Audio feedback problem

[Mikebits]

I just caught that. Switcher???

I've got to see the filter on this. Of course you would not get away with that on any transmitter of significant power. Well maybe FM.

But I'm getting the pdf and I got the one in noise figure. Reading it now. I see what they are saying. Inner band IMD. I'll go along with that.

Look into Mu-metal, makes a good shield for switch supplies. Then you just have to filter the DC.

Magnetic Field Shielding Materials

That R3030 was a real nice radio. At the time it sold for about $10k, military will pay anything I guess.

 

[Mikebits]

If you want to show people what you have done, produce some specs of your radio like NF or MDS. Also include your test method

 

[Leftyretro]

If you want some ideas for receiver design. I found this site that host one of Cubic Comms old receiver designs. It was the bread and butter for CCI for a long time, and it was our flagship radio back in the 80's.
**broken link removed**

Notice, the radio used switcher supplies.

Several years ago I bought the first IF module from this radio from Fair Radio Sales. It was (is?) going to be the heart of my dream radio. Still working on a LO that I can build and afford, needs 40-70mhz range. Anyway it's a hell of a front end mixer, with a 15khz wide 'roofing' crystal filter. Would be so cool if I could find the 455khz filter module that this receiver uses, but I'm sure I wouldn't want to pay what it's worth even if avalible.

Lefty

 

[Mikebits]

Several years ago I bought the first IF module from this radio from Fair Radio Sales. It was (is?) going to be the heart of my dream radio. Still working on a LO that I can build and afford, needs 40-70mhz range. Anyway it's a hell of a front end mixer, with a 15khz wide 'roofing' crystal filter. Would be so cool if I could find the 455khz filter module that this receiver uses, but I'm sure I wouldn't want to pay what it's worth even if avalible.

Lefty

The 455KHz filters we used were very expensive as they were mechanical filters as they called them, but I bet you could find some on ebay for cheap. I will try and find the company name for you. I still have a few peeps I can call, wait! I just remembered. The filters were made by Rockwell International,or maybe Rockwell Collins, if that helps any

 

[Mikebits]

Not what I had in mind but hmm.
**broken link removed**

Second thought, way to narrow

 

[Mikebits]

This is what the 455KHz filters looked like. These are from Collins. Found on ebay $35.00 wrong freq range though.


**broken link removed**

 

[Leftyretro]

Thanks;

Yes I tracked 455khz collins mechanical filters on E-bay for quite awhile, they always fetch pretty high prices in the end.

Really the local oscillator design and construction should be my first priority, as affordable ceramic second IF filters at 455khz are pretty common and I have obtained a few 4 and 5 section models. IF amp should be pretty simple with the great chip amps avalible today. The AGC will be a challenge, demodulator (AM/SSB/CW) should be pretty simple and I all ready have a nice audio amp module.

So got any ideas on a clean, stable, affordable, constructable local oscillator? I have a mini-circuit 40-70mhz VCO module but have not been able to find a PLL circuit to use it with that I feel I could successfully reproduce. A DDS module would be cool and the chip prices have come down some but I'm too old to try and solder those too many pins SMD devices.

Lefty

 

[flat5]

About 1978 I built a 40 & 80 meter ssb receiver I was very proud of
I "borrowed" circuit ideas from Ham Radio Magazine and the ARRL Handbook.
It used the Collins mechanical filter (2.8k) and the MC1496 in the if and mixer/detector.

For 40 meters I just used a 40 meter converter to 80 meters.
Because of a preselector in front this worked well enough.

I miss that receiver!

 

[Space Varmint]

Alright Alright! Radio chatter! See? We got some radio lovers, you'all just wont speak up.

I got a Collins 455 mechanical filter but I'm not using it in this design. I have my reasons for that.
But Lefty, if you need a cheap 455 KHz ceramic filter, you can pull one out of about any cheap old radio. Just look for a rectangular shaped plastic thing near the audio section with 3 pins on it. That will be it. They come in everything. Little FM Receivers, ...you name it.

Mike, I'm not trying to call you out. I know you know your stuff, but let me tell you what happened......

Yesterday I was enjoying WWCR on 3.210MHz and at about 5 or 6 AM they switch frequencies to 9.495 MHz. I tried to follow them and could not pick them up. But I could get WWV at 10MHz. So I started reworking my preselector which has a 5 position rotary switch.

I got so frustrated I tore the whole thing up. Not the radio, the preselector. I began reconstructiong it and got so tired I fell out. After recuperating, I'm back checking everything and still got my 40 & 80 meter coverage. But there are no hetrodynes or intermod this morning. Do you think I could have forced some intermod through the pre-selector?
Tell ya what I hate, the dern PS from the laptop just kills the signal. It is so noisy! Don't figure I can do anything about that on the radio end?

Oh, Lefty, man do need a VFO still? I got a some real simple Hartly oscillators in my schematic. What is the frequency of your 1st IF?

