Jim,
interesting replies there. I would like to add some comments, for the
possible benefit of readers:
when using a Flex transceiver with the amp, there is no control
cable between it and the transceiver. Both plug into the internet and
all communication is via the internet.
I would think that the LAN (local area network) is meant, rather than
the internet. Your LAN might or might not be attached to the internet.
If any radio actually requires a functioning internet connection, that
would be a serious reason against purchasing that radio!
> (Also, Flex transceivers time
shift CW as it's sent to allow any other brand of amp to come on-line
gracefully and to eliminate any potential latency. I don't believe other
transceivers have this capability.)
Flex transceivers are SDRs. Every SDR can easily time-shift signals.
Most modern transceivers, even if they aren't true full SDRs, do use DSP
for modulation, demodulation, filtering, etc, so they are SDRs in this
limited sense, and can do time shifting. Of course it's up to the
manufacturers to decide whether or not they include software to adjust
the time shift.
What's more of a problem is that SDRs cannot work WITHOUT time shifting.
The digital processing of signals requires many samples of the signal,
both from "before" and from "after" the current sample. So they must
keep a certain number of samples in memory, which means that the signal
going out is always somewhat time-delayed relative to the input signal.
While completely analog transceivers also have some signal delay, most
of it in the crystal filters, that's pretty short. The delay caused by
digital signal processing is typically longer, but is under control of
the software, allowing trade-offs between the amount of time delay and
the quality of filtering.
Depending on the implementation and configuration, an SDR's delay might
be anything from a few milliseconds to several hundred milliseconds.
Only the shortest of these delays allow QSK, while non-QSK operation is
comfortable up to at least 100ms delay, and possible even with several
hundred ms delay.
If a radio can intentionally add a delay to the signal, to cope with a
slow amplifier, that's great and useful, but the combination definitely
cannot do QSK.
Just for reference, some data on mu Kenwood TS-450SAT, which I measured
in RX mode many years ago. With the stock 2.4kHz second IF filter, and
no first IF filter, the delay is 1.22ms. With its widest filter, a 12kHz
wide one, it's just 0.35ms, while the combination of the two narrowest
filters I have (1.8kHz in the first IF and 500Hz in the second IF)
causes a delay of 3.50ms.
In TX the delay in SSB should be about the same as in RX with the 2.4kHz
filter, and in CW it could be much shorter, because no IF filter is
necessary.
The delays of my SDR, based on a Red Pitaya board and PowerSDR software,
are much longer, but highly configurable.
In addition, on CW the amplifier
achieves about 70 percent efficiency, which allows it to run cooler than
most solid state amps, thus allowing less fan noise.
This is something that really every power amplifier can do, but most
radio manufacturers don't take advantage of this and run the amplifiers
in fully linear mode even on CW. On the other hand, transmitting CW with
a saturated amplifier results in a less than optimal keying waveform.
Most operators wouldn't worry about this, but I know CW purists who do
worry, and only use highly linear amplifiers even for CW!
*The current recommended transmit delay is 20 ms but we will drop that
to 10-12 ms soon subject to further testing. **For FlexRadio only, this
added delay is about to go away and will be incorporated into the
handshake interchange, so any transmit delay is transparent to the
customer.? For Flex radios only, the radio delays the start of the CW
transmission, so no leading CW elements are lost. **For other brands of
radios, we will soon see a shortening to less than 15 ms. Other brands
of radios are not as sophisticated as to delay the transmit stream.*
A comment about this reply: This time delay implemented in SDRs will
certainly cause the station's transmission to get out without any
missing or shortened dits - but more time-delayed than the transmission
of a non-SDR. When trying to break in, your transmission will always
come late. When briefly switching to RX between dits, even if the radio
hears anything it will get through to the speaker much delayed, making
QSK less practical, or perhaps not practical at all. How is that, QSK
operators? When you listen between dits, is it OK to hear what was sent
by the other station a few dits ago, or does it have to be current?
The SDR might actually put the received signal on top of what you are
transmitting, in your headphones.
In my opinion, QSK and SDR don't go together very well. Good QSK is
easier to implement in conventional radios.
*The relays are rated for a maximum contact bounce of 7 ms.? That plus
some time to control the relay we allow for 10 ms.? This is on the order
of the fastest transceiver key down to RF out.? As stated above, the
relays are not hot switched.? The relays are rated for 10 million
mechanical cycles.? You can see the Finder 40.52 specification sheet
attached. Contacts are AgNi.*
Flex has a point there. Modern relays, even quite cheap ones, are faster
and more enduring than those of olden times.
Of course PIN diodes are even much faster...
*We have significantly improved fan noise beginning with firmware 2.8.7
or later.? CW mode operates at 70% efficiency and a fairly low duty
cycle compared to RTTY and FT8 so fans typically will remain on the
lowest speed in most CW operation.*
The best solution to fan noise is adopting high efficiency
amplification, to reduce heat generation so much that either fans become
completely unnecessary, or can run at very low speed. I'm working on
it... Maybe in 50 years I finish the project! Fat chance... ;-)
Manfred
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