This is why I run 10 watts mobile with the KX2 or KX3 :) Last time I tried this, using 10 W into a Hustler 40-m whip, I worked JA1NUT on CW and had no trouble checking into a statewide net on SSB. Also had quite a few SSB QSOs on 17 m.
So if you find all this excellent information about mobile/QRO overwhelming, try mobile/QRP. Wayne N6KR ---- http://www.elecraft.com > On Apr 15, 2017, at 8:55 AM, Colin Brench via Elecraft > <elecraft@mailman.qth.net> wrote: > > Greetings to all, > I thought I would start a separate thread to expand this topic is a slightly > different direction as this topic touches on a number of areas. > The exposure discussion is very valid especially in today's vehicles that > often contain composites rather than metal panels, but I will leave this to > others. My expertise is in EMI control and so I can provide some background > to how unexpected things happen. > The DC issues are clear - you need to provide enough power cleanly to an > inverter. Well over 100 Amps peak with acceptable drop. This is all very > low resistance but not necessarily low impedance at the high frequencies > being used. So some serious EMI filtering may be needed to keep things > stable. > RF fields around the antenna will be high and most mobile antennas have a low > input impedance. To fully understand EMI risk you need to understand where > the RF current will go, and simply put you need to consider the antenna as > every conductor in the vicinity of the actual radiator. The one rule of > antennas is that current goes to zero/reflect back from an end. This is how > NEC works - it solves for the current distribution over the entire structure > be it a dipole or frigate, these currents are then used to calculate the > antenna effect. Now for a vehicle the antenna and car body are the most > obvious conductors to consider and may be OK for the antenna analysis. > However, considering all conductors is essential for EMI analysis, so add in > all the cables, door slots (well insulated breaks in the 'Faraday cage'), all > other antennas, engine and mounts ground straps etc. Picking which can be > ignored in a given situation requires serious expertise. > For QRO operation these directly induced currents are very critical. > Unwanted high current on any electronically controlled function can have > unexpected and potentially unpleasant results. The addition of the ham > antenna, DC wiring, other control wires combined with the possible positions > for each part of the system may drastically change the results of the system > analysis performed by the vehicle designers. So caution is certainly called > for. > EMI testing has a number of aspects, using a radiated field of 200V/m is one > typical test for remote EMI risks. Direct current injection is used to > simulate near effects such as cells phones of an on-board transceiver of > 'moderate' power. If you can find out how the vehicle you have was tested, > then it is possible to get an idea of how much risk there might be (using NEC > to guesstimate the induced currents on each band). this is not easy,,,, > Today's vehicles have so many safety critical electronic circuits that > manufacturers do go to extremes to keep everything bullet proof, but 1kW to a > (by necessity poor) antenna is most likely outside their considerations. EMI > issues won't show all the time, as effects can interact, there is a stream of > data being passed at all times and upsetting some data patterns can be easier > than others. Because of this testing takes a long time to get a high > confidence that vehicle performance is reliable or at least will fail to a > safe mode > OK. all said what is practical here? First I would consider how much power I > really want to use as the problems grow rapidly with higher power. Seek the > advice of someone familiar with both QRO operation and your specific vehicle > if possible (as was done on this list). Be cautious and aware of the vehicle > behavior until you are sure all is well. I would happily run a 1kW in my > 1969 vehicle, but would be extremely cautious abut that in my 2015 minivan! > Though ensuring good general RF design consideration I would not worry about > 100W in the minivan, maybe 200W, after that I would be in caution zone. > A call to the vehicle manufacturer might shed light on what they consider > reasonable or possible (though they might just say don't do that :-/ ) > Very 73, > Colin.. WDJR > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to n...@elecraft.com ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
