Messages

61

The RF Workbench / Common and Precious IV - Construction phase

« on: October 21, 2016, 1702 UTC »

Hey,

so, this is the board of the Beacon that I took with me on vacation during Autumn 2015. It Outputs approx 10W+ @ 13V. I wanted to play a bit with push-pull PAs. It's simple: oscillator, keyed buffer, driver and PA. PA (final) and oscillator/driver are feed seperately. Which allows me to feed the PA with higher voltages seperately.

Since I have no use for this as a Beacon any longer (got replaced by the 30W Class D CW Beacon) I'm planning to turn this one into a small AM transmitter for experimenting and having some fun.

The big AM Transmitter project (300W+) already goes by the name "Dirty Phoenix". So I call this one "Dirty Phoenix Jr."

Next todo: mounting it to a chassis with proper heatsink and cleaning up the inductor mess.

Kind Greetings,
Zazzle

62

The RF Workbench / Re: Beacon Project #3 - 5W, 11m Band

« on: October 21, 2016, 1649 UTC »

So!

26.510kHz it is!

I'm done here. Now... hello Antenna!

63

General Radio Discussion / Re: What does AM have to lose?

« on: October 20, 2016, 0142 UTC »

Hey there,

contrary to my own feeling: AM has nothing to lose or gain. It's not about the programm. It's about technology.

As soon as people learn that someone's doing fancy stuff on AM that attracts listeners (customers) they'll try it on other stations as well. And I can't deny that other ways of broadcasting are more welcome. FM doesn't have static noise, like from my neighbour running his vacuum cleaner, or fading. Internet radio works in my pocket even in the subway. Buffering doesn't care about some connection interruptions and I can hear my favorite radio station even when I'm somewhere else in the world. I don't net to bug about antennas and such. Oh. And I don't need to wait for the weather forcast. The App tells me while listening to the station.

AM is for those to love the romantic touch of days gone by. Which isn't a bad thing - don't get me wrong. I love listening to AM. But only when I want to listen to AM. When I want music while working, AM annoys the f* out of me.

FM (analog) will die in a time not long ahead. Where I live they turned off analog TV broadcasting four years ago. Analog FM shutdown is scheduled for 2024 (but I think that'll take somewhat longer). DAB V2 is running since years in parallel.

Content doesn't matter. What matters is circumstances. Even with AM being the most energy inefficient way to broadcast, receivers are easy to build and even the oldest radio can receive AM. AM Radio is highly used in third world countries. Transmitters are cheap to build and radios are cheap to get. Easy to reach the people. Those countries have no interest in new technologies. Transmitters may be within the budget frame but the audience doesn't have the money nor intereste to buy new radios.

The last struggle to make AM bands attractive again was with the introduction of DRM. But no one cared. I loved DRM for the features it offered. But it was not usable for mainstream people. The first contact I made with a DIY IF mixer and a professional communications receiver AND an big antenna. I got curious and brought a DRM capable Radio for (!!!!) EUR 200,00. I was disappointed. Fancy looking, bad to work with (the menue was a pain) and the reception was horrible. I read reports about other models (there were 2 more on the market in 2003). None was rated better. Maybe they should have had local stations TXing in DRM in each city to get people used to it but, eh, people don't care about what a radio station xyz has to say in Sri Lanka in the english tongue.

It's with CB radio. In 1990 you were cool when you had a CB Radio. And you were the king of the gang when you had Packet Radio. Today... the CB-Bands are dead. Internet replaced it.

Maybe they'll make use of the AM Band for some digital services in future. But with fading and all that stuff I don't think AM is of interest at all.

People want it easy. And they want it in a way they're used to. Sorry to be that hard about. :/

Kind greetings,
Zazzle

64

The RF Workbench / Re: DIY OpAmp AM Modulator

« on: October 20, 2016, 0049 UTC »

Hi again,

It's like with all Forums on the net. You post something and people say "yes, but xyz works better". Had that on a Linux fourm yesterday. Someone asked a Debian specific question and someone else said "but, but... Ubuntu is better!". Some people just can't let it be.

Anyway. Of course there always something more state-of-the-art. Like PWM in this case. Btw: I deem PWM pretty much digital because it converts analog with a reference to something digital. Not with a bit-pattern but width length. And we ned a circuit (low pass) to integrate to convert it to analog again. Of course we ca say "a free variable width length is analog". We could have a pages long discussion now.

Mind, PWM isn't that "just take some parts". If you want to use the controller referenced you need to come up with:

• A circuit that adapts the input signal to the 0-1V signal (or a lesser frame, see Data sheet).
• The input circuit also needs to perform Level-Shift since pos.-peak equals 100% Mod and neg.-peak equals 0% Mod. Also, peak sensing would be nice to not run into clipping.
  
