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Topics - OgreVorbis

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The RF Workbench / Question about stretchy 350W SiC deck
« on: December 02, 2019, 0203 UTC »
Hey stretchy,

I am back at the shortwave transmitter again. I've had it working great below 4 MHz, but now I am back to trying to make it work higher again. I thought I had it at 87% efficiency, but I looked on a spectrum analyzer and it's terrible. When I run it next to the filter, then it's great, but only 76% efficiency @ 6.8 MHz. I am almost 100% sure it has to do with my broadband output match.

Anyway, I'm thinking about buying your SiC RF deck. The 350W one with 4 fets I believe. How much would that cost?

I know you use those T200-2s. What else do you have to match the output beside the transformer?
Yours is not wideband, right? you have to tune it to the band?

General Radio Discussion / Direction finding of a skywave signal
« on: October 29, 2019, 0906 UTC »
With all the shortwave pirates here, I am curious about how easy it is for the FCC to direction find a skywave signal. I would assume it is much harder than for VHF bands. Is it really even practical to do on a vehicle?

The RF Workbench / C-QUAM stereo on PWM TX
« on: October 29, 2019, 0045 UTC »

Redhat, your mention of c-quam with a PWM transmitter got me interested, so I thought I should make a separate thread about it.

As I understand it, you modulate the PWM as you normally would with left and right channels mixed together. Then for the c-quam, you need a device that will offer a phase modulated TTL square wave and you feed that in where you would normally have your crystal oscillator?

Do such devices exist? Could a regular part 15 100mW c-quam transmitter have this extracted from somewhere in the circuit or do I need to build my own device that produces it?

As a side note: It also got me thinking - what would happen if you got two PWMs and fed each side of the amp separately (assuming push-pull design)? would it make an ISB type stereo?

The RF Workbench / NCP driver sucks
« on: October 13, 2019, 1749 UTC »
I'm on my 4th revision of my PCB and the first one was the best. On the first one, I used TC4452 because I didn't know about the IXDD614 at that point. After that I found out about the NCP and thought it would be better than the 614 and so I built my last three PCBs based on it. It was a big mistake and I wasted so much time on it and now if I want to use the 614s, I have to basically start over at square one. So I am giving up for at least a year. It pisses me off because I'm not the type to be able to put something like this down, but it's not worth it to get angry over something like this.

BTW: The waves going in and out of them are square as can be (as square as the crystal source which is connected with very short straight traces).

So what's wrong with them?
1. They get dangerously hot at 12V and above - they may do 15V with a heatsink on top, but they were emitting a smell like they were about to pop (and I did pop several).
2. The datasheet (especially the truth table) is either just really confusing or the design is just wrong. Based on the truth table, there is no way to use the inverting input as the output will always be low. I found this to be the case in practice also.

So yeah, I think it will work with GaN cause they only need about 8V, but if you got it working with SiC at higher voltages, then you must have magical powers.

So for now, I'm just going to use my original design board that works good below 5 MHz. I guess I won't be on the 'fun' band any time soon lol  :)


Here's the datasheet: https://www.onsemi.com/pub/Collateral/NCP81074-D.PDF

Truth table page 5.

The RF Workbench / IXYS-RF better than GaN?
« on: October 07, 2019, 2256 UTC »
I just came across these mosfets that are designed specifically for class D or E amplifiers. I knew about SiC and GaN being good options, but I didn't know they made fets for this specific purpose. Do you think they would be better than GaN? The RDS on doesn't look as good as the Gan, but what do you think? Maybe it's just older technology being advertised for this purpose?



They're kind of expensive, but I might try them at some point.

General Radio Discussion / Are there no radio laws in Greece?
« on: October 06, 2019, 2041 UTC »
There are so many pirate rig builders in Greece. Specifically AM, but I see a lot of HF and FM stuff also.
Does anyone know the details of this?

The RF Workbench / Class D output match
« on: September 02, 2019, 2050 UTC »
Hello Stretchy and Redhat, I'm back.

I am going to change the output match on my transmitter to T200-2 or T200A-2 because the binocular thing is not working very well.
I am not sure how to do the windings. How many turns? Maybe either of you have a photo of how you wrapped it.
If I am doing class D, I shouldn't need any other components for matching, just the balun?

Is this how it's done?

Thanks  :)

Equipment / Inverted L ground plane
« on: August 28, 2019, 1059 UTC »
If I have an inverted L, is it better to put most of the radials under the horizontal section? Should I just use a normal circular pattern around the antenna and don't emphasize under the horizontal?

Should the radials under the horizontal extend out more (as if the end of the horizontal is the center of the antenna)? This should form a jelly bean type shape.

Aside from that, it there anything you would recommend for an inverted L (not to purchase; ideas)?

For Sale / Wanted / Looking for AM broadcast monitor/processor
« on: August 21, 2019, 2017 UTC »

I am in need of an AM broadcast monitor/receiver. It does not necessarily need to be a professional unit you would find in a radio station studio. I just need a high quality AM receiver with flat response up to 10 KHZ. More would be nice, but not necessary.

A real broadcast monitor with % modulation would be nice, but I am only wanting to pay a couple hundred or less.

I am also interested in an AM broadcast processor. I already found something that pretty much fits the bill, but if any of you have any suggestions, I'd be happy to hear them.

Equipment / Inverted V yagi aiming up into the sky
« on: July 19, 2019, 0147 UTC »
So I'm curious why I have not seen this type of antenna before. Basically what it would be is 3 or more inverted Vs stacked on top of each other along the length of the mast. I've seen something somewhat similar with inverted Vs, but not aiming upwards. With HF, we want the signal in the ionosphere, so why not aim it up? Why do hams always aim their yagis horizontally?

