|[AMRadio] receiver tests for Theo|
John E. Coleman (ARS WA5BXO)
wa5bxo2005 at pctechref.com
Tue Mar 7 10:15:03 EST 2006
A typical sound card will record in 16 bit number per sample and at
least 32K samples per second (I think that may be a conservative figure and
it might be 44K some odd samples per second). At any rate the sampling is
faster than the bias frequency on tape. And the 16 bit number means that
you can get have a max number of 65,535 (64K). That is -32K down and +32K
up. This means that each sample is represented as a number from - 32K to
+32K. This is CD quality. The trick is to record it as close to max input
as possible without any sample hitting the top or bottom number.
What many folks do wrong is to record at too low of a level so that
their max number hits 10K or 20K. They digitally "normalize" (Bringing the
largest number = to +-32K and setting all other numbers to the percentage of
increase). This puts a much larger voltage gap between samples than was
there originally. This can cause the lower level nuances to become fuzzy
sounding. I have made a number of very good recordings using a 16 bit sound
card but it generally takes a couple of stabs at it to get the level set
just right and not over drive.
The alternative is to get a 24 bit sound card where max number is
16,777, 216 (16.7M) and sample rate is 96K /sec. With this sound card you
can record at 10% of the max and still use more numbers than a 16 bit card
would. After normalizing you will want to convert to 16 bit or high quality
MP3 to be compatible for 16 bit card playback.
Hope this helps.
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of Brett gazdzinski
Sent: Tuesday, March 07, 2006 8:36 AM
To: 'Discussion of AM Radio'
Subject: RE: [AMRadio] receiver tests for Theo
My recording setup is an old cassette tape deck that happens
to be rack mount.
The receiver filter is 5.5Kc since my ears don't work well
at high frequencies, so the recording is limited...
I have never taken an analog tape and converted it to
a digital format.
I would wonder how good a typical sound card would work
converting analog to digital.
On the subject of picking a receiver, I got tired of
the limitations or flaws of all the commercial stuff, it
seems every receiver is a compromise between cost and function,
some had great audio but you had no idea of the frequency you were on.
Others did SSB very well, and AM lousy.
Some did AM well, and ssb poorly.
Some looked very cool, some were very ugly.
Some drifted, some were stable.
Some were very quiet (old stuff) some were very noisy (new stuff).
Some had good bandwidth choices, others had poor or no
Some make no provision for TX muting.
If you don't want to band hop, the r390 series works very well on AM,
although it needs outboard audio and is on the noisy side.
My homebrew receivers were built to function, I want low noise,
low distortion, accurate frequency readout, 160, 80 and 40 meter
coverage, a xtal BFO for zero beating AM signals, a scope output,
an S meter, and good AM selectivity choices.
As an added benefit, I made it look like the rest of the
home brew stuff, and made it so when you switch bands it goes
from 1880, to 3880, to 7290 when you change bands.
They SEEM to work well, but I need someone with good hearing
to really nit pick them.
Eventually, I want to add many bandwidth choices, 4, 5, 6, and 8Khz maybe.
Other than the homebrews, I only have the G76 and an Icom 756 pro.
The G76 has audio amp limitations, the 756 is very noisy, and rolls
off the low end even with outboard audio.
There are many times I could not copy signals on the R390a or the 756
that were good copy on the homebrews, weak signals on quiet bands is
where the homebrews really shine.
I would think an NC300 or 303 with outboard audio might be reasonable
and sound good.
The R390 series has a scope output built in, and it works well
on receive and transmit. Its got muting, its accurate, but it
is expensive and trouble prone..
Just my two cents...
> -----Original Message-----
> From: amradio-bounces at mailman.qth.net
> [mailto:amradio-bounces at mailman.qth.net] On Behalf Of VJB
> Sent: Monday, March 06, 2006 2:01 PM
> To: amradio at mailman.qth.net
> Subject: [AMRadio] receiver tests for Theo
> In addition to looking up some AMers around your area,
> I'd recommend asking for some sound files from people
> who can record from the receiver candidates.
> This past weekend Brett N2DTS and myself were in QSO
> on 40m with a fellow running a very clean sounding
> DX-100. We both rolled tape on a specific part of the
> guy's transmission. Brett if you still have that sound
> file, maybe render it down to an MP3 and I'll do the
> We can then describe receivers.
> Meantime, there are some other sound files kicking
> around that are worth downloading. I've got a few that
> I remember what receiver I used:
> >From the diode of an SP600 at 13Kc selectivity:
> >From the diode of an R390 at 16kc selectivity:
> >From the "line output" of an R390A at 8Kc:
> Steve, WB3HUZ has a pile o' files too:
> Here is the sound of a 51S-1F up on 10 meters AM:
> In addition, check this batch of wav and MP3:
> These will give a continuum of sound quality for sure.
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