[TenTec] 2nd Try: SDR Technology ?

[Carl Moreschi]

I wouldn't worry too much about BDR3 with the panadapter radio.  It's 
your main radio that is important.

The rule for DSP is the highest frequency you can get is half of the 
sampling rate.  That's from the Nyquist theorem.



Carl Moreschi N4PY
58 Hogwood Rd
Louisburg, NC 27549
www.n4py.com

On 12/27/2014 4:06 PM, Rick - DJ0IP / NJ0IP wrote:
> Carl,
>
> That was beneficial.  Tnx.
> I had seen 96kHz sound cards but didn't realize there were 192kHz sound
> cards.
>
> Isn't there some kind of rule like the radio can display about half the
> sampling rate, so a 192kHz sound card would display 96kHz. (?)
>
> So with these low cost radios, what does one have to look for to get a
> better BDR3?
> As I pointed out earlier, the BDR3 is not great with these low cost SDRs.
> Of course it is fantastic with the direct sampling SDR - but slightly out of
> my price class.  ;-0
>
> 73 - Rick, DJ0IP
> (Nr. Frankfurt am Main)
>
>
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Carl
> Moreschi
> Sent: Saturday, December 27, 2014 6:22 PM
> To: Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] 2nd Try: SDR Technology ?
>
> Let me take a shot at this.
>
> There are basically two types of SDR panadapter receivers.
>
> 1) Direct converison receivers.  These use the same method as the old Tentec
> Century 21 and convert RF directly to audio and then digitize it.
>    The audio image is removed by the phasing method like the very old
> original SSB transmitters.  The disadvantage to these radios is you might
> hear the oscillator running and this might appear on the display.
>    Normally they run the oscillator with a 10 khz offset to get it away form
> the signal of interest.  The other disadvantage of this type of receiver is
> it will use your sound card.  The stock sound card in most computers only
> allows 48 khz of spectrum.  You can get a more expensive sound card to put
> in your computer that can increase the spectrum to 192 khz.  Examples of
> this type are all the Softrock receives.  All the Flex radios prior to the
> 6000 series use this method.
>
> 2) Direct sampling receivers.  These radios convert the RF signal at the
> antenna directly to digital.  They do not use your computer sound card.
>    They are normally very sensitive.  They usually can display many mhz of
> spectrum.  Examples of these receivers are the Tapr Hermes, Flex 6000
> series, Elad FDM-S2, Microtelecom Perseus.
>
> Clearly the direct sampling receivers are better but they also cost a lot
> more. And if the direct conversion radios are done correctly, they can also
> work very well.
>
> Carl Moreschi N4PY
> 58 Hogwood Rd
> Louisburg, NC 27549
> www.n4py.com
>
> On 12/27/2014 5:35 AM, Rick - DJ0IP / NJ0IP wrote:
>> First pass brought a lot of suggestions for SDR models, and I have an
> exact plan about how I want to attach the receiver to my Eagle, and manage
> it with N4PY software.  I have a short list of 2 receivers.  I may possibly
> be able to borrow a Flex 1500 for a couple of months and use it as a
> receiver.
>>
>> However, my fundamental question did not get answered, in fact not even
> really addressed.
>>
>> "What technology differences do we compare when evaluating SDR receivers?"
>> (Let's stick with the low cost - under $300 -  for this thread
>> please.)
>>
>> Basically all of the SDR radios are sensitive enough.
>> I guess, at least for the low cost models, the selectivity is determined
> by the sound card.
>>
>> I want to compare radios that have built in sound cards because I don't
> want lots of wires running to my laptop.
>> But what do I look at?
>> Do we compare sound card chips in this case?
>> If so, what specs of the sound card chip are important?
>>
>> What else?
>>
>>>  From what I have been able to find on the web, all of these low cost
> models have a close in BDR3 ranging from about 65 to 75dB.  Not great but
> acceptable for daily use, at least in SSB.  Better receivers go for $500 or
> more.  No surprises there.
>>
>> For my initial project, I will just use some simple stuff, but I'm curious
> to learn more about this technology.
>> It won't be too much longer before the theory we all learned is school is
> not even used anymore.
>>
>> BTW, this is one of the best pages I have found so far on this topic:
>> http://www.rtl-sdr.com/roundup-software-defined-radios/
>>
>> 73 - Rick, DJ0IP
>> (Nr. Frankfurt am Main)
>>
>>
>>
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