Discussion in 'Amateur Radio Amplifiers' started by KA5ROW, Jun 13, 2012.
G'day Rich,---Not joining the conversation,just saying Hello!
Unfortunatly the contents of this thread indicates otherwise. It just means it will be debated, with thinly disguised malice, forever.
The problem with parasitic suppression is it's not an exact science.
Anybody who thinks it is is more than welcome to demonstrate their opinion by modeling the condition on a computer using any of the available design tools.
We have already been through this in a couple of threads here with the result that it's not piratical to model.
Can you stop parasitic oscillations by more than one means?
Yes you can. Are some methods better than others?, some people believe so.
We seem to go through this debate in cycles of about three months or so....
To be fair I think my previous attempts at using modelling aimed at modelling a particular mode of instability that can affect even a basic
amplifier model. The aim was to demonstrate the role of the classic RL suppressor to combat unwanted hi impedance states at a particular segment of the VHF spectrum that can appear at the anode due to a typical amplifier layout.
What I learned from this excercise was that many people on here still think it is 1965. Also some didn't realise you can model a complex
linear system is a few seconds using data from a modern vector network analyser.
This applies even if the system is an amplifer with complicated physical layout and all manner of stray reactances.
The VNA can still capture all this and produce a working model to export to a computer in seconds.
Of course not all modes of instability can be modelled using linear models and a linear simulator but it is an established method that has been used in RF engineering for decades and should therefore be shown (some) respect.
When I demonstrated this with a practical demonstration using real hardware the thread ended with no response to this from W8JI who had previously dismissed any hope of modelling a tube in a socket etc. As he was the one who started the thread then I assumed I had made my point by the lack of his reply
Here's a link to how that thread ended.
As long as it continues to annoy the pompous who prefers to talk down to everone it serves its purpose. Perhaps you might find a better audience back on Eham?
I think that is the tragedy of the whole subject. Ideally, there should be enough collective knowledge on here to pool together and produce
a (peer reviewed) paper on the subject.
Nothing fancy, just a basic explanation using basic RF fundamentals that allow someone to understand HOW the suppressor reduces the
load impedance at the problem frequency.
Instead the subject is used as a platform for a personal bunfight.
Carl, part of the problem here is that it is very difficult (for me at least) to write text on a forum in a way that all readers will interpret it as intended by the writer.
So once you label someone as pompous you can choose to see pomposity in much of their posts.
I'm just an engineer (and therefore not skilled in communicating tactfully via forum posts) and if you heard me 'speak' my posts you would not see me as pompous at all.
Also, I don't quite get the thing about Eham. I don't recall spending much time there. My profile says I've made 1 post there. I think I've contributed to a couple of equipment reviews but that's it?
The subject was covered in sufficient detail in QST as far back as the late 50's. The problem is that most have no idea how to do their own research and peer review is worthless since way too many have their own agenda, or think that the 73 Magazine school of design is adequate....fill up a resistor with wire and one size fits all tubes, or have a totally distorted view on the subject. It took me decades before even JI started to agree that the only purpose of the suppressor is to stop a parasitic from even starting. If one has already started then there is something wrong with the suppressor and logic offers 2 choices.....the coil or resistor. No fancy pants collection of learned words and extensive formulas and models are needed for 99.9% of those wanting to know. I prefer the KISS principle which many disagree with because they want to spend days, weeks, years, impressing others with endless discussions to show how much they can blather on about nothing.
I try not to apply that label lightly, it takes repeated exposure.
I'm also an engineer but spent many years as a production, service, engineering tech, and engineering positions before finally getting the degrees late in life and still equate more to the in the trenches approach on these forums. Perhaps 24 years in the USN Reserves mostly as an electronics instructor molded me more than I realize as I can be a bit brusque and grumpy at times and its not all due to old age.
I also see you as having a couple of strikes against you as being from the UK you have a different way of speech that drips upper class pomposity; you are not alone on QRZ. The other I believe is that you are a bit young and spend considerable time in a lab pushing buttons or on a PC in a one person office which is something very few on here can relate to. Correct me if Im wrong and dont go Cockney on me now
Perhaps I have you confused with another G who got into rather long discussions with JI and his camp followers, sorry about that and I apologize.
Like I said I'm not skilled at communicating via text so maybe that explains why I sound repeatedly pompous to you. Maybe the other G0 on Eham has tainted your view of me too.
I'm certainly not upper class... I'm a very scruffy engineer
My background is that I'm an RF design engineer. I've worked for the same UK defence company almost all my working life. Yes, I work in an engineering lab alongside dozens of other engineers covering RF/SW/FW/DSP/PCB/Mechanical design. There are a few pompous ones in some of the labs but they manage to do it with humour and we all get along.
I don't specialise in any particular area in RF design but have designed a lot of receiver and transmitter products over the years covering LF to many GHz. So I'm kind of a jack of all trades RF designer (master of none?) but RF modelling is one of my passions and I have been doing this all my design career.
To me the role of the suppressor is very straightforward and so are its limitations.
Part of my frustration on this subject is that people keep linking to the W8JI website as a technical reference on this subject and (at the risk of sounding pompous) it has a lot of good stuff but it just isn't presented correctly with lots of vagueness and there's several statements that I think are clearly false.
Also, the VNA plots on his site look suspiciously wrong. To me the responses look like they have been rotated by an additional transmission line because they just don't make sense. I work with RF design tools every working day of my life so (at the risk of sounding pompous again) I am pretty sharp at spotting stuff that isn't right.
Some things are false Jeremy - but his groupies are too uneducated to realize it - but some things are correct - which helps hide the falsities/specious reasoning. . . Carl KM1H summed JI up pretty well.
••• A story from Paul Pagel, N1FB, QST Associate Technical Editor: Paul told me that after the article "Parasitics Revisited" was published in QST in September, 1990, when he arrived at HQ in the morning to unlock the building and he opened the door he could hear the telephone ringing on his desk at the back of the building. It was JI calling to complain about the article. Paul said this went on for weeks and that JI was quite agitated.