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Receiver Design Help

Discussion in 'Homebrew and Kit Projects' started by NC4JB, Jul 16, 2010.

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  1. NC4JB

    NC4JB Ham Member QRZ Page

    I'd eventually like to start building my own rigs, and to start with I'd like to build a good quality general coverage receiver. Gotta crawl before you walk tho, so I figured I'd start out with a simple "crystal" receiver like the one in the Forest Mimms book.

    I know this is a very basic design for a receiver that won't really cut it. I'm familiar with the basic elements of a receiver: local oscillator, mixer, detector, and so on, but I'm not really sure what makes a receiver better. There don't really seem to be a whole lot of resources online that explain this either. Is there a book that starts with building a basic receiver and then goes through progressively more complicated receivers with better performance, explaining WHY and HOW they perform better? Or maybe someone can give me an explanation here about what makes a good receiver and what makes a better one?

    After I've gotten my feet wet and built a decent tube receiver, then I'll worry about transmitting :cool:
  2. W3JN

    W3JN Ham Member QRZ Page

    There's a pretty good book by Joseph Carr on receiver design, written for beginners. Has plenty of projects.

    The best reference source would be one of the old Radio Handbooks (aka "the West Coast Handbook") or just about any ARRL handbook. If you're interested in building a tube receiver, go for a late 50s/early 60s edition.

    For more advanced theories, Dr. Ulrich Rohde (of Rohde and Schwarz) has written a couple books on the subject.

    Finally, Google is your friend! There's a ton of info on HB receivers on the net.
  3. KI6J

    KI6J Ham Member QRZ Page

    "...maybe someone can give me an explanation here about what makes a good receiver and what makes a better one?"

    Frequency STABILITY, signal SELECTIVITY, and incoming signal SENSITIVITY. I think there are a few others, like noise floor and dynamic range, but they might be related to the first three. To improve these, you must add circuit COMPLEXITY.
  4. AB8RO

    AB8RO Ham Member QRZ Page

    IMNSHO, you won't really learn much from a crystal receiver. Doug Demaw suggests that a regen is great starting point. Many suggest starting with a direct conversion receiver.

    To some extent what you're looking for will come with understanding. Give it time. Build a simple receiver without worrying too much about what comes next. Then ask what are its limitations? You usually trying to balance a number of competing qualities.

    Although there are other considerations, Doug Demaw, in his book "Practical RF design Manaul", highlights Dynamic Range, Selectivity, and Sensitivity, and describes how each quality would affect the performance of a communication receiver. I think that book is great and very readable, however, it does not include complete projects.

    I also like "Solid State Design for the Radio Amateur", and "Experimental Methods in RF design." Although both have many projects, I think that you get the most satisfaction out of extracting the elements and "designing" your own.

    I'd start by building an audio amplifier, then an on frequency VFO or VXO and you are most of the way to a direct conversion receiver. You could then think about what changes would be necessary to make it a single conversion superhet. What would be the advantages of doing so? For example, how do you improve selectivity in a direct conversion receiver vs a superhet. What are the advantages and disadvantages of each method.
  5. NC4JB

    NC4JB Ham Member QRZ Page

    Lots of good info to go on, thanks folks!

    I do have some basic schematics for direct conversion AM receivers. As far as I understand I can change the intended frequency range by adjusting the LC values? Maybe someone can correct me on that, but if it's true then I know there are tons and tons of schematics online for regen and superhet receivers that I can modify to encompass the frequency range I want, then experiment with to add features and improve performance.

    I have the ARRL 2010 handbook but it seems to sacrifice detailed information on the building blocks in favor of more information about digital frequency synthesis and phase locked loops, which is all fine and dandy but I don't want to build radio-on-a-chip rigs :rolleyes:
  6. AB9LZ

    AB9LZ Ham Member QRZ Page

    Heh, that question probably has been the subject of many a doctoral thesis and pretty hard to answer in one paragraph.

