VE7BPO on "Killing Q"

I'm still scratching my head a bit about HOW the resistor prescribed by Edgardo, LU1AR, cured the 250 kHz oscillation problem that was plaguing the JBOT amplifier in my 20 meter DSB rig.   Earlier I'd posted an excerpt from a CQ article in which Doug DeMaw talks about swamping and Q killing.   Last week I got a very thoughtful e-mail from esteemed homebrewer Todd,  VE7BPO.  Here is an excerpt :

Thoughts and Considerations
Let’s discuss squashing low frequency oscillations in a QRP transmitter; say at 200 KHz or so. A low value resistor across the coil (12t -- FT37-43) often works well to stop these.
Oscillations come from the transistor: gain versus frequency isn’t linear, nor is impedance at transistor ports. We’ll often add negative feedback and such to stabilize an amplifier towards unconditional status. In my Tx circuit that oscillated, no feedback was applied. 
 In the case of an inductor wound on a FT37-43 or FT50-43, the Q is already low (say 8- 15 or so). Obviously a resistor in parallel with such a coil is not going to lower Q since Q is already quite low. That R will reduce the inductor impedance and thus may serve to decrease the low frequency gain of the RF amplifier to stop any low frequency oscillations. This might not work so well with a way-high fT transistor where decoupling might be hampered if UHF oscillations are singing. 
Doug DeMaw often referred to the parallel resistor as a Q-killer. If we examine the equations describing parallel, or series resonant circuits -- if the Q of a tank is high enough, we can practically ignore the effect of resistance at resonance. Conversely if we add a resistance and make it high enough, we might even obliterate the resonant frequency or “kill the Q”. Engineers have long placed an R into a parallel-tuned circuit to drop Q and stop oscillations — they refer to it as damping. 1 example might be in old TV sets where a variable resistance was added to peaking coils to prevent a tank from ringing at a frequency determined by the coil L and distributed C. This applies to higher Q inductors and not our FT37-43 inductor. 
Decoupling
Our teacher, Wes, teaches us in EMRFD that coupling often occurs along the DC power supply lines.  Further, he’s taught us to decouple AC by placing high impedance in this path.  Often the impedance is a low-pass filter with series element(s) of a high Z and shunt element(s) with a low Z.  The filter must present a simple short circuit (or perhaps just a resistance) at low frequency so DC flows to the amplifier.    
Final 
Oscillations should likely be identified and treated according their frequency. This topic looks advanced and all RLC networks deserve more attention from us.
Todd, VE7BPO --- Feb 27, 2013  

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Three Great Videos from Alan W2AEW

Bill:

While not really homebrew, they do deal with QRP and RF.  The first two are walk-throughs of the schematics of two QRP transceivers, and the last is a discussion of how diodes can be used as RF switches.  I thought you'd find them interesting.

MFJ-9340 QRP Cub CW Transceiver kit schematic review:

http://www.youtube.com/watch?v=2QSwXv2RJzw

 

Heathkit HW-9 schematic walk-through:

http://www.youtube.com/watch?v=rPM1vvGorTo

Using diodes as RF switches:

https://www.youtube.com/watch?v=YBNIq_d56sA

73,

Alan
Http://www.youtube.com/w2aew

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

QRO Problem, and THE KLUGER

Hi Bill,

I've been enjoying your podcasts for a couple of years now and have read both of your books. Please keep up the good work it is much appreciated. In fact, as I can now have both your books and your podcasts on my iPod they are quite literally held close to my heart.

Inspired by your "Kludge Controversy" - enclosed are a couple of photos that I took while on Mount Wellington in Tasmania.


THE POWER OF RADIO

Mount Wellington is a high mountain and is a good launch point for radio waves over the city of Hobart. The visitor lookout has this fantastic warning sign "Electronic disturbances to your vehicle" warning that the transmitter on the mountain can seriously interfere with your car and it may not start, the doors may not open, and the immobiliser may permanently immobilise it. The advice is "A metallic sunshade may reflect radio waves away from the vehicle" and allow you to start it. I'm sure your QRP rigs need no such dire warnings!