• You ned to pay attention to a PWM frequency highter 10 times the max expected audio frequency to prevent aliasing.
• Inductors must be choosen properly regarding core saturation and material.
• For best performans and low distortion it's important to calculate the proper values for the Lowpass filter.
• A FET-Driver is needed, like IR2xxx something (too lazy to look the exact number up).
• Oh, and that FET-Driver needs be be capable of doing level shift since we wanna have the best efficiency and want to use a low Rs(on) N-Ch FET.
• Given that we work with high emergency pulses we also need to pick capacitors that can handle those.
• Layout may become critcal.
• We need to deal with RFI suppression or otherwiese we may build a broad-spectrum neighbour annoyer.

And all the other stuff that may inexperienced people stumple upon their way to build "something such simple".

The intention, why I posted that, was to leave it for people who wanna get started with a simple modulator with standard parts. And yep. Even an rail-to-rail Op-Amp would have made the thing even more simple. As for myself: i just need a simple modulator that can run with a 30W TX. PWM is just overdone in my case since testing comes before building a solid thing.

But to do something good: I'll post some Quad-OpAmp based 'simple' PWM-Modulator in future.

I hope that sets your troubled soul free so it can move on.

Kind gretings,
Zazzle

65

HF Beacons / Re: Common and Precious II 6.398.5 kHz 2354 UTC 9 Sep 2016

« on: October 13, 2016, 1820 UTC »

ORRRF!!! What a backlog!

I've printed QSL cards and spend some hours digging through my backlog. With the result: I ran out of QSL-Cards! Again!  

I think I wrote everyone with a missing address a Mail or DM.

Pipe up when you feel left out!

Greetings,
Zazzle

66

HF Beacons / Re: Common and Precious II 6.398.5 kHz 2354 UTC 9 Sep 2016

« on: October 13, 2016, 1818 UTC »

Hey!

Heard at approximately 2350 Z, 9 Sept '16, very faint but copyable. Was tuned to 6399 LSB.

Can't DM you.

Wanna get a QSL Card? Send me a DM with address and such.

Greetings,
Zazzle,

67

The RF Workbench / Re: DIY OpAmp AM Modulator

« on: October 13, 2016, 0941 UTC »

You could use PWM perhaps?

Hahaha. I *knew* someone would come up with that.

In fact, yes, I could use PWM but I decided against. It's an emotional reason. Analog stuff has it's charm and with just ~30W it's okay to turn some Watts into heat. I mean, It's a fun project and no comptetion for the most high tech and efficient projekt. Less is more sometimes.

In my old workplace I've engineered multi-KW SMPS for (fast) charging forklifter (etc). And I know that, when I start building a PWM driver now, I'll end up with overengineering it to the point where it's not fun anymore. I' ll have enough opportunities to overengineer stuff when I'm building that 500W Class D Transmitter next year.

Greetings,
Zazzle

68

The RF Workbench / Re: DIY OpAmp AM Modulator

« on: October 13, 2016, 0935 UTC »

Hi,

On paper this looks pretty similar to Dave Martin's design, which works well, I might add.  The only issue I see arising when this is committed to copper is going to be the differential stage. (...)

Well, I guess I stuck to the basics that'll required to make it operate. I'm not surprised that other people came up with such before, too.
Can you link me the curcuit Dave came up with?

Any yeah, a matched pair is required.  I'll solve that by using combo-transistors. Those for high class amps where two transistor are on the same die. Have some flying around. But good point mentioning it. I'm so familiar with that stuff that I forgot that it's worth being mentioned.

Kind greetins,
Zazzle

69

The RF Workbench / DIY OpAmp AM Modulator

« on: October 12, 2016, 1051 UTC »

Hey,

I'd like to share this. It's an AM Modulation Driver. So far it's just a simulation. I've to re-calculate some values to minimise component stress and power loss. I tested the simulation from 8-48V. All it needs it to adapt R6 (voltage feedback to full swing). I think I'll build a H/W version in November.

Just some words on the Bakckground: I have this 10W CW-Beacon that I took on a vacation last year in the shelf. The PA exists of a push-pull configuration. I thought about modulating the PA feed with Audio, turning the Beacon into an AM Transmitter. First I thought about using a TDA2030 with transistorfollower (more current). But, eh, the voltage swing isn't that nice. And I also only need a positive swing. An yeeeeess. I could use an rail2rail OpAmp and give it some transistorfollower to get the current I want. But buying isn't as much fun as building. And, you can build this thing here with simple components you have in your junkbox.

