Re: [AMRadio] AM Linear Operation
Hi Mike, I'm sure it's been all hashed --- and re-hashed! --- here before, but a good rule of them is this: to determine the (safe!) carrier output capability of your linear amplifier in the AM mode, take note of the plate dissipation of your tube(s) from the tube manual, then divide by two... Example --- I have a pair of 813's in parallel here: a single 813 can dissipate 125-watts, so that's 62+ watts of dissipation, times two, equals 125-watts in total. Adjust your drive accordingly so as not to exceed this value, all the while monitoring RF output on a watt meter. When speaking, it's always advisable to monitor your signal on a scope, too...I use a Heathkit SB-610 monitorscope here, in the trapezoidal position... Works for me! ~73~ Eddy VE3CUI - VE3XZ - Original Message - From: Mike Duke, K5XU [EMAIL PROTECTED] To: Discussion of AM Radio amradio@mailman.qth.net Sent: Friday, March 17, 2006 11:21 PM Subject: [AMRadio] AM Linear Operation I've been reading this AM linear thread with great interest. I currently run a TS570 which gives me no more than 25 watts of carrier, plus a bit more on modulation peaks. I have an unmodified DX60 that I intend to put back in service later this summer after a shack painting project is finished. (No need to move it twice!) Because I enjoy operating, and would like to do so with enough signal to be heard reasonably well on 80 and 40 meters, I too have been considering which linear to run on AM. This discussion of linears on AM has caused me to reason that there is no exact magic combination of carrier drive level and audio level which is guaranteed to produce a cleanly amplified AM signal. For me, at least, this apparent fact is most unfortunate indeed. My signature will give you a hint of the usefulness of a scope in my shack. So, do I sit on my hands and wait for better propogation on the higher bands, or do I continue serving as the pin-drop test for all those restored 75A4's, HQ170's etc? Mike Duke, K5XU American Council of Blind Radio Amateurs __ AMRadio mailing list Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net AMfone Website: http://www.amfone.net AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb
Re: [AMRadio] AM Linear Operation
Mike, It might be doable to use a watt meter that either looks at RMS carrier power, and PEP power by the flick of a switch. Since on AM the PEP at 100% plus modulation is ideally 4 times carrier power, the watt meter will show that, say for a 100 watt carrier, you should get 400 watts PEP. If you have a watt meter that can work this way and communicate to you by talking, tones, or whatever, then setting a linear amplifier up into a dummy load is doable. Just advance the RF drive until the four to one ratio drops, and then back off the drive a little from there. If you can follow this approach you will have a linear amp running AM set up better than many others. You will need to juggle the mic gain, drive level, and linear loading to see how much carrier you can transmit while preserving the 1 to 4 ratio, and do so without the visual aid of a scope. This will take some experimentation. Once everything is set, then your antenna must appear identical to your dummy load, or the linear plate loading controls must be readjusted. If this is the case leave the mic gain and drive alone for this final step. Making the antenna appear the same as the dummy load sure simplifies things, and a tuner may be helpful. Regards, Jim WD5JKO --- Mike Duke, K5XU [EMAIL PROTECTED] wrote: I've been reading this AM linear thread with great interest. I currently run a TS570 which gives me no more than 25 watts of carrier, plus a bit more on modulation peaks. I have an unmodified DX60 that I intend to put back in service later this summer after a shack painting project is finished. (No need to move it twice!) Because I enjoy operating, and would like to do so with enough signal to be heard reasonably well on 80 and 40 meters, I too have been considering which linear to run on AM. This discussion of linears on AM has caused me to reason that there is no exact magic combination of carrier drive level and audio level which is guaranteed to produce a cleanly amplified AM signal. For me, at least, this apparent fact is most unfortunate indeed. My signature will give you a hint of the usefulness of a scope in my shack. So, do I sit on my hands and wait for better propogation on the higher bands, or do I continue serving as the pin-drop test for all those restored 75A4's, HQ170's etc? Mike Duke, K5XU American Council of Blind Radio Amateurs __ AMRadio mailing list Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net AMfone Website: http://www.amfone.net AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb
[AMRadio] AM Linear Operation
I've been reading this AM linear thread with great interest. I currently run a TS570 which gives me no more than 25 watts of carrier, plus a bit more on modulation peaks. I have an unmodified DX60 that I intend to put back in service later this summer after a shack painting project is finished. (No need to move it twice!) Because I enjoy operating, and would like to do so with enough signal to be heard reasonably well on 80 and 40 meters, I too have been considering which linear to run on AM. This discussion of linears on AM has caused me to reason that there is no exact magic combination of carrier drive level and audio level which is guaranteed to produce a cleanly amplified AM signal. For me, at least, this apparent fact is most unfortunate indeed. My signature will give you a hint of the usefulness of a scope in my shack. So, do I sit on my hands and wait for better propogation on the higher bands, or do I continue serving as the pin-drop test for all those restored 75A4's, HQ170's etc? Mike Duke, K5XU American Council of Blind Radio Amateurs
Re: [AMRadio] AM Linear Operation
Mike, I have two Ameritron AL-1200's and one AL-1500. I like the AL-1200's better as they provide a good match for the 22-25 watt level driver. With 22 watts of carrier, the AL-1200 will put out 375 watts of carrier with 1500 watts PEP with a real nice scope pattern. The Al-1500 needs only about 10 watts of carrier to do the same job, but if during the course of a long transmission, should you overmodulate on some rare voice peak, the 1500 will kick off its overload circuit. Some may say this is a good thing. Since my amps are in the garage attached to the shack, I don't find it convienent to run out and reset the beast. The DX-60 will have too much drive for these amplifiers. I remember putting a dummy load on a T connector with one of my driver transmitters, but I don't remember how much lower the power was with this setup. Hope to hear you on AM in the future Mike. 73, Ken W2DTC Because I enjoy operating, and would like to do so with enough signal to be heard reasonably well on 80 and 40 meters, I too have been considering which linear to run on AM.
