[UK-CONTEST] OT- Attenuation and IMD3

[Stewart Rolfe]

--- On Tue, 27/10/09, Clive Whelan <clive.whelan at btinternet.com> wrote:

> From: Clive Whelan <clive.whelan at btinternet.com>

> 
> Let me declare that I am not  a techie, at least not
> in the engineering 
> or radio field, just a hopeless appliance operator.
> We  all know I 
> suspect, that in a less than perfectly  linear
> receiver that two 
> interfering signals on F1 and F2 will generate spurious (
> phantom) 
> signals on 2xF1-F2 and/or 2xF2-F1, and if this product
> falls within our 
> passband will generate QRM. 

Another non-techie here Clive but remember the spurii you refer to are 3rd order and therefore a reduction in received (fundamental) signal strength of xdB will drop them by 3xdB. So 10dB of front-end rx attenuation will reduce these in band ghosts(cw)/pseudo splatter(ssb) by 30dB....and this is the 'test' you do *before* you accuse someone of transmitting splatter. I'm sure you probably knew all this anyway!

Ofcourse if you have something like a K3 and a preference for cw you can simply use a 250Hz roofing filter and keep many/most of the offending close in 'end stoppers' apart and thus prevent the mixing from ever occuring.

73,

Stewart Rolfe, GW0ETF

PS Thanks for being my only 'G' in the log in the Eu Sprint CW. Wyboston obviously took it's toll on the normal UK entry....