Modulated 5W NS40

[Antennae]

I met a guy at a bar a few months ago and we were talking about the FM radio on the shelf. Anyway, it ends up he was a ham.  And at the time, he had a 5-10W transmitter that was meant for morse code, the NS40:

http://www.4sqrp.com/NS40.php

He mentioned that he modulated the NS40 transmitter using the schematic shown below.  He's been testing it on a dummy load using an .MP3 player with pre-recorded speeches of him giving his callsign and calling CQ.  He said he could get audio out.  Also the audio is copied better if its compressed and limited.  But he doesn't think its modulating very well and he wants to know why.  He told a sad story of how his favorite car audio amplifier was destroyed.  It was a 100w amp.  He used an .MP3 player as input and he kept turning up the amp's output that went into the transmitter.  Eventually he was getting good power out as shown by the swing on the tuner's meter. But the amp got hot and died.  Any idea what might be the problemo?

[redhat]

Either the inductance of the 'modulation choke' wasn't sufficient to keep the audio out of the power supply bypass circuity, or the turn on surge made its way into the amp and killed it.  My bet is on the former, because if the input impedance is too low, the amp won't be happy.  Its also possible that there is a shorted turn in the winding of the choke he's trying to use, and that will severely lower the drive impedance too.

+-RH

[Antennae]

Thanks for your knowledge Redhat.  I'll pass that along to Jerry, I was hoping to get some pointers here.  I see him from time to time.  Impedance, he was mentioning something about that.  Like he thought there was an impedance mismatch somewhere.  Say it was an impedance mismatch.  If the .mp3 player's impedance is too low, would it effect the modulation?  I was thinking that the amp getting killed has something to do with the low modulation. 

[redhat]

...A lightbulb just went off.  Have him check and see if the output stage in his dead amp is BTL (bridge transformerless)  If so, shorting the negative output to ground could destroy half the output stage in the amplifier.  BTL is becoming more popular because for the same supply voltage and speaker impedance, it allows four time the audio power (double the voltage swing).

The source impedance of the amplifier is generally unimportant, and under normal circumstances shouldn't bother the amp.

+-RH

[Fred Smith]

Did something similar with Michigan might mite. Used a input transformer which did not work very well. So I fed the circuit with an LM386 AND took the transformer out. Worked ok the wave form look pretty good on the SDR. I've not gotten back to that.project. I just wanted to broadcast in my house in AM. Which it did on about 6925 KHz.

[Antennae]

Redhat, the amp was a Rockford Punch 100a2 from late 90's.  Made in 'merica.  Not sure about the BTL or not.

Fred Smith, I made one of those mighty mites too. It worked. I made the transistor blow because I had a 20w amp in place of the LM386. And it kept sounding better and better as I turned the volume up on the amp until the transmitter quit working. 

[redhat]

I looked at the book for that amp, and its output stage is conventional, but they do warn against tying any of the speaker leads to ground as it may cause 'unstable operation' whatever that means.  There is also a phenomena that occurs during high trough (>-100%) modulation.  Most mosfets have an intrinsic body diode that when the drain-source junction becomes reverse biased, it will begin to conduct like any ordinary diode.  If you try to push the fet beyond -100% modulation (IE push the modulator voltage into negative territory), that body diode will begin to conduct, and the amplifier will see a virtual dead short across its output.  In cases like this, a low value series resistor, 2 ohms or so placed between the amplifier and the transmitter, will prevent the nosedive impedance problems and may have saved the amp.

**Edit** This is another reason why it's risky to feed any transmitter unprocessed raw audio, as you do not have control over absolute peak amplitude, spectral issues and transmitter damage can occur.

+-RH

[Stretchyman]

It's a flawed design especially if you try and A.M. it.

There's NO PROTECTION on the FET gate from back EMF from the modulation inductor.

PLEASE just build a LULU (or preferably buy one from me!!) it's been proven to work and output 10W CW and 40W pep A.M.

There is NO OTHER DESIGN as simple or as good, 1 chip, 1 FET, SIMPLE as it gets.

Also stop using these silly mod trannies that weren't made for the job, just wind a proper one.

Mod amps just use the TPA3116D2, less than $10 and will output 100W with 24V into 2R. Why use anything else?

