Hi -
I'm new here. I am experienced in analog and digital electronics but have never worked with RF to any appreciable degree.
I started playing around with a simple AM detector (crystal) set and find out that I LOVE THIS SUBJECT.
I am having problems, though. I am starting very simple, with AM, to get a "feel" for it, and using normal lab equipment and components. But I am finding RF inductors are "build your own" and variable capacitors that I have never seen, and ganged capacitors, and in many articles there is an implicit assumption that you "just know" stuff as the lingo, matched impedances, etc.
An example might help. I am attempting an extremely crude superhet AM receiver. I have some dual-gate MOSFETs (NTE222). N-channel depletion/enhancement mode. I made two stages, nearly identical.
The first stage I simply used a "wire" coupled through a 100nF cap to Gate 1 with 100k to ground for an antenna. (I also use a function generator to verify amplification.) On Gate 2 I use a function generator for an LO that is also similarly AC-coupled. The source is grounded. On the drain I have a tank with a resonant frequency of around 500kHz (closest I could get to 455).
I can get that resonating fine. I attach the output of that amp to the 2nd stage G1 which I consider to be the IF amp. I fine-tuned the tank on the drain by adding teeny caps because of tolerance differences between "same" Ls and Cs, so get the same resonant frequency. I get a gain of around 5 on each amp. (I put a variable voltage on G2 of the 2nd amp so I can add some oomph if I need it and since I don't know how to "do" AGC yet.)
Then I diode detect and buffer with an op-amp and feed a 386.
I do get reception, but it's really crummy, and it is because I really do not know how to properly design this stuff, and do not know the rudiments of impedance matching an antenna to the FET, and do no pre-selection because I can't do ganged caps because I don't know what they look like, how to attach them. Plus I do the whole thing on a breadboard (please don't laugh heh). I can't wind my own coils. There is no real mentor in this area and the whole thing seems like a dying art.
BUT I LOVE THIS STUFF.
And I want to learn it and build it all, starting at ground zero.
I have the most recent ARRL. I have texts. I'm motivated and not (too) stupid. I have lab equipment.
My question is this. Is there a SEMINAL beginners guide for doing this? I want to build receiver after receiver after receiver. TRF, Superhet, BJT, and FET. Sure would appreciate the help if you know.
One more thing. Would THIS work? I want to use one of these dual gate MOSFETs to simply amplify RF coming in. I have a bunch of 455 ceramic filters. So I'd feed the amplified RF to a ceramic filter, amplify it again, then hit another ceramic, then amplify and listen is my thinking.
But naturally, I would need to tune the thing, impedance match, properly design the MOSFET (and designing MOSFET amps makes me feel dumb anyway due to non-linearity and the wide spec range). I've never used one of these ceramic filters, and I'm sure there are gotchas there.
Please believe I am not asking anyone to do this work for me. But I have been all over the web and find stuff that's either doing far too advanced calc etc, for my purposes - Wiley books etc, or is just plopped in front of my face "do this." I know calc btw. But I want to get at meat and potatoes of practical design and make this a hobby but I'm having real trouble getting started.
Anything you can provide as advice would be greatly appreciated.
Regards,
Robert
I'm new here. I am experienced in analog and digital electronics but have never worked with RF to any appreciable degree.
I started playing around with a simple AM detector (crystal) set and find out that I LOVE THIS SUBJECT.
I am having problems, though. I am starting very simple, with AM, to get a "feel" for it, and using normal lab equipment and components. But I am finding RF inductors are "build your own" and variable capacitors that I have never seen, and ganged capacitors, and in many articles there is an implicit assumption that you "just know" stuff as the lingo, matched impedances, etc.
An example might help. I am attempting an extremely crude superhet AM receiver. I have some dual-gate MOSFETs (NTE222). N-channel depletion/enhancement mode. I made two stages, nearly identical.
The first stage I simply used a "wire" coupled through a 100nF cap to Gate 1 with 100k to ground for an antenna. (I also use a function generator to verify amplification.) On Gate 2 I use a function generator for an LO that is also similarly AC-coupled. The source is grounded. On the drain I have a tank with a resonant frequency of around 500kHz (closest I could get to 455).
I can get that resonating fine. I attach the output of that amp to the 2nd stage G1 which I consider to be the IF amp. I fine-tuned the tank on the drain by adding teeny caps because of tolerance differences between "same" Ls and Cs, so get the same resonant frequency. I get a gain of around 5 on each amp. (I put a variable voltage on G2 of the 2nd amp so I can add some oomph if I need it and since I don't know how to "do" AGC yet.)
Then I diode detect and buffer with an op-amp and feed a 386.
I do get reception, but it's really crummy, and it is because I really do not know how to properly design this stuff, and do not know the rudiments of impedance matching an antenna to the FET, and do no pre-selection because I can't do ganged caps because I don't know what they look like, how to attach them. Plus I do the whole thing on a breadboard (please don't laugh heh). I can't wind my own coils. There is no real mentor in this area and the whole thing seems like a dying art.
BUT I LOVE THIS STUFF.
And I want to learn it and build it all, starting at ground zero.
I have the most recent ARRL. I have texts. I'm motivated and not (too) stupid. I have lab equipment.
My question is this. Is there a SEMINAL beginners guide for doing this? I want to build receiver after receiver after receiver. TRF, Superhet, BJT, and FET. Sure would appreciate the help if you know.
One more thing. Would THIS work? I want to use one of these dual gate MOSFETs to simply amplify RF coming in. I have a bunch of 455 ceramic filters. So I'd feed the amplified RF to a ceramic filter, amplify it again, then hit another ceramic, then amplify and listen is my thinking.
But naturally, I would need to tune the thing, impedance match, properly design the MOSFET (and designing MOSFET amps makes me feel dumb anyway due to non-linearity and the wide spec range). I've never used one of these ceramic filters, and I'm sure there are gotchas there.
Please believe I am not asking anyone to do this work for me. But I have been all over the web and find stuff that's either doing far too advanced calc etc, for my purposes - Wiley books etc, or is just plopped in front of my face "do this." I know calc btw. But I want to get at meat and potatoes of practical design and make this a hobby but I'm having real trouble getting started.
Anything you can provide as advice would be greatly appreciated.
Regards,
Robert
