A New Look at BITX Carrier Suppression; N6QW IN EMRFD!

Bert, WF7I, was recently struggling to get his BITX 20 going and he asked some good questions about carrier suppression.  I realized that I hadn't really paid much attention to this.  Perhaps as a result of my long experience with DSB, I was happy as long as I was able to null out MOST of the carrier. 

I fired up the scope and took a look at the output from the BITX 2040 on 40 meters.  Here's the test setup:  Coax from the antenna terminal to a 50 ohm resistive load at the Rigol O'scope probe.  Just keying the transmitter (no mic connected),  carrier was at 980 millivolts rms or about 19 milliwatts.  I then connected an AF sig generator into the mic in connector and pumped in some 1000 Hz sine wave. Peak output was 20.7 volts rms, or about 8.6 watts.   That puts the carrier about 27 db down.  I felt I should be doing better. 

I took a look at the shape of my crystal filter and the frequency placement of my carrier oscillator.  I noticed that the carrier oscillator freq was fairly close to the bandpass portion of the crystal filter -- fairly high up the skirt, only about 9 db below the passband level.   I figured that if I just moved that carrier oscillator up around 300 Hz, I would get around 10 db of additional carrier suppression. 

Sure enough,  with the carrier moved a mere 300 Hz further away from the passband,  the residual carrier dropped to 346 millivolts rms, or about 2.4 milliwatts.    Now peak output was 20.9 volts rms, or 8.7 watts.  36 db of carrier suppression. 

I guess I could do better if I moved the carrier up another little bit, but I like the sound of it now.  I may have been able to better if I'd fiddled with the balanced modulator diodes a bit more.  But what do you guys think?  Should I worry about 2 milliwatts of residual carrier?  Heck I once ran a CW rig (W1VD' VXO 6 watter) that kept the oscillator running on key up, producing about 15 mw of "backwave." No damage was done, few noticed, no one complained.

Oh yea, is this the way to measure carrier suppression? 

----

While doing all this, I pulled out my trusty copy of EMRFD.  The index led me to the balanced modulator section on page 6.56.  There I spotted a familiar call:  W6JFR!!!  That's Pete Juliano, N6QW!  Pete is credited with a mod to the SBL-1 mixer that adds a balance control pot to the device.   Wow, actually being IN EMRFD fully confirms Pete's homebrew guru status.


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SolderSmoke Podcast #162: Part II with Pete Juliano, N6QW

 

SolderSmoke 162 is now available at  http://soldersmoke.com/soldersmoke162.mp3
 
June 21, 2014
Part II of our interview with Pete Juliano, N6QW
 
-- Bill's Moxon Monstrosity
-- Amplifiers and Exorcisms (See slideshow link below)
-- Varactor tuning
-- Polivaricon capacitors
-- The challenge of building small rigs
-- Heat, layout, components and VFO stability
-- "No frills" as a building philosophy
-- The future of Bill's Heathkit HW-101    
 
We still have a lot more to talk about.  Stay tuned for Part III!

Slideshow of Pete's RF Amplifiers: 
https://onedrive.live.com/?cid=4f1e8c71e0d4f1dc&id=4F1E8C71E0D4F1DC%212640&Bsrc=Photomail&Bpub=SDX.Photos&sff=1&authkey=!AGq3hc4UajARH1s




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

Bert WF7I Finishes BITX, WORKS ITALY

 

That, my friends, is the look of exhausted contentment that comes after you have FINALLY gotten your new homebrew rig to work, and were rewarded by crossing the mighty Atlantic on your first call.    Congrats Bert!   Details here:

 

http://wf7ihomebrew.wordpress.com/2014/06/18/bitx20a-on-the-air/



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

Confucian Wisdom from VU2BK in Hyderabad

I'm not a big collector of QSL cards, but this one has been kicking around in boxes and on various hamshack walls for more than 20 years.  I like the bit of Confucian wisdom that arrived in Santo Domingo all the way from Hyderabad.  I was running my trusty HT-37 and Drake 2-B.  Anyone know OM Kab, VU2BK?

