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Topics - OgreVorbis

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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)?

MW Free Radio / UNID 1720 AM ~0445 UTC 11 Oct 2018
« on: October 11, 2018, 0532 UTC »
Did anyone hear it?
Begins with a carrier on and off and then music.

Software / Pitch shift idea
« on: July 06, 2018, 0020 UTC »
So I was thinking about the limitations of audio bandwidth for broadcasting. I was wondering what it would sound like if instead of filtering at something like 2-5khz (which is around the standard), you instead pitch shift down everything above that. I don't mean pitch shift everything, just what is above where the filter cuts off. What would this sound like? Clearly it would sound lower, but would it improve the quality of the music without using more bandwidth?

Also is this possible in any software (like audacity maybe)?

Equipment / AM broadcast pirate PWM
« on: May 01, 2018, 0410 UTC »
I am making this post to show some good options if you're looking to pirate on AM broadcast band and are not skilled enough for home-brewing a transmitter.


Broadcast Announcements / Testing CW on 14400 khz
« on: September 05, 2016, 2117 UTC »
I'm testing 15W CW on 14400 right now in east coast US. Maybe later AM.

General Radio Discussion / Why 69xx kHz?
« on: May 03, 2016, 0055 UTC »
So I'm new to this forum, but not to pirate radio in general. I pirated before on 1710khz, but the antenna construction is hard and I never seemed to get out very far (plus the ground conductivity where I am is really bad).

Anyway, I want to try pirating on HF and I'm wondering why most people use 69xx khz because for me it would be much easier to make an antenna for around 10-15 MHz. Does anybody listen for pirates around those frequencies? Do they get out as far?

See the graph on this site: http://www.voacap.com/antennas/squeezing-decibels-out-of-dipole/

You can see that if I created an antenna for 10-15, it is very doable to get the peak gain out of the antenna based on the distance from ground. However, if I were to use 69xx, it would be very hard for me to get more than 40ft from the ground and so not much gain...

So would pirating around 10-15 be better?

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