+++++++++++++++++ Reply-To: From: "Ron D'Eau Claire" To: Subject: RE: [Elecraft] high ref warning Date: Sat, 26 Oct 2002 17:58:55 -0700 Ken W8OB wrote: I just noticed while running 100 watts output on 10 m ssb that voice peaks or a whistle will sometimes give me a high reflected warning. The vswr on the antenna is 1.3 to 1 where I was operating and I noticed what looked to be a bit of oscillation also. Anyone else run it this? I have the station gear well grounded to a separate rf only ground here. I could not get the problem to duplicate on other bands only ten meters ========================== The first thing to do is to run the amp at 100 watts output into a dummy load and see if the problem goes away. That will ensure the problem is in the antennas system and not in the amp. One very common reason for this behavior is an antenna system with a toroidal balun. If the toroid is not big enough to handle the magnetic flux, it will saturate causing a big spike in the SWR on the line. This will happen when the power level gets too high, producing too strong of a current in the windings. Your SWR meter may not be quick enough to show the jump in SWR, but the KPA100 SWR protection circuit may well be. That's certainly not the ONLY reason for this to happen, but if you have a toroid in the antenna system, it's a good bet. Especially if things look fine at lower power levels. Other reasons in the antenna system can be arcing. This can happen in baluns too when the line is at a high impedance where the balun is inserted. The turn-to-turn voltage may exceed the capabilities of the insulation. Also, a marginal connection anywhere, or marginal insulation anywhere in the feeder or at the high-impedance points of the antenna can cause this behavior. Ron AC7AC K2 # 1289 +++++++++++++++++ Date: Sat, 26 Oct 2002 20:51:54 -0500 From: "George, W5YR" Organization: AT&T WorldNet Service To: ken cubilo electric Cc: elecraft at mailman.qth.net Subject: Re: [Elecraft] high ref warning Disconnect the r-f ground and see if the problem continues . . . 73/72, George Amateur Radio W5YR - the Yellow Rose of Texas In the 57th year and it just keeps getting better! Fairview, TX 30 mi NE of Dallas in Collin county EM13qe K2 #489 Icom IC-765 #2349 Icom IC-756 PRO #2121 ken cubilo electric wrote: > > I just noticed while running 100 watts output on 10 m ssb that voice > peaks or a whistle will sometimes give me a high reflected warning. The > vswr on the antenna is 1.3 to 1 where I was operating and I noticed what > looked to be a bit of oscillation also. Anyone else run it this? I have > the station gear well grounded to a separate rf only ground here. I > could not get the problem to duplicate on other bands only ten meters > ken w8ob #2864 ++++++++++++++++++++ Date: Sun, 27 Oct 2002 09:39:12 -0500 From: ken cubilo electric To: elecraft at mailman.qth.net Subject: [Elecraft] re 10m instability fixed....I hope ok guys here's what i did re the 10 meter ssb oscillations. They were being caused by stray rf from the kpa100 getting into the k2 main board and I suspect via way of the ssb module. I took G3PJT's advise and installed additional shielding around j2 the coax connector on the kpa100. I checked out the placement of l10 and that was ok. I used braid from a piece of rg/8m cable and using two strips soldered on the shield across the opening for j2 and resoldered at the first screw holding the shield closest to j2. I then tried out the rig and found it had quieted down quite a bit but was still getting a bit of rf in the modulation but no longer getting oscillations. I added a 2nd strap from the ground point of the ksb2 module to one of the screws on the kpa100 shield directly above it making it as short as possible with access through the side panel and bingo she is clear as a bell. I am not going to do the happy dance just yet as this type of problem being so border line from full stability sometimes has a tendency to return. Anyway I tested her out on 10m this morning working a few dozen stations and doing lots of whistling and cannot get the rig to take off now.. Thanks to all who responded to this. It looks like the fix might be to make the kpa shield a real tight fit to j2 with cutouts for j2s mounting nuts. I might also add that since making this mod the current drawn from the power supply for 100w output has dropped 1.5 amps and the high speed fan takes a bit longer to kick on now. before a single 3 by 3 cq call on 10m would generate enough heat to kick er on. Lets knock on wood 73 ken w8ob #2864 owner of the best transceiver ever made +++++++++++++++ From: "Douglas Westover" To: "ken cubilo electric" , Subject: Re: [Elecraft] re osc problem on kpa100 Date: Sun, 27 Oct 2002 11:32:04 -0800 I had (have?) a very similar problem and tore my hair out trying to solve it. It only occured on SSB and only with a "real" antenna, dummy loads worked fine. My first thought was the bias adjustment which I redid and the problem seemed to disappear. However, since then I've had the "top" off a couple of times and the problem recurrs everytime I put it back together, suggesting that its a loose connection problem or a lead dressing problem. I've not been able to find anything loose, but I do find that if I take the right (as viewed from the front) side panel off when re-installing the top and then dress the interconnects AWAY from the SSB board that the problem goes away. Go figure. 73, Doug W6JD K2/100 #1626 ----- Original Message ----- From: "ken cubilo electric" To: Sent: Saturday, October 26, 2002 12:09 PM Subject: [Elecraft] re osc problem on kpa100 > I did a little more checking into this problem and find that it will > occur at just about anypower level that the pa is switched into the > transmit path, also when the high ref warning goes off pressing the mike > button results in power outputs of 100-150 watts regardless of the power > setting on the front panel, it will reset when you press the mode button > and then reset the high ref alarm, it will not happen with a 50 ohm > dummy load in line. My memory seems to recall someone else on the list > was having a problem like this. anyway it kind of sounds like rf is > getting into the unit somewhere. I just went thru and did a alignment on > both the k2 and the kpa100 and double checked the bias adjustment on the > kpa100. anyone got any ideas? > ken w8ob ++++++++++++++++