As one who has been playing with small inexpensive SDRs since the days of the Softrock, I've been amazed by how well the simple yet very effective Quadrature Sampling Detector aka "Tayloe Detector" (named after it's inventor Dan Tayloe) actually works. Using calibrated equipment I've measured the Minimum Detectable Signal (MDS) at -122dBm using the same 3dB in 500 Hz bandwidth method that Rob Sherwood, ARRL, and other test labs use. That translates to .17uV RMS, which is to say that the QSD will hear any signal that is above the noise floor unless you get to the upper range of the HF spectrum or are in a very quiet rural location. In short, the QSD is often a better front-end than the DSP in the radios it is usually connected to.
I've verified this by feeding the QSD output from my uSDX into a PC via a good soundcard and running SDR# or HDSDR on a PC. There are several reason for this: the ADCs in the soundcard provide better resolution and lower noise, DSP calculations can be done using more precise floating point math, filters can be MUCH better, and most importantly, a Low-IF architecture can be implemented. The uSDX and most other simple SDRs use a zero-IF or direct conversion method and anyone who has built a direct conversion receiver knows that there is always noise and unwanted signal components such as LO leakage and 1/f noise at the "center spike" or Zero Hz. While this can be minimized, a side-by-side comparison of zero-IF (uSDX) and low-IF on the PC with the same signals shows a significant improvement with the Low-IF. Typically this is done by offsetting the frequency from 10 to 20 kHz for demodulation at a spot that is clear of all the spectral debris at the center (basically creating a superhet receiver). However this requires significant computational resources that are impossible on the uSDX. The difference is especially noticeable when listening to AM where the zero Hz noise mixes with the desired signal to produce unwanted and annoying heterodyne tones in the audio, or when a spectrum/waterfall display is desired. (The Xiegu G90 is a good example of a small SDR that implements a Low-IF architecture to provide a clean display and noise-free demodulation). To be useful as a tuning and band visualization aid, a spectrum/waterfall display also needs to provide sufficient resolution and a color display is a huge benefit.
Of course having to have a bulky, power-hungry PC or laptop connected to provide these functions isn't quite compatible with how many users wish to use their uSDX and similar radios. So I'm excited when I recently learned of a new product, the Quantum Spectrum DSP accessory, that provides many of the same benefits in a small portable hand-held sized package: https://quantumsdr.com/
While the initial offering does not include an audio capability, the company has hinted that this may be possible if demand warrants (which it no doubt will!). But the Quantum Spectrum add-on takes IQ output from any receiver or transceiver that can provide it and generates a spectrum and waterfall display on it's 320x240 pixel color touchscreen display. It also can control the radio via a serial CAT interface, so the radio can be tuned by touch! I've linked a short demo video and the company's website on my website here: https://tinyurl.com/mpur4bk7
I have no connection with the manufacturer but there is a link on their site to "store" where at present a 1GBP ($1.14USD) deposit can be made to be part of a group buy that is planned for late April delivery. Since I'm always missing out on group buys I wanted to pass this along for anyone who might be interested.
With a simple plug-in connection the Quantum Spectrum display looks to be a much more natural companion for a small portable SDR radio - I'll know for sure after the group buy is completed and I get hands on one. And if the promise of adding audio output is met in the future, it will be capable of bringing out most of the capability the QSD has to offer, and at a fraction of the price of other panadaptor/display units on the market.
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LTSice is a powerful simulation tool that is provided free by Linear Technology Corp. It comes with a complete library of passive and common analog solid-state components but if you want to use it to simulate vacuum tubes, it doesen't work as-is. Even though triode and pentode symbols can be found in the "Misc" folder, they are just schematic symbols and... READ MORE
- Robert Nickels (ranickels), 09/267/2023
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Comments from Robert Nickels W9RAN, July 27, 2023:There is nothing worse for a ham radio operator than to see a beloved friends callsign with the letters "SK" behind them. Yet sadly, that's what happened on July 23, 2023, when I learned of the passsing of Merv Schweigert, K9FD. While many of our ham radio interests were different - Merv was a... READ MORE
- Robert Nickels (ranickels), 07/208/2023
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I know many of us who enjoy restoring and repairing vintage gear look forward to winter when there is less competition for time and energy, and a chance to really make a dent in our "to be fixed" piles. A couple of years ago I set time aside for "Heathkit Singlebander Week" and went through every one of them I had, with the result that they're all working ... READ MORE
- Robert Nickels (ranickels), 01/19/2023
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Leo Meyerson had been in the ham radio retail and manufacturing business for over 25 years, and by 1970 he was ready to retire. His son took over the WRL distribution and retail business but the Galaxy Electronics manufacturing operation was sold to his long-time friend Andy Andros WØLTE, founder and president of Hy Gain Electronics in nearby Lincoln NE. The CB radio eleme... READ MORE
- Robert Nickels (ranickels), 11/330/2022
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Most of the articles on this site are about hams, or ham radio. This one is not about a ham but about a man who built as much a reputation through HF radio as any ham on top of the BPL ever did. Don Taylor is one of those rugged independent-minded people who thrive on a lifestyle most of us couldn't even imagine - as a trapper in Canada's Yukon wildernes... READ MORE
- Robert Nickels (ranickels), 10/304/2022
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Most radio fans know the history of KDKA but maybe not "the rest of the story".In November 1920 the Westinghouse Electric and Manufacturing Company began operation of a radio broadcasting station, KDKA, in East Pittsburgh, Pennsylvania, often described as the "Pioneer Broadcasting Station of the World." KDKA is generally considered to be the first commercially... READ MORE
- Robert Nickels (ranickels), 09/252/2022
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The microwave network constructed by AT&T Long Lines and other telecommunications companies in the past 50 years were engineering masterpieces using state-of-the-art technologies and some were designed to withstand nuclear attack during that Cold War era. This is a non-hardened site on top of a mountain in upstate New York that existed long enough for graffiti taggers t... READ MORE
- Robert Nickels (ranickels), 09/251/2022
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In 1917 a missionary named William Cameron Townsend went to Guatemala to sell Spanish Bibles. But he was shocked when many people couldn’t understand the books. They spoke Cakchiquel, a language without a Bible. He believed everyone should understand the Bible, so he started a linguistics school (the Summer Institute of Linguistics, known today as SIL) that trained people to do Bible ... READ MORE
- Robert Nickels (ranickels), 07/183/2022
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Visitors to the Elgin National Historic area along the Fox River in Elgin Illinois may not realize they are at the site of a famous shortwave radio station - W9XAM - the time signal station operated by the Elgin Watch Company.Elgin was the only watch company maintaining an observatory that observed, recorded and broadcasted time from the stars correct to the hundredths of a second. Located a... READ MORE
- Robert Nickels (ranickels), 05/129/2022
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The Mosley CM-1 receiver is quite well known and not especially hard to find in the US even though it was the only radio produced by the company that has been well-known for antennas since 1939. Or is it...?A full-page ad (advert for you on the other side of the pond) appeared in the RSGB Bulletin in 1963 for a nice looking and very capable SSB transmitter called the "Commando II&... READ MORE
- Robert Nickels (ranickels), 04/105/2022
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