Hi all
I have released firmware 1_00_017 at
The most important features are the AGC and S-meter.?
S-meter: it appears in the 3 characters to the right of the mode indicator character, when S-meter is enabled. The 15 vertical bars are worth 6dB each and therefore correspond to levels from S0 to S9 (9 bars) and?on up at S9+6dB, S9+12dB etc to S9+36dB when all three are full solid. The scale is calibrated in real decibels, but the accuracy of S0 relative to an actual signal input depends on the level of the gain setting you set for various bands in the Band Configuration terminal menu.?
AGC: it's a quite complex sub-system and I have documented the concepts and parameters in the 1_00_017 operating manual at , section 5.21 pages 52-57 inclusive. Briefly...?
AGC operates in the decibel domain, not linear. There is an AGC threshold below which AGC does not operate, it's a parameter specified in S-meter units. There's an impulse noise filter whose duration is configurable. The AGC slope is configurable so you can adjust it to your taste, you can have a gentle AGC action where strong signals are louder than weak ones, or an aggressive one where the AGC system makes everything the same volume. Hang time and recovery rate are also configurable.?
The AGC system creates an audio sample delay line, which it analyzes for impulse peaks then applies the calculated AGC gain (attenuation) to the sound samples in the delay line. The action of the AGC is therefore effectively instant; no matter how strong the incoming signal, the time taken for the AGC to react to it and protect your ears is always zero,?no piece of strong signal reaches your ears. The length of the delay line is configurable and needs to be a minimum 1.3ms for CW. SSB has a lower minimum audio frequency so a longer delay line is required; the maximum configuration is 6ms which would be able to handle signals down to 83 Hz. Either way, it's a very small latency.?
The S-meter also has a configurable "AGC action" display; if enabled, the S-meter looks like the Power/SWR meter function (during transmit) with two bars. The upper bar is the S-meter and the lower bar is the AGC action, with a configurable number of dB per pixel. It just helps you to see when AGC is active.?
The S-meter configuration parameters were moved to their own sub-menu under the Display/controls menu, and include an S-meter update interval parameter.?
I created a short demonstration YouTube video? . In this video I used a QCX, with about 150cm of wire attached to the antenna port, to generate a strong CW test signal. The BS170s in the QCX are toasted so this just produces very little actual power output but of course we are in close proximity, so the signal level "received" by the QMX is enormous, approx S9+30dB. In the video you can see heavy clipping when the AGC is off, which would no doubt generate a gigantic headache if you had earphones on; when I switch AGC on the signal is reduced to a comfortable S9 level.?
I also tested the QMX with AGC on 40m at night, tuning around for strong signals with and without AGC and I believe it is highly effective.?
The system is highly configurable, I suspect it may be TOO configurable; I will look forward to your feedback and suggestions on how it may be improved, and in particular it may be possible to remove some of these configurations, or derive or calculate them. The attached screenshot shows the configuration I used for the video. I must say though that it does not appear to be a delicate act, balancing parameters carefully; it seems generally to be very effective and insensitive to the exact settings.?
I do highly recommend though that you read the operating manual pages 52-57 carefully; initially all the parameters will be zero and you need to set it up carefully, before enabling AGC. At the moment there are no default values. So let's see.?
Other than that, I also added an LPF sweep tool (see example attached), which was discussed some time ago here. It "transmits" at 1/4 full power, into a dummy load (DO connect a dummy load!) while sweeping the transmit frequency, and plots the measured power output, after conversion to dB and normalizing the center frequency measurement as 0dB. It's indicative only, but quite interesting to see and educational, perhaps useful for debugging too.?
Plus a couple of bug fixes; change list is:
- Bug fix: '5351 synth code for setting TX params could lock up in some circumstances
- New LPF Sweep application in the terminal
- Added S-meter
- Added AGC implementation and supporting configuration menu parameters
- Bug fix: Parameter corruption (incl IQ Mode setting lost) in Digi config menu
So that's my week's work here.?
73 Hans G0UPL
Paul Christensen