Date   

The Discovery Of Radio Waves

Aaron K6ABJ
 

Excerpts from the Wikipedia page of Heinrich Rudolf Hertz...

In 1864 Scottish mathematical physicist James Clerk Maxwell through mathematical equations predicted that coupled electric and magnetic fields could travel through space as an "electromagnetic wave". Maxwell proposed that light consisted of electromagnetic waves of short wavelength, but no one had been able to prove this, or generate or detect electromagnetic waves of other wavelengths.

During Heinrich Hertz's studies in 1879 it was suggested to him that his doctoral dissertation be on testing Maxwell's theory. Not seeing any way to build an apparatus to experimentally test this, Hertz thought it was too difficult, and worked on electromagnetic induction instead.

After Hertz received his professorship at Karlsruhe he was experimenting with a pair of Riess spirals in the autumn of 1886 when he noticed that discharging a Leyden jar into one of these coils would produce a spark in the other coil. With an idea on how to build an apparatus, Hertz now had a way to prove Maxwell's theory. He used a Ruhmkorff coil-driven spark gap and one-meter wire pair as a radiator. Capacity spheres were present at the ends for circuit resonance adjustments. His receiver was a loop antenna with a micrometer spark gap between the elements. 

Between 1886 and 1889 Hertz conducted further research and measured Maxwell's waves and demonstrated that the velocity of these waves was equal to the velocity of light. The electric field intensitypolarization and reflection of the waves were also measured by Hertz. These experiments established that light and these waves were both a form of electromagnetic radiation obeying the Maxwell equations.

Hertz did not realize the practical importance of his radio wave experiments. He stated that,

"It's of no use whatsoever[...] this is just an experiment that proves Maestro Maxwell was right—we just have these mysterious electromagnetic waves that we cannot see with the naked eye. But they are there."

Asked about the applications of his discoveries, Hertz replied,

"Nothing, I guess."

Hertz's proof of the existence of airborne electromagnetic waves led to an explosion of experimentation with this new form of electromagnetic radiation, which was called "Hertzian waves" until around 1910 when the term "radio waves" became current term. 

Researchers such as Oliver LodgeFerdinand Braun, and Guglielmo Marconi employed radio waves in the first wireless telegraphy radio.  In 1909, Braun and Marconi received the Nobel Prize in physics for their "contributions to the development of wireless telegraphy".  


SFARC Net - Thu, 10/22/2020 #cal-notice

sfarc@w6ek.groups.io Calendar <noreply@...>
 

SFARC Net

When:
Thursday, 22 October 2020
7:30pm to 8:30pm
(GMT-07:00) America/Los Angeles

Where:
W6EK Repeater - 145.430 -600, PL162.2

Description:
Check-in for Club updates from Officers and members, QSTs and more. Everyone is welcome!


Re: Elmer Net - Wed, 10/21/2020 7:30pm-8:30pm #cal-reminder

carl.wf6j@gmail.com
 

See ya’ll at 7:30 on the ELMER NET!

73,
Carl, WF6J
ARRL PIO
Elmer Net Control

On Oct 20, 2020, at 7:30 PM, sfarc@w6ek.groups.io Calendar <sfarc@w6ek.groups.io> wrote:

Reminder: Elmer Net

When: Wednesday, 21 October 2020, 7:30pm to 8:30pm, (GMT-07:00) America/Los Angeles

Where:W6EK Repeater - 145.30 - pl162.2

View Event

Organizer: Carl - WF6J

Description:

The Elmer Net meets the 1st and 3rd Wednesday each month, and is devoted to answering your questions, solving puzzling issues related to ham radio, and scheduling help for all Hams. No question is "stupid". We encourage everyone to ask away so we can all learn and grow our knowledge together. Web address: http://w6ek.org/nets.html



October 2020 El Dorado County Amateur Radio Club Online Meeting and Presentation on Deep Space Communications: The Next 50 Years

Alan - W6WN
 

You are invited to the Monthly Meeting of The El Dorado County Amateur Radio Club 
 
When: Thursday, October 22nd
6:30-7:00 PM (PST) - Chat
7:00 PM - Presentation
 
Registration is required to join the meeting:
 
After registering, you will receive a confirmation email containing information about joining the meeting.
 
Topic: Deep Space Communications: The Next 50 Years
 
Dr. Les Deutsch
Jet Propulsion Laboratory
California Institute of Technology
 
We have been sending spacecraft to explore the Solar System since the 1960s. In these intervening 60 years we have improved the performance of our radio links between Earth and deep space by some thirteen orders of magnitude (a factor of 10,000,000,000,000.) These radio links not only provide all communications to and from deep space, but they also serve as the main way of navigating our spacecraft to their destinations. As our space missions become more capable and complex, we predict a need to increase communications efficiency by a further factor of ten for each decade for the next 50 years. We are already putting in place the improvements needed for the next 20 years.
 
