Don't they produce a lot of distortion?
Hi SV! I've collected a lot of parts to build a SSB receiver.
What I don't have is blank pcb, a nibbler or drill to make islands (manhatten), toroids (t37-2 & t50-2 I guess), coil wire (#28 ?), and a good magnifier lamp
I also have not decided on band(s) or circuits. I think lower 40 to start. I'd like to use a igmosfet for first mixer and mc1496 for detector. I've built the audio amp (lm380n) already. Have 10 8mhz xtals so will use them for filter and bfo. Should be ok for lower 40 and 80 or 20 in the future, I hope. Even have an 8mhz osc. in a xtal package to play with. It might be the bfo, I'l see.
Whatever you do, don't take any advice or ideas from SV, he doesn't have the slightest clue about any kind of design, and his radio is a complete disaster.
Buy yourself a copy of either the ARRL or RSGB manuals, and build a proper radio.
No.Darlingtons work very well in rf. A Darlington is actually an ECL device and they switch faster than CE amps. Thats why cray computers use ECL in the data & address busses.
In my apartment I'm afraid I won't hear much. I'll have to go to a park or waterfront to try to get away from all the !@#$%^& RF interference. Everybody has multiple RF noise generators around here. I suspect the ADSL in the phone lines also contributes. It's very depressing trying to listen to the ham bands on a Sony ICF-7600DS. 25 years ago it was more effective.
I know most of the general concepts of receiver design but don't have experience with toroids. 30 years ago when I made a SSB receiver I used Miller coil forms. So, SV, you suggest #36 wire. Should I get other sizes too for receiver work?
I think I'll avoid broadband to use a variable tuning preselector. I'll also try a variable front attenuator instead of a switch. Not really sure. A minor point.
The first mixer is the pivotal part of the design as I see it. If I use an active mixer I probably don't need an RF amp in front. Just a very good filter. If I use a Mini-Circuits diode ring I'll want an RF stage ahead of it. The antenna will most likely be a few feet of wire.
After that, the VFO will be the real challange.
I've had really poor results using darlingtons for RF, too. You can get some improvement adding a pull-down resistor to the base of Q41 there, but they still aren't super-fast.
No.
A darlington transistor is very slow and is hopeless at radio frequencies. I won't use them for high quality audio. The problem is that the second transistor "floats" off slowly.
An ECL logic circuit is very fast because it uses an emitter-coupled differential amplifier that is not allowed to saturate. It is completely different to a darlington, but The Space Varmint draws his darlingtons with one transistor backwards so it resembles the look of an ECL differential amplifier.[/QUOTE
Nothing turns off Q41...oh brother, where do you the signal output comes from on Q41 idget?
Also even in audio it has become common practice to use Darlingtons for speaker drivers instead of using audio transformers. Integrated packages like the TIP120 are good for this.
The whole trick to using them in rf is to match the impedance. It's very simple. The input Z is R1 / R2 and the output impedance is RE. They perform a whole host of very useful and desirable functions in rf as I mentioned above.
Oh but I can't make a receiver. My crappy receiver only pulled out a 5 watt station form Australia one night and a 2 watt station from Australia the next. Now nit pick away. Jealousy only makes you look stupid.
Space Varmint,
I showed your slow darlington emitter-followers and I showed an extremely fast ECL gate with its emitters coupled together. They are completely different.
Darlington emitter-followers are not the same as an ECL differential amplifier.
Guess What ECL means? Emitter Coupled Logic. The emitters are coupled together.
Your darlington emitter-followers have the base of the second transistor connected to the emitter of the first transistor and their emitters are not connected together.
A TIP120 darlington has built-in resistors to turn off the transistors as fast as possible. Your darlingtons have nothing to turn off the second transistor. It slowly floats off.
The datasheet for the TIP120 darlington transistor shows that its current gain is half at only 50kHz and is 1/10th at only 200kHz. It is 1/100th at 800kHz.
It was used in very poor quality cheap stereos about 30 years ago.
Darlington pair transistor circuits are not normally used for high frequency applications. The Darlington pair is inherently relatively slow because the base current for the output transistor cannot shut off instantly. As a result Darlington pairs are generally used in low frequency applications including in power supplies or areas where a very high input impedance is needed.
Flat5, I am passing on a message from "Space Vomit" who says that he is locked out of this/these forum(s). Could you please let him back in.
His message to me can be found here.
Aaron's Homepage Forum - Radio Newbie
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