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Thread: DDS VFO

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  1. #11
    Join Date
    Jul 2003
    Location
    Located 5 miles north of downtown OKC in Edmond, OK.
    Posts
    1,141

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    Quote Originally Posted by WA6TLP View Post
    Ha, ha. Thanks very much Don.

    Read your bio page and man oh man, you are guy after my own heart -- tubes and all. I used a triode/pentode for a receiver mixer just to avoid the noise you mentioned, but really didn't notice it was any quieter than a pentagrid such as you used. Sure would like to QSO with you sometime, but it appears you are a CW man and I'm not. I nearly scrubbed out of Radioman 'A' school because I just couldn't pass the 16WPM code requirement. Finally squeaked by after sweating bullets, then the next year they dropped the code altogether. Just barely got my general/advanced because of the code. Always had a disconnect in my brain for sound patterns, most likely.

    Perhaps you are a more careful worker and are able to build robust and drift free VFO's but all my attempts were failures and my rig would drift especially while transmitting when the final would cause the chassis to heat up. If you are having any problem with drift and/or you want to bring your rig up to date with a digital readout, I highly recommend using some kind of DDS like mine, but don't mess around with a mechanical encoder, go for a optical one for more money.

    73's.
    Ham radio is just a reason to build something. All the better if it is made with tubes. Looking at your rig it reminds me how much black crinkle say “vintage homebrew”.

    I still get a thrill building analog VFO’s or VXO’s for receivers, transmitters or transceivers. Building a stable oscillator is still a challenge for me but a lot of the fun, too. But I did look at the same DDS you are using a while back. I am building a 15M CW transceiver and needed a 30.3MHz local oscillator. My IF is 9.216MHz and the high side LO must cover 30.216 to 30.366 for 21 to 21.150 MHz coverage. The DDS would have been perfect but I ended up building a heterodyne oscillator using a 28.248MHz crystal and a 1.967 to 2.177 LC VFO. The transceiver is a work in process because I wanted to finish another 40M transceiver for the 4SQRP Wed and Friday CW nets @ 7.122MHz. But a stable LO is 80% of the work. Like you say drift is hard to handle.

    I appreciate the workmanship that went into your rig. Don’t feel bad about not working CW. I can’t work voice modes either.

    Thanks for showing your rig.

    73

    K5UOS

  2. #12

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    Quote Originally Posted by K5UOS View Post
    I appreciate the workmanship that went into your rig.
    John's rig is amazing, I can only imagine the tremendous amount of work that went into that thing, but as he's finding out, now the fun begins! I usually spend more time debugging and optimizing "finished" projects than I do building them in the first place. That thing will provide a lifetime of tinkering It's sad to see that beautiful analog dial go tho.

    Don’t feel bad about not working CW. I can’t work voice modes either.
    Heh, I have that same problem

    After my last experience, I'm sold on using DDS's for three reasons...

    1) Frequency agility, large frequency hops are almost instantaneous, implementing a RX/TX IF shift allows you to completely eliminate all of the transmit mixer components (lo, mixer, BPF's) from your project... makes building multiband rigs far easier. RIT and unlimited splits are a simple matter of programming.

    2) Stability...

    3) Having a powerful computer/display at your disposal to do other stuff, like co-ordinate bandswitching relays, S, SWR and voltage metering (the PIC's have built in AD converters) etc.

    73 m/4

  3. #13
    Join Date
    Jul 2003
    Location
    Located 5 miles north of downtown OKC in Edmond, OK.
    Posts
    1,141

    Default

    Quote Originally Posted by AB9LZ View Post

    After my last experience, I'm sold on using DDS's for three reasons...

    1) Frequency agility, large frequency hops are almost instantaneous, implementing a RX/TX IF shift allows you to completely eliminate all of the transmit mixer components (lo, mixer, BPF's) from your project... makes building multiband rigs far easier. RIT and unlimited splits are a simple matter of programming.

    2) Stability...

    3) Having a powerful computer/display at your disposal to do other stuff, like co-ordinate bandswitching relays, S, SWR and voltage metering (the PIC's have built in AD converters) etc.

    73 m/4
    Mark, I think John's vintage rig is one of the best I've seen in a while. The analog dial did give it a beautiful vintage face but if the mods make it more stable I understand why he is pleased with the change.

    I agree on all the above particularly 1). Your point about eliminating the transmit mixing circuit is a big selling point.
    I just can't bring myself into the 21st century. I think I am hopelessly analog!

    I hope the OP is finding what he needs.

    BTW, tomorrow the Classic Exchange starts for CW.

    http://www.classicexchange.org/sep11/sept11ann.html

    73, K5UOS

  4. #14

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    Quote Originally Posted by KC4DYM View Post
    Bought a AD9851 moduel off ebay want to use in the dds any good ideas ?
    Ray,

    It may be the module I just bought. I've been using mine to build a DDS drop-in replacement for my Ten-Tec Corsair II 5-5.5MHz PTO. Here are some photos:

    http://www.karinya.net/g3txq/corsair_pto/pto_parts.jpg
    http://www.karinya.net/g3txq/corsair_pto/pto_top.jpg
    http://www.karinya.net/g3txq/corsair_pto/pto_bottom.jpg

    I hope to post the schematic on my web site soon.

    73,
    Steve G3TXQ

  5. #15

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    Which microcontroller did you use, and did you find source code somewhere, or start from scratch?

    73 m/4

  6. #16

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    I used a PIC 16F716. I wanted something simple, but with an A/D input to handle the Corsair II offset tuning voltage.

    I wrote the code from scratch in assembly language.

    73,
    Steve G3TXQ

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