This talk will examine past and present NASA deep space missions from a communications perspective. We will then consider some of the possible future missions and the corresponding communications system improvements.
 
---------------------
 
Les is the Deputy Director of the Interplanetary Network Directorate at NASA’s Jet propulsion Laboratory.  This Directorate provides information services to spacecraft exploring the solar system and beyond. The Directorate’s facilities include NASA's Deep Space Network, the giant antennas used to communicate with these spacecraft.
 
Dr. Deutsch, a Mathematics graduate of Caltech, has held various positions during his years at JPL including management of several technology programs.  He introduced advanced communications technology to the Galileo mission, en route to Jupiter, to compensate for the loss of its main antenna. He also was the NASA lead for the NASA/ESA team that redesigned the Huygens Probe mission to Titan to mitigate an anomaly in the Cassini relay radio system. Les was JPL's Chief Technologist for the 2002 fiscal year and developed JPL's strategy for technology development.

Along the way Dr. Deutsch has published over 60 papers in the fields of communications, microelectronics, and spacecraft systems.  He also has been awarded more than 25 patents, mostly in electronic music.
 
Les also travels the world performing in jazz festivals and giving organ concerts. He also holds an official joint appointment at Caltech – as the Institute’s Organist.


Elmer Net - Wed, 10/21/2020 7:30pm-8:30pm #cal-reminder

sfarc@w6ek.groups.io Calendar <sfarc@...>
 

Reminder: Elmer Net

When: Wednesday, 21 October 2020, 7:30pm to 8:30pm, (GMT-07:00) America/Los Angeles

Where:W6EK Repeater - 145.30 - pl162.2

View Event

Organizer: Carl - WF6J

Description:

The Elmer Net meets the 1st and 3rd Wednesday each month, and is devoted to answering your questions, solving puzzling issues related to ham radio, and scheduling help for all Hams. No question is "stupid". We encourage everyone to ask away so we can all learn and grow our knowledge together. Web address: http://w6ek.org/nets.html


SFARC Net - Thu, 10/22/2020 7:30pm-8:30pm #cal-reminder

sfarc@w6ek.groups.io Calendar <sfarc@...>
 

Reminder: SFARC Net

When: Thursday, 22 October 2020, 7:30pm to 8:30pm, (GMT-07:00) America/Los Angeles

Where:W6EK Repeater - 145.430 -600, PL162.2

View Event

Description: Check-in for Club updates from Officers and members, QSTs and more. Everyone is welcome!


Re: Using a CB Antenna with an SDR receiver #antennas #elmer #howto #antennas #elmer #howto

Jef - N5JEF
 



On Tue, Oct 20, 2020 at 6:05 AM Jef - N5JEF via groups.io <jef=jefallbright.net@groups.io> wrote:
Here's a picture of my 10-ft diameter loop for 40-60-80 meters, a work in progress.

image.png

image.png

Here's the flanges for attachment to the vacuum variable capacitor:

image.png
 


Amateur Radio for Emergency Managers FEMA Online Presentation

Alan - W6WN
 

When: Thursday 22 October 2020, 03:00 PM - 04:00 PM
Time Zone: (GMT-05:00) Eastern Time (US and Canada) (Please note that Daylight Saving Time (+01:00 hr) is in effect during this time)

To know more about the event, the speakers for the event and to stay updated, please visit:

https://fema.connectsolutions.com/amateurradio/event/event_info.html

Thank you,
Region II National Preparedness Division 


Please join the Region II National Preparedness Division for a webinar on how an amateur radios can be a usual tool before, during and after disasters.
Amateur or “HAM” radio has proven to be indispensable in the aftermath of Hurricanes Katrina, Harvey, Irma, Michael and Maria. Historically, amateur radio has been a valuable resource in the Response and Recovery phases of many disasters, providing expedient communications when standard public safety and commercial telecommunications infrastructure has been severely impacted or completely overwhelmed. This webinar will provide guidance to Emergency Managers on establishing a viable, NIMS compliant, AUXCOMM ( Auxiliary Communications ) program as part of your EOP. Learn how to add the ready resource of amateur radio as a component of your ESF-2.

Who should attend? Whole community with a particular emphasis on Local, State, and Federal Emergency Managers, CERT Program Leaders, Health Departments, and NGO’s


Re: Using a CB Antenna with an SDR receiver #antennas #elmer #howto #antennas #elmer #howto

Skip - K6DGW
 

A small loop mounted horizontally behaves like an E-field antenna and needs to be elevated. I tried it once out a 4th floor hotel window. Didn't work well.