    The ever popluar NE-602 - SA-612 based direct conversion RX's are a good place to start. They (unlike the regen's) use the basic building blocks of most modern receiver designs, and can be decent performers.... i.e. regens can be pretty fickle at times.

    If you are new to electroncis, I'd shy away from the tube stuff until you get a few solid state projects up a running. Even with published designs, there is still quite a bit of trial and error / trouble shooting involved in getting homebrew stuff to work... and being able to touch a *live* circuit without hurting yourself is something to think about as you'll have your fingers all over that thing trying to get it to work.

    Cost is another factor, building tube gear these days is expensive if you don't have a deep junkbox to rely on.

    73 m/4
  7. NC4JB

    NC4JB Ham Member QRZ Page

    Do you know where I can get NE-602s? I've used one before in a Ramsey kit and it seemed pretty straightforward, but I've been unable to locate anywhere that sells them in a DIP package. Mouser and Digikey were no help.
  8. W3JN

    W3JN Ham Member QRZ Page

  9. AI3V

    AI3V Ham Member QRZ Page

    Like has been posted, a good receiver is a balance of many things.

    Frequency stability, slow drift is obviously bad, but fast drift- or phase noise is bad too. think of phase noise a a very fast drift of the vfo, for some fraction of time you simply are listening to a different frequency!

    Sensitivity-more sensitive is better, untill you run into "KTB" noise, then you cannot improve sensitivity further.

    Strong signal handling- in general a receiver that uses amplifiers that can handle more power (signal) will be harder to overload, we do this by using amplifiers that have more dc power going thru them AND local oscillators that provide more power to the mixer, the tradeoff to more lo power is that signal will tend to escape from the receiver (be radiated) and interfere with other receivers, that's what the FCC "part 15" notice on the back of yout clock radio is about. Also, the more current needed in a amplifier will be directly opposite what you want for backpacking, a low power draw set. (To use a TX analogy, you cannot expect to get 1 watt from a 1/2 watt battery!)

    Selectivity- should match the "occupied bandwidth" of the transmitted signal, and this selectivity should be as close to the antenna as you can afford (as opposed to being on the speaker end of things), by stopping off frequency signals (and noise!) from ever getting to the circutry, you prevent the strong signals from overloading that circuitry!

    Then you get into features,

    If shift
    Noise blanker
    Multi mode/multi band
    Digital display
    Computer interface

    There is nothing quite like the thrill of using a set you designed and built yourself.

    Good luck in you journey!:)

  10. AI3V

    AI3V Ham Member QRZ Page

    Yep, this is about it.

    Keep in mind that if you make HUGH QSY- say trying a 160M design on 70CM that things won't scale well.

    Try "Dan's small parts" He's got the "good stuff" for experimentors:cool:

  11. KB9BVN

    KB9BVN Ham Member QRZ Page

    W8DIZ has them...

    Use SA-612 or equiv
  12. K5UOS

    K5UOS Premium Subscriber QRZ Page

    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.


  13. KA4DPO

    KA4DPO Ham Member QRZ Page

    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.
  14. AB9LZ

    AB9LZ Ham Member QRZ Page

    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.

    73 m/4
  15. NC4JB

    NC4JB Ham Member QRZ Page

    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 :confused:
  16. AB9LZ

    AB9LZ Ham Member QRZ Page

    Ramsey kits are junk... that said, I'm guessing you don't have the thing aligned correctly, I've seen one of those work.

    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).

    73 m/4
  17. WA4NJY

    WA4NJY Ham Member QRZ Page

    Homebrew Receiver

    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.
    Ed WA4NJY
  18. W0BTU

    W0BTU Ham Member QRZ Page

    Good reply. Here's my $.02.

    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.
  19. NC4JB

    NC4JB Ham Member QRZ Page

    Is this the binaural receiver you're referring to? files/BIQR/biqr.pdf

    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.
  20. W0BTU

    W0BTU Ham Member QRZ Page

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