[time-nuts] Data collection cycle -- multiple sources toonecounter?

David Kirkby david.kirkby at onetel.net
Sun Jun 19 13:34:18 EDT 2005

Bill Hawkins wrote:
> Tom,
> You mentioned the effect of using an unterminated switch, or
> even manually switching cables to a counter.
> I'd'a thought that a buffer amplifier or emitter follower
> would in fact buffer the oscillator from load changes. If
> the standard is affected, would an external buffer (like a
> line driver) isolate the effects of load changes? Any numbers
> on the size of the effect?
> How about permanently terminating all cables at the switch
> and running a 10" cable to a counter set for high impedance
> input?
> Bill Hawkins
An attenuator of X dB on the output of a RF source will cause a return 
loss of at least 2 X dB (worst case, assuming 100% reflection), since 
any signal has to pass through the attenuator twice.

The attenuator will reduce a 1W source to 250mW (6dB attenuation). 
Assuming the load on the output of the attenuator is open or short (so 
100% reflection), the power will be reduced by another factor of 4 (to 
62.5mW) before it reaches the source. So only 6.25% is reflected back to 
the source. That's a VSWR of less than 1.7.

Whether or not you can afford the 6dB loss is another matter, but 
attenuators are pretty good at reducing the effect of any change in the 
load impedance.

David Kirkby,

Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/

More information about the time-nuts mailing list