WHAT WERE THEY THINKING

And in the very same car park I see this car called a Kluger. In what flavour of English is that a good idea? I know the Brits and Yanks differ over a few phrases but I've never before come across an Oz word that means the exact opposite.

Thanks again for all your many inspiring "broadcasts", and may the Magic Smoke (http://en.wikipedia.org/wiki/Magic_smoke) always stay where it should!


Steven
G6VRD


Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

73 -- The BEST Number

My kids watch this show.   This appears to be one of the only interesting comments to come from it:

"The best number is 73. Why? 73 is the 21st prime number. Its mirror (37) is the 12th and its mirror (21) is the product of multiplying, 7 and 3. ... In binary, 73 is a palindrome, 1001001 which backwards is 1001001."

-Dr. Sheldon Cooper, (Jim Parsons), "Big Bang Theory"

"Just to invite your attention to "73" in Morse code--also a palindrome."

-W9JEF

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Kludge Controversy Continues

Forget about the sequester!  The real issue facing our country is the proper pronunciation of the word Kludge.   Several visitors to the SolderSmoke table at last weekend's Winterfest weighed in on this issue.   SolderSmoke Lexicographer Steve Silverman wrote to inform me that I had totally misinterpreted his e-mail -- he is in fact rather firmly in the Klooge as in Stooge camp.  I, however, am sticking to Kludge as in Fudge.  It just feels right.  And I may use the awesome power of the SolderSmoke media empire to actually CHANGE the way people pronounce this word.

Check out the California Kilowatt ad.  In retrospect, probably a poor choice of brand name.


Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

SolderSmoke Podcast #149

Podcast #149 is now available:  http://soldersmoke.com/soldersmoke149.mp3

17 February 2012

IGY intro
Cappuccio turns off TV on New Year's Eve
Pre-inaugural day on the National Mall
The importance of audio bandwidth in DSB rigs
On 15 meters with the HT-37 and the Drake 2B
Q Killing and Swamping
Adding a Filter the Mighty Midget Receiver
Italian lessons via Echolink
Billy and the Raspberry Pi -- Three Cheers for Ada Fruit
Translate Button on the Blog page (upper right)
C.F Rockey SK
Mailbag: Kludge or Klooge?  

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Carl Sagan, Astronomy, and the Zen Pencil

We presented Carl Sagan's beautiful "Pale Blue Dot" quote back in September 2011, along with a nice video.    This week a friend in Kathmandu sent me a link to a web site called The Zen Pencil.   This fellow takes great quotes and draws cartoons to accompany them.   I liked his cartoon for The Pale Blue Dot:

http://zenpencils.com/comic/100-carl-sagan-pale-blue-dot/ 


Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

SolderSmoke Blog in Gujarati, Arabic, Chinese (and many others)!

SolderSmoke الأخبار اليومية

خدمة المجتمع في جميع أنحاء العالم من الراديو الإلكترونية من يقومون بذلك. تقديم الدعم إلى بلوق بودكاست

Pretty cool, don't you think?    This morning I added a little Google Translate button to the SolderSmoke Daily News.  It is in the upper right.  This makes the blog available in many, many languages.  I made a quick check of the translation to Italian and Spanish -- not bad.  Not perfect, but not bad. 

Please spread the word, especially to Knack victims who may have been struggling with English.  (Use the little e-mail button at the bottom of this post.)

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

On 15 with HT-37 and Drake 2B

W7FE's Shack and Hex Beam

After I replaced the 6U8 first mixer tube on the trusty Drake 2-B I tuned around a bit on 15 meters.  IZ4NIC was loud, all the way from Bologna.  I gave him a call and we had a nice QSO in Italian.  then I talked to F4GBU.  I was using my 40 meter dipole, but I thought I might do better with my 17 meter dipole (it is higher up in the trees).  I called CQ 15 and got into a very nice QSO with Jim, W0JLG in Wichita.  Jim has a very impressive collection of Boatanchors.  We were soon joined by Stu, W7FE.  Stu was using a Central Electronics 100v from the early 1960s.  Wow, the three of us had a nice long contact. 

