++++++++++++++++ Date: Sun, 16 Dec 2001 09:24:21 -0500 From: Don Jones Subject: [Elecraft] Stray RF and the K2 One last question before I tell St. Nick to fetch me a K2. I live on a small lot and have almost zero flexibility in my antenna arrangements. For 80 through 30 meters I use an 80 meter Zepp, fed with 450-ohm ladder line all the way back to my ancient Heathkit tuner. It is only about 38 feet high at the apex and one descending leg passes almost over the shack. It is probably no more than 15-20 feet straight-line from my transceiver to that leg. I have seen fairly significant evidence of RF sneaking back into the shack. It is enough to drive my computer speakers crazy on some bands, but has never crashed my computer nor caused interference to the display. On 30 meters it has frequently caused my CW sidetone to "whoop". This has been while running 100w with a TS440S. Although I really do enjoy QRP, I am not (yet) a purist and will almost certainly add the 100 watt PA module very soon. Now - has anyone had any significant problems with RF disrupting the stability of the K2 VFOs - especially while driving a PA of any kind? And does anyone have testimony of trouble free operation in close proximity to their antennas? I was recently on the verge of buying a TenTec Jupiter and learned that this was probably a strong concern with that rig (resulting in frequency jumping). I certainly hope that it is not a problem with the K2. I just have this stubborn opinion that HF transceivers should not be overly prone to choking to death on their own juices! Thanks! - Don N4TN ++++++++++++++++++ Date: Sun, 16 Dec 2001 08:20:12 -0800 From: Vic Rosenthal Subject: Re: [Elecraft] Stray RF and the K2 Don Jones wrote: > > For 80 through 30 meters I use an 80 meter Zepp, fed with 450-ohm ladder > line all the way back to my ancient Heathkit tuner. It is only about 38 > feet high at the apex and one descending leg passes almost over the > shack. It is probably no more than 15-20 feet straight-line from my > transceiver to that leg. I have seen fairly significant evidence of RF > sneaking back into the shack. It is doubtful that the proximity to the antenna will cause problems in the K2 or any other rig as a result of direct pickup. I've run 800 watts to a vertical whose base is about 10 feet from my K2 (driving a couple of amplifiers) with no problems. Radios are built in metal cases with filtered power leads to prevent this (unlike, for exaple, your computer speakers). Having said that, really enormous quantities of rf can appear on the supposedly grounded parts of your station under certain circumstances, like feeding an unbalanced antenna. If your antenna is much higher on one side than another, there will be unbalanced currents in the parallel feeders, causing radiation from the feedline all the way to the tuner. A balun will help in some cases. Your heathkit tuner probably has a balun in it, but the balun is effective only when the impedance it sees is within a narrow range, likely only on a couple of bands. You might find it possible to change the bands on which you have problems by changing the length of the feedline. Coax-fed antennas often has the same problem as a result of antenna currents flowing over the outside of the shield. One solution to this problem is to establish an RF ground by connecting a 1/4 wavelength wire (for each band on which your equipment is 'hot') to the ground post of your tuner. The 'artificial ground' unit made by MFJ in effect does this with one wire by kaming it tunable. I think the K2 is relatively well-shielded, and should not be more susceptible to RF than other radios. I suspect that problems reported with the Jupiter are more due to RF getting into the computer than the rig itself. Computers seem to pick up (and radiate) RF via monitor, keyboard, port, and speaker leads. 73, Vic, K2VCO Fresno CA ++++++++++++++++ Date: Mon, 17 Dec 2001 18:37:44 -0000 From: "Dave Johnson" Subject: Re: [Elecraft] Stray RF and the K2 Don I use an open wire fed doublet, 100 foot long, apex at 31 feet, runs within 10 feet of the shack. Fed with open wire line, 4:1 balun and a choice of manual ATU or LDG Z-11 auto ATU. No problem on the K2 at all, either CW with paddles or on SSB with Kenwood MC-43S microphone. I run all bands 80 to 10. 73's Dave, G4AON K2 #1892 >One last question before I tell St. Nick to fetch me a K2. I live on a >small lot and have almost zero flexibility in my antenna arrangements. >For 80 through 30 meters I use an 80 meter Zepp, fed with 450-ohm ladder >line all the way back to my ancient Heathkit tuner +++++++++++++++++