Topband: (no subject)

Lee A Crocker lee_crocker at
Fri Feb 16 01:51:00 EST 2007


<We hoped the SDR-1000 band display would, as another
operator claimed, give Mark B the advantage of "seeing
pileups" when new stations or multipliers arrived on
the band. Unfortunately we learned it could not do
that, the wide-spaced dynamic range not able to handle
the transmitter's signal despite being connected to a
low dipole thousands of feet away. The display dynamic
range, like the receiver dynamic range, was only in
the mid to upper 80dB range.

Despite being able to duplex with near noise floor
signals on the conventional gear, the SDR1000 could
not handle the strong transmitter signal. If you want
to know when a new stations comes on, you either have
to use packet or tune a second receiver around and
check the band frequency by frequency. It still takes
a frequency converter and conventional filter to
handle a contesting environment and legal power. We
can't imagine how bad it would be with 6dB (or more)
gain Eimac radials!>


I live in an orange grove in rual Florida, but my road
is paved with the black tar cause I'm uppity.

Aside from the comment about active radials, I think
the last few llines above are actually the point of
this analysis.  You chose the SDR-1000 for its unique
panadapter display, and it in fact does behave like a
panadapter.  That is the design philosophy of the
radio.  To then indict the radio because it doesn't
behave like a radio with a roofing filter design
philosophy is kind of like indicting an apple because
it's not an orange.  

In your previous post to me, the defense was basically
that the $1700 SDR radio didn't behave as well in a
high RF situation as your $4000 radio plus your
$40,000 FFT spectrum analyzer.  Unlike the SDR-1000
these 2 pieces of gear are not integrated in any kind
of systemic way, so the real analysis should be
between the $1700 SDR's panadapter and the $40,000
spectrum analyzer.  In order to visually search for
the red meat you need a screen not a speaker.  I think
it's a bit disingenuous to expect a $1700 radio to
behave like $40k worth of equipment.

I also think your hyperbole is a bit out of line in
regards to the notion that SDR is a good radio as long
as there are no stations on the band and you live in a
noisy location.  My example went directly against this
conclusion, since I conducted my experiment during a
160M DX contest on signals on the order of -115dBm to
-127dBm.  Rural FL is not quite as quiet as rural GA
but we are close.  This experiment was performed with
a different sound card than you used and with a
different sample rate.  I used the same sound card and
sample rate as the ARRL test.

So your real conclusion is that given the hardware
setup you and your friend concocted the radio failed
to provide you with the panadapter display you
desired, and therefore you had to revert to tuning the
band in a slow, aural, blind, first in first out
fashion. Certainly that means is not much more useful
than an RF overwhelmed SDR, so your $4000 radio was
not in the end any more efficient that my $1700 radio
at accomplishing your task of swooping down on newly
minted packet pileups.  Actually if you had given
yourself some quiet periods like occasional 10 second
respites between "CQ contest", you could have used the
SDR to do your packet swooping and you may have
increased your score.  The criticism that the radio
failed to meet your needs is certainly a fair
conclusion.  The rest to me at least is a mixture of
interesting analysis, because I always have something
to think about when you unleash, but also some rather
extreme hyperbole.  

As I stated before I have noted the FA-66 which is the
soundcard you were using, seems to be more sensitive
to high RF environments than the other soundcards, and
also sampling rate seems to be a factor in the mix. 
The FA-66 also has a fixed gain control which allows
the dynamic range of the device to be set
independently.  If you turn this control up you get
much increased sensitivity at the expense of range,
the opposite is true of turning this control down, so
I also wonder if you tuned the soundcard for best high
RF environment conditions.  Also I would think that
swooping on pileups would not need as much sensitivity
as pileups tend to occupy a lot of bandwidth with
stations that produce a lot of amplitude.  

In conclusion I think there are several variables in
your experiment that were not well characterized or
controlled for and the SDR may in fact behave in a
somewhat better manner if it was tuned for best
performance in a high RF environment to for allow
visually guided pileup swooping.  After all isn't this
the reason you use heavily modified R4-C's and not
stock ones?  

My own experience is that the radio performs well in
DX and contest situations in crowded bands using
reasonably good antennas.  I do hear an occasional
boop or beep that should not be there but not very
many.  I have not tried to use it as a pile up
spotting panadapter against 1500W 20khz up the band. 
My general experience is that the radio properly set
up would experience about 20 to 30 db of desense in
that situation, (i.e the noise floor would be around
-85dBm instead of -115) with antennas much closer than
"thousands" of feet apart.  My experience is with
antennas on the order of 1 or 2 hundred feet apart. 
30dB of desense still lets you see S-7 signals, and
one would expect a packet pileup would have many
stations at least S-7.  If I get the chance I will try
this experiment on a different sound card than the
FA-66, (which is the soundcard I am presently using)
and see what happens. 

73  W9OY

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