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Messages - OgreVorbis

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1

i'm 24 and probably come here from a different path than most of you. i'm not into amateur radio and have no interest in transmitting. i got interested in radio as part of my greater interest in the electromagnetic spectrum. i'm an astronomy major and though i have always been fascinated by the sky as a girl scout we got a visit of a grad student from the local university's astronomy program. the way she enthusiastically talked about electromagnetic waves as distant info messengers sounded like magic! from that moment on i knew what i wanted to do. she sort of became my mentor and we exchanged a lot of emails! she's now a radio astronomer and has been to some pretty exotic places like the atacama large millimeter array in chile!

i experimented for awhile and learned the rtl dongle while good for vhf and above was not the best for HF so i bought an sdrplay rsp1a from ham radio outlet about a month ago. it was a definite upgrade and so now i'm looking to upgrade my antenna. i don't have a lot of space and learned there are some compact antennas like the mini whip and magnetic loops (maybe too expensive for me on a student budget). most of all i want to take down the wire in the house lol so any advice on how to replace it would be great. there is space to mount a compact antenna outside so that is my next step.

on a personal note i was reluctant to post here as most of the people here are old enough to be my dad or in many cases grand dad and i hadn't come across another female but i at least found a thread with some people closer to my age.

btw: we dont just listen to lady gaga and justin bieber, most of us listen to everything and have tons of spotify and/or pandora playlists.  don't hate me cause i like ariana grande and charlie puth ;)

My family has a background in astronomy and my dad's first major project was building an observatory for a university. I am into radio purely because of it's interesting properties. I've thought about connecting the two areas, but I'm more concentrated on my HF projects now.

Anyway, it really depends on exactly how much space you have, but a full size antenna is always best. There really is no good way of cheating the system and making something smaller that works better. You may find something decent, but not better.

It's fun to take advantage of the surrounding resources in a clever way. Like for example if there is a large metal fence or water main, you can use that for grounding a 1/4 wave vertical. Using a slingshot or crossbow to launch fishing line into a tree and then raising the antenna with that is another way.

If you don't have any grounding resources, then my opinion is to go for an inverted V. The cable goes up a tree to a branch and the two lengths of antenna slope down to the ground (it's a sloping version of a dipole.)

Good luck and don't feel intimidated to come back :)

2
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

3
The RF Workbench / Re: Simple SiC TX
« on: June 15, 2019, 0524 UTC »
Same ones I'm currently using, C2M0080120D's and C2M0045170D's.  Of course its all theory until you build one... 

A big part of the problem in getting above 1KW is the thermal management.  Large bonded fin heatsinks and fan capacities over 200CFM become mandatory, especially for gear meant to survive operation in outdoor summer conditions.

It will be quite the feat when it is running.

+-RH

https://www.fischerelektronik.de/web_fischer/en_US/K%C3%BChlk%C3%B6rper/D/L%C3%BCfteraggregate/index.xhtml

These are a bit pricey, but it's a good company and they have everything.

4
The RF Workbench / Re: Simple SiC TX
« on: June 14, 2019, 0028 UTC »

Sometime in the future a new PA layout is in order...2 RF fets for 1.5KW, 4 for 2.5KW...carrier that is.  5KW in 5 rack units, for the power modules anyway....wow.

+-RH

What FETs are you talking about? What frequency? That's an insane amount of power. Is this some design you are currently working on?

5
The RF Workbench / Re: Simple SiC TX
« on: June 12, 2019, 2307 UTC »
HI folks

Ok, undestood. Thanks for the advice.

The main issue is not the size of the components but the fact that I cannot buy the new-and-faster ones here. They are unobtanium for me right now.

There are some ixys that are mentioned elsewhere in the forum that maybe I could get.

Cheers.

I know from personal experience that the 4422's are no good above 5 MHz. The NCPs I am about to test in a few days.
If you can't source those, then get the IXDN614's. I know these work at 7 MHz if the board is done right.

6
The RF Workbench / Re: Beginner class D design
« on: June 12, 2019, 2122 UTC »
I have resumed work on the project. It is very near completion. I just need a good heatsink for the FETs and I'm searching for one now. I want a cooling aggregate type.

I still don't know what to do to the transformer when I add another pair of FETs.

Do I change nothing?
Do I need to add another winding on the secondary?
Do I need to add more than four cores for eight FETs?

7
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?

8
The RF Workbench / Re: Beginner class D design
« on: April 15, 2019, 1734 UTC »

To drive a High side and Low side Devices I guess? Or tie them together for single FET. Just use a dual Inverter from the O/P of your Osc. Sine in and square out, inverted and double inverted to drive either side.

Str.

Sorry, I don't understand the term "high/low side device". Does this mean the devices on one side of a push-pull amplifier (like what I'm building)? So then I don't need an inverter. Just use the NCPs?

