Hi, bear in mind that one of the main reasons a balanced (push-pull) amp puts out harmonics isn't because they're being generated inside the well designed exciting radio. It's because harmonics are being generated by an imbalance in the amp. If the propagation delay i.e. phase, from the positive half is any different than that of the negative half, the combined output will be loaded with harmonics. Take a look at the output of this amp before the RF enters the LPF. You'll see two separate 27MHz sinewaves, slightly out of phase. That's why it's generating the harmonics. Add some type of means to make an adjustable phase delay on the "early" waveform. If you do it on the output your variable capacitor or inductor has to be rated for at least 1/2 the output power. If instead you put a very small trimmer capacitor on the "early" side of the input spliter, you can tweak the cap while you watch the two separate output waveforms combine perfectly into a single, high powered one that exhibits very low harmonic content. You might be amazed at how the power output that was lost by filtering out the original harmonics will come back and on the correct frequency. Put your oscilloscope probe on the output combiner and see two separate waveforms. That's supposed to be just one big one.
great filter board. that a better way to filter that amp. they make external low pass filters . but that can pad the receive a tad. really needs to be on output of the amp before the TX/RX relay . I am working on band pass filters now for LD mos. . them block above and below frequency's out side of the band that is selected. doing both input and out put filtering . makes a very clean amp. if radio has any splatter the input filter will take that out before the amp makes that worse. every amp should have some kind of a filter to keep the power on the frequency you want it. a small low pass or band pass can be added to the input as well. if transmitter has any splatter this will block it before it is amplified . working on 65V LD mos. going from 160 meters to 6 meters . and needs to be clean on all bands. lots of filters. I can just slap it together make the power but will splatter all over. wasted power and not very nice to outher bands. great job cleaning up that amp. that 2nd Harmonic is low now. the antenna it self can block the rest. if a mono band 11 meter one. 73's
It seems like a low pass filter is kind of a necessity with those LDMOS style amps. I guess because of the wide band operating potential of the transistors. Bipolars don't have nearly as broad as a response.
Thanks for your great videos! I want to learn about those transformers, like what cores to use and how many. Maybe what type of compensation capacitor to use. Do you know any good references?
What would a base amp of that size run money wise just curious, needing an Amp for my shack looking at all options any suggestions ? I would be using my Ranger 99N1 to drive it.
North Central OH between Columbus and Cleveland and I am using a Bird Sampling tap but they do make similar ones that are pretty good also. as far as freqs go I hang out on 27.425 and 27.395 and sometimes 27.385 when the nuthouse is in session.
right on, im just east of Columbus near buckeye lake, do you have any you would recommend? ill have to get my 11m back up and see if itll reach out. play on 2m at all?@@NeedleBender785
Ótimo parabéns muito bom trabalho xou perfeito bazuka Foz do Iguaçu PR Brazil 🇧🇷🇧🇷
Hi, bear in mind that one of the main reasons a balanced (push-pull) amp puts out harmonics isn't because they're being generated inside the well designed exciting radio. It's because harmonics are being generated by an imbalance in the amp. If the propagation delay i.e. phase, from the positive half is any different than that of the negative half, the combined output will be loaded with harmonics. Take a look at the output of this amp before the RF enters the LPF. You'll see two separate 27MHz sinewaves, slightly out of phase. That's why it's generating the harmonics.
Add some type of means to make an adjustable phase delay on the "early" waveform. If you do it on the output your variable capacitor or inductor has to be rated for at least 1/2 the output power. If instead you put a very small trimmer capacitor on the "early" side of the input spliter, you can tweak the cap while you watch the two separate output waveforms combine perfectly into a single, high powered one that exhibits very low harmonic content. You might be amazed at how the power output that was lost by filtering out the original harmonics will come back and on the correct frequency.
Put your oscilloscope probe on the output combiner and see two separate waveforms. That's supposed to be just one big one.
Very nice work 😎
Thanks Dallas.
great filter board. that a better way to filter that amp. they make external low pass filters . but that can pad the receive a tad. really needs to be on output of the amp before the TX/RX relay . I am working on band pass filters now for LD mos. . them block above and below frequency's out side of the band that is selected. doing both input and out put filtering . makes a very clean amp. if radio has any splatter the input filter will take that out before the amp makes that worse. every amp should have some kind of a filter to keep the power on the frequency you want it. a small low pass or band pass can be added to the input as well. if transmitter has any splatter this will block it before it is amplified . working on 65V LD mos. going from 160 meters to 6 meters . and needs to be clean on all bands. lots of filters. I can just slap it together make the power but will splatter all over. wasted power and not very nice to outher bands. great job cleaning up that amp. that 2nd Harmonic is low now. the antenna it self can block the rest. if a mono band 11 meter one. 73's
Thanks for all that info, I always appreciate your knowledge and your comments.. 73s~
It seems like a low pass filter is kind of a necessity with those LDMOS style amps. I guess because of the wide band operating potential of the transistors. Bipolars don't have nearly as broad as a response.
Its absolutely a necessity and I never run them on the air without at least a Pi network.
Hello
Thanks for your great videos! I want to learn about those transformers, like what cores to use and how many. Maybe what type of compensation capacitor to use. Do you know any good references?
I want one.
What would a base amp of that size run money wise just curious, needing an Amp for my shack looking at all options any suggestions ? I would be using my Ranger 99N1 to drive it.
could you please email me at sales@xelectroshop.com
what sampling tap are you using? I just got the same SA and fear blowing the front end up, where about in ohio and what freq do you play on? 73's
North Central OH between Columbus and Cleveland and I am using a Bird Sampling tap but they do make similar ones that are pretty good also. as far as freqs go I hang out on 27.425 and 27.395 and sometimes 27.385 when the nuthouse is in session.
right on, im just east of Columbus near buckeye lake, do you have any you would recommend? ill have to get my 11m back up and see if itll reach out. play on 2m at all?@@NeedleBender785