Kind greetings,
Zazzle

70

The RF Workbench / Re: Beacon Project #3 - 5W, 11m Band

« on: October 10, 2016, 1042 UTC »

Hey,

<Note: I changed the projekt title>

It's funny how projects change while they're being build. I intended to go with 500mW because that works well on 11m. Now I'm stuck with 8W. Opsie~. How could that eeeeeeeeeeever happen.

Btw: I'm a bit embarrassed to share the pictures attached. That's the most ugly thing I've ever build when it come sto RF. But the board has that lovely oldschool "RF from scratch"-look.

Well, I somehow wanted to play a bit with impedance matching between stages and what's the best way to drive a class C amp from a class A stage. I guess I accomplished the mission. The circuit runs stable from 8-16V and from -30°C to 80°C. Of course the power drops a bit when the unit heats up. From 8W to 6W. But the circuit stays stable, the effiency is OK and the output signal always clean and strong.

What's still missing is some components around the ATTINY25. And, of course, the µC itself.

I've found an old 5/8 CB Antenna in the basement. That'll go through a modification.

I still ponder the frequency to use...

• 27.185kHz (EU-Wide CB Channel #19)
• 26.510kHz (Allocated to some CB Channel only in Poland)

Your opinion on that?

I guess I'll go with 26.510kHz. Less chances of pissing someone off who'll file a complain that leads to investigations.

(Well, and given that I'm from Germany... I guess I should follow tradition and invade Poland. ;p [J/K!!])

Kind greeting,
Zazzle

71

The RF Workbench / Re: TA7642 AM radio chip

« on: October 04, 2016, 1541 UTC »

TDA1072

TDA 440

72

The RF Workbench / Re: TA7642 AM radio chip

« on: September 27, 2016, 0917 UTC »

Hi there!

The TA7642 is the follow-up to the famous ZN 414 (MK). It has ups and down. They go along with the simplicity of it. You can build an AM-Radio just with a few components. But on the other hand you won't get great results from it. It can't handle large signals and with a powerful station around you will have a hard time receiving any other stations. And forget about selectivity. During night in a good location without much noises it sounds like you're in a big room with a dozen people talking.

But you can thinker with it and explore how IF-Stages work. It can be used as a -Last-IF-Amp-and-Demodulator-in-one-Chip component.

Given it's simple features it won't make much sense to use it in a receiver with a high class and complex IF setup. More than one leading IF-Stage doesn't make sense.

What I recommend is to build a classy radio frontend. Tuned circuit that mixes with a second frequency (let's say 455kHz higher than the desired frequency) followed by a simple IF-Filter. The filter can be a classy inductor based or a ceramic filter.

If you still experience trouble with strong stations still going through you can add a leading notch filter or something like that.

I hope that got you some ideas for your winter project to come.

Kind greetings,
Zazzle.

73

The RF Workbench / Re: Beacon Project #2 - 500mW, 10m Band

« on: September 15, 2016, 1027 UTC »

Hey,

I had some fun during the last evenings. And leaned quite a lot about signal multiplication and filtering. I also learned that SPICE-Simulations are b*tches, even when using non-perfect components in regard to RF-stuff. But anyway! The current circuit outputs a perfect Sine-wave with approx 1,3W. Some short caculations on paper show that I should   eable to boost the power to approx 5-6W with proper stage matching. Well, let's see what the real stuff says to that.

Kind greetings,
~Zazzle

74

The RF Workbench / Re: Beacon Project "Common and Precious II" (on air, 6.398.5kHz, 30W)

« on: September 09, 2016, 0832 UTC »

Hey!

Is the beacon on 24/7 or specific times ? Will keep an ear out for it. Would be my first beacon to listen for. Guess I should expand my SWL hobbies ; )

It runs 24/7. And with you being in the area of NY you have a good chance to pick a signal, even if somewhat noisy and weak. From the reports I got so far mostly in the morning hours.

Also, try your luck with the 30M-Band Beacon at 10.237.800Hz.

Greetings!
~Zazzle

75

The RF Workbench / Re: Building an RF Noise Generator For Testing Filters

« on: September 08, 2016, 1533 UTC »

Hey Chris,

Oh, I didn't knew that Z-Diodes produce that much noise as well.

I've build such, too but used a BC547. Basically with C left open, B connected to the Amp stage and E being fed with a tiny current. Actually, it's the voltage level that get's the thing going. The key is to bias the Diode section (whether it may be an actual diode or transistor) in reverse direction until it hits the breakdown limit. What produces the noise is actually thd "current jumping over the barrier". Since this happens not on a constant level but in small peaks it'll produce that broadband white noise.

Funny fact: couple the outputs of two noise generators and hook them up to your home PA. The signal you'll get sounds like you're at the beach of the sea, with waves rushing in again and again.

Kind gereetings,
~Zazzle.