9
The RF Workbench / Re: Beginner class D design
« on: April 15, 2019, 1119 UTC »
See last two posts.

I realized after my design that it looks like the NCP drivers have an inverter built-in. The truth table in the datasheet makes it look like it won't work for this purpose though, but I don't know why else they would have such a feature. Is this to use in a push-pull amplifier with one square wave input? If so, then I don't even need the inverter :P

10
The RF Workbench / Re: Beginner class D design
« on: April 14, 2019, 2359 UTC »
Do you have any spare boards to sell although I believe you'll need to re-do them should you decide to use the above drivers. So cheap now I'd gladly contribute to any updated board.

I forgot to answer the question. Yes, I do have 4 more of the old PCBs left if you want one. I don't have time to sell a parts kit right now though. Maybe when I finish development and I'm at a good stopping point.
I've been looking to sell them anyway. They work perfectly up to 5 MHz, but no higher. This new design you see above should do 10 MHz easily, I hope. . . I can also easily swap the MOSFET pins to make it work with GaN devices in the same package. If it works, then I will also sell a GaN version of the board. The cheapest GaN to work with it costs about $20 each and the SiC are only $3.50.

11
The RF Workbench / Re: Beginner class D design
« on: April 14, 2019, 2347 UTC »
OV,

Here is Nigel's (VE3ELQ) response to my question re driver chips;

"The best RF deck FET drivers I have tried by a wide margin are the NCP81074A.  With a Tr/Tf of 4 ns, matched delays, and 10A of source/sink they are both super fast and capable of driving higher gate C FETs. No problem with the 150pf SIC FETs at 7.3 mhz or the newer GaN FETs.  They are inexpensive and small so I recommend 1 driver per FET up nice and close to keep the gate lead as short as practicable. They work great.

https://www.onsemi.com/pub/Collateral/NCP81074-D.PDF"

Do you have any spare boards to sell although I believe you'll need to re-do them should you decide to use the above drivers. So cheap now I'd gladly contribute to any updated board.

I do like the look of your 8 device boards.

Transmitter Man

My new updated board should be here for experimentation in a few weeks.
RH: I tried that logic circuit that you posted. I'm assuming this is to prevent cross conduction. Well, I tried it with the 74LS86 and a 74HC04E (didn't have the 7406) and it doesn't seem any different than my simple circuit with 74AHCT14N, so I stuck with that for this design. It does cross for a couple ns at a really low level, so I think it's OK.


12
The RF Workbench / Re: Beginner class D design
« on: March 25, 2019, 1846 UTC »
I'm on my way with the updated design and I have a few questions.

I have this audio amplifier: https://www.parts-express.com/wondom-aa-ab31242-1x600w-class-d-audio-amplifier-board-(t-amp-technology)--320-3346

It is a class D design and I was originally going to use it with a transformer, but I think I may be able to use it directly. What do you think?

Here is the datasheet for the IC it is using: https://www.ti.com/lit/ds/symlink/tas5630.pdf

So I have to check if the ground is isolated, right?
Then I need to apply whatever voltage I need for the carrier at the ground?

Is this how it should be done?

My other question is about the inverter circuit. I don't have too much experience with logic circuits, but I know I probably need one of these: SN74HC132N, SN74AHCT14N, or CD74HCU04E
Which should I use? I am going to use it along with a crystal oscillator to generate the inverted wave.

13
The RF Workbench / Re: Beginner class D design
« on: March 07, 2019, 1703 UTC »
I just had a thought. Is there a reason why there is always PWM to the drain of the mosfets? Why not apply PWM into the drivers instead and eliminate a separate PWM board. Why is it not done this way?

14
The RF Workbench / Re: Beginner class D design
« on: February 28, 2019, 1451 UTC »
Using the NCP drivers which are super fast BTW, I've never bothered with any dead time adjustment and driven the gates directly from both O/P pins, DC coupled with NO RES.

Mind you I have been using the GaN fets, again super fast, but previously used SiC and they were fine only having to use 15V rather than 6V as the driving Vcc.

Again I'd point you toward the article on AMFONE, there's even better FET drivers now with an RF isolated barrier (what next!) but the NCP jobbies are fine.

Str.

I looked at that amfone link, but it lead me to an image. I managed to get the thread from the URL, but I didn't find anything in the thread discussing a better driver than the NCP. What is the name of it?


On my new board I need to make sure that I have enough space for my output transformer. Can I use only 4 cores for 8 fets? Would I just need to alter the windings to compensate or will it overheat or not match? If not, I asked before, but can I stack the cores on top of each other? This should be the last question I have before I can begin designing. It will really change my layout depending on the answer to this.

15
The RF Workbench / Re: Beginner class D design
« on: February 26, 2019, 2014 UTC »
How are you introducing 'dead time' into the phases of the RF drive?  At 7MHz, you will need about 40% duty cycle on each phase to prevent cross conduction (shoot through).  This could be one of the reasons for the relatively poor efficiency on 7 MHz.

+-RH

Does that mean 40% on, 60% off, or the opposite? And it's not relative to each other, it is just on time vs off time for each phase individually?
I want to make sure I did this right. I have a feeling I did it backwards.

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