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Author Topic: LULU Modulation article posted in 30 Below  (Read 2438 times)

Offline ff

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LULU Modulation article posted in 30 Below
« on: September 07, 2013, 1613 UTC »
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!
Hailing from the upstate boondocks region of the progressive paradise which once was New York State

Offline ChrisSmolinski

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Re: LULU Modulation article posted in 30 Below
« Reply #1 on: September 07, 2013, 1629 UTC »
Just reading it now, thanks for the great post!
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 270 ft west-south-west beverage / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop

Offline Pigmeat

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Re: LULU Modulation article posted in 30 Below
« Reply #2 on: September 09, 2013, 0525 UTC »
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.

Offline ff

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Re: LULU Modulation article posted in 30 Below
« Reply #3 on: September 10, 2013, 1315 UTC »
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!
Hailing from the upstate boondocks region of the progressive paradise which once was New York State

Offline ROY

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Re: LULU Modulation article posted in 30 Below
« Reply #4 on: October 30, 2018, 1711 UTC »
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:

Offline Stretchyman

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Re: LULU Modulation article posted in 30 Below
« Reply #5 on: October 30, 2018, 1749 UTC »
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..
'It's better to give than receive' so why RX when you can TX!

                            Buy one from me, NOW!

Great discounts on ALL my transmitters if purchased via HFUnderground


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Offline Pigmeat

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Re: LULU Modulation article posted in 30 Below
« Reply #6 on: October 31, 2018, 1455 UTC »
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:


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

Offline Stretchyman

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Re: LULU Modulation article posted in 30 Below
« Reply #7 on: October 31, 2018, 1546 UTC »
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.
« Last Edit: October 31, 2018, 1608 UTC by Stretchyman »
'It's better to give than receive' so why RX when you can TX!

                            Buy one from me, NOW!

Great discounts on ALL my transmitters if purchased via HFUnderground


                                              ;)

Offline ROY

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Re: LULU Modulation article posted in 30 Below
« Reply #8 on: October 31, 2018, 1957 UTC »
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.

Offline Stretchyman

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Re: LULU Modulation article posted in 30 Below
« Reply #9 on: October 31, 2018, 2109 UTC »
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.
'It's better to give than receive' so why RX when you can TX!

                            Buy one from me, NOW!

Great discounts on ALL my transmitters if purchased via HFUnderground


                                              ;)

Offline ROY

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Re: LULU Modulation article posted in 30 Below
« Reply #10 on: November 03, 2018, 2148 UTC »
I found transformer from a ceiling speakers like this:



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:



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:

« Last Edit: November 04, 2018, 1213 UTC by ROY »

Offline Stretchyman

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Re: LULU Modulation article posted in 30 Below
« Reply #11 on: November 08, 2018, 0756 UTC »
meant to say....

Post up a picture of the unmodulated drain waveform so we can see if it's Class E 'like'

Str.
'It's better to give than receive' so why RX when you can TX!

                            Buy one from me, NOW!

Great discounts on ALL my transmitters if purchased via HFUnderground


                                              ;)

Offline ROY

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Re: LULU Modulation article posted in 30 Below
« Reply #12 on: November 08, 2018, 0854 UTC »
On the last picture in the my last post above is the unmodulated drain carrier waveform: https://i.imgur.com/QwdO3Nv.jpg

Offline redhat

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Re: LULU Modulation article posted in 30 Below
« Reply #13 on: November 08, 2018, 1657 UTC »
The previously mentioned link is here 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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