HFU HF Underground
Technical Topics => The RF Workbench => Topic started by: ff on September 07, 2013, 1613 UTC
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Puff, puff, puff, pant... pant... whew! It took some time but I finally posted the conclusion to Building the Basic LULU on 30 Below. If you've been waiting, I apologize for the delay. Two weeks of jury duty really put me behind on everything. I hope you'll find it worth the wait. Enjoy!
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Just reading it now, thanks for the great post!
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I still have nightmares about a three month stint on jury duty in the late 80's, FF. 6 weeks of it on one f'ing trial.
Yet another reason to never register to vote.
Let me mosby over to blog to see what you've got up on the Lulu.
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I still have nightmares about a three month stint on jury duty in the late 80's, FF. 6 weeks of it on one f'ing trial.
Ugh! Geez Pigmeat - I can't even imagine 6 weeks of that. I sat in the box for a medical malpractice civil suit that had been dragged out by the insurance carrier for over 6 years. Lots and lots and LOTS of 20 dollar medical terms, language, charts, pictures, and expert testimonies... what a friggin' snoozefest. The judge was merciful though. He would recess for 10 minutes about every two hours so we could go back into the deliberation room and stretch, throw cold water on the face, slam our fingers in the door, and any other wake-up tricks that came to mind. Thankfully we came to a consensus on all points in only two days. It ended up being (only) 10 days of torture... ugh!
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Hi all! Thank you for a good explanation about building this small and beautiful transmitter. I try to build one using a scheme posted by mr. Stretchyman (with IRL510, thanks for him too!) I have already done with oscillator and filter parts and now it show about 10-11 Vpp carrier before the filter (measured with 50 Ohm dummy load and nothing connected to MOD input).
I have an public address 60W amplifier and thinking about to use it as an modulated voltage source. It have one 4 Ohm output and two high impedance outs: 75V (81 Ohm) and 100V (166 Ohm).
Also, 120W version of this amplifier have another impedances: 41 Ohm at 70V output - it is very close to 50 Ohm what we need, am I right?
Question is: can I connect 75V PA output dirrectly to the MOD input of the transmitter without modulated transformer?
This is an amplifier's output transformer:
(https://i.imgur.com/ayB8vMP.jpg)
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Hi Roy, I'd suggest winding your own.
Plenty of transformer manufactures in your country (wherever you are??!).
You can buy a bobbin and laminations very cheaply and wind your own.
Alternatively there's a post on her (somewhere?) describing how to use a class D amp as a modulator without using a MT.
It def works but you'll need 24V to get the full O/P rather than 12.
Str.
p.s. the modulating impedance is close to 8R NOT 50R as that's the RF O/P impedance.
Give your tran a try anyway, wont hurt..
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Hi all! Thank you for a good explanation about building this small and beautiful transmitter. I try to build one using a scheme posted by mr. Stretchyman (with IRL510, thanks for him too!) I have already done with oscillator and filter parts and now it show about 10-11 Vpp carrier before the filter (measured with 50 Ohm dummy load and nothing connected to MOD input).
I have an public address 60W amplifier and thinking about to use it as an modulated voltage source. It have one 4 Ohm output and two high impedance outs: 75V (81 Ohm) and 100V (166 Ohm).
Also, 120W version of this amplifier have another impedances: 41 Ohm at 70V output - it is very close to 50 Ohm what we need, am I right?
Question is: can I connect 75V PA output dirrectly to the MOD input of the transmitter without modulated transformer?
This is an amplifier's output transformer:
(https://i.imgur.com/ayB8vMP.jpg)
No, but from what I can remember it simply involves getting another output transformer to place between the output of the amp and the input of the transmitter and flipping the output side of the new transformer to wire it up in reverse.
That's as far as I'm going with it. I wish Fearless was still hanging out here, he could explain it to you in depth in his sleep.
It's a method guys running vintage AM mode gear for pirating are able to feed Hi-Fi audio into those tube rigs. There should be one of 'em wandering around here somewhere
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Drive the 4R side with your audio amp.
Try the 4R secondary but at 1:1 it may not fully mod the carrier
The other impedances are way to high, so I'd try Vcc on the 100V tap and attached the 70V to your RF, may work.
You'll need to check with a scope to see if the carrier is fully modulated.
For $20 you can buy an amp and the mod tranny bits anyway and will be 1/10 of the size of the PA amp thing!
Also 10-11 Vpp carrier (250mW) before the filter is way too low, should be more like 60V p-p
Str.
p.s. checking the orig design, C8 should be 680pF and the IRF510 wont work (you know already) the coupling cap (0.22) MUST BE COG/NPO, forget those crappy disc things just buy some KEMETS.
