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Wednesday, November 22, 2017

iPhone Direct Conversion Receiver with Variable Ceramic Oscillator


A while back Bob N7SUR got us talking about winter projects.  Receivers.  Of course, Pete and I quickly went down different paths.  Pete is making great progress with lots of interesting digital circuitry.  He is going over to the dark side. Check it out here: 

I went with simplicity.  Extreme simplicity.  Direct Conversion (thanks Wes!).  Discrete components.  No chips.  Analog Oscillator.  40 meters -- monoband.   


There it is.  You can click on the picture to make it larger. Here is an outline of the circuitry: 

-- Single tuned circuit bandpass filter preceded by a simple pot that serves as a gain control. 
-- JFET RF amp
-- Singly balanced passive mixer inspired by F5LVG's RX-20 in SPRAT 100.  For the coil I used one of the many trifilar toroids that Farhan gave me. 
-- The local oscillator is the coolest stage.  I used a 7.37 MHz ceramic resonator and a circuit inspired by Miguel PY2OHH. With a polivaricon I can tune the entire 40 meter band. I put a reduction drive int here to make tuning easier. 
-- The AF amp is an op-amp free design.  It works well into ear buds or into a computer speaker. 
-- Perhaps in an effort to catch the attention of the younger generation, I built it into an iPhone box.  

Please let me know if you spot any flaws in the circuit, or see any places where it might be improved. 

More to follow.   This prototype is now in the mail, en route to my nephew John Henry who will be testing it for me. 





Saturday, November 18, 2017

China and SETI: What Happens if China Makes First Contact?


Here is a really amazing article from The Atlantic.  It is very thought provoking.  Mind blowing.  Strongly recommended. 

You can read it here: 

https://www.theatlantic.com/magazine/archive/2017/12/what-happens-if-china-makes-first-contact/544131/

Or you can listen to a reading of it (like a podcast) here: 

https://soundcloud.com/user-154380542/what-happens-if-china-makes-first-contact-the-atlantic-ross-andersen

Thanks to Mike Rainey AA1TJ for alerting us to this. 

Friday, November 17, 2017

Jeff Murray's Grumpy Audio Guy from 40 meters

I've talked to this guy several times.  He usually waits until I'm testing a new rig.  

https://www.facebook.com/6sj7jeff/videos/10208309648978285/

I'm sure Pete has worked him too.  

Saturday, November 11, 2017

Amazing Homebrew/Boatanchors QSOs on 40 --Six solder melters in a row!

Al W8VR
After a day of happy tinkering with the Direct Conversion receiver I've been working on, I turned off the soldering iron and got on 40 meter SSB with my BITX Digi-Tia. 

First -- Steve W4IJ came back to my CQ.  Steve is a boatanchor enthusiast and has written for Electric Radio magazine.  FB. 
W4IJ Boatanchors
When Steve signed off, I got into a contact with Pete W8NBO.  We had spoken before and he had told me of a homebrew transmitter he'd built as a kid.  This time I asked for details: It was a 6AG7 oscillator to a 6L6 amplifier.  He ran it with an S38 (brave man!).  He described what must have been a very painful effort to hack (literally) the needed holes in the transmitter chassis using just a spike, a hammer and a file.  I told him this brought back my memories of similarly painful chassis work (mine was for a power supply for a Heath HW-32A).

At this point we were joined by Arnie, W2HDI.   Arnie's rig is in Stowe Vermont, but he was running it remote from the South of France where he and his wife were celebrating their 50th wedding anniversary.  Arnie shared with us memories of similar chassis pain -- his were related to an external modulator that he built for a DX-40. I think he said that all he had was a hole punch and a file.  Oh, the humanity! 

Then Al W8VR joined the conversation.  Al said that he's been in the game so long that his early rigs were built using cigar boxes as chassis.  I pointed to a connection:  I noted that my BITX rigs are enclosed in what could be considered cigar boxes.  Al's QRZ page picture has a magnificent AM rack rig that he said was actually built twice.  There is also an HRO-60 in the picture.  FB. Check it all out at Al's web site.  Click on the mic for the write ups, the key for the pictures.  http://www.w8vr.org/

Then Dennis K0EOO called in.  Holy Cow!   Dennis and I spoke not long ago.  You may recall my enthusiastic write up of his beautiful 1974 SSB rig: 
and

This was almost too much.  Rarely will you spontaneously come across so many hams who have melted so much solder.  FB. 

Icing on the cake:   When I returned to the bench, I fired up the DC receiver and heard Mike KN4EAR talking about his BITX40.  I switched to the Digi-Tia and gave Mike a call.  He reports making many contacts with his rig. FB. 

TRGHS. 

Wednesday, November 8, 2017

Beautiful QSL by Jeff Murray K1NSS


Here's a reminder of the amazing art work of Jeff Murray K1NSS. 
You can have him draw a QSL for you:   Go here:
https://www.jeffk1nss.com/hamgraphics/

Jeff writes: 
Well, I got as far as high school intermediate algebra and then I saw a squirrel.
Thank goodness others like Ken N2WWD were paying attention and went on to surf gravity's rainbow of flight dynamics, all in a day's work and play for rocket scientists. Tandem surfing and professional activities somewhat aside, Ken is also actively involved with ARISS, i.e. Amateur Radio on the International Space Station, the group guiding ham radio operations aboard ISS. So Kelvin cool to work with Ken on this New One, with Ken cooking up a special Easter Egg for all you galactic hitchhikers!

What might I draw with you?https://www.jeffk1nss.com/hamgraphics/

Monday, November 6, 2017

Jan's FB Slovakian SMD TIA Boards


Hello,

I have put up my SMD version of the TIA amplifier boards online, in case
someone wants it. The files are here:


and direct OSHPark order link:

73!, Jan

Designer: Douglas Bowman | Dimodifikasi oleh Abdul Munir Original Posting Rounders 3 Column