[Amps] Advice on instruments for ham use

[G3rzp at aol.com]

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