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Amp bypass SWR 160M SSB only with LMR 400 COAX

Jerry Raia All Messages By This Member #612 This might be the strangest behavior of this amp I have heard of so far. I have a 257' EF wire with a 9 to 1 UNUN (grounded). My HF-AUTO tuner shows SWR 1.08 for example. Only in SSB as soon as I begin to talk the amp trips off with the SWR. I'm watching the SWR on the tuner, its not budging but on the amp it is jumping all over until it bypasses. Driving the amp with only 10 watts causes this to happen and I have tried it with my 7610, 7300, and 991A. Now what I'm not understanding is this. This behavior occurs only when I use a 75' run of LMR 400 coax. I have even tried a different piece of 75' LMR 400 and the result is the same. If I use a 150' run of LMR 240 the amp doesn't trip at all. I have replaced all the jumpers between the components to eliminate them as the cause. Same result. I can tune this same wire for 80M and the amp works fine regardless of the coax feed. Any thoughts? -- 73, Jerry
Alan Baker #613 开云体育 Hi Jerry I also have the LA-1K and HF-Auto tuner and I have quirky things happen when I am on 160 mtrs . My situation is with a 75’ run of high quality RG213 where the tuner is set for 1.08 to 1 and the amp matches at 1.1 to 1 transmitting with 700 watts CW. As I transmit the SWR on both the amp and tuner slowly rise over a 20 sec period to 1.7 to 1 and trips off to Bypass. My research narrows my problem down to two possibilities. One the dielectric in the coax is heating up and changes characteristics effecting the tuner settings for minimum SWR. The second though is that the 4:1 Balun at the base of my vertical is over heating and looses its magnetic properties. I do not experience this problem on any other band. I wonder if you added a ferrite isolator on the coax just before it enters your shack if that would alleviate the problem. After this weekend’s 160 mtr CW contest ends I will do some more investigation of my problem by installing a dummy load at the coax end that would connect to the Vertical. Good luck Alan W1BQ? toggle quoted message Show quoted text On Dec 4, 2020, at 6:22 PM, JERRY <JERRY@...> wrote: ?This might be the strangest behavior of this amp I have heard of so far. I have a 257' EF wire with a 9 to 1 UNUN (grounded). My HF-AUTO tuner shows SWR 1.08 for example. Only in SSB as soon as I begin to talk the amp trips off with the SWR. I'm watching the SWR on the tuner, its not budging but on the amp it is jumping all over until it bypasses. Driving the amp with only 10 watts causes this to happen and I have tried it with my 7610, 7300, and 991A. Now what I'm not understanding is this. This behavior occurs only when I use a 75' run of LMR 400 coax. I have even tried a different piece of 75' LMR 400 and the result is the same. If I use a 150' run of LMR 240 the amp doesn't trip at all. I have replaced all the jumpers between the components to eliminate them as the cause. Same result. I can tune this same wire for 80M and the amp works fine regardless of the coax feed. Any thoughts? -- 73, Jerry
Dennis All Messages By This Member #614 Good Morning, ?? One thing to keep in mind when operating on 160 with short antennas.?? These antennas (if properly constructed) will have a very hi Q.? You'll note that if you move as little as 5khz the SWR will rise quickly.?? If you're running fairly wide audio bandwidth your SWR instantly rises with modulation.? While it usually wouldn't be enough to fault-off the amplifier, it may be enough to put it "over the edge" of 2.5 if it's already at, say, 1.2 or 1.5:1.? ?? In one of my installations I run 12khz wide audio on 160 meters AM.? My antenna is a dipole with a fairly hi-Q tuner (although not as high as a 40' vertical would be) and I see excursions with modulation. ??? Also worth noting, a recent update of LA-1K firmware has initiated a delay before SWR cut-out to prevent transient events (like a spark gap jumping) from causing unnecessary faults.? It's actually a three-step program that has two different delay times depending on the severity of the mismatch, then goes to an instant disconnect if the SWR is greater than 6:1. ?? If anyone is interested I'll present the exact profile of this mod and the serial number of the update that presented it. (don't have it with me now) Best, Dennis toggle quoted message Show quoted text On 12/5/2020 at 6:57 AM, "Alan Baker" <alwbaker@...> wrote: Hi Jerry I also have the LA-1K and HF-Auto tuner and I have quirky things happen when I am on 160 mtrs . My situation is with a 75’ run of high quality RG213 where the tuner is set for 1.08 to 1 and the amp matches at 1.1 to 1 transmitting with 700 watts CW. As I transmit the SWR on both the amp and tuner slowly rise over a 20 sec period to 1.7 to 1 and trips off to Bypass. My research narrows my problem down to two possibilities. One the dielectric in the coax is heating up and changes characteristics effecting the tuner settings for minimum SWR. The second though is that the 4:1 Balun at the base of my vertical is over heating and looses its magnetic properties. I do not experience this problem on any other band. I wonder if you added a ferrite isolator on the coax just before it enters your shack if that would alleviate the problem. After this weekend’s 160 mtr CW contest ends I will do some more investigation of my problem by installing a dummy load at the coax end that would connect to the Vertical. Good luck Alan W1BQ? On Dec 4, 2020, at 6:22 PM, JERRY <JERRY@...> wrote: ?This might be the strangest behavior of this amp I have heard of so far. I have a 257' EF wire with a 9 to 1 UNUN (grounded). My HF-AUTO tuner shows SWR 1.08 for example. Only in SSB as soon as I begin to talk the amp trips off with the SWR. I'm watching the SWR on the tuner, its not budging but on the amp it is jumping all over until it bypasses. Driving the amp with only 10 watts causes this to happen and I have tried it with my 7610, 7300, and 991A. Now what I'm not understanding is this. This behavior occurs only when I use a 75' run of LMR 400 coax. I have even tried a different piece of 75' LMR 400 and the result is the same. If I use a 150' run of LMR 240 the amp doesn't trip at all. I have replaced all the jumpers between the components to eliminate them as the cause. Same result. I can tune this same wire for 80M and the amp works fine regardless of the coax feed. Any thoughts? -- 73, Jerry
Jerry Raia All Messages By This Member #615 Alan, Thanks for the thoughts. It seems more likely as your experience shows it is feed related. In my case the higher loss coax stops the issue. This amplifier is good at protecting itself from myself :) -- 73, Jerry
Jerry Raia All Messages By This Member #616 Dennis, Thanks for the reply. Interesting things you bring up. I am running 1.07M which is the last firmware revision on the amp I have access to on the web site. -- 73, Jerry
Eric Clanton All Messages By This Member #617 I have an Alpha Antenna portable and he makes it very clear it will do wired things when using LMR 400. Could be a similar situation. I use LMR400 for everything else but it.?

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