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Thursday, November 30, 2017

VK3YE QRP by the Bay Goes VHF/UHF



Peter Parker again hosted the VK3 radio amateurs.  This time the event fell on VHF/UHF Field Day weekend.   So Peter and his friends went up in frequency and up into SPACE!  

VK3HN has a nice blog post here:

https://vk3hn.wordpress.com/2017/11/25/qrp-by-the-bay-chelsea-beach-melbourne-25-11-2017/

Be sure to read about Peter's ankle manacles -- he apparently uses them to get a good ground (sea) plane while running pedestrian mobile on the sea shore. Peter is DEDICATED! 

Wednesday, November 29, 2017

Listening for Your Own Signals on the Long Long Long Path


I heard some guys talking about this on 40 SSB last night.  A very cool use of the bidirectional pattern of the W8JK beam. 
From: http://qrznow.com/the-w8jk-is-a-famous-and-effective-dx-antenna/

Round-the-world paths The bi-directional nature of this antenna makes it possible to discover open round-the-world paths, something not possible with a normal beam antenna. The technique used by Kraus is to rotate the beam slowly, sending short Morse code dots, with a full-break-in or QSK transceiver. The delay time for the signal to return is about one seventh of a second, so there is plenty of time for your transceiver to switch to receive mode. When you have found and peaked an open round-the-world path, call CQ, and you may be rewarded with DX anywhere along the path. Also, the question of Long-path and Short-path does not arise – you are transmitting on both paths at once, giving you a greater chance of catching the other station’s beam direction….


Tuesday, November 28, 2017

Videos of iPhone Box DC Receiver






These are just a couple of short videos that I made for my nephew before sending him this receiver. 

As you can hear, deafness is not a problem with this design!   I did make some frequency stability improvements after this video was made -- I think you can hear a bit of drift.  Still, not bad for a very simple circuit using a polyvaricon superglued to the back of a cardboard box.  

I'll post more videos of the second version of this receiver.  There are further improvements in frequency stability.  My goal:  "Juliano Si5351" levels of stable-ness.  

Saturday, November 25, 2017

Polyvaricon Variations -- Polyvaricons Are Not all The Same


When I built the first prototype of the iPhone DC receiver, I just reached into my junk box and used a polyvaricon capacitor for the main tuning control. It was marked PL 051.  I was really pleasantly suprised at the stability of the Variable Ceramic Oscillator circuit.  I could tune the entire 40 meter band with complete stability -- Juliano levels of stability. 

By the time I put the second version into its box (see above), I used a different polyvaricon (the one pictured below).  It worked, but with this part the receiver drifted noticeably.  So this morning I pulled it out and put in a second PL 051 Polyvaricon.  Viola!  Eccolo!  Success.  Drift eliminated.  Rock stable.    

Has anyone else noticed variations like this in the stabilty of polyvaricons?  

The dial in this version is an Archer device that has been kicking around in my junkbox for more than 20  years.  I think it was given to me by my old friend Pericles HI8P -- this adds a tremendous amount of soul to this new machine).   The box is an old Bud aluminum chassis.  Man, this thing sounds great.  I will try to post a video soon. 


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.   

Schematic updated 29 November 2017
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.  
Designer: Douglas Bowman | Dimodifikasi oleh Abdul Munir Original Posting Rounders 3 Column