I think what really surprised me personally is the (comparatively speaking) unimpressive numbers yielded up by the Drake '4-line' receiver design; there was a time during which my R4B figured prominently in my daily life when I was stationed overseas (the day would not have been complete without getting the news from the VOA and the BBC).
I'm left wondering how much more close-in dynamic range can be squeezed out of chips that can be put into designs that we hams can afford ?
(Didn't someone look into using active devices that would normally have been considered part of a transmitter design in an attempt to cobble together a receiver with an almost uncrunchable front-end ? I believe that it was the Squires-Sanders receiver of the 1960s that put a 7360 mixer as the first active device.)
- Paul, WB5AGF
To some extent aren’t many of the improvements technology is providing bringing us closer to the point where we can measure the improvement, but it’s extremely difficult to easily realize the improvement?
My first PC was an IBM running at 4.77 mhz. I upgraded to a 20 mhz “286” CPU which was four times faster. That was a very noticeable speed increase. Today, the technology has advanced to the point where CPU’s are running at GHZ speeds. While we can benchmark incremental increases, the actual user's perception is barely noticeable. Given the amount of RF pollution that is present, isn’t all this added sensitivity / selectivity less significant (for most locations)?
I read some were that technology has advanced faster in the last 30 years then it did in 200 years before that. Because things were understood for the first time it led to new directions. I wonder were we will be next time we understand something we don't get yet?
Given that, my guess is we're already talking about dancing angels on the pin's head.
We are close to the fundamental physical limits on receivers. Our transmitters are about to follow with predistortion. I have not yet calculated the impact on phase noise but there is a reason the most expensive single component in a Flex 6000 series without a GPSDO is the oscillator.'
We are close to the end and now it is time to work on software, features, future, decreasing cost of components, etc.
Remember, this is one person's opinion, I am so on the edge of Flex decision making these days that the first I knew of Maestro was the day I could put a deposit on one.
I am speaking for myself and not Flex.
Yes the laws of physics have practical limits...
For some factor we are already beyond the practical limits
One of my favorite specifications is MINIMUM DISCERABLE SIGNAL.. MDS
Radio manufactures play the specification bragging game claiming they have the best MDS with ranges below -140dBm or ever better.. yet for most practical purposes such as receiving in a city on say 20M, your background noise level will be at least -120dBM or greater.. so with -140dBm you are just amplifying the noise... hence.. we are already past the practical limit for that specification.
Another is Dynamic Range.. with Legacy Technology achieving dynamic range greater than 85 dB is actually pretty hard to do. you need all sorts of roofing filters and other techniques to push the range higher ... With SDR technology achieving dynamic ranges higher than 85 dB is much easier... the dynamic range is done is math and it is a direct function of the number of bits in the A/D converter. So a 16 Bit A/D gives you 96 dB of dynamic range... So how does Flex with their 16 Bit A/D produce Dynamic Ranges over 100dB. they use a very fast A/D converter and over sample each bit so effectively they are simulating a 20 bit A/D.... Already in the audio world you can find inexpensive 24Bit A/D giving 144dB dynamic ranges... it should happen in the RF world soon too...
However.. what it the practical reality... Sherwood states that most hams in normal use likely only need about 85 dB of dynamic range... Realistically if you are in a contest or have a strong nearby signal every dB of dynamic range will help but for the rest of the time... we are likely already there...
I started with CB Radio and Fox Hunting. Today its Cell Phones (Public Transceivers) looking for virtual intelligence. Technology improvements will keep us inspired for years to come. Wait for these young people to figure out what we old timers do for fun. Happy Hunting!!
In digital photography there are two types of people who buy
a camera. First, there is the customer who wants a camera to take good photos, a
real photographer. We also have the customer who examines every photo at 300%
of the normal size, looking for artifacts that 99% of the people aren’t even
aware that they exist. This is what we call a “pixel-peeper”. We hams fall into
two groups also – those who bought the radio to chat and enjoy the hobby (me),
and those are just obsessed with the quest to have the best specifications that
money can buy. Maybe it’s time to sit back on 75m and smell the coffee? Time to chill out and be happy your name wasn't listed in this month's "Silent Keys"!
HOWEVER... SDR's do offer lots of future opportunities to do a lot more than currently being done by Legacy Technology...Bob hit on the concepts of noise mitigation where the ability to add new noise mitigation mechanisms is rather limited in Legacy technology..
But there are other areas where SDR's are superior.. just look at the fact that Flex added several new modes such as DStar --- and of course the available API so that users can add features and functions they dream up...