W8DIZ has them...
Originally Posted by KJ4VAC
Use SA-612 or equiv
God bless America
First RX projects
Great post and responses. Such a fun subject!
When I was a novice perhaps 1 in 10 QSO's was with a guy using a scratch homebrew receiver. Probably a pretty high percentage.
Now, I can go months without hearing a fella talk about a simple homebrew transmitter let alone a receiver or complete station. I admit my fondness for hanging around the limited 40M CW spots so I miss alot.
Any kind of receiver you build will bring you a thrill. Any kind of mixer (active or passive) will do. I can honestly say I enjoyed my 1st tube regen as much as my last solid state superhet.
Homebrewing is something where each successive project builds your knowledge.
I agree with Daryl, there is not much to learn from a crystal set considering your goal of a general coverage receiver.
The NE602 was mentioned. I have always enjoyed direct conversion type for 1st receiver projects. I prefer passive diode mixers but have used the MC1496 and the NE602 as well as dual gate mosfets (uugghhh!).
For reference - the minimalist Neophyte was the 1st receiver I remember using this particular active Gilbert cell mixer.
It is a handy mixer because the oscillator is on board and there is some gain rather than the loss experienced with the passive mixers.
Lots of copycats followed. The Sudden has a better input filter.
There is a nice thing about simple DC receivers. Once you have mastered them you can take the next step and convert them to a more complex superhetrodyne receiver.
These simple DC RX's can become the product detector and audio amp for a superhet design by replacing the L/C oscillator with a crystal (BFO) and adding a front end with IF filter and IF amp.
The NE602 is the PD in the Elecraft K2. The K2 receiver is a good circuit to study.
Actually, I have built a number of Direct Conversion receivers including I/Q receivers. They do have some good qualities and can be used with an outboard DSP system to create a very good receiver.
Having said that, I much prefer regenerative receivers for a number of reasons. Regens are way more sensitive, more selective (without processing), and easier to build. DC receivers require a very stable high level VFO and suffer from adjacent signal overload due to poor selectivity. Audio processing helps but can't fix the problems in the mixer and front end.
A regen is a Q multiplier so if you use a high Q tuned circuit in the detector the selectivity can be quite good. This can also be followed with audio filtering or DSP using a laptop. Regenerative receivers can also demodulate AM signals which DC receivers can't do. Build a regen, they are fun and almost magical little devices.
I'm sorry you don't have the experience or understanding to realize that others possess a skill set that you seem to dismiss as fantastical.
The nice thing about the NE-602 / SA-612 direct conversion receiver is that it can be used as a building block as part of a good learning experience.
Get the DC receiver working, play with it for a bit, then yank the bfo parts and replace with a crystal to make a bfo/product detector, add another '602, move the vfo bits over to that chip, and stick a simple computer crystal lattice filter in between... and you'll have a decent (and quite usable) superhet.
If you keep the now working bfo/product detector/audio amp on a separate board, you can then experiment with different mixers (say diode ring, or H-bridge) and filter combinations.
Next think you know, you'll have a homebrew receiver that gives your fancy store bought rig a run for it's money.
In case anyone else picks up this thread in a search for information, I found this project online for a regenerative receiver that covers 3.5-12 MHz, and uses all discrete components.
This site has a lot of good info on the basics of receiver design, but be prepared for a lot of math! None of it is terribly difficult if you're familiar with algebra, but there is quite a bit of it.
I've used the 602 before in a Ramsey kit (the 2m FM receiver), and I wasn't very impressed with the performance, although it was pretty easy to put together. Maybe this is because of the way the rest of the circuit was designed, but I can tune across the whole range with the kit and hear nothing, while my mobile rig is picking up convos on every local repeater
Ramsey kits are junk... that said, I'm guessing you don't have the thing aligned correctly, I've seen one of those work.
Originally Posted by KJ4VAC
However, for proof that the 602 works really well, you don't have to look any further than rigs like the Elecraft K1 (uses 602's for both the first and second mixers) the K2 (uses a 602 as the product detector, and the SWL SW+, (again first and second mixers).
I case you are interested, I have a very well built 8 tube HB 80 meter receiver and seperate PS. Has large Millen dial and some other goodies.
Seems to be late 40's to early 50's design and parts.
I have not put any time into testing, so selling as non-working but all there.
Write back if you want further info. It may be Monday before I respond. My internet is down at home.
Good reply. Here's my $.02.
Originally Posted by AB8RO
A good friend (Howard, AE0KU) came over a few months ago and we played with crystal receivers, connected to my Beverage antennas. (He's an expert on crystal radios.) We used galena and pyrite for the crystal, and tried a lot of different circuits trying to balance sensitivity with selectivity. I never knew something so simple could be so much fun! From him, I came to realize that there's more to know about crystal radio design than first meets the eye.
My first homebrew receiver was a crystal radio on the AM BC band, but the one that I had the most fun with was a triode regenerative receiver I built when I was in high school. It had plug-in coils to change bands, and I eventually added an audio stage to it. I think I had as much fun modifying it as I did listening.
Having said all this, you should absolutely build a direct conversion receiver someday, regardless of what receiver that you build first. The idea is to have fun, not to build things in the order that someone else thinks they ought to be built in, right?
There's a design in the ARRL handbook for a binaural direct conversion receiver. When you find it and read it, you'll want to build it, too.
Is this the binaural receiver you're referring to?
In looking over the regen receiver I posted a link to earlier, I really think it will work well as my first project. From my reading it seems that regens are just as selective as superhets, if not more so, but they can be tricky to operate and as such aren't as popular.
That's the one! Let us know how it works out for you.
Originally Posted by KJ4VAC