The QSO was a real trip down memory lane for me:  My sister Trish is visiting us.  We had been talking about how when we were kids she would come into the shack to watch me try to talk to people... with the very same HT-37 and Drake 2B.  I was 15 and she was 10.   That was 39 years ago!  Here we were again, sitting in front of the same old rig.   It was a lot of fun.

Stu has some great info on his very impressive radio shack.  You guys will really enjoy a visit to his QRZ.com site:  http://www.qrz.com/db/W7FE   

And check out his switching system for all those rigs: http://www.qsl.net/w7fe/ 

Wow,  his site makes me want o move out to the shed and put up a hex beam! 

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Rich Arland's "Commo Bunker"

Well known QRP author Rich Arland has launched a new blog called "The Commo Bunker."   I'm pleased that one of his first articles deals with Boatanchor radios in general and the Drake 2B in particular.

Check out his blog: http://commobunker.blogspot.com/

Rich's article came at a good time for me, because today's task in the SolderSmoke HQ shack is fixing my suddenly deaf Drake 2B.  Without even taking it out of the case, I think I have most of the troubleshooting done:  signals make it through, but very weak.  And the S-meter is now resting far below zero.  The S meter is a bridge circuit that looks at current through the RF amp stage (V1) and the IF amp (V5).  So my guess is one of these tubes has gone soft.  This should be an easy fix.

I have a nostalgic reason for fixing this rig.  My sister is visiting us. When I was 15 and she was 10  she would sometimes sit with me in the shack as I used the HT-37 and the 2B.   Those same rigs are still with me and we hope to make a few contacts with them this weekend. 

UPDATE:   I fixed the 2B.   V2, the 6U8 used as first mixer and crystal oscillator had gone soft.  This may also explain difficulties I had in getting the rig to work with a crystal in the E band socket.


Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Filter Pinout: P, E, B, G Explained

I few days ago I asked about the significance of the P, E, B, and G markings on my junkbox Toyo CM 455 kc filter (1969 vintage). PA3BCB -- in yet another example of the power of the International Brotherhood of Electronic Wizards --  was the first to provide the needed info.  And in another example of IBEW awesomeness,  KA0LDB noted that the markings are explained in the 1971 RSGB Handbook.   

P = Plate = filter input
B = B+     = mixer B+ plus if needed or input ground
G = Grid = filter output
E = Earth = Ground

I like the switched filter arrangement presented above (from the RSGB Handbook);  the 2.4 kc bandwidth is great for SSB, but a little tight for AM.  I might put in a DPDT switch in the circuit so as to be able to go back to the "broad as a barn door" selectivity provided by just the 455 kc IF cans.  


  

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Knack Pronunciation Guide: Kludge (as in Fudge)

A SolderSmoke listener (who will remain unnamed) recently corrected me on my pronunciation of an important Knack-related word:  Kludge.   I kludge as in fudge or judge.  He said it should be Kluge as in stooge.  I think we need a ruling her from our etymologist Steve Silverman.   Steve? 

I grew up listening to the 75 meter AM Northeast USA gang.  They said Kludge as in stooge, so I hope we stick with that.  

Wiki has an intereting (and seemingly endless) discussion on this topic: 
http://en.wikipedia.org/wiki/Kludge

Excerpts:


 'An ill-assorted collection of poorly-matching parts, forming a distressing whole' 

"There is a certain, indefinable, masochistic finesse that must go into true Kludge building. The professional can spot it instantly. The amateur may readily presume that "that's the way computers are." 

"The result of this history is a tangle. Many younger U.S. hackers pronounce the word as /klooj/ but spell it, incorrectly for its meaning and pronunciation, as 'kludge'. … British hackers mostly learned /kluhj/ orally, use it in a restricted negative sense and are at least consistent. European hackers have mostly learned the word from written American sources and tend to pronounce it /kluhj/ but use the wider American meaning! Some observers consider this mess appropriate in view of the word's meaning."

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20