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4 Watt transmitter question

Discussion in 'Electronic Design' started by Mike Bates, Nov 15, 2004.

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  1. Mike Bates

    Mike Bates Guest

  2. Mike Bates

    Mike Bates Guest

    I also know this is no way in the world that this is going to perform 45W
    http://www.electronics-lab.com/projects/rf/019/index.html

    The 807's maximum plate dissapation is about 25watts.

    how do you get 45watts out of 25watts?

    im looking for a good performing, but simple (im limited to radio shack
    parts) fm or am transmitter. Am is a better choice, since there are about 3
    or 4 i can pick up only. there are a ton of FM stations.
     
  3. No chance.
    The text doesn't make much sense, either.
     
  4. Mike Bates

    Mike Bates Guest

    kinda figured that.

    id say about 100mw at best.
     
  5. Andrew Holme

    Andrew Holme Guest

  6. Tim Wescott

    Tim Wescott Guest

    Assuming that you can get enough power out of that funky oscillator then
    you could, in theory, get 4W out of the thing -- but the inevitable
    result of taking lots of power out of your oscillator is frequency
    instability.

    The thing that makes me suspicious is the dinky 2N2219 -- it's basically
    a 2N2222 in a larger can, and you probably can't get better than 60%
    collector efficiency out of it at 100MHz, which means dissipating over
    2-1/2 watts.

    With different transistors and proper biasing (and assuming that it'll
    oscillate at all) you could probably pour lots of electrons through and
    get power out of it, but why bother?
     
  7. Tim Wescott

    Tim Wescott Guest

    You get 45 watts out with 25 watts plate dissipation by running at 65%
    plate efficiency or better. At 30MHz you could definitely do so with an
    '807 as an amplifier, I'm not sure you could at 100MHz, or with the tube
    used as a power oscillator.

    Don't get me wrong about either of these circuits: they won't make you
    happy. But either of them may be made to work for a little while, if
    you're lucky, before the smoke comes out.
     
  8. john jardine

    john jardine Guest

    I'd say about 750mW at 16V in. Any takers?.
     
  9. Rich Grise

    Rich Grise Guest

    No, an 807 (note: no apostrophe - "807" is the whole type number!) starts
    dropping off well below 100 MHz (I'd have to look up the actual numbers,
    but am too lazy), and I think the reason is conceptually equivalent to
    propagation delay.
    Well, also notice T2 in the first one:
    http://www.electronics-lab.com/projects/rf/021/index.html
    "Wants refrigerator". Maybe it needs a place to store its beers. ;-)

    According to the data sheet, max. dissipation is listed as 800 mW,
    but it also lists 50 K/W junction to case, so if you had some liquid
    nitrogen.... ;-)

    Cheers!
    Rich
     
  10. Rich Grise

    Rich Grise Guest

    Tim Wescott answered this one for you, but it's not an 807. The
    807 is a triode. I have no idea what an AYXNIA is.

    And I also have no idea why they'd want to transmit AM in the FM
    broadcast band, unless that's supposed to be a reactance modulator,
    in which case it's a really crappy one.

    Good Luck!
    Rich
     
  11. Rich Grise

    Rich Grise Guest

    Oh, easily. I wouldn't be surprised if you could a good
    solid watt out of it - it's FM, so you can run class "C".
    I haven't analyzed the circuit, but that would seem the
    most logical in my mind.

    Thanks,
    Rich
     
  12. Tim Wescott

    Tim Wescott Guest

    The 807 (at least without the apostrophe) is a beam tetrode, similar to
    the 6L6 but heftier and good up to 60MHz before it starts dropping off
    -- you can use it at reduced input at 100MHz, but I don't think you can
    get 45W out of it as a self-excited oscillator; I'm not even sure you
    could put 45W _into_ it as a self-excited oscillator at that frequency
    and have the plate stay in one piece.

    Any time you modulate an oscillator you'll get FM _and_ AM -- in this
    case you'll have both, so you can choose which you want to call it.
     
  13. Rich Grise

    Rich Grise Guest

    Well, rats! Of course you're right. Now I even remember the 807W/5933,
    the same size as the 6146. But I _know_ there was some popular triode
    in a big tall tube like the 807s, but not as big as an 813.

