Re: Newbie material on HF+(more)
On 20180409 21:35, Leif Asbrink wrote:
Hi Joanne,For one none of those terms imply the numbers you cite.I just think "There are rather few radios in the handsYou wrote "2) There are rather few radios in the handsMany, yes. I suspect "most" is still, by far, older
Second, if it is in a drawer as a curiosity it doesn't
count except as a means to distort conversations.
After reading here for as long as I have I rather doubtThe ham market needs a complementary HF transmitter toWhy is that? The old analog transmitter will continue
this is taking place all that often given the level of
technical expertise I hear on the ham bands when I listen
Even if it develops 20 dBm the FCC could determine it is(And both will lead to annoying interaction withI do not think the FCC would create problems for someone
a transmitter that can transmit outside ham bands and as
such faces FCC type acceptance and other blathers of FCC
regulations. (I have a poor opinion of the FCC likening
the intelligence of its leadership to that of a randy
hedgehog. Never Ever make laws or in their case regulations
you do not enforce. Lack of enforcement leads to lack of
respect for those laws and regulations. That leads to the
overgrown patches of chaos I hear on VHF and HF these days.)
In bands were it is permitted 50 mW is the typical power
limit for something sold as a transmitter.
The softrock is not a transmitter. It is a building blockNot sold as a transmitter, although it can be used as such.
If so used it would be illegal unless used by a ham within
I do not think the modest number of SDR transmitters isCan you apply the technology that developers using the
ANAN SDR transmitters have for dramatically reducing IMD?
And without that reduction why is a fancy SDR needed for
The FFT calculated number is an average already. In factIt is actually easier than it sounds. RMS power is computedWell, I wrote peak power, but of course the meterTrue - depending on whether it is done sample by sample
if you make a really fine grain FFT and don't use overlapped
computation techniques you're averaging over syllables which
won't catch the peak. All I'm saying is that the measuring
the peak of a signal is not as simple as falling out of bed.
It takes some thought. Many digital modulation techniques
featuring multiple tones have a very high peak to average
power. That's why they are best run at power levels well
below the peak the transmitter can develop. The human
voice also has that problem. By comparison CW is really
simple. And will your RMS give the same reading for an
extended key down, a series of Morse code dahs, and a
series of Morse code dits?
Of course, the average power over a period of seconds
is probably more important for the transfer of
information for most modes. But you need to know the
peaks in order to avoid overloading the A/D or D/A
elements in the system. They would set your compression
level in a simple manual or automatic gain control operation.
That is on the order of the sample rate for the ANAN SDRs.If I make a single 10 ns wide I and Q sample of RF asThe bandwidth of interest is perhaps 2.4 kHz for SSB.
What is grotesque about that?
It is done every day. But usually the filter is placed atI can square I and Q, add them, and square root the result.Dear Joanne, this question is irrelevant. Nobody would
the lower frequency after filtering and decimation to
minimize computation. But the result is equivalent to
filtering at the D/A output. The problem remains even if
I gave 10,000 theoretically instantaneous samples per
second with a 2.4 kHz bandwidth SSB signal. One sample
can give you anything from 0 to the power at the peak
of a sinewave. It takes a fairly long term sample to
extract the average power. And the peak power is of use
when trying to gain control so that ranges of D/A
converters on the audio outputs are not exceeded.
You say you have I and Q samples separated by 10 ns. ThatNo, it means I used real hardware and sampled at some
unstated rate that may be as low as 4.8 ksps for a
2,4 kHz filter. You read into what I stated more than
What we do is to decimate, apply a filter with a bandwidthAnd all that fancy processing is equivalent to placing a
2.4 kHz wide filter on the output of the A/D converter. You
just get fewer samples to mess around with.
Yes, now think in terms of the pathological cases and tellThat demands another question. Is there a material"the averaging above" ???
me what range of answer you get with a 1.5 kHz sine wave
in a 300Hz to 2700 Hz filter sampled at say 10kHz after
all the decimation. For various averaging times what is
the peak to peak variation in the measurement with time?
Alternatively one could use a 128 times larger fft withWhen you stop tilting at windmills I did not pose as
examples and concentrate on what I did say it might all
be more obvious. Even if you want to imagine sampling a
single 1.5 kHz signal out of a precision generator at some
frequency at 100 Msps what happens if you average over a
variable period of time and plot the output of the average
for several seconds before changing the averaging period?
This is easier to visualize, and probably more accurate,
than working with a low sample rate above the Nyquist
limit. Even an FFT derived FFT would show some variance
in measured signal level from FFT to FFT on a signal
at random frequencies. And human voices are a particularly
vicious thing on which to try to get a good peak reading
without resorting to the relatively meaningless largest
single sample. And that number does matter with respect
to limiting in equipment. But for things like SSB or
high peak to average digital waveforms the average power
over seconds is what matters more in the information
theory world. So to get back to where we started, what
number do we report to the person who just asked us for
an S-Meter reading? With SDRs we have more practical
answers to that question than with analog equipment.