Help with QRP Notebook SSB Phasing exciter

Discussion in 'Homebrew and Kit Projects' started by KG4GUF, Jun 30, 2008.

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  1. AB8RO

    AB8RO Ham Member QRZ Page

    Matt,

    Let's keep the discussion going on here as well. There are too few discussions about building. What do you think about building a DSB radio? You could certainly fit something simple like that in an Altoids can although I doubt it would be much more than a conversation piece.
     
  2. VK2TIL

    VK2TIL Ham Member QRZ Page

    "What approach do you use for building filters? I have a whole bunch of 11.998 Mhz crystals that I'd like to design a Cohn filter around but I have no idea what the motional parameters of the crystals are as they were surplus".

    Time you got a copy of EMRFD; this subject is well-covered there and you get W7ZOI's filter design programs as well.

    In the meantime, look at the AADE site;

    http://www.aade.com/

    for an excellent and well-documented program.

    This;

    http://www.cliftonlaboratories.com/Documents/Crystal Motional Parameters.pdf

    is a wonderful description of measurement & calculation methods for crystal parameters.
     
  3. AB8RO

    AB8RO Ham Member QRZ Page

    Hi,

    I have EMRFD which is what inspired the question. So to be clear, I'm aware of that approach and am in the process of building the various test bits. But, my question was more about how do other people do it.

    For example, there is apparently an article in Jul 87 QST (Which I don't have) by W7ZOI that, I believe, is primarily about Cohn filters and gives some simplified equations? I'm extrapolating this from a discussion on this site.

    http://www.pan-tex.net/usr/r/receivers/cryfil.htm

    The author implies that the values don't vary much on what crystal you use given that they are 3.457 Mhz computer cyrstals.

    I have a very strong impression of a discussion about a transmitter I was building when I was younger and I was trying to find a certain BW coil stock so I could cut so many turns as the plans suggested. One of the old guys who I often went to for advice and parts grabbed a fairly crusty looking piece of hand wound coil from his junk box and said "here, this will resonate on 40m."

    Again, the author has this to say

    So, I'd certainly like to see that article. But I'd also like to know what people do. Do you, like my old friend with the crusty coils just wing it from experience? Do you get the caps in the right ballpack and test? Or, do you do the simple calculations? Do you do the full monty every time?

    The basic Cohn design has ALL of the cap values the same. So, how much variation should one expect from one crystal to the next of the same frequency?


    I'd also like to see this article "A Tester for Crystal F, Q and R" in QST Jan 1990. I know that it's in W1FB's Design Notebook but I don't have that particular book.

    One thing I should mention is that I don't have a boatload of test equipment and I have no desire to change that. I have an o-scope, frequency counters, DMMs, a VERY basic RF sweep generator which is not particularly well suited for measuring narrow filter bandwidths and whatever I build.
     
    Last edited: Jul 3, 2008
  4. VK2TIL

    VK2TIL Ham Member QRZ Page

    I suppose it depends on how "fussy" you are.

    The author of that webpage tells us that all his filters "worked fine"; that's a subjective opinion. That's not to criticise him or subjective opinions in general; if it sounds OK and rejects pesky QRM it's a good design.

    When you start to measure you learn a lot. Here are two filters; each is Gaussian-to-6 dB. The first has had a fair bit of bench work (measurements every 10-Hz!!) and it's as good as I can get;

    [​IMG]

    The second has a long way to go as far as I'm concerned;

    [​IMG]

    but it would probably sound & work OK in a practical application.

    You must have good crystal measurements to begin with; the Carver paper on the EMRFD CD stresses this.

    The Crystal Tester article is a bit outdated today; it also has a defect in the use of an internal pot for Rs measurement; there are too many "strays" in this arrangement.

    Of the measurement methods, I have used the series-resonance method and the G3UUR method as per EMRFD;

    [​IMG]

    I have used both 1-ohm (Carver) & 50-ohms (EMRFD) in the series fixture. I may try the "standard" 12.5 ohms one day.

    I have also used the vector-voltmeter method; I have a HP 8405A.

    All give fairly consistent results; I find the series method easiest but others prefer the G3UUR method. W7ZOI has said that he prefers the G3UUR method. Each to his own.

    The G3UUR method only requires a frequency counter; the series method requires a very "clean" generator (but see the Carver paper).

    I commend the Carver paper to you.

    And the later paper by W7ZOI is also on the CD.
     
    Last edited: Jul 3, 2008
  5. AB8RO

    AB8RO Ham Member QRZ Page

    Sure, I take your point. But, I'm not so sure that I could hear the difference either.

    I try to find the sweet spot. What measurements give you 80% of the gain for 20% of the effort/test equipment cost? Or, how can I enjoy building without spending all of my time trying to measure and adjust things that won't matter in the end. I suspect that the standards improve with the skill. I've certainly found that this is true with almost every other endeavor.

    Yes, I have both, thanks for the link. I knew of the paper on the CD.
     
