Question about an example in the book RF circuit design by Chris Bowick

[Horsty]

Hi.

I'm stuck with a calculation example in the book RF circuit design by Chris Bowick. It's about Fig. 2-16 in the chapter resonant circuits and the question of how to determine the equivalent parallel resistance Rp.

In fig. 2-16, an inductance with a component Q of 10 should be converted into its equivalent parallel circuit. Unfortunately, I cannot obtain the value of 4.5k using the values given and the formulas given earlier in the book.

Does anyone have the book and can give me a tip on how to calculate? It's probably really simple, but I can't figure it out. 

thx

[shabaz]

That's a great book, it's one of my favorites, since it is easy to follow (mostly!).
I have it on my Kindle account, I grabbed a screenshot (attached). I think it's OK to legally share that snippet, because this seems to be fair use, to understand a specific exercise.

I believe (unless I'm mistaken) they have a typo and are off by a decimal place, i.e. it should be 450 ohm (447.21 ohm with a few more significant values).

[Horsty]

Thanks for the quick response. 

I am not sure that there is a typo because the 4.5k matches the claimed output voltage of 0.45 Vin exactly.

[shabaz]

Hi,

There's definitely a mistake somewhere, and depending on what the mistake is, it may have a knock-on effect with the remainder calculations. It won't be 0.45 Vin, it will be lower, if the mistake is deemed to be that the resistance should have been 450 ohm.

On the other hand, maybe the typo was the Q value, i.e. maybe it was supposed to be 100 instead of 10. In that case, the 4.5k value is valid. There's a good possibility the author may have intended a Q of 100 (but I've not read that chapter, I only looked at that example, so I don't know the context to better determine which value was the erroneous one).

If the author really did mean a Q of 10, then the 4.5k value is incorrect. Hard to know what the intent was, since that would entail reading the author's mind unfortunately (unless it is in the remainder context in that chapter).

[Horsty]

The value 100 for Q would work, but the number seems high to me and also the author on the page before explicitly said that Q equals 10. Two typos seem strange to me. 

Thank you for your help.

[CaptDon]

I noticed in vacuum tube tank circuits for R.F. amplifiers where a desired Q of 10 is common The Xc and Xl of the resonant tank circuit figure at around 450 ohms creating what the 'plate' sees as a 4.5K operating impedance. The plate voltage and current seem to agree with this observation.

[G0HZU]

That old Bowick book does have quite a few errors or dodgy approximations in it. I think the Q should be 100 in your example as this is a typical Q for 50nH up at VHF. It is possible to only achieve a Q of 10 for a 50nH inductor up at VHF but it would be not suitable for most applications up at VHF.

The copy of Bowick in the engineering library at work (first edition) has lots of corrections or warnings pencilled into it. These were gradually added by various engineers about 30-35 years ago. There are also better equations available for some of the examples that otherwise only approximate the correct answers. These were also added by pencil.

I also recall that the JFET biasing examples were wrong and several network examples had incorrect results. There were other issues with that book as well.

Despite this, it is a good book as long as you accept the various errors in the worked examples.

What I found disappointing was that the second edition seems to have the same errors littered throughout the book. I doubt this book was ever peer reviewed before publication and the same applies for the second edition.

[shabaz]

I have the paperback second edition, and can confirm that didn't come with any errata sheets either (at least not when I bought it).

I got the impression that the author must have had a spurt of enthusiasm and wrote well, but they didn't see it through to the end because the book also misses many topics that would be great in a beginner book. The book is quite short. But what the author did cover, can be quite useful since he wrote it in plain, simple terms, albeit annoyingly with errors as you mention.

[bostonman]

That old Bowick book does have quite a few errors or dodgy approximations in it.

Is the book worth purchasing then?

Knowing errors exist helps, however, for anyone who wants to purchase this as a learning tool will have confusion.

[shabaz]

Personally, I've found it very useful; it's like a beginner's book to RF and is a very friendly entry into that subject. It covers some things very well (particularly inductors, ferrite, and iron powder cores and how to use a Smith Chart). It gave me the confidence as a new engineer, to want to learn more and experiment.
Of all the RF books I'm aware of, this might be amongst the friendliest for newcomers. It might be worth looking out for it in used condition, too.

Other friendly resources include some amateur radio books/journals, but the book is more concise (and misses a lot of topics, unfortunately, but radio is a big topic).

If you're interested in radio, even if you're not interested in ham radio, it could be worth joining an amateur radio group. Most are (hopefully) friendly, and you'll learn bits and pieces from each other just from interaction, even if that's just occasionally reading e-mails from group members. That provides some practical awareness, which makes what you learn relatable. For instance, if you've learned about ferrites and inductors from a book, and you'll notice that when radio people attach an antenna, very often they too use a ferrite core, and all of a sudden, you'll know the reason why, and you may be able to help them too.

[bostonman]

I was asking as a general question for myself and others.

I have an understanding of RF and I'm an Engineer, however, many concepts I know about, but not an expert. Sometimes having basic, well written books in my library is good to help learn.

As you can imagine though, I'd like to avoid books that have wrong information.

[jwet]

I'm +1 for the Bowick book.  Its very readable and covers stuff that I haven't seen covered well else where.  I may have noticed a couple of mistakes but this isn't all that uncommon.  I still think its a winner.

[bostonman]

I’ll add it to my list of presents for myself.

The more important question about the mistakes are whether they are obvious. If someone is new to electronics, can they pick up the errors or will they learn incorrect concepts?