I have been working on a new AM transmitter since the old one kicked the bucket.
Anyone know what would be the better method to modulate the PA section? My old rig was built around using a modulation transformer which worked nice but I am pretty sure I wasn't getting 100% modulation. Probably more around 80-90%.
So I was reading that using a modulation transistor in series with the PA would achive 100% modulation with better audio quality? I am thinking of doing that then.
Also I looked into heising modulation which still uses a transformer but is able to produce 100% right?
I looked into cathode modulation but it seems a little more then what I want to go for right now. Too bad I didn't have the knowledge on digital modulation like the big boys use.
So any help would be greatful.
I plan to make this rig around 75 watts carrier. My last one was 50 watts using mosfet but one of the RF coils shorted out and blew up the mosfet lol.
Post by Radio Ramona on Jan 26, 2008 16:47:07 GMT -6
We are using Heising modulation at the moment, i didn't know what to expect but it sounds like a clock and needs less audio drive. still have the warm modtrafo sound. but much clearer. we use it it on a transistor tx.
Try the Amfone site. I'm not sure about the link,google it.
It's ham related but most of those guys are serious builders and many are broadcast engineers. (a few are ex-pirates) There's plenty of stuff to keep you busy there. From modulation schemes to refurbishing old broadcast transmitters to sound sweetening it's there.
Nice. Thanks for the help guys. I will be getting an oscilloscope soon from a friend since my old one died off so that should help me out a lot. I will try a few different methods and see what works best and with the scope it should give me a good idea of how clear the modulation really is.
I'm guessing cathode modulation can be done with transistors or mosfets right? Well I got a lot of research to do. I want to build this thing the right way .
There's a lot of info on Class E rigs and how to modulate them on that AM Fone site. Seems like most of those guys want to go the Pulse Width route but I don't have the background to grasp it.
Dave Martin of WNKR Radio in the UK has widely available schematics for a low powered Class E rig (6-10 watts carrier out) called the Corsair that uses series modulation. Several are being used by HF pirates.
I wonder if it would be possible to use it as driver for the final section of one of these higher powered Class E rigs?
Post by Radio Ramona on Feb 3, 2008 13:29:16 GMT -6
pigmeat said:
There's a lot of info on Class E rigs and how to modulate them on that AM Fone site. Seems like most of those guys want to go the Pulse Width route but I don't have the background to grasp it.
Dave Martin of WNKR Radio in the UK has widely available schematics for a low powered Class E rig (6-10 watts carrier out) called the Corsair that uses series modulation. Several are being used by HF pirates.
I wonder if it would be possible to use it as driver for the final section of one of these higher powered Class E rigs?
yes that's possible. i'm working on that. i finnished my end stage but still need to test it with 2 irfp450 25 a 30 watts in and 400 watt out with 2 x irfp460. schematics are here of a complete class e tx. but i builded only the amp stage ar.geocities.com/lu3_bae/
Hi John i'm still working on PWM and PDM for 100W classE. Both work at 75 KHZ, but push pull 100W giving spuri harmonics from carrier oscilator will put filter in front of buffer.
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