[RTTY] K3

[Kok Chen]

On Jan 6, 2009, at 1:06 PM, Joe Subich, W4TV wrote:

> Having both the Elecraft (Inrad) 250 Hz and 400 Hz filters
> is a bit redundant.  Per data on the Elecraft web site
> (http://www.elecraft.com/K3/K3_8_pole_plots.htm), the 400 Hz
> filter is 435 Hz wide (-6 dB) and the 250 Hz filter is 370 Hz
> wide (-6 dB).  There is hardly enough difference to justify
> the cost of the 250 Hz filter.

I skipped the 250 Hz roofing filter, and went with the 400 Hz 8 pole  
filter (together with a 2.8 kHz and 6 kHz filters in the first  
receiver and a 2.8 kHz filter for the second receiver).

However, I stuck with my FT-1000MP for Roundup.

As many of you know, I use waveshaped AFSK for RTTY to tightly control  
the FSK keying sidebands, and the K3 has an AFSK transmit IMD that is  
a little high for my taste.  With my K3, I'd measured about -24 dB IMD  
at 70 watts peak power using a two tone signal.  With my 1000MP, I get  
about 4 dB cleaner transmit IMD when I operate AFSK.

With the PA turned off, the K3 does manage to achieve a very clean -34  
dB transmit IMD at 10 watts and below (rising again below 500 mW to  
-29 dB IMD by 200 mW).  But then, at 5 watts, I get a whopping -40 dB  
IMD with the MP.

As Joe W4TV mentioned on a different reflector, a high voltage PA  
would be most welcome.

Except for some small issues on digital modes (which a firmware  
upgrade should solve, and an LP-PAN will also solve nicely), I have no  
problem with the K3 receiver, so I am still debating if I should just  
go ahead and transmit with the K3.  My signals are so weak, most  
people can't copy even my baseband signal!

73
Chen, W7AY