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Author Topic: Cheap Radio  (Read 644 times)
K5MBV
Member

Posts: 265




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« on: August 02, 2009, 06:32:20 AM »

I posted this already in DIGITAL and got no replys. That may have been the wrong forum, so I would like to delete it to repost here, but can't find out how to delete so it is being posted in both forums. I'm sure someone will tell me how to delete the old post even if they don't answer the question.

  Does the type of soundcard make a difference in decoding
digital modes like WSJT etc.?

My SignaLink soundcard sample rates drift and I don't
seem to copy other stations in FSK441 mode as well as
others hear me. The problem may be something else
like the receiver (FT100D) and the fact that the
AGC can't be turned off.

Has anyone compared soundcards to see if there is any
difference in how well they decode?

I'm considering buying a M Audio Delta 44 PCI soundcard, but
$150 is a lot for me if a top quality soundcard won't help.

73 Ken K5MBV
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N5LRZ
Member

Posts: 0




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« Reply #1 on: August 03, 2009, 10:17:43 AM »

Some soundcards are better than others, but in general if you are using just common SSTV and or common Digital Image modes a common generic card will do an adequate job when it comes to daily use.

Now if you want to still spend that unspent money then get yourself another video card and monitor.  Set your computer to display two monitors so as to enable you to see log etc on one monitor and incomeing pictures on the other.
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K0BT
Member

Posts: 186




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« Reply #2 on: August 03, 2009, 11:55:06 AM »

Can you elaborate on the symnptoms?  The actual sound card sample rate doesn't drift.

The rig frequency might drift a bit.  I'd try to isolate the problem a bit more before spending money on another sound card.  I've found the SignaLink to be a very good interface and I seriously doubt that another sound card would work any better.
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K5MBV
Member

Posts: 265




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« Reply #3 on: August 03, 2009, 02:38:07 PM »

The symptoms are difficulty decoding with this interface.

The output sample rate drifts from
1.0059 to 1.0068. The input sample rate stays
at .9999 or 1.0000. WSJT requires they both be between
.9995 and 1.0005 or they have to be corrected in the
program setup. The output drift is too much to stay
within the tolerance required even after correction.

That doesn't mean that this is causing my decoding
problem, but it is the only thing that's obvious.

Someone said the sample rate is crystal controlled
as if that meant they didn't drift. The crystal isn't
in an oven. Even if it were, there would still be some drift.

I don't know about the quality, but
this soundcard has a minimum of parts compared to some others.
I'm sure some or maybe most SignaLink interfaces
are great, but they can't all be perfect.

Ken  K5MBV
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K5MBV
Member

Posts: 265




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« Reply #4 on: August 03, 2009, 02:47:55 PM »

N5RLZ, I'm not looking at SSTV or WEFAX pictures using the interface.
I'm decoding weak signals using the WSJT modes. WSJT is somewhat
more demanding of the soundcard.

A 16 bit soundcard seems to work OK, but a 24 bit A/D might do a better job ...I don't know.

Ken  K5MBV
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K5MBV
Member

Posts: 265




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« Reply #5 on: August 03, 2009, 02:51:53 PM »

Here is what the WSJT operation manual says
about sample rate:

"7. Take note of two numbers in the first panel of the status bar at lower left of the main screen. After WSJT has been running for a minute or so they should stabilize at values close to 1.0000. If both numbers are between 0.9995 and 1.0005, the input and output sampling rates of your soundcard are close to the nominal 11025 Hz. If either number is outside this range, enter it as Rate in (first number) or Rate out (second number) on the Options screen. WSJT will then make necessary adjustments for the incorrect hardware sampling rate or rates."

Ken  K5MBV
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N5LRZ
Member

Posts: 0




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« Reply #6 on: August 04, 2009, 07:26:08 AM »

If your goal is to run programs that require extreme sensitivity when it comes to sound then you are going to probably have to spend several hundred dollars on a top o the line soundcard.

But then as I have always said as pure absolute undenyable fact: amateur radio is not for poor people.
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AA4PB
Member

Posts: 12856




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« Reply #7 on: August 04, 2009, 08:09:16 AM »

Does the sample rate number continue to drift up and down? The sample rate reading is an average that will normally change for the first 30 seconds or so until you collect enough readings to get a good average. The actual sound card sample rate is not drifting in that case, its a matter of the measurement technique.

Its true that even crystals have some drift, but what do they use in a $150 sound card that would make it more stable? My guess is that the SignaLink uses a standard codec and chip set just like most sound cards.

I'm not convinced that purchasing a $150 sound card is going to buy you a more stable sample rate oscillator. It'll buy you a lot of special features that audio people need and probably lower noise analog amplifier stages but perhaps nothing that you need for amateur radio work.

Is there a way you can borrow another SignaLink from somebody or perhaps try another sound card. Maybe there is a defect in your SignaLink - unless other WSJT users are reporting the same issue with SignaLink.
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K5MBV
Member

Posts: 265




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« Reply #8 on: August 04, 2009, 04:08:19 PM »

AA4PB, no, other WSJT users don't seem to be having this
problem, but they aren't having difficulty decoding
either. The decoding problem is worse with weaker
signals but it doesn't seem to be a problem for those
stations to decode my transmissions.

It may be that this soundcard is marginal or the problem may
not even be related to SignaLink. Spending
$150 for more to find does seem excessive.

I don't have any problems decoding PSK31 and RTTY
type programs in Digipan and Multipsk etc. Right now I'm
only using WSJT for meteor scatter, but planning to
use it for 2304 MHz EME soon. These signals will
nearly all be very weak, so a decoding problem doesn't
need to become an additional handicap.

It looks like nobody has run into this before and so
answers aren't going to come easy. Some kind of tests
need to be done, but I don't have the knowledge or the
equipment to do them. Maybe I can borrow another SignaLink
from someone to compare.

Ken  K5MBV
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WB2WIK
Member

Posts: 20603




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« Reply #9 on: August 04, 2009, 05:08:36 PM »

Have you tried asking Joe K1JT directly?  He has more experience with hardware compatibility for WSJT than anybody, and is very easy to contact.
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K5MBV
Member

Posts: 265




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« Reply #10 on: August 04, 2009, 06:29:23 PM »

I haven't contacted K1JT yet because I'm sure he has
enough people emailing him regarding his program and
don't want to bother him if I can get an answer here
or another forum. It seems like there are no answers
to be had here, so I probably will have to contact him.

Ken  K5MBV
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