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Sunday, August 14, 2011

Bike Radio

As I mentioned on the podcast, I've been riding my bike to work lately. I really enjoy it. We have great bike trails in this area. They use paths of defunct railroad lines -- I ride Washington and Old Dominion Trail.

My bike is a bit of a boatanchor. It was made in Japan. I bought it 22 years ago when I was in Spain. I've used it in Spain, The Dominican Republic, the UK, Portugal, Italy, and in the U.S.

Of course, my thoughts have turned to putting some sort of HF radio on the bike, probably just a receiver. I still have a little handle-bar AM radio that I added shortly after I bought it. The handle bar mount is still good. See above. I'm pleased to see that it looks very simple, with discrete components. The AF amps are obviously off to the left of the speaker. To the right of the speaker we obviously have the RF and IF circuits. There are some nice tuned transformers there (from the "Chop Shing" company), and three transistors and a diode. What would the standard lineup be for a simple AM radio of this type? Maybe just an RF amp in the front end, a local oscillator, one stage of IF amplification and the diode as the detector?

What do you guys think? Make use of some of the existing circuitry? Start over?

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  1. Good for you Bill for riding to work and taking advantage of nearby rail-trail systems. It's a 12 mile ride on the road to get to my nearest rail-trail.

    Wow your bike has worked as much DX as I have. Hi!

    Great blog and podcast. I have been following with interest.

    Mike KD8JHJ

  2. I don't know Bill, this really ups on to the next level of geekness. Be careful that you don't end up like those folks walking down the street with an radio in their hands or even worse headphones with build inn radio and antenna sticking up.....
    Good for you to enjoy the bike ride dough!

  3. That thing is too new-fangled. You need something older:

    Watch out for the B+ !

    Bill N5AB

  4. Typically they use a combination LO/mixer, an I.F. amp, a diode det., an audio pre-amp. and a 2-transistor audio p.a., push-pull and transformer coupled. Sometimes the detector audio is pumped back through the mixer in a reflex arrangement to get a bit more audio 'oomph'.

    Using that thing as-is would be a challenge and probably a silk purse/sow's ear situation but what the heck, nothing ventured, nothing gained. I say take a whack at it.

    To get away from BCB 'ingress' and use the radio as a 'back-end' for a xtal-controlled converter, you could raise the frequency up to some lesser used frequency band. You may need to either ditch the ferrite rod antenna (which would require winding a new antenna transformer) or completely shield the rod. However, ditching the rod antenna opens up another can of worms.

    FWIW, I grab any road-kill A.M. portable I find. They're a good source of parts for experiments and for the "Impoverished Radio Experimenter"


    From the former home of "Sears By The Sea" (there's quite a story behind that one),

    73.......Steve Smith WB6TNL
    "Snort Rosin"

  5. You could add down converter build out of a ne602 and add a 455kc oscillator for bfo, BUT it would be much easier to just build a direct conversion receiver using a '602 and LM386 audio amp. You would probably want to use an external oscillator for LO, or a xtal and cap for minor adjustment.

  6. Hi Bill.

    As Steve says the usual line-up comprised 6 transistors and a diode. There appears to be only 3 transistors in the bike radio so you're starting from an unusual arrangement. A ferrite rod antenna is a directional device which may add difficulties even if rewound which I wouldn't recommend.

    'Christmas tree' the radio for parts like the case, speaker, etc. and start from scratch. It would make and interesting project to design a front end with a telescopic antenna from a standard BCB road kill receiver.

    As you always say, if you can get a receiver working, the transmitter should be relatively easy.

    73 David M0VTG


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