开云体育

[SoftwareControlledHamRadio] Rob Sherwood Presentation Slides on Amateur Radio Transceiver Performance

K9HZ All Messages By This Member #6028 开云体育 A couple comments on Rob’s talks… there are plenty more of them in addition to these. ? Rob has done a wonderful job of evaluating radio transceivers… I’ve been to his house/ lab and he has the perfect location for his evaluations.? He will always give you an honest evaluation answer but never recommend a radio.? He does have some peculiar operating habits, like all of us, that causes him to identify waterfalls and knobs that he likes… that might not be your cup of tea.? In the past 5+ years Rob has been on an SSB IMD tirade, pushing predistortion accommodations with the top commercial radio manufacturers.? It’s all good stuff but he tends to extend that to the builder and hobbyist level at times that doesn’t always resonate with some of us.? In any case, he does tout using class-A final RF amplifiers in the transmit stages of radios because they, by shear design, will generate less IMD. ? If any of you want to join the “Class-A” club, my 20W and 100W amplifiers will operate in Class-A operation.? The amps have plenty of head-room in terms of dissipation to perform this task, but at a reduced power and efficiency.? My original PA designs contained hardware to adjust the bias to perform this, but I was worried that people would try to keep the PA at the 20W level while in this pseudo class-A operation at about 28% efficiency.? Now will this be of use with the T41… hmmm that is left to the reader. ? I will publish instructions on how to put the 20W PA in class-A operation by readjusting the bias.? Have fun with this but also have a extra set of transistors laying around!? Expect about 5 watts out for a safe level of performance. ? ? Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ VP2EHZ ? Owner - Operator Big Signal Ranch – K9ZC Staunton, Illinois ? Owner – Operator Villa Grand Piton – J68HZ Soufriere, St. Lucia W.I. Rent it: ? Moderator: North American QRO Group at Groups.IO. Moderator: Amateur Radio Builders Group at Groups.IO. ? email:? bill@... ? ? toggle quoted message Show quoted text From: [email protected] <[email protected]> On Behalf Of Greg KF5N via groups.io Sent: Monday, February 10, 2025 8:15 AM To: [email protected] Subject: [SoftwareControlledHamRadio] Rob Sherwood Presentation Slides on Amateur Radio Transceiver Performance ? The slides are here: /g/SoftwareControlledHamRadio/files/Sherwood_Presentations I attempted to video the presentation at Hamcation.? Unfortunately the acoustics and noise at the venue were quite bad. Here are the videos: ? -- 73 Greg KF5N
K9HZ All Messages By This Member #6029 开云体育 For those who are interested…. Here is a tutorial on Class-A operation of transistor amplifiers:? ? ? ? Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ VP2EHZ ? Owner - Operator Big Signal Ranch – K9ZC Staunton, Illinois ? Owner – Operator Villa Grand Piton – J68HZ Soufriere, St. Lucia W.I. Rent it: ? Moderator: North American QRO Group at Groups.IO. Moderator: Amateur Radio Builders Group at Groups.IO. ? email:? bill@... ? ? toggle quoted message Show quoted text From: [email protected] <[email protected]> On Behalf Of K9HZ Sent: Monday, February 10, 2025 1:34 PM To: [email protected]; [email protected] Subject: Re: [AmateurRadioBuilders] [SoftwareControlledHamRadio] Rob Sherwood Presentation Slides on Amateur Radio Transceiver Performance ? A couple comments on Rob’s talks… there are plenty more of them in addition to these. ? Rob has done a wonderful job of evaluating radio transceivers… I’ve been to his house/ lab and he has the perfect location for his evaluations.? He will always give you an honest evaluation answer but never recommend a radio.? He does have some peculiar operating habits, like all of us, that causes him to identify waterfalls and knobs that he likes… that might not be your cup of tea.? In the past 5+ years Rob has been on an SSB IMD tirade, pushing predistortion accommodations with the top commercial radio manufacturers.? It’s all good stuff but he tends to extend that to the builder and hobbyist level at times that doesn’t always resonate with some of us.? In any case, he does tout using class-A final RF amplifiers in the transmit stages of radios because they, by shear design, will generate less IMD. ? If any of you want to join the “Class-A” club, my 20W and 100W amplifiers will operate in Class-A operation.? The amps have plenty of head-room in terms of dissipation to perform this task, but at a reduced power and efficiency.? My original PA designs contained hardware to adjust the bias to perform this, but I was worried that people would try to keep the PA at the 20W level while in this pseudo class-A operation at about 28% efficiency.? Now will this be of use with the T41… hmmm that is left to the reader. ? I will publish instructions on how to put the 20W PA in class-A operation by readjusting the bias.? Have fun with this but also have a extra set of transistors laying around!? Expect about 5 watts out for a safe level of performance. ? ? Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ VP2EHZ ? Owner - Operator Big Signal Ranch – K9ZC Staunton, Illinois ? Owner – Operator Villa Grand Piton – J68HZ Soufriere, St. Lucia W.I. Rent it: ? Moderator: North American QRO Group at Groups.IO. Moderator: Amateur Radio Builders Group at Groups.IO. ? email:? bill@... ? ? From: [email protected] <[email protected]> On Behalf Of Greg KF5N via groups.io Sent: Monday, February 10, 2025 8:15 AM To: [email protected] Subject: [SoftwareControlledHamRadio] Rob Sherwood Presentation Slides on Amateur Radio Transceiver Performance ? The slides are here: /g/SoftwareControlledHamRadio/files/Sherwood_Presentations I attempted to video the presentation at Hamcation.? Unfortunately the acoustics and noise at the venue were quite bad. Here are the videos: ? -- 73 Greg KF5N
