Your reference to G8JNJ's article is appreciated in a timely manor. Due to its clear and basic explanation, I will probably include it in our Level-1 classes. With today's newer technologies, especially SDR-type architecture, performing bench-test S/N measurements on some of the newer receivers can bring us down close to the test equipment's residual noise figures. For several years now, we have included the Minimum Discernible Signal (MDS) figure. (I believe created in the ARRL labs) That method gives a reference that is easier to quantify in the real-world use of the receiver without having formulas and mathematics involved. Many of our customers do not have a good grasp on the relevance of? S/N or SNR, but can easily qualify MDS.
Recently, We were doing our own comparison between the W-J 8711 and Tentec R340. This is an ongoing and unsolvable topic. Not unlike going to the drag races and asking who has the most-winning cars...Chevy or Ford.
But when dealing with receivers that can "hear" in the -127dB to the mid -130dB signal levels, just a simple conversion to microvolts for the customer's understanding seems to be all they need on the S/N topic. When I tell someone that this radio can hear a 1 uV signal (-107dB), whereas this other one hears -127dB (0.1 uV) they can better understand the weak signal capabilities. Many of our civilian clients are involved in weak signal things like digtal-mode recovery, BCB chasing, Radio Astronomy and CW DXing. I'm one of them. With the right equipment, it's no problem to measure the radio's terminated input noise vs. the injected test signal in decreasing increments.
Sorry this is off-topic, but I was really impressed G8JNJ's article.
Good signals to all,
Bob, N1KPR
AmComm
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On Wednesday, February 22, 2023 at 08:25:30 AM EST, Martin via groups.io <martin_ehrenfried@...> wrote:
On Tue, Feb 21, 2023 at 05:46 PM, vbifyz wrote:
The input filtering may need more work to handle strong nearby broadcast stations better.
Hi Mike,
A good project.
I'm a bit concerned about the value of the input capacitors which are shown as being 1nF, with a comment to reduce them to 100pF if there are no strong FM stations nearby.
Using 1nF capacitors a typical 1m diameter loop, having an inductance value around 2.5uH, will bring the loop to resonance at around 4MHz, which is not desirable if you wish to have good performance over a wide frequency range.
Ideally the value of the input capacitors (and resistors) should be chosen in conjunction with the actual value of loop inductance, in order to provide a suitable matched characteristic and impedance tracking across the whole of the desired frequency range.
Some further notes on this subject can be found here.
Bob, N1KPR