And when I say aiming up, I want to be clear. I do know that hams mount horizontally and vertically which is not what I'm talking about. I mean the yagi is pointing up into the sky. I figure with a dipole, the radiation angle wouldn't be right, but with an inverted V I think it would. Plus, it is much easier to install.

The RF Workbench / Class D V2.0
« on: June 22, 2019, 2041 UTC »
So I have finished my new design with the NCP drivers and eight SiC FETs and I tested it. I am having a bit of a problem with it. Some of the NCPs are heating up and eventually blowing out. It is not happening on a single side of the amp. I currently have only four of the eight FETs along with four drivers populated and two of the four drivers keep blowing out.

Do they need to be balanced somehow? Maybe a current limiting resistor. Right now they are just running in parallel with the 5V square wave drive.

I left out R3 - R6
Here is the schematic:

Equipment / Looking to upgrade - SDR or traditional?
« on: June 15, 2019, 1038 UTC »
So I spend most my time building and experimenting with shortwave transmitters, but so far my experience in the receiver department has been limited. I currently have two receivers. The Tecsun PL-360 and this Chinese SDR: https://www.ebay.com/itm/RTL2832U-R820T2-chip-Set-100KHz-1-7GHz-UpConverter-HF-UHF-VHF-RTL-SDR-Receiver/132465613216

I'm looking for something with very good receive sensitivity. I am not sure whether I want a traditional radio or a better SDR. It is nice to have that spectrum analyzer type view, but my main focus is on sensitivity. I am not looking to spend very much < $300.

The Airspy HF Discovery looks good. What would you recommend?
How does an SDR perform compared to a Double or Triple conversion superhet?

These traditional receivers look good, but they are a little above my price point: Alinco DX-R8T or ICOM IC-R75

So I'm interested in finding out if there is anyone under 30 y.o. on this forum. It seems to me like the only people interested in this hobby are older (maybe 50-60).
If you are younger, how did you get into the hobby?

For me this all started with an interest in computers which then moved to electronics and then to radio.
I was somewhat interested in radio when I was only 15 y.o. but I didn't have the skills required to do anything really interesting.

The part where I think I differ from most people who are into radio is that I am not into it to make contacts or to do other ham-like activities and I am not into it even to play music (but that's part of it). There is just a huge excitement I get from putting out the waves and knowing that it's going very far. The physics of it just makes me really happy. Am I the only one who's like this?

The RF Workbench / Beginner class D design
« on: November 12, 2018, 0104 UTC »
As I am building the transmitter discussed in this thread, I decided to document the progress on my blog. If you're looking to build your own class D, check it out. There is a massive archive of PDFs and schematics in there as well as an in depth explanation. I am not as experienced as some here, but I always update any inaccuracies. I also approach the topic from a novice's perspective.


Original message:

I am trying to gain a better understanding of a class D transmitter, and while I do understand most of the concepts, I need a little clarification.

So I am probably going to start with this design: http://www.w1vd.com/40M375WclassDRev2.0.pdf
Yes, I know it's old. And I think there might be some parts left out. It looks like there is an unlabeled resistor at the gate of each FET.

First thing I am not clear on is if the exciter needs to be biphasic in order to make a class D or E amp. You can see in the schematic I linked that it has phase 1 and 2 input and it says 12V, but how many amps does it need (on the input)? Can I build half of the amp and use a normal single output DDS module? I am not sure how to make a two phase exciter. I think class D is more broadband, so I want to go with that. I'm still not even exactly sure what the difference is between D and E despite them being described so often. I never find a clear difference.

So when I have the amp and exciter built, I think I'll start trying to drive it with a mod transformer instead of PWM just to start because it's easier. So how many ohms do I need to match right at the drain of the FETs? Is it 50? No, probably not because that's after the matching right? So if I use a generic audio amp, what transformer ratio do I need? I think I'll use a microwave oven transformer. I have one that has all coils removed, so it's just a bare core I can wrap around.

If I need a two phase exciter. Where can I find one? I do know about the classeradio.com guy, but he only sells the PWM and not the exciter. He didn't respond anyway. Probably because I'm not ham.

And, yes, Stretchyman, I know you're here too. Your transmitter is tempting, but I don't want to just buy it without understanding how it works because that gets annoying in the long run.

Would you mind explaining a little to me? Mostly on how your DDS module works (I assume you use DDS). Is it a two phase thing or is it essentially just a 9850 and a PIC on a board - like what you can get on eBay? I would really like to see the schematics and also if you can clarify how the exciter module works. If you'd like a small payment for your schematics, I'd be willing. I'd just buy the whole thing if you can tell me how to change it for more bandwidth.

If I was building it myself I'd have used Class D for more bandwidth, so it's not perfect from my standpoint. What about your amp makes it Class E and could it be changed to D? I've seen a class D 100W amp that was using two SiC devices and it works 3-8 MHz. What makes yours only 200 Khz range?

I know that's a lot of questions and I am being very critical of the design. I know it is better than most others out there given that it's using the newest GaN and drivers. I hope you understand I'm am trying to learn w/o just buying stuff and wiring it up. That's too easy for this hobby and it makes it boring.

The RF Workbench / PWM a BLF188XR?
« on: November 10, 2018, 0744 UTC »
This may sound like a stupid question to those who know more about RF engineering, but...
Why have I never seen an RF MOSFET PWM modulated or other high level modulated?
They are always used as linear amplifiers.

I have a BLF188XR amplifier board and I was wondering if it is possible to modulate it this way? Is low level modulation the only option with this?
Why does every PWM use GaN or SiC or those IRFP (whatever they're called)?

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