I ask you!



Stretchy.

[Antennae]

Stretchy,
Hmm, so would a diode help out the FET gate? 

Thanks for making your LULU available.   BUT I think the NS40 is more simple, its inductors are built into the PCB.  NS stands for None Simpler and you can't argue with that because its in writing on their website.  If one were to build your'n, they would need to wind those nasty little toroids while investing in the proper gauge wiring.  Then that person would need to tune them with some test equipment...and don't forget the knowhow to use the test equipment.  And then they would need to wind the bigger toroids with more investment in the proper gauge wire.  The NS40 can do 10W as well if you up the voltage to 12v.  Its lowly transformer happens to handle the FULL BASS from an audio source, can YOUR modulator handle full bass?  Full bass handling makes an operator-friendly transmitter.

[redhat]

His rig is PWM (like all good rigs IMHO) and yeah, it can modulated down to DC with pretty low distortion.

+-RH

[Stretchyman]

Hmm Antennae, where do I start......

Oh & the LuLu design has nothing to do with me, I have simply made a PCB and supply the parts for a kit or sell it built and tested.
However I do advocate it's use as it's an easy to reproduce, stable design with decent power and efficiency.


so would a diode help out the FET gate?  

OK the diode stops back EMF from the inductor taking out the FET gate, do some research, it's a common problem and why the LuLu design has one.


BUT I think the NS40 is more simple, its inductors are built into the PCB.  
NS stands for None Simpler and you can't argue with that because its in writing on their website.

Oh is it, well I can argue as much as I like and can safely tell you there is no such design as simple, as powerful as reproducible as small as the LuLu, simple as!
'Simple' BTW doesn't ness mean 'Good', it usually means 'Compromised' except in the case of LuLu!  

Oh, you want to TX CW, you can do that with a single transistor, actually simpler than the NS40, don't believe what you read, Jeez!


If one were to build your'n, they would need to wind those nasty little toroids while investing in the proper gauge wiring.  

What have people got with toroids? they're simple, the wiring gauge doesn't matter (within reason), anyway that's why I sell it built! Jeez (again)


Then that person would need to tune them with some test equipment...and don't forget the knowhow to use the test equipment.

Yes, well it's about time you got some and learnt to use it as it's essential to the hobby, just having a 'scope (dirt cheap second hand) enables you to actually see what's going on, simple as...and FFS it's not difficult to learn is it, surely that's what this is all about or am I missing something here  

Anyway to 'tune' the inductors you just squeeze and stretch the turns whilst looking for the most power, hardly technical at all!


The NS40 can do 10W as well if you up the voltage to 12v.

Yeh right with a 2.5 W carrier! a world of difference!


Its lowly transformer happens to handle the FULL BASS from an audio source, can YOUR modulator handle full bass?  Full bass handling makes an operator-friendly transmitter.

Yes of course it can, I custom make the mod trannies BTW (Yes it's transformer modulated BTW and Yes I have PWM too but pointless for a 10W, 12V carrier)

Operator friendly? What does that mean?? Also 'Full Bass', WTF?? Please specify??

 
Look Bud, I run a full lab with 26GHz Spectrum analyser (like I'm ever going to use it above 10MHz!), Network analyser, 1GHz DSO scope, Metcal Iron etc.

I've been 'doing radio' for over 40 years, run my own RF TEST company and actually know what I'm talking about, BTW.

So there!

 
 
Looking forward to your reply!
 

[EliteData]

i think it would be easier (at least for me) to build a double balanced AM RF mixer circuit using this integrated circuit > SN16913.
this IC can be used to modulate or demodulate RF and is very commonly used in AM/SSB transceiver gear.
this PDF easily explains the dynamics, functions and operation of RF mixing and modulation > http://www.qsl.net/va3iul/RF%20Mixers/RF_Mixers.pdf

[Stretchyman]

Too complicated and need a linear amp = not power efficient!

Even simpler (similar) method that will also need a linear is described here; 'Amplitude Modulation of the AD9850 Direct Digital Synthesizer'.

So LuLu wins again, no contest.

