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Re: [IC-7000] ALC question
I don't dispute what you are saying (other than "the ALC display is wrong"), but what you are doing does NOT measure the problem with many modern radios' ALC circuit. You are measuring a static level two-tone signal and seeing that the ALC prevents over-modulation (clipping).
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The problem I am describing results from the DYNAMIC performance of an ALC circuit with too short of a time constant (plus other things), that results in a rapid amplitude modulation of the IF stages (and thus driver and PA). This ALC signal modulation introduces higher harmonics (not related to the baseband audio signal frequencies) that results in a form of IMD that significantly increases the bandwidth of the desired signal, out to tens of KHz. I'm focused on several projects for the next week that limit my time to collect more data and graphs, but for an example of how running one of the currently best rigs (FTdx5000D) in class A mode with no ALC versus 50% (3 dB) ALC, download: This is a 45 minute (39 MB) presentation by Rob Sherwood for the PVRC Webinar series. At time marker 23:11 he begins discussing TX bandwidth measurements using white noise audio, instead of two-tone, to better represent complex waveforms. At 25:52 is a spectrogram of the effect moderate ALC has on one of the best radios. What I'm seeing on the 7K is much worse. If the ALC level is greater than 50%, the TX bandwidth increases to 20+ KHz with some components only 40 dB below PEP. What I haven't looked into is why turning on compression to only 3-5 makes it so much worse, compared to other radios (such as the K3). This isn't just a theoretical problem seen on a lab analyzer. It has been confirmed multiple times in on-the-air contacts, by having the receiving station tune slowly off frequency (using a narrow roofing filter) and listening for spurious emmisions. This problem isn't unique to the 7K either. Many operators run their radios with excessive ALC and they are easily spotted on a spectrum analyzer if their signal is at least an -70 dBm and the band noise isn't too high. The 7K's ALC indicator isn't broken in SSB mode. Steve, W3AHL --- In ic7000@..., "ludoradio@..." <ludoradio@...> wrote:
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Re: ALC question
Yes, the ALC indicator does tend to go to full scale and into the red zone with compression on, but that doesn't mean it isn't creating splatter. Here is what I see on an Agilent 8924C analyzer hooked to the 7K's HF antenna output via a 30 dB attenuator, with 300 Hz sample bandwidth with a span of 40 KHz. The audio source was a stock HM-151 mic with a long AHHHH. Mic gain was set at 35% with two narrow bars of ALC showing when compression is off.
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With compression on, running 80 watts PEP on 14.2 MHz and with the ALC showing all green bars on, I see splatter +/- 20KHz or more from the sideband peak (carrier frequency + 1.5 KHz for USB) at -40 dBc (40 dB below carrier, which is the peak sideband level in this case). Assuming I was running a full 100 watts, which is 50 dBm, then the IMD products are 50 dBM -40dB = 10 dBm. Free space path loss at 30 miles from the antenna is aobut 90dB, so stations within 30 miles would receive my splatter at 10 dBm-90dB = -80 dBm, which is a little more than S9 on the S-meter on a 7k with the pre-amp on. If you are running an amplifier, the problem is of course worse. This splatter exists when the ALC exceeds 50% of the green bars on. At 50% ALC, the splatter is below about -55 dBc. Below 30% ALC I could not see any splatter above -65 dBc. Which is why I don't use compression often and am very careful with the mic gain and background noise levels when I do. I have too many ham friends that share the bands within a 30-mile radius. Steve, W3AHL --- In ic7000@..., "P.C." <pcsalley@...> wrote:
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Re: SWR not working.
I had a 7K on the bench for a minor repair and measured the IC960-1 voltage with a 25 ohm load (two dummy loads in parallel) at 14.3MHz with 50 watts TX PO setting. It was 1.16 VDC and the SWR meter display was exactly 2:1.
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If you saw a similar voltage, then the problem may be in the LOGIC board or CPU input pin. Steve, W3AHL --- In ic7000@..., "baulard69" <georges@...> wrote:
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Steve W3AHL