This cap can be any value and you adjust the series L to suit as it's essentially a BPF on not quite the right freq.
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Thank you all for replies! I'm from Eastern Ukraine. My mistake - I did not apply power to the MOSFET, now with a 12V DC at the MOD (for the test) I have 40 Vpp sinus at output. C8 is 470 pF now. Soon I will make tests with an amplifier and transformers. It seems I beginning to understand how this thing works.
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Cool, sounds better. Check the waveform at the drain for classic 'half sine' class E style. You should be able to get 60+V p-p.
Keep Tweaking!
Str.
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I found transformer from a ceiling speakers like this:
(https://i.imgur.com/kPCBx5o.png)
Result is something like Pigmeat says - 100V/6W side connected to 100V amp output and 4 Ohm side is connected to transmitter. This is modulation I have with this configuration for 1 kHz signal:
(https://i.imgur.com/6NX5Naj.jpg)
Is it something about 50% mod, what do you think?
I still can not receive 60V from a MOSFET's drain - my maximum is 40. I tryed to increase C8 but it give me only few more volts. Maybe I should try to decreese it a bit...
This is how my "drain-sine" looks like:
(https://i.imgur.com/QwdO3Nv.jpg)
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meant to say....
Post up a picture of the unmodulated drain waveform so we can see if it's Class E 'like'
Str.
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On the last picture in the my last post above is the unmodulated drain carrier waveform: https://i.imgur.com/QwdO3Nv.jpg (https://i.imgur.com/QwdO3Nv.jpg)
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The previously mentioned link is here https://www.hfunderground.com/board/index.php/topic,40717.0.html (https://www.hfunderground.com/board/index.php/topic,40717.0.html)
I've got one of those cheesy 15W class D amps from Drok making about 15-17W carrier from a 26V supply. It does the job, and all the stuff is off the shelf. It does exhibit a fair amount of tilt distortion as the amplifier is AC coupled.
+-RH
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Well... I read everything that I could find about class-E amplifiers. Then I tuned my amplifier correctly, so now I have a good "Class-E" waveform as it should be (I used tuning procedure from N. Sokal's documentation). (Also I tried IRF510 and it is work too - in the same way as IRL). But... I still have just about 40 Vpp drain output from a 12V power supply. The whole circuit (oscillator + MOSFET) consumes about 0.7 A of current. I don't understand guys how did you get 10-15W output from this thing.
PS: Did you use this formula to calculate an output power? - P = (Vp * 0.707)^2 / R
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Nearly there.....
12V @ 0A7 is ONLY 8W4 I/P so should give 6-7W with reasonable efficiency.
To Measure power correctly use (Peak to Peak X 0.35)Squared/50. So (40x0.35)sqr/50=4W.
You want around 70V (12W) with 13V8.
I'd keep tweaking.
The IRF wont work with ONLY 8V on the gate but the IRL will.
Tune past the best looking waveform till the baseline starts to rise, you'll get way more power whilst sacrificing some efficiency.
Just squeeze and stretch the turns on the O/P toroid to get max power. Leave off the LPF while you do this, can be attached later and it shouldn't change the O/P much...
Str.
p.s. Check my schematic in the ; 'A newbie question about a transmitter' post
sub a 1nF cap for the 1n5 and remove the LPF. So the RF goes thru the 0u1, 7T L, across 1nF to load, simple as..
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CoolAMRadio - Google-Drive # Special Information folder
Transmitters/Antennas/Datasheets/Service Manuals- & many more interesting items!
https://drive.google.com/drive/folders/1Ut2VGzfKbNttZePKZhX83wg23p7zfq3v?usp=sharing (https://drive.google.com/drive/folders/1Ut2VGzfKbNttZePKZhX83wg23p7zfq3v?usp=sharing)
André
CoolAM Radio - Shortwave
the Netherlands
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Just more old stuff gleaned from th' net.
There's nothing new there at all.
Infact the newest thing there's the FAT5 PA which is actually ok if 10 years old.
Please will folk stop posting this stuff, we've all seen it all before.
MOAN...
Sorry...
;)
Str.
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No problem, but there are always interested people!
And, btw, who are you to tell me not to post these items?
Seems to me, you're posting lots of postings trying to sell
your transmitters!
lol!
no hard feelings!
André
CoolAM Radio
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How TRUE!
However Please show us something we haven't seen.
I see no point in posting circuits that cant be built.
Str.