[AMRadio] SDR IQ

Jay Bromley jayw5jay at cox.net
Wed Mar 31 04:13:52 EDT 2010

Hi Don,
As Brett mentioned most laptops sound cards are not that great.  However 
some of the high end jobs had special cards that are better than average, 
but these are rare.  Once you know what to look for in the spectrum wave 
forms it's really not all that bad, just be aware of problems that can creep 
into mix.

What I do is just be sure everything is clean before I power up up the 
device I am testing.  You can run some simple tests with your audio 
generator to get a better feel for this.  Some sound cards you have to be 
real careful on the levels you are feeding it.  On the lower end sound cards 
and on some of the older on board sound cards it is very easy to see 
spurious signals pop up from overloading.  Fun to inject a signal to see 
what you can get away with before overloading makes some dandy harmonics. 
Some software will also tell you when the level is too hot.

I would probably find a old junk desktop and add a nice card to get the most 
from the spectrum software.  Computers are so cheap these days!  You can 
find some great high end sound cards that really make a nice setup for you. 
Find a kid that loves to have the latest in gaming hardware and he would 
more than likely give you a nice card that cost him big bucks a few months 
back!  Dare I say, keep an eye open on Epay for card that cost hundreds of 
dollars just a few months ago, now going for under $40!  You can make do 
with the on board card, but my experience is there is huge improvement going 
to an aftermarket sound card.

It sounds like a huge mess, but don't let my comments scare you off! 
Software like you are looking at is very nice addition to ones shack for 
testing, especially on receivers.  Many of the Japanese rigs I have messed 
with didn't have that great or flat response, but making and saving graphs 
as you make changes is really helpful.  Much easier and faster than sweeping 
the old way, plus you get to see how good the filters are in addition to the 
audio section.

It is amazing how close you can plot a friend's audio off the air with 
spectra programs once you open up the receiver's bandpass and have a flat 
audio amp!  Another area the SDR shines in, but careful attention to any 
receiver will have similar results.

73 de w5jay/jay..

From: "D. Chester" <k4kyv at charter.net>
Sent: Tuesday, March 30, 2010 6:24 PM
To: <amradio at mailman.qth.net>
Subject: Re: [AMRadio] SDR IQ

>> From: "Jay Bromley" <jayw5jay at cox.net>
>> For years I have used SpectraPlus.  They sure seem to be pricey these
>> days,
>> since I have purchased the software.  Here is the link:
>> http://www.spectraplus.com/  I guess 14 years or more has flown by since 
>> I
>> purchased mine?  Seems it was expensive then, but I can't remember how
>> much.
>> I am still using he original copy without any problems.  I have sure got
>> my
>> money worth out of it.  Works great, but a few times I have had ground
>> loops
>> throw me off until I figured out what was going on.  Computer power
>> supplies
>> are horrible in this regard.
> That one is a lot more expensive than the True Audio.
> I have had so much trouble with these problems, that I wouldn't even 
> attempt
> to cope with the ground loops and hum issues that would inevitably result
> from using any kind of audio test software with a computer with a.c. 
> supply.
> I have a laptop that is faster, has a bigger HDD and more memory than my
> regular computer has, so I would install the spectrum analyser in the 
> laptop
> and run it off battery-only when using the analyser.  It looks like that
> software could convert a laptop into a lab instrument that would be more
> expensive than the laptop itself if purchased in the form of a dedicated
> unit.
> Don k4kyv
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