    Hmmm. Guess I'm gonna have to go on a google hunt ...;-)

    811! That's the one I'm thinking. It'll do 45 watts without even getting
    warm. ;-)
    Thanks!
    Rich
     
  14. Hi,
    There is more than one method of rating a transmitter's power
    and simple DC input is a common way to do that. Seen this way, in
    the circuit given the power input lies between 1.2W and 6.4W and
    4W is then a conservative figure. How long it would last, and how
    efficient it would be, is another story.

    Radio amateurs are required to use this method because it is
    simple to implement and relieves them of the necessity of having
    accurate power output meters. It must be presumed that here the
    builder checked the supply voltage and current before posting
    them.

    However, he must have kept it in the refrigerator he specifies
    and used a frequency-agile receiver to track it as it drifted up
    and down the band.


    Cheers - Joe
     
  15. Tam/WB2TT

    Tam/WB2TT Guest

    I think you hit the nail on the head. I once ran a 2N2219 at 28 MHz off a
    20V supply, and got a couple of W out of it. Would not expect anywhere that
    much at 100 MHz. First thing it would need is a BIG heat sink.

    On the tube amp, I have the 807 data sheet, and that looks like it may
    legally do 20W out at 100MHz. Somebody mentioned the 6146, which sort of
    replaced the 807, 50 some years ago. It will do around 40W at 100 MHz, but
    has nothing in common with the 807. Different size, and different number of
    pins. I don't know where the EL34, or equivalent, comes in. I thought that
    was a single ended audio tube.

    Tam
     
  16. Tim Wescott

    Tim Wescott Guest

    The 807, 6146 and EL34 are all beam power tetrodes with similar power
    ratings, with circuit adjustments and taking frequency limitations into
    account they could probably each do about the same thing. The EL34
    possibly has the same frequency capabilities as the 807, possibly less.
     
  17. Dbowey

    Dbowey Guest

    Tam posted:

    (snip)

    << On the tube amp, I have the 807 data sheet, and that looks like it may
    legally do 20W out at 100MHz. Somebody mentioned the 6146, which sort of
    replaced the 807, 50 some years ago. It will do around 40W at 100 MHz, but
    has nothing in common with the 807. Different size, and different number of
    pins. I don't know where the EL34, or equivalent, comes in. I thought that
    was a single ended audio tube.
    In the 50s, when the Novice license began, they were permitted to use AM on 2
    Meters. The Harvey Wells TBS50 transmitter helped fill that market. It's 807
    final could provide 5 Watts input at 145 MHz. On HF it would coast at 50W.

    Don
     
  18. Mike Bates

    Mike Bates Guest

    so, are we saying that tube design would work?

    BTW. I want no more than 500mw to a watt out of that solid state FM
    transmitter. Will that circuit do about 500mw with 2n3053? its rated at
    100mhz, and I have 2 of those on hand. If i build that circuit with those 2
    transistors, and should I expect about 500mw to a watt? or so?

    im just looking for a simple easily makable FM or AM transmitter that is
    about 1 to 4 watts or so.

    i already have a 1 watt AM transmitter, but it dont get crap for range. 30
    feet at most.
     
  19. Dbowey

    Dbowey Guest

    Mike posted:

    <<
    so, are we saying that tube design would work?

    BTW. I want no more than 500mw to a watt out of that solid state FM
    transmitter. Will that circuit do about 500mw with 2n3053? its rated at
    100mhz, and I have 2 of those on hand. If i build that circuit with those 2
    transistors, and should I expect about 500mw to a watt? or so?

    im just looking for a simple easily makable FM or AM transmitter that is
    about 1 to 4 watts or so.

    i already have a 1 watt AM transmitter, but it dont get crap for range. 30
    feet at most.


    I was commenting on the 807 posts, not an FM transmitter.

    Building an 807 transmitter for the FM band is a really bad idea. Not only is
    it inefficient, it requires about 400 Volt, which is dangerous, and the
    filament current alone could power a decent xstr amp.

    The xstr FM transmitter, to which you posted a link, is a poor design using a
    puny final.

    Also, what you want to do is illegal, so I can't help you.

    Don
     
  20. Tim Wescott

    Tim Wescott Guest

    An f_t of 100MHz means that you don't want to try to use it above about
    10MHz. A 2N3866 would be a classic for this application (and yes, it
    only has an f_t of 500MHz, but it's made for UHF).

    http://www.ramseyelectronics.com/ should have a number of kits that
    would work for you, and there are other kit vendors. They tend to be a
    bit cheezy, but if give it some effort you can get them to work.
     
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