a 2N3906 PNP transistor
- to use Radio Shack p/n 273-102 100 micro-Henry inductors,
at $1.49 each, take the wire off, break them in half to
make 2 inductors out of each.
- and trimmed for operation using 13.8 volts as the supply
and operation around 7 MHz.
I used to get emails about "collecting parts" to build it, and now
I read these posts about the inductor problems.
But good to read that others have made it work.
So yesterday while it was so hot outside down here in the Gulf Coast,
I went at it in my cool air conditioned lab, and easily got a tunable
5 to 10 watts of RF. But did not modulate it yet.
So will fine tune and see what is best here, and will post it.
Those that built it with that last fickle RF transformer output stage
can easily change it to this one, to easily get 7 or so watts out.
the goal here in KISS ! ! ! !
http://www.angelfire.com/de/RadioAnarchy/ (http://www.angelfire.com/de/RadioAnarchy/)
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Thanks for the post RadioAnarchy! The new design sounds nice. If you post it, I for one will build it.
Toroids for inductors aren't too hard to find these days, as Universal Radio has a good selection of values. I'm not sure if they always had these and I wasn't aware, or if they recently started carrying them. Either way, it's a good place to stock up. Not as common as Radio Shack, but purchasable.
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OK, I put some stuff on my website... damn, been 2 years since I did that ! ! !
I will make a better drawing, and info here in the next few days.
so you can change the output of other versions to this one..
OK,,gotta run... we are off to get beer and pizza ! !
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A few weeks ago I thought of getting back into it, to change
The Guerrilla tx to be a little more simple and reliable to make,
and easier to get parts
Hey RA - It's great to hear that you're pitching back in to the Guerilla project again! Your present design is, hands down, the easiest way to get on the air and I'm juiced to see what changes you'll be making. The Guerilla is definitely where any budding transmitter builder should start, and if it could use 100% E-Z-2-find and Rad Shack parts, well, that's about as good as it gets...
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OK, updated my drawing on my website this Thursday evening.
let's see if someone else can make it work!! ! !
make an AM transmitter, or a beacon out of it.
.
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Awesome, looks good! I'm hoping to get enough time to myself this weekend to build it. At the very least I should have enough time to get it started. I'll post results when I have them.
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OK, cool "makeRF"
let us know.
I just updated and made a few more comments about
how to test it and tuning up.
My prototype, as many, was just super-glued to a piece of
copper-clad board. But this weekend I would like to build
another, in a better way, using them Radio Shack
mentioned parts.
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Out of curiosity, do you happen to know the approx uH values for L1 - L3?
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nope. do not know. not much math involved.
Plus I have made so many different transmitters,
I just know what will work.
these class-E switching transmitters are different.
still kinda an experiment.
Actully, when I first started making these with the
IRF510 back many years ago, I cound not figure out my
problems. I did not know there was anything
called class-E amplifiers. or G, or H.
After I learned that stuff, then I figured out
the problems I always have had.
L4 does no matter, as long as it is over a certain amount.
L3 is determined experimentaly, to tune up. there is really no
math formula for what this should be,
L2 does not matter, as long as it is in a certain range,
with a core that works for RF. L2 stores the energy pulse
to be supplied, and smoothed out with C5, to the network of L3 / C6.
L1 was just made to have a high enough reactance for the oscillator circuit
to work.
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OK Brother RA. I have finished my basic Guerilla build. So far I have only been able to get 1.1 watts out of it, but I will continue to tinker. I am powering from a 12V gel cell. The oscillator is putting out a nice 11.6 Vp-p signal so I feel that section is doing its job. With L3 originally 4 turns on a half ferrite, I was able to get a range of 0.9-1.7 watts output, depending on turns spread. At 1.7 watts the final stage was drawing about 420 mA and the IRF was getting hot quickly. Deciding I needed more inductance, I took a WHOLE ferrite and wound 5 turns on it. With a good spread I'm only getting the aforementioned 1.1 watts output. However, now the IRF stays stone cold and is only drawing 280 mA. I feel that with mine, I still need to add more inductance, but I've run out of free time for now. I know that from building many LULUs, the IRF 510s vary greatly and that could be another reason for low output. I'm looking forward to playing some more and will keep you appraised of the situation... 73
BEHOLD! - My messy workbench...
http://groups.yahoo.com/group/homebrewpirateradio/photos/album/2045009962/pic/1809712089/view?picmode=&mode=tn&order=ordinal&start=1&count=20&dir=asc
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"ff" - yes, I changed to a PNP transistor at the oscillator, to cut out a few parts.
so across L1 to ground the signal should go up to at least 5 or 6 V and then go
down below ground level about the same amount.. and it is a dirty signal waveform,
but it works. .
the way I test all this is to put a 47 to 100 Ohm 2 Watt resistor in the place
of where L2 is in circuit with the IRF510 drain. and also disconnect the output network (L3), and
shunt capacitor (C5). then you can see an almost square-wave across this resistor
going from ground to 12 volts. the IRF510 just needs to be ON about half of the time.
with the circuit all together, for C5, from 470 to 1000 picoFarad is OK...
you can take this part out, for another check, but then there will be a big
flyback voltage spike up to 100 volts or so, and the internal protection Zener
diode will conduct. This will clip out positive going modulation.
and the output power, the load on the IRF510 drain is determined by L3 and C6.
so maybe lower C6 to 680 or 470, and play with L3. add more turns then
spread them out.
I have never had any problems getting 10 watts or more output with this type of
circuit, the flyback mode circuit. I just throw it together and it works.
I have made many like this. I will build
another one as this circuit shows in the next few days or so.
also. measuring the output power... into a 50 Ohm dummy load.
and you have an oscilloscope. look for about 25 to 27 volts going
in each direction (50 to 54 volts peak to peak) that is around 6 to 7 Watts.
just some tips, in case somebody does not know.
after all, this is a "Black Art"
.....