Hi to all, This is not a critical issue, but it might interest some. It's also not necessarily specific to K3's. Keywords might be "switching power supply", "inverter", and "grounding".
The problem I describe below was never experienced with the K2, only with the K3. I exchanged the two radios to confirm this experimentally. The power supply scenario is as follows. Qty 2 - 50W Siemens solar panels on the roof above the shack supply a 12V 100A-Hr SLA battery. The battery is charged through a Micro-X charge controller, and this arrangement has been used for a few years with my K2. It seems to work well under all conditions. The K2 is the low power QRP version, and generally draws less than 2.5 A from the battery at power levels I run. The battery is connected to a Xantrex RS-400 sine wave inverter. THD on the 60 Hz output is supposed to be < 3%. Looking at its output via a Tek 2465A scope shows a very clean sine wave, even under the max 400W load. The inverter is rated 400W, with surge to 800W. The inverter feeds an Astron SL-11A switching power supply that powers the K3/10. Its output is 13.6V, and under max load at the K3 we're talking about 2.8A, or 39W. All units described above are bond-grounded to each other using a 1/2" braided strap. The strap drops 10 feet or so to an 8 foot ground rod. The ground rod is also bonded to the house ground nearby. The house ground is used for all main and backup loads for a much larger Solar PV system that we use to power the house here. When using the Battery => Inverter => SL-11A power supply => K3 power supply path to power the radio, the switching supply hums quite a lot in weird non-periodic ways. I can sometimes hear the same hum on the K3 RX audio, but have had no reports of it showing up on TX audio when I asked the other party. "Very clean audio", they would always say. Given the long-winded narrative above, does anyone have an idea about the rx noise I'm hearing? Seems like it's not getting in through the DC, since it doesn't show on SSB TX. So maybe I'm hearing it over the air? I thought this might be common mode noise, but the TX reports I've got with this power supply setup won't support that. Grounding can affect that, but since low impedance paths are connecting all the inline stuff, this doesn't seem the easy answer either. Sorry to take up so much bandwidth, but it's possible another Elecrafter type might face a similar issue. So it seemed worth the bits. BTW, connecting the K3 directly to the 12V SLA battery has none of the above effects and works fine. Please - no flames over the easy answer, OK? :) 73 and thanks for any thoughts, matt zilmer, WA6EGJ K2 s/n 2810 K3 s/n 0024 _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