  6. K5UOS

    K5UOS Ham Member QRZ Page

    I can't add to Kerry's suggestion to buy EMRFD. The software is worth the purchase price. There is a website based on the book and all the authors are available. There are very simple transmitters and receivers all the way to complex transceivers in the book. The book assumes some prior electronics knowledge and some basic math. The fact is that success for projects requires a certain amount of reading and experimenting. This book helps trim some of the benchwork.

    http://groups.yahoo.com/group/emrfd/?yguid=228425588

    I remember the QRP notebook experimental phasing circuit. I recollect it was a modern version of an old tube circuit and I believe W1FB said he had never implemented the circuit.

    EMRFD has examples of passive phasing type circuits and might be a better starting point. This following link might be of interest - 1993 phasing article from one of the authors of EMRFD KK7B

    http://www.arrl.org/tis/info/pdf/9304027.pdf

    Other stuff:

    http://people.wallawalla.edu/~Rob.Frohne/R2_DSP/R2-DSP.html

    I think QST had another recent phasing transmitter article by KK7B but I may be wrong.

    I have never built a KK7B phasing transmitter/receiver but I have built/used some of KK7B's DC (direct conversion) receiver information to build product detectors and audio amps for superhet and DC receivers. Some of the circuits are in the links above. The diplexer and audio filter information in EMRFD is fantastic.

    I think DSB transmitters are tremendous fun to build. Simple transceivers are possible as the TX and RX can use the same oscillator. I worked 7 states with my 6W (3W per SB) 40M DSB transceiver on FD. I had to wait until late at night for some contacts due to the power level. I think a DSB TX for 10M or 6M would be great fun.

    Often the talk about crystal filters tends to be purist in nature. My experience is that for someone new to crystal filter design, start off simple with one of the basic design processes. I know this will produce a filter that will produce suprising results.


    K5UOS
     
  7. KB1GMX

    KB1GMX Ham Member QRZ Page

    Quote:
    >There's a 6 meter SSB transceiver in Spring, 2008 QRP Quarterly (QRPARCI.ORG) by Allison, KB1GMX, but it's mostly a concept type article rather than a howto type. You could probably scale it for other bands. But I doubt it will fit in an Altoids tin.<

    See the summer issue... It's got many states to its credit. True on concept and at 6m few are going to build it owing to intimidation factor but it's a simple thing as filter type exciters go. The basic sled (dead bug in slab)
    is roughtly a bit larger than two altoids tins but that not the complet radio as TR switching, PLL for LO and a few other bigger bits are not on that
    and would fill a third and fourth altoids tin.

    It would be tough to get a whole transceiver in an altoids tin without resorting to SMT parts. The other problem is cooling a 5W final is going to need some space and a good heatsink.

    However if your doing an exciter and not a phasing transceiver then an altoids tin could hold the low level stuff easily.

    The real problem is ok, you got it in the tin and it works but the battery to run a 1Wssb still needs to be 12V worth of AA cells. SSB radios are power hungry due to the use of linear stages.

    Small is not always an answer.

    Allison
     
  8. AC0FP

    AC0FP Ham Member QRZ Page

    Let me say thank you for the subject, keep home brew alive!

    When I first started in electronics, I ended up working near Ken Shubert, K0KS in an engineering lab. Ken was the originator of the article on the phasing method for SSB using flip-flops back in the early 70's. With that said, my first SSB radio used items I was familiar with like mini-circuit labs double balanced SRA-1 & Hi mixers. I wasn't going to reinvent the wheel so I used a commercial (ad in QST) KVG 8 pole crystal filter for a 9 MHz IF in my 6 meter SSB transceiver. Switching between a SRA mixer and a SRA-Hi balanced modulator at 9 MHz was handled by CD4066 bilateral switches (quite advanced for its time) for changing between transmit and receive. Running the transmitter 9 MHz SSB IF signal through the crystal filter on transmit made me popular with other ham's operating on 6 meters because of my clean signal. My receiver demodulator was the old trusty MC1496. Tuning was done by a LO side VCO and was tuned with a variable capacitor connected to a "Jackson drive" turns reducer and a protractor as a frequency scale.

    Keep on building! ;)

    73,

    Frank:)
     
  9. AB8RO

    AB8RO Ham Member QRZ Page

    For those interested, both of these articles are in the help file of the AADE filter software which is free to download.

    http://www.aade.com/filter.htm
     
  10. VK2TIL

    VK2TIL Ham Member QRZ Page

    I see that this thread has re-surfaced. Great; homebrew forever!!

    Re the discussion on crystal testers; I stumbled-on this article the other day;

    http://home.earthlink.net/~christrask/Crystal Test Set.pdf

    It gives very good background on crystals & measuring them; I may build the test set to see how well it works.

    As I posted earlier, I think that there are better test sets & techniques than the W1FB tester; nothing against W1FB, one of my all-time heroes, but our knowledge has improved since that article was written.

    There's other good stuff on the site as well.
     
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