Topband: SDR-1000 IMD-DR, blocking dynamic range, IP3, and IP2 measurements

Michael Tope W4EF at dellroy.com
Thu Feb 15 23:48:04 EST 2007


----- Original Message ----- 
From: "Tom Rauch" <w8ji at contesting.com>

> ...and therein lies the problem that stopped us from using 
> the radio as we hoped.
> 
> Even 80-85dB close spaced IM3 DR is enough here if the 
> receiver only has to handle a window a few kHz wide, but the 
> problem is the entire 160 band is just packed full of strong 
> stations during a contest. While a regular superheterodyne 
> receiver only has to handle things in a couple stages that 
> can easily be made very stout before hitting a filter, a 
> direct conversion receiver has to handle the entire mess. 
> There is a huge increase in overall signal power in that 
> entire wide window.
> 
> While the FT1000MP MK V with preamp on (-135dBm sensitivity) 
> had a blocking DR of around 140 dB at wide spacing and 
> around 135 dB at 20kHz spacing, the SDR radio only had  ~ 
> 99dB blocking at any spacing (with preamp set to essentially 
> the same sensitivity as the Yaesu). Wide-spaced dynamics 
> that were already marginal decreased by 30 to 40dB, and 
> meant the radio could not be used for what we were trying to 
> do.
> 

This thread puzzled me as it seemed that Tom and Bob were
vehemently agreeing with each other. Let me explain:

a) What did Tom W8JI say when asked what was so bad 
about the SDR-1000? 

"It has essentially the same dynamic range regardless
of tone spacing"

b) What did Bob N4HY say when asked what was so great 
about the SDR-1000?

"It has essentially the same dynamic range regardless
of tone spacing"

73 Mike, W4EF......................................






More information about the Topband mailing list