 

[Antennae]

Well; its not as easy as you think, I figure you are one of those really smart people that can't comprehend people that aren't oriented to electronics like you are therefore you don't understand why they can't do it.   

Constructive marketing; I think there's a large market of people that would like to put a kit together without knowing much about electronics.  It would really help if the thing didn't need any fancy tuning equipment like a oscilloscope. They're the people that just like to put stuff together and don't have the interest or time to study electrical engineering which is pretty deep stuff.  I've scraped the surface with my mental shovel, saw the thick soil, and put the dirt back. But I have money and would like to buy things. If there was a kit out there that had a modular design, like the option of a VFO vs a crystal, a wound modulator vs. a PWM thing, maybe a bluetooth receiver to transfer the music, even the option to add SSB, and of course a powerful amp to top it off. And make the thing usable on different bands to expand the market to hams, THAT would sell like hotcakes. And it kindly introduces newbies into the art instead of scaring them away with advanced stuff. 
Here's a cool transmitter here: http://www.tentec.com/?p=1456, you can plug in a little screen to the arduino part. But you need to ad some software first.  People like plugging in stuff to make it better. 

The bass; so if I play some rap music with heavy bass through your setup, the amp isn't going to shut off? 

Feat of strength; I bet if I took my transformer by the wires, swung it around my head, and whacked your transformer with it, mine would still work and your'n would break.   

[Stretchyman]

I'm not going to apologise for thinking it's simple because it is, just depends who's explain it; a good teacher will make it easy to understand.

There really is very little to comprehend and I mentor and show people on a daily basis.
There's way too much BS associated with electronics and most of it quite basic stuff.

The 'Scope is no 'Fancy tuning instrument' and is basically a volt and frequency meter with two knobs i.e. one more than a standard multimeter, one knob for up and down aka VOLTS and another for left and right aka TIME (1/FREQUENCY).

I totally fail to see what is complicated about that, I really do.

Again way too much BS around and all most folk need is a couple of hours with someone who actually knows what they are doing with no BS or acronym rich bollocks!

Even a Spectrum analyser is nothing more than a radio receiver with a window on it, I bet you've never heard it described so simply! but that's all it is and even a Network analyser is just a swept TX with tracking RX. Anyway I digress........

Constructive marketing, yeh like the phone they're gonna make with all the bits you can bolt on, hmm it wont catch on and neither will your idea as it's not commercially viable.

The idea of building an electronics kit is you will actually learn something, that's the whole idea, to push the boundaries of one's knowledge and progress.

I sell most of the things you mention and even advertised a DDS 64 CH Xtal replacement so you could put your TX on ANY frequency and how many did I sell......

NONE!

I've sold maybe 5 PWM's and they're spot on (built in BPF and compressor now!) and will mod to 500W but everyone (most people) windged and said they're no good for 12V so I made a mod tranny version and have now sold over 80.

BTW you can't just 'add SSB' it's a completely different process and amplification method.

Powerful amp? loads of them on eBay using the BLX LDMOS FET, just get one of those and drive it with 5W, simple, what are you waiting for?

The TX I'm selling works on ANY frequency up to 10MHz so does everything you want, does it not? I sell to Hams also, 80W on Top band with same design!

Yeh the TEN-TEC is OK, oh just checked the front end and it's got a 612, FFS will fall apart on 40m......I really with people would stop using them as a front end mixer they are not any good and you need a passive mixer or the AD831 which is OK.

Bass wise OK, yes my mod tranny / modulator combo is fine and doesn't saturate (TPA3116D2 has built in protection and turns off then resets if this occurs) as I've rolled the bass of below 100Hz (as per many requests BTW). To get down REALLY low you need an enormous >3" core and I just thought it a bit silly for such a small Tx. and Yes I have such a mod tranny if you really wanted one, ANYONE??

SO far, I understand you've got a big mod tranny and met a guy in a bar, hmm.......!

Good luck from me, I'm sure we could go on and on but my technical knowledge is well learnt with much self tuition by trail and error and some top mentoring from the designers of cutting edge radio equipment (mainly phone base station stuff)

I'm only a test engineer (Tech) and have always wanted to build and sell some form of radio kit and I am so my dream is coming true but I fear your dream is but a dream.....

Ahhhh...