[Skimmertalk] Modus operandi?

[Clive Whelan]

Thanks Pete. I guess I just have a  problem of perception as in my my 
brain audio = ~ 50Hz to 20kHz, i.e what the human ear can deal with, but 
this is clearly arbitrary.


Hmmm TS940 eh. I guess not the 930? At least I've never been aware of 
that , and I still have one ( with a PIEXX board) in the cupboard 
gathering dust. Anyone know if this is a candidate for Skimmer? I'd be 
reasonably happy still to use this as my second radio in the SO2R set up 
here. Sadly, as you know the ICOMs only have capability of an external 
antenna ( say Beverage ) and not for an external rx afaik

73


Clive
GW3NJW

Pete Smith wrote:
> The secret is that Skimmer works with the digitized I/Q data.  Sound cards 
> are available with reasonably flat response up to 192 KHz, and 96 KHz sound 
> cards are dirt cheap.  So if you are using an SDR that relies on the 
> computer sound card to produce the I/Q data stream, like a SoftRock, then 
> your sound card determines the maximum bandwidth Skimmer can deal with - 
> +/- 48 KHz for a 96 KHz sound card, for example - with the center frequency 
> being set by the receiver.  Many modern SDRs have their own digitizing 
> capability built in, and produce the necessary digital data stream for 
> transmission via USB or a serial port to the computer.
>
> The way to attach a Skimmer to the IF of any receiver is to take the RF out 
> before the roofing filter, where the bandwidth is much larger, and then mix 
> it down to a frequency that a simple SDR can handle.  Back in the neolithic 
> era, radios like the TS-940 had this capability built in, for use with the 
> Kenwood SM-220 monitor scope.
>
> 73, Pete N4ZR
>
> At 07:11 AM 11/12/2008, Clive Whelan wrote:
>   
>> This will probably look like a pdq, but hey I'm just a CW operator  ;-)
>>
>> I can see how e.g Skimmer is working in a 3kHz b/w by looking
>> sequentially ( or simultaneously?) at all audio tones in the passband
>> and using its clever decoding algorithms.
>>
>> But how does it do this in say a 75kHz b/w ( assuming appropriate rx
>> filters) when a sound card with response presumably limited to say 15kHz
>> is being used to sample the output? Does it actually sample the passband
>> in say 15kHz chunks and remember where it has been?
>>
>> As well as an academic interest, I am given to wonder whether modern
>> receivers with only a 3kHz IF capability could achieve wider coverage (
>> albeit not strictly in real time) by using their own internal scanning
>> functions to cover the 75kHz capability of Skimmer?
>>
>> 73
>>
>> Clive
>> GW3NJW
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>
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