[TenTec] 2nd Try: SDR Technology ?

Rick - DJ0IP / NJ0IP Rick at DJ0IP.de
Sat Dec 27 16:06:37 EST 2014


That was beneficial.  Tnx.
I had seen 96kHz sound cards but didn't realize there were 192kHz sound

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
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

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
> 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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> TenTec at contesting.com
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