jerry-KF6VB All Messages By This Member #6030 On 2025-02-10 11:34, K9HZ wrote: In any case, he does tout using class-A final RF amplifiers in the transmit stages of radios because they, by shear design, will generate less IMD. *** NO thanks. A 100W transmitter the size of a Heathkit Apache? Or a legal-limit rig the size of a Piper Apache? Predistortion is interesting. Right now, all implementations that I know of are closely held commercial secrets. Anybody know of an open-source attempt to do it? It doesn't seem THAT complicated. Basically, the power amp's gain gets a little lower as it approaches its amplitude limit. So you compensate for that by raising the gain a little - only for the tips of the low-level RF. You "exaggerate the tips" a little. Sort of a negative feedback situation. But what about actual negative feedback? Won't work, because there's too much delay in the RF chain. Guaranteed, at some frequency or frequencies, it would ring like a bird. Yet, the commercial systems apparently do feed RF back into the exciter. Do they "SSB-detect" it, turn it back into audio, and compare that to the audio being input? - Jerry, KF6VB
Gary All Messages By This Member #6031 Jerry, The Thetis software for the Hermes Lite, ANAN and radioberry radios has adaptive predistortion and you can examine the source files to see how it works. Thise radios have the capability of operating full duplex so they use the receiver to listen to a sample of the transmitter output and down convert it to baseband where the predistortion is calculated and applied to the baseband transmitter before upconversion. Gary W9TD
K9HZ All Messages By This Member #6032 开云体育 The new attenuator/ 20W dummy load I made can be used as just a 40db tap on the RF line for feedback for something like this (besides the radio calibration).? I don’t think it’s that difficult to design a filter that notches out the salient part of the RF spectrum and add the inverse of the garbage back to the signal at the correct amplitude and phase to cancel the garbage out.? I’ve worked on problems like this before… if I get time to do it… I’ll have a look. ? ? Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ VP2EHZ ? Owner - Operator Big Signal Ranch – K9ZC Staunton, Illinois ? Owner – Operator Villa Grand Piton – J68HZ Soufriere, St. Lucia W.I. Rent it: ? Moderator: North American QRO Group at Groups.IO. Moderator: Amateur Radio Builders Group at Groups.IO. ? email:? bill@... ? ? toggle quoted message Show quoted text From: [email protected] <[email protected]> On Behalf Of jerry-KF6VB Sent: Monday, February 10, 2025 2:25 PM To: [email protected] Cc: [email protected] Subject: Re: [AmateurRadioBuilders] [SoftwareControlledHamRadio] Rob Sherwood Presentation Slides on Amateur Radio Transceiver Performance ? On 2025-02-10 11:34, K9HZ wrote: In any case, he does tout using class-A final RF amplifiers in the transmit stages of radios because they, by shear design, will generate less IMD. *** NO thanks. A 100W transmitter the size of a Heathkit Apache? Or a legal-limit rig the size of a Piper Apache? Predistortion is interesting. Right now, all implementations that I know of are closely held commercial secrets. Anybody know of an open-source attempt to do it? It doesn't seem THAT complicated. Basically, the power amp's gain gets a little lower as it approaches its amplitude limit. So you compensate for that by raising the gain a little - only for the tips of the low-level RF. You "exaggerate the tips" a little. Sort of a negative feedback situation. But what about actual negative feedback? Won't work, because there's too much delay in the RF chain. Guaranteed, at some frequency or frequencies, it would ring like a bird. Yet, the commercial systems apparently do feed RF back into the exciter. Do they "SSB-detect" it, turn it back into audio, and compare that to the audio being input? - Jerry, KF6VB
K9HZ All Messages By This Member #6033 开云体育 Could be that John Melton worked on some of that… ? ? Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ VP2EHZ ? Owner - Operator Big Signal Ranch – K9ZC Staunton, Illinois ? Owner – Operator Villa Grand Piton – J68HZ Soufriere, St. Lucia W.I. Rent it: ? Moderator: North American QRO Group at Groups.IO. Moderator: Amateur Radio Builders Group at Groups.IO. ? email:? bill@... ? ? toggle quoted message Show quoted text From: [email protected] <[email protected]> On Behalf Of Gary via groups.io Sent: Monday, February 10, 2025 3:11 PM To: [email protected] Subject: Re: [AmateurRadioBuilders] [SoftwareControlledHamRadio] Rob Sherwood Presentation Slides on Amateur Radio Transceiver Performance ? Jerry, The Thetis software for the Hermes Lite, ANAN and radioberry radios has adaptive predistortion and you can examine the source files to see how it works. Thise radios have the capability of operating full duplex so they use the receiver to listen to a sample of the transmitter output and down convert it to baseband where the predistortion is calculated and applied to the baseband transmitter before upconversion. Gary W9TD
Greg KF5N All Messages By This Member #6034 T41 V11 operates in full duplex during transmit calibration.? So perhaps predistortion can be applied.? That would be an interesting experiment.? But V12 will not work, unless the TX calibration issues are solved, or a 2nd receiver is added. The next question would be whether or not the Teensy has the horsepower to do the job. ? 73 Greg KF5N

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