Not having any particular axe to grind, I'll pile on a bit with some
comments.
1. The superhet/SDR vs direct sampling radio manufacturer and
technology competition is and will continue to be very good for the ham
community.
2. The early days of CD audio yielded, "I can't stand the sound" for
which there were sound engineering reasons. Today with 24bit 196KHz
sampling and playback, I think it is impossible to discern that analog
signals via LP vinyl are technically superior. However, that won't sway
a number of folks who "like the sound of analog". Sounding "different"
will always appeal to some segment Direct Sampling vs superhet/IF DSP vs
pure superhet. btw I suspect that the inherent amplitude/phase
distortions at the audio level of different amateur radio filtering
techniques affects intelligibility more than is commonly recognized.
3. Unfortunately, the ham radio market isn't currently large enough for
a major Si firm to design for our needs. The requirements are driven by
the cell base station market and perhaps a bit of military needs. So
sample rates are going up beyond the current 300 MSPS rather than more
bits of resolution which would solve the overload concerns. However, as
the technology of fast + wide A to D's disperses, there may be a
boutique firm that takes up the challenge as has happened in the audio
market where the best A/D's are not made by Analog Devices, TI, or
Linear Tech.
4. It seems that the overload issue is now confined by consensus to
duplex operations on the same band since high pass and bandpass filters
and stubs take care of most BCB/MW/multi multi overload situations. I
agree that overload otherwise is a minor concern.
5. As always there will be a range of good and not as good
implementations of technologies. Also, the terminology of "SDR" is a
mess since it is applied to several generations - 1. outboard audio DSP,
2. integrated audio DSP, 3. integrated IF DSP, and 4. direct RF
sampling. Many posts seem to me to confuse generations 3 and 4 and
perhaps different capability radios.
6. Moore's Law continues and more MIPS and FPGA gates will become
cheaper and better. It seems to me that the direct sampling technology
offers a number of opportunities for better signal processing than IF
SDR's. Maybe not, time will tell. FLEX has a teaser with "wide band
noise reduction" in their latest 6000 release. What is that?
7. One thing unlikely in affordable superhets in the opportunity to
decode many signals on many bands simultaneously. The contest rule
writers have/are going to have increasing difficulty with what that
capability means to contesting. e.g. a 5 band skimmer for SSB? (since
my Samsung S5 has nearly perfect speech recognition in a noisy car, is
that too far out?).
8. The content (syntax and semantics) of contest and DX messages are
mostly proscribed, so our brains ability to discern (or make a good
guess) of content in very poor signal to noise and QRM/QRN situations is
pretty impressive and varies hugely among operators. (rant: why do
DXpedition callers insist on telling me their state or they are QRP or
are running 50w to a dipole in the basement?)
9. This thread has been quite interesting and informative.
73,
Grant KZ1W
ex TX5D, TX7G, E51MKW
On 10/19/2015 13:06 PM, Tom W8JI wrote:
I'm still of the opinion --right or wrong-- that there will *always* be
hams using analog technology that will be able to out-hear anyone
using an
SDR (even DDS) to copy very weak CW signals at the low end of 160.
*But I
have an open mind.* I think it was Barry N1EU that disagreed with me on
that (I think he has an Anan DDS SDR). But we need people like him that
drive us to investigate SDR further. :-)
I think it depends on the individual. If an individual has the mental
ability to "process" noise out of the signal, external filtering and
"noise reduction" won't mean nearly as much. Some people I've operated
with are better than I am, some the same, and many others just cannot
hear the signals unless they are crystal clear.
I'm poor at SSB, but good at tone.
My first experience with this was when a group of people came over to
pick me up to go to the Cincinnati hamfest. I was working VK's on 160
(using a modified SX101) through heavy noise, copying the callsigns
fairly easy, but no one else could even tell there were signals.
Another case was at Dayton, when MFJ was demonstrating a DSP. I could
hear the signals the same with or without the DSP, and people walking
up were marveling. Others walking up couldn't hear the difference.
When a human is part of the decoding system, results will vary.
A similar thing is true for results at different stations, when we
talk about overload. One size does not fit all applications. I see now
where the one station's comments about a bunch of modest signals
overloading an SDR kicked off the "popular folklore" rebuttal, but
1500 watt transmitters into antennas less than 2 wavelengths from an
RX antenna are not the same as something far out of band one or more
miles away.
We have to read carefully, and not mix cases. :)
73 Tom
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|