 

[Space Varmint]

Shew....10Hz step resolution!

That's some sh__!

 

[Space Varmint]

I'll say one thing for my little radio. When you hear both ends of every conversation on a 10 foot piece of wire in a basement, something working right.

Don't like my design Nigel? You don't have to buddy. I works! It works damn good!!! When you say it has too many stages and they are a waste, that's where your designs are crap on mine are superb. I'm a firm believer in buffering. It comes from experience Nigel. Build a couple of receivers and find out.

 

[audioguru]

Your audio amplifier has many stages with a lot of gain. Then many attenuators. You end up with reduced bandwidth and distortion.

Your circuit has many transistors at max gain without any negative feedback. You should have used negative feedback to reduce the distortion. Attenuators do not reduce the distortion.

My simulation shows a high voltage gain and 40% distortion.
The second half of my sim has much less distortion due to negative feedback but the gain is reduced.

 

[Nigel Goodwin]

Don't like my design Nigel? You don't have to buddy. I works! It works damn good!!! When you say it has too many stages and they are a waste, that's where your designs are crap on mine are superb. I'm a firm believer in buffering. It comes from experience Nigel. Build a couple of receivers and find out.

Your stages aren't buffering, they are simply a waste and performing really badly - I don't think any single stage is designed anywhere near correctly?.

I'm not trying to build a radio, I did all that decades ago - but never built one as poor as this.

 

[Space Varmint]

Your audio amplifier has many stages with a lot of gain. Then many attenuators. You end up with reduced bandwidth and distortion.

Your circuit has many transistors at max gain without any negative feedback. You should have used negative feedback to reduce the distortion. Attenuators do not reduce the distortion.

My simulation shows a high voltage gain and 40% distortion.
The second half of my sim has much less distortion due to negative feedback but the gain is reduced.

Yes Sir!

Now I respect what you say. I am sure my audio can be improved but radio wise, this guy does the job! I don't give a crap about what Nigel says. He's just jealous. He's been on my arse since I joined this site.

Nigel, buffers are not a waist...take a lesson in radio.

 

[Space Varmint]

See, Nigel goes out and buys a couple of ICs that say they are the best and he thinks he's done something. Nigel, you need to leave radio to the big boys. It's out of your league.

 

[audioguru]

Your four buffers look like differential amplifiers but they are actually just useless darlingtons that are not needed.

A darlington has a very high input impedance that is not needed.
A darlington has a very low output impedance that is not needed.
A darlington has no voltage gain.

 

[Space Varmint]

Your stages aren't buffering, they are simply a waste and performing really badly - I don't think any single stage is designed anywhere near correctly?.

I'm not trying to build a radio, I did all that decades ago - but never built one as poor as this.

Well...let's see some of your old crappy designs from decades ago.

What do got? A couple of 6L6's in some sort of direct conversion garbage?

 

[Space Varmint]

Your four buffers look like differential amplifiers but they are actually just useless darlingtons that are not needed.

A darlington has a very high input impedance that is not needed.
A darlington has a very low output impedance that is not needed.
A darlington has no voltage gain.

Ah....that's where you are wrong. They are deliberately Darlington amps. What do you think a Darlinton is? I'll tell you. It's a BUFFER.

Yes they have high input impedance and low output impedance.

Precisely what I was after.

 

[Space Varmint]

Bottom line is performance. If you can add low power with performance than I would say that is the trend.

I'm not afraid of digital at all. I got a PLL loop for 40 Meters ready to insert. But first I wanted the S/N top notch which it is.

Trust me, this is communications quality. But I can still enjoy some AM. It's kinda of low quality AM because the crystal filter is kinda sharp. Hey, you can only process what you are handed.

But as far as SSB and CW..........no problem. No problem at all. In fact, quite exquisit if I do say so myself. Like I said, "I hear both ends of every conversation even on the NETs. That's with a 10 foot piece of wire as an antenna in my basement".

Now, talk to me.

 

[Space Varmint]

Look at Nigel's signature. PIC processors...lol. Easy sh_t. Dude, I was programming and designing with the latest Intell embedded processors before I heard of Microchip. In fact I kept telling Intel to put some SRAM in them sand they wouldn't listen so Microchip got the bizz.

You don't even want to see some of the device drivers I've written Nigel. Windows claims you can't access other processes memory. Bunk. I've modified NTOSKERNL.exe to add new services. Digital is just one side of electronics. There is plenty of room on the analogue side of things. Do it right! Don't cut corners. In radio....buffer and shield everything you can manage.

Shoot, the best receiver I ever made had about 30 aluminum boxes inside the tin boxes. Shielded. Even the mixers. Everything was shielded. But this one is right up there with it. Using the self shielding properties of toroids and knowing when and when not I can get away with it.

Shielding and buffering are key in good radio design.