[Central-Electronics] 200V transmit bandwidth

[Robert Nickels]

On 2/28/2021 11:15 PM, Kihwal Lee via Central-Electronics wrote:
> I noticed that the transmit bandwidth is at least 4kc.  Is it normal?  The manual says 200-3500kc. Has anyone tweaked the filter module to make it narrower?

I have not, but I recently had the filter module on the bench and swept 
it,  and can confirm that the high end rolloff is around 4 kHz.  I 
didn't take data as I was just looking for distortion but you're seeing 
what I saw from the filter.    I made some IQ recordings on an 
attenuated SDR for offline analysis and as you can see from the image at 
the link below,  transmitted signal with the filter installed does 
extend beyond the 2.7 kHz of the bandpass I used, but with my voice/mic 
at least, not much energy is present there.

https://i.imgur.com/9eimEAA.png

Fortunately it's easy to remove and install something else through a 6 
pin plug that mates with the filter connector as long as  you pay 
attention to signal levels and proper grounding and shielding.   You 
might be able to use a filter design program like Elsie to model each 
section of the CE filter to get an idea of how it works (remember CE 
designed it with maybe a slide rule!)   It should even be feasible to 
route the filter in and out signals to outboard audio  filtering or 
other processing if desired.

The modularity of the 100V certainly is a plus for troubleshooting and 
repair, but is also no doubt one of the factors that affected its 
profitability for CE.

73, Bob W9RAN