[Elecraft] [P3] How to measure bandwidth of RX signal

[Vic Rosenthal K2VCO]

'Bandwidth' is measured by specifying some number of dB that a signal is 
down at a particular offset from the center frequency. A measurement in 
Hz alone is therefore meaningless.

I suspect that the number of dB needed to make the waterfall display of 
a signal disappear depends on various things, like the gain setting. So 
this is not an accurate way to measure it.

What should work is to use the spectrum display of the P3. If you want 
to know, for example, the bandwidth of a signal at 30 dB down, you just 
find the points where the 'skirts' of the signal are 30 dB below the 
peak. This is easy to do on the P3 which can display the signal strength 
in dBm.

On 4/28/2014 7:08 AM, David Cole wrote:
> Hi,
>
> All the ESSB talk got me wondering about how accurate the P3 might be
> for measuring bandwidth.  Could someone review my method for this
> outlined below and comment please:
>
> 1.  Use ATT if needed to avoid very strong signals
> 2.  Set bandwidth to 4 KHz.  See note below.
> 3.  Adjust Span on P3 5 KHz per side
> 4.  Shaded area above waterfall indicates K3 bandwidth
>
> Watch P3.  Can one trust the waterfall display to show actual bandwidth?
> If so, how accurate would it be?
>
> Note:
> I believe that the P3 is tapped prior to any BW restrictions, (of merit
> to this exercise), so I understand that step 2 is just for my ears only,
> and does not affect BW display on the P3.  Is that a correct assumption?
>

-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/