Very true my main HF amps are like that both Alphas an 87A and a 9500. Other amps like my KPA500, Yaesu 1000 series SS units are fine to tune at low power. Fred N0AZZ
Sent via the Samsung Galaxy S6 edge+, an AT&T 4G LTE smartphone-------- Original message --------From: Edward R Cole <kl...@acsalaska.net> Date: 09/18/2015 6:14 PM (GMT-06:00) To: ae...@carolinaheli.com, Elecraft@mailman.qth.net Subject: Re: [Elecraft] Product Suggestion - 500W Dummy Load Jerry, Certainly its appropriate to tune your antenna tuner at low power. I have an "ancient" Drake MN-2000 which is rated for 2000w PEP but I can tune it with 10w from my K3/10 with my linear off. Then I turn on my station control panel which enables PTT to the amp. Lately been using my AN-762 140w amp from CCI which I drive to about 120w with 5.6w. http://www.communication-concepts.com/140-watt/ I set the tuner on the 200w range to measure fwd and ref power. Sometimes I will touch up the tuner with the amp online as the amp and K3 are separated by 8-foot of coax and that appears to affect tuning (a little). But that only takes a couple seconds. Marking down cap settings for favorite frequencies is a good idea. But tuning a high-power tube amp at greatly lowered output does not work. Because the internal impedance of the tube shifts as anode current rises. My 8877 is about 5500-ohms at 1400w so you need to adjust it at working voltage and current. Input impedance changes radically from 100w to 1300w. So, unless you run high-power tube amps, you probably can get away with tuning the antenna on low power. Situation changes if you are using a sspa instead of tubes. 73, Ed - KL7UW At 10:16 AM 9/18/2015, ae...@carolinaheli.com wrote: >Forgive me in advance if this is a stupid question. > >Is there any reason you have to tune at full power? It seems to me that >tuning can be accomplished easily with much lower power. The same thing goes >for the ATU to the antenna. I don't see why we need more than a few MW at >most for the ATU to Antenna link. > > > >Rightly or wrongly when I was in the hobby the first time I ran a TS-850 >into an SB-220 to an MFJ roller tuner connected to an antenna switch >feeding: 80m inverted V, 30m/40m rotatable dipoles, and a triband beam. >Whenever I tuned on the inverted V or outer band limits of where my antennas >where tuned I ended up putting labels on the ATU on cap position and a >number/clock combo that represented a roller inductor position for each band >area I cared about. It ended up I rarely had to tune up anything one the air >because I knew where the antenna tuning was using just the Rig and ATU; >tuned the APM into a paintcan MFJ load then switch it inline. I was all set >and never had issues when I needed to kick in the horses. > >Now my debate is 500w vs 800w... there's a larger difference between 500w >and 800w than between 800w and 2.5kw signal wise if I understand >correctly... > > >Jerry Moore >AE4PB, K3S - S.N. 010324 > > > >-----Original Message----- >From: Elecraft [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Edward >R Cole >Sent: Friday, September 18, 2015 2:00 PM >To: Elecraft@mailman.qth.net >Subject: Re: [Elecraft] Product Suggestion - 500W Dummy Load > >Don't have much to say: > >Had a Cantenna from Heath in the 60's - knocked over; spilt mineral oil on >the floor, threw can away! > >I have acquired "dry" loads over the years rated into UHF and sometimes to >mw at flea markets and swaps. My highest power load is 500w Sierra with >power meter and switch for 150 or 500w (probably good to 1000-MHz). Have a >couple Bird terminations rated 50w. Most can handled double their rating >for short duration. > >The hardest duty on my loads is when optimizing the output of a new unit >where I'm keyed up longer than I should. > >But I do have a question on how adjusting a tuner into a 50-ohm load saves >one from transmitting a signal once the tuner is connected to an antenna >that may not be 50-ohms. On 600m my inverted-L is Z = 0.8 >+j680. Tuning into a 50-ohm load does nothing to help match the >antenna. The amplifier is solid state with input and output transformers >(no adjustment). > >I think, unless you use a high power tetrode or triode, that no one tunes >amplifiers anymore. Solid state amps are broadband and need LP filters to >keep from amplifying harmonics. BTW my 2m-8877 is capable of 2000w* RF >output so pretty hard to find a dummy load to take that. Fortunately the >amp does not change much so very little tuning is ever needed (of course I >am on a small segment of one band about 200-KHz wide). Of course the answer >is to tune antenna at lower power and hope the High Power amp will always be >looking at 50-ohms. > >I do not have a QRO 2m antenna tuner but the antenna SWR < 1.25 so only the >anode tuning needs a light adjustment occasionally (loading has not be >adjusted for 8 years). My "dummy load" has 19.2 dBd gain and radiates well. > >*I operate at 1365w CW which allows for about 9% variance in meter accuracy >to stay legal. > >73, Ed - KL7UW >http://www.kl7uw.com > "Kits made by KL7UW" >Dubus Mag business: > dubus...@gmail.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 je...@carolinaheli.com 73, Ed - KL7UW http://www.kl7uw.com "Kits made by KL7UW" Dubus Mag business: dubus...@gmail.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 m...@totalhighspeed.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