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

BITX 5 Watter Makes the Trip to Tokyo

The solar flux index was only 151 this morning, but grey line conditions to Japan were very good.  Yoshi, JA1OJJ, was booming in on 17 meters.   We had a nice chat.  He said I was 55.  His 5 element quad helped a lot!   

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

F6FEO's BITX 20 (and DSB Rig)

This morning I was looking at F6FEO's wonderful web site (Frank, KM4AXA is building the 28 Mhz DSB rig from Michel's site) .  The drawings have a nice JF1OZL feel to them.

Check out Michel's site.  Just hit the translate button if you have trouble with the French language:
http://f6feo.homebuilder.free.fr/index.html

Merci Michel! 



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

MOXON Antenna Project -- Need Rotator Advice

 

 

I've been put together a fishing pole MOXON antenna for 17 meters.  It will be used with my 5 Watt BITX rig.  I need something to spin it around.   I know that many of the cheap TV rotators don't hold up very well.  I had one die quickly out in the Azores.  There seems to be several brands out there, but the rotators and the control boxes look suspiciously similar. 

 

Is there any brand out there that is more robust and reliable than rest? 

I came up with a pretty cool way of affixing the corners of the antenna elements to the fishing poles.  That coil-like thing is the wire part of a bungee cord.  It fits nicely into the end of the fiberglass pole. You have to be sure to get the pole length and the element dimensions properly proportioned, with a sufficient amount of bend in the poles.

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

Fireballs Emitting RF at HF!

Yea, and that damn gamma ray bust static has been totally messing up the 12 meter band! Someone should complain to the FCC!

https://medium.com/the-physics-arxiv-blog/1382596c320d

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

Some DX That You Can Never Work. Never.

There is some amazing info in this site. It is worth reading.

https://medium.com/starts-with-a-bang/the-disappearing-universe-d7447467c63a

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

Pete Juliano's Enclosures

 

I'm sure many of you are, like me, impressed with the enclosures that Pete Juliano has been using with his rigs.   Here's an e-mail that he sent yesterday to Bert. 

Hi Bert,

 

You have a ready source of material right there in Seattle and they will cut it to size. Check out On-Line Metals. The transceiver project has a 4 x 8 inch base plate I bought from them and the front and back are pieces of single sided copper PC Board. The support material is 1/2 inch aluminum angle stock (Home Depot). Interesting use of round aluminum pillars. The front and back are stabilized using 1/4 inch threaded aluminum spacers that were fitted inside of small diameter hollow aluminum tube I bought in a hobby shop. A dab of Gorilla Glue holds the spacers inside the tubing and it forms a rigid support structure.

 

The subject of mechanical construction is a good one and perhaps Bill would like to cover that in a future podcast. That said I do have a bench top 3 axis manual milling machine and a 3 axis CNC milling machine (that one cost me about $250K). The cost was not in the machine but the cost of sending my youngest son to WSU where he got an ME degree. He designed and built the machine for me.

 

Boeing Surplus (now gone) in Kent used to sell aluminum plate by the pound and a lot of my stock (now all gone) came from there. As a retired Boeing employee I used to get a discount.

 

73’s

Pete

And here is a slide show illustrating Pete's technique:

https://onedrive.live.com/?cid=4f1e8c71e0d4f1dc&id=4F1E8C71E0D4F1DC%212607&Bsrc=Photomail&Bpub=SDX.Photos&sff=1&authkey=!ADzJ4SgPn5OzRqk


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

Video of Pete Juliano's 20-40 Bilateral Rig

Wow, what a beautiful rig.  Nice work Pete.  Kind of eerie how we both chose the 20/40 combination after building 17 meter rigs. We'll have to talk more about this in SolderSmoke 162.  Soon!

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

A Post Card from Paris

This arrived from Paris, from our friend Rogier, PA1ZZ KJ6ETL. "Men are like computers: one never knows what's going on inside."  But it looks to me like the OM in the picture knows EXACTLY what's going on inside that rig.  So I guess this is commentary on the perils of black boxes, and the benefits of an analog, discrete component, Hardware Defined Radio approach.    I'm with you Rogier!  Merci!


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