[Amps] Advice on instruments for ham use

[Gary Smith]

Peter & all: thank you for the info, and yes, the primary use of the `scope would be for hf audio/signal observation.
73
Gary
WA6FGI

snip


  ----- Original Message ----- 
  From: G3rzp at aol.com 
  To: wa6fgi at sbcglobal.net ; dezrat1242 at ispwest.com ; amps at contesting.com 
  Sent: Friday, November 26, 2004 1:20 PM
  Subject: Re: [Amps] Advice on instruments for ham use


  In a message dated 26/11/2004 19:32:47 GMT Standard Time, wa6fgi at sbcglobal.net writes:
    What would be a good (cheap) analog  (or digital ) scope to use for the sole purpose of observing my transmitted signal?
    And being I have zero experience with a scope, what would be the easiest method of hooking it up? 

  What frequency? In the HF band, the easy way is a T piece and and a short coax to the scope. If you're running the full gallon, you'll need an attenuator, and that needs to be high impedance - a small series capacitor. A 50 ohm attenuator will not do.

  If you want to be 'posh', use a directional coupler. Take an aluminium box, fir a pair of SO239 or N type or whatever. Cut a strip of metallised PC Board about 0.18 inch wide for fibreglass 1/16 inch thick, and glue it (superglue) so that reaches pretty well between the two sockets: connect each end to the sockets.

  Now cut another strip, and glue it parallel to the first, with about 1/8 inch separation. Connect one end to a BNC socket, and the other through a 47 ohm metal film resistor to ground. Connect the tx to one end of the through line and the antenna to the other. Connect the scope to the BNC. Fire up to 100w atts, measure the volts on the scope. reverse the antenna and tx connections and measure again. Connect so you get maximum on the scope.

  Now you have a directional coupler, used 30 or 40 years ago for SWR measurements. The coupled signal increases at 6dB per octave - i.e., going from 7 to 14 MHz for the same power, you'll get twice the voltage, but this shouldn't be a problem. If it is, put in  a series R, and parallel C combination to give an inverse slope.

  There was a book in France called ' La Radio - c'est plus simple' (Radio - it's very easy)

  Sometimes it's so. A French review of Scroggie's book  'Second Thoughts on Radio Theory@ (highly recommended, by the way) suggested that perhaps it should be called 'La radio - ca n'est pas si simple' (Radio isn't that easy). But in this case, it is.

  73

  Peter G3RZP