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qrp-gaijin: Building a 7 MHz small transmitting loop antenna, part 2

http://qrp-gaijin.blogspot.com/2015/01/building-7-mhz-small-transmitting-loop.html

Building a 7 MHz small transmitting loop antenna, part 2. I did some more exploratory work on the mechanics of constructing my 7 MHz small transmitting loop. Fitting copper pipes together. The copper pipes I am using are 6mm in diameter with a wall thickness of 0.5 mm. This means that the inner diameter should be 5mm. Therefore, I needed to swage open the ends of the 6mm copper pipe, creating a flared opening at the pipe end, so that the 5mm pipe could fit inside. Then, the pipes will be soldered together.

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qrp-gaijin: Building a 7 MHz small transmitting loop antenna, part 3

http://qrp-gaijin.blogspot.com/2015/01/building-7-mhz-small-transmitting-loop_10.html

Building a 7 MHz small transmitting loop antenna, part 3. Part 3 of this article series focuses on the mechanics of the motorised variable capacitor. Mounting the capacitor and motor. And, this link describes in detail various loss mechanisms of air variable capacitors, including dielectric losses: http:/ g3rbj.co.uk/wp-content/uploads/2013/10/Measurements of Loss in Variable Capacitors issue 2.pdf. The capacitor is mounted on the polyethylene board as follows. The motor looks as follows. The current mot...

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qrp-gaijin: 4月 2014

http://qrp-gaijin.blogspot.com/2014_04_01_archive.html

A simulated 40m multi-turn small transmitting loop. To open the model in 4nec2, copy and paste the text between the dashed lines and save it to a file, then open the file in 4nec2. CM 3D multi-turn loop. CM qrp.gaijin@yahoo.com (2014/04). The simulation results are as shown in the following image. It follows that by adjusting the turn spacing or diameter, the structure can be made self-resonant with no need for an additional resonating capacitor. Roger G3XBM's Amateur Radio Blog. 10m JT65 since breakfast.

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qrp-gaijin: Fringe howling regenerative receiver

http://qrp-gaijin.blogspot.com/2014/10/fringe-howling-regenerative-receiver.html

Fringe howling regenerative receiver. Schematic diagram of fringe-howling regenerative receiver. The following video illustrates the fringe howl occurring in the receiver prototype. Although the audio and video quality are low, and the prototype circuit layout is not visually pleasing, I felt it important to create an audio-visual recording of the fringe howl phenomenon, because there is (as far as I know) no existing audio-visual documentation of the phenomenon, only written descriptions. Video from 02:...

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qrp-gaijin: 6月 2014

http://qrp-gaijin.blogspot.com/2014_06_01_archive.html

Qrp-gaijin small transmitting loop calculator. Loop side length m. Loop area m 2. Conductor cross sectional shape. Equivalent round conductor diameter for RF resistance. Equivalent conductor diameter for loop inductance. Loop conductor inductance uH. Loop conductor bulk resistivity Wm. Loop conductor loss multiplier (braid:4-16). Length of capacitor connecting wires mm. Connecting wire cross sectional shape. Connecting wire diameter mm. Connecing wire width mm. Connecting wire thickness mm. This calculat...

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qrp-gaijin: Building a 7 MHz small transmitting loop antenna, part 4

http://qrp-gaijin.blogspot.com/2015/01/building-7-mhz-small-transmitting-loop_13.html

Building a 7 MHz small transmitting loop antenna, part 4. Part 4 of this article series focuses on the PWM circuit for precise and slow control of the motor that drives the capacitor. Attempt 1: Analog-to-analog motor control circuit. Before discussing the final PWM circuit I used to control my motor, allow me to discuss another highly interesting circuit: the 7N3WVM "Remote Motor Controller" described here: http:/ www.qsl.net/7n3wvm/DC mot control.html. Please have a look at that page before proceeding.

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qrp-gaijin: 1月 2015

http://qrp-gaijin.blogspot.com/2015_01_01_archive.html

Building a 7 MHz small transmitting loop antenna, part 5. Part 5 of this series describes some mechanical design changes and first disappointing tests with the loop. First design change: From copper pipe to copper strap. As described in parts 1 and 2 of this series, the original design for the 3m x 2m loop radiator was to construct it using several 1m-length segments of 6mm-diameter thin-wall copper pipe. However, such a structure, once built, is impossible to move or alter without tedious disassembly.

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qrp-gaijin: 9月 2014

http://qrp-gaijin.blogspot.com/2014_09_01_archive.html

The Wheatstone Bridge Regenerative (WBR) receiver: how does it really work? If you're not familiar with the WBR circuit, AA1TJ writes more about it here: http:/ aa1tj.blogspot.jp/2011/08/ancients-have-stolen-our-inventions.html. Please see that article to understand the basic idea. I have seen no references in online discussions to this patent; I found it myself after a lengthy period of investigation, while attempting to understand the operation of and research the background of the WBR receiver. Instea...

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qrp-gaijin: 7月 2013

http://qrp-gaijin.blogspot.com/2013_07_01_archive.html

Good day, dear visitor. I've had this blog open for a while, but haven't posted anything yet. On and off I've thought about starting it and posting some contents here. As an experiment, I decided to make my first posting here, just to familiarize myself with the blog system. Please feel free to leave any comments. Roger G3XBM's Amateur Radio Blog. 10m JT65 since breakfast. Speaker-microphones and DMR portables. VE7SL - Steve - Amateur Radio Blog. Mailbox, Coffee And The 'Stew'. Ham Radio Blog by AG1LE.