[Elecraft] Fw: RTTY Questions

[Joe Subich, W4TV]

On 4/19/2012 12:54 AM, Jim Brown wrote:
 >
 > Right, and I've long promoted that concept.  BUT -- I've recently been
 > comparing several (five so far) outboard A/D converters, four models
 > that connect to the computer via USB, on that uses Firewire, and I've
 > found that all of them result in noticeably more reliable decoding of
 > RTTY and JT65 signals, especially weaker signals.

This is because the computer based sound cards - particularly those in
laptops and netbooks - are so bad.  The internal power supplies are
typically very noisy and the computer main board designers do not take
care of things like common audio return paths, proper power supply
bypassing, "pin 1" issues, etc.

The external sound cards (A/D converters) are generally powered from
the computer's USB supply which is separate from the digital (bus)
5V supplies and much cleaner.  In addition, good external sound card
designs add a significant amount of power supply bypassing, keep the
input and output returns separate from power supply returns to the
extent possible and often provide additional power supply regulation.

Several years ago I measured the noise floor of a couple laptops,
a couple generic PCI add on cards, a typical USB sound card and
the sound card in the original microHAM Digikeyer.  The laptops
had the worst noise floors, the PCI add-ons were slightly better,
the USB soundcard (an original Creative SoundBlaster MP3) was 10
dB lower than the laptops and the DigiKeyer was another 3 dB better
than the Creative).

I have not repeated those measurements recently but given the
performance of laptops I've seen since then (and reports from EME
users of current microHAM interfaces) I do not expect there has
been much change in the relative performance.

73,

    ... Joe, W4TV


On 4/19/2012 12:54 AM, Jim Brown wrote:
> On 4/18/2012 7:11 PM, Tony Estep wrote:
>> It's worth pointing out that no interface is necessary with the K3. You
>> don't need a Signalink or Rigblaster or whatever. All interfacing can be
>> done with cables directly from K3 to PC.
>
> Right, and I've long promoted that concept.  BUT -- I've recently been
> comparing several (five so far) outboard A/D converters, four models
> that connect to the computer via USB, on that uses Firewire, and I've
> found that all of them result in noticeably more reliable decoding of
> RTTY and JT65 signals, especially weaker signals.
>
> I use MMTTY with N1MM for RTTY contesting, and MMTTY with DXKeeper for
> general operating.  I use AFSK and VOX.  As K6DGW has observed, as long
> as you take reasonable care to get levels right, it's just as clean and
> reliable as FSK, and the hook up is really simple.
>
> 73, Jim K9YC
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