fan email to Ian Purdie VK2TIP

Ian Purdie's Amateur Radio Tutorial Pages

you can have this page translated /vous pouvez faire traduire ces pages /Sie können lassen diese Seiten übersetzen /potete fare queste tradurre pagine /você pode ter estas páginas traduzido /usted puede hacer estas paginaciones traducir

Please visit VK2TIP's Book Shelf. My personal recommendations, thanks.

fan email to Ian Purdie VK2TIP about his site




Obviously much of this email goes back to my original site which I started back in 1998. Over the course of time my site has been expanded quite considerably. These (genuine) emails were unsolicited and I am most grateful to receive them because I would never have known what a valuable resouce this site would become for such a great number of people from all walks of life, from all age groups, from all parts of the world.

It is factually correct to say these people, so generous in their comments, are the REAL driving force behind this site. These courteous emails are merely a very tiny representative sample based on age groups, backgrounds etc. To put them all in here would simply bore you to death. These are merely a representative cross section.

I receive on average a few emails every day, so I literally have hundreds on file! Thanks a whole bunch folks.

As part of my commitment to privacy anything which may identify a particular individual has been XXXX out but, where very relevant - I have not deleted the organisation. Some typos have been corrected and I have provided further explanations between [ ] where I deemed it was appropriate for clarity.

Subject: Thanks for the website!

Date: Thu, 03 Jun 1999 14:15:53 -0700

From: "xxx yyyy (rrrrrr)" <>



I've been doing digital hardware design for about 15 years and now I'm designing a signal path for the front end of a DTV tuner [for high definition TV - HDTV]. Your tutorials are very helpful!

I got a lot out of your amplifier design tutorial, although I feel like I need to go through it again. I wish your LC filter tutorial was on one page so I could print it out. I anxiously await your receiver design tutorial!

Best Regards,


PS. I have a webpage devoted to slide rules:

Subject: your radio web site

Date: Fri, 13 Aug 1999 21:54:41 -0300

From: "XXXXXXXX" <>

To: <>

Hello Mr Purdie...

I am an electrical engineer from Canada, my specialty is aerospace communications. I really like what I see on your website and will visit it again in the future after you have completed the various topic sections. Please keep up the good work.


Subject: Radios

Date: Tue, 27 Apr 1999 17:40:05 -0400

From: XXXXXX<;>

To: <>


You don't know me but I just found your site today. I'm a youngin' interested in learning how to build radios, mainly from scratch. I got into it last summer and spent a while learning how they work and reading up all I could, but never got a chance to build one (because of something called school, heh) so this summer I'm going to try and attempt it. I was just looking through your site and from the moment it loaded I though this is gonna be one to bookmark!

Anyways I saw your Power Supply Design page and it looked pretty detailed and I actually understood some of it! I'm mainly interested in the trasmitting stuff so I'm looking forward to that tutorial as well as Oscillators and Amplification, but the Power Supply gives me a place to start with.

Well, I just thought I'd let you know that I'm interested in what you're doing,


Date: Tue, 25 May 1999 23:16:40

Subject: Great Site!


To: <>

Hi Ian!

I love your site. I have been looking for a good RF design theory website for a while now and yours seems to be the best around, and even better because its in Australia!!

I just finished a Uni degree that included electronics but they forget to teach you how to sit down and design a circuit even though you cover all the theory. I want to start designing my own RF circuits for data communications and the stuff on your website looks great. It will help me a lot.

Thanks and keep up the good work!!!

Subject: R.F. Amplifier Design

Date: Fri, 02 Jul 1999 10:51:51 -0500

From: xxxxx <;>

Organization: Alcatel U.S.A.



Good page. I'm a 5th year electrical engineering student at Texas A&M in the U.S. I have to say that your page is good for me because it takes all the theory I just learned about analog design and puts it in a more practical light.


Subject: Active Balun

Date: Wed, 09 Jun 1999 11:31:30 +0200

From: xxxxxx yyyyyy <;>

Organization: Delco Electronics


Hi there,

I am working in receiver design (Car radio application) and I am looking for an active balun with very low noise figure (front-end design application).

Can you help me?


Subject: Amplitude Modulation and mixers

Date: Thu, 15 Jul 1999 05:41:47 -0400

From: wwww xxxx


TO: Newsgroups: sci.electronics.basics

This morning I came across a very good basic electronics web site:

While going through the site, some lingering questions from our marathon discussion of AM and mixing came to mind. I sent my questions to Ian the web site owner and repeat them here in order to get comments from the group:


Ian: I really like your pages. I've built a number of receivers. See my Web site:

I have a question about the theory behind the mixer stage: As was done on your page, explanations of this stage are usually limied to stating that the active device is operated in the non-linear portion of the curve and this results in its operation as a mixer. Given that this is the heart of superhetrodyne operation, I've always wished that the explanations would go a bit deeper.

We recently had a very lengthy and interesting discussion on this in the sci.electronics.basics newsgroup. I came to some conclusions about mixer operation that (I hope) may provide the kind of explanation that I think is needed for beginners and non-engineers to understand mixers:

--When we say that the active device is operated in the non-linear portion of its operating curve, we are really saying that we are biasing it so that each of the two input signals will -- in effect -- vary the amount of amplfication that the other receives from the device.

-- When this happens, the output of the device is a waveform that contains sum and difference frequencies. If we ask WHY this happens, we have to be satisfied with an answer that points to mathematics: If you combine two signals in the manner described above, mathematical principles dictate that the resulting waveform contains sum and difference frequencies.

Please let me know what you think of this explanation -- does it make sense, is it consistent with accepted theory?

Again, thanks for the great web site. I will be visiting often.

73 xxxx Nzzz

[I replied with a mathematical analysis you would probably NOT want to read}

Subject: Subscribe Newsletter

Date: Wed, 26 Jan 2000 23:49:52 +0200

From: "nick abcdef"


Dear Mr. Purdie

The first decent engineering text for undergrads on the net.


Please keep me informed (when you post new documents). Can't you also describe Hifi ClassA Output stages in such a practical manner too?

If you are interested in number of hits do your well explained tutorials telling the HiFi-DIY-community how to design a supersymmetrical, no global feedback, IRFP-Mosfet, 200Watt@4ohm, 1 volt input sensitivity, using only 2 series pieces of silicon in the signal path, producing only even-order harmonics class A audio amp using 40kg's of heat sink and forced cooling. This is the sort of audiophile dream-stuff you read about at

If you could do this you should soon be overwhelmed by selling spaces for advert-banners due to hit rates. It would also be the first site telling you "How to design a $100,000 amplifier and sell the same thing for $1,000 to fellow students."

You should start writing your tutorials as whole textbooks, as an easier to understand, alternative way to pass your exams.


Nick Abcdef


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