All the loop needs is a capacitor to tune it to resonance. Anything else just increases the non-radiating losses. Based on what the calculator finds for the voltage[s], it can be a any transmitting cap with sufficient voltage rating. Most use vacuum variables since it is outside at the loop and even if in a box, is still exposed to outdoor humidity. One approach I've used is to fit a smaller copper pipe into a piece of Schedule 40 or 80 PVC and then fit that coaxially into a larger copper pipe. A long threaded rod then moves the inner pipe in and out. I used wide copper strap for the connections for more surface area. The advantage is that you can get away without needing a reduction gear box, I had an 18 RPM reversible DC motor that just drove the threaded rod until it was at zero phase difference. Do not use ABS pipe for the dielectric, it isn't a dielectric. You can test plastic parts by putting them in a microwave and nuking them for varying times. Any that get warm are not suitable.

Regarding conductor diameter and thickness: The RF current is confined to the outer surface ... thickness doesn't add any benefits except mechanically. The larger the surface area of the loop, the lower the loss. Most of the loss in a well-built loop will be in the connections to the capacitor. Regardless of how you do it however, the loop MUST operate at resonance if you intend to work anyone with it. I can sit under my Alexloop [making it tunable without having to move back and forth] because I run my K2 at 5-7 watts when in the field. If you're running 100+ watts, you should tune it remotely for safety reasons. 73,

Fred ["Skip"] K6DGW
Sparks, NV


Re: Using a CB Antenna with an SDR receiver #antennas #elmer #howto #antennas #elmer #howto

Jef - N5JEF
 

Here's a picture of my 10-ft diameter loop for 40-60-80 meters, a work in progress.

image.png

image.png



On Tue, Oct 20, 2020 at 1:18 AM Aaron K6ABJ <aaron@...> wrote:

Thank you Skip for the link to the loop antenna radiation calculator.  I was looking for that, but couldn't find it! Are you operating your Alex Loop in a horizontal position so the null is towards you? Unless a person is operating from a second story or higher, as I understand its best to have a loop antenna in a vertical orientation. I am trying to picture your setup, and how I will do mine when I get a Magnetic Loop Antenna.

Jeff piqued my interest in Magnetic Loop Antennas, and the more I have learned the more interested I have become. Being a high Q antenna, they have a VERY narrow bandwidth, but their OUTSTANDING efficiency, small size, and lack of need for a mast make these antennas VERY appealing to me. I have enjoyed learning about and researching Loop Antennas the last few days! These antennas wouldn’t work well in a contest for Searching and Pouncing, but if Running (which I prefer to do) it would do great!

Their extremely high voltage, current and non-ionizing radiation creates real safety concerns. These issues however are a good sign that the antenna will get me the DX I want! I will simply mitigate the safety issues by securely supporting the antenna and ensuring I and others maintain enough distance from it while transmitting. The challenge before me now is how do I get one!?

Building one is possibly the most affordable option, but sourcing a capable capacitor is a significant challenge! Building the loop using 3/8 inch flexible copper pipe would be a good material as it is relatively thick and could be made out of a single piece. Perhaps cut the ends using a dremel to create flat copper tabs to directly attach the loop to the capacitor.

MFJ’s products have significant workmanship/assembly issues, so I generally avoid MFJ, but they have three High-Efficiency Loop Tuners to choose from that would solve the capacitor sourcing problem. The only difference between the MFJ 933 ($209.95) and 935B ($249.59) is that the 935B includes an Antenna Current Meter. The MFJ 936B ($299.85) is like the others, but it takes up more space, includes an SWR Meter, a Current Meter, and adds 60 Meters. For me, I think the 935B is the best option. The nice thing about going with one of these as opposed to something else is that they are good for up to 150 watts, 10-40 meters, and I can make my own loop. By making my own loop I can experiment with various materials, can have a greater variety of loop circumferences allowing for greater performance and more bands, and I can roll the loop up for greater portability. I do however see two downsides to going this route: 1) The MFJ 1788 Super Hi-Q Loop Antenna ($559.95) comes with a loop that is an inch thick so would significantly improve performance over a loop I could make myself, and 2) The MFJ 1788 comes with a controller that allows the operator to tune the Antenna from afar, something that seems like a very good idea given the extreme voltage and non-ionizing radiation that occurs with these antennas.

The MFJ 1788 is rated for 150 watts, just like the loop tuners, but it is only good for 15-40 meters. Whether the efficiency of having a thicker loop would more than make up for the ability to have loops for each band, I do not know. Aside from the added cost, the other potential problem with the 1788 is that it relies on an electronic tuner and motor, which given that its made by MFJ could fail. Still, the ability to be able to tune the antenna from afar given the amount of radiation that is involved, if cost wasn’t a factor I think I would go for the 1788 over the 935B.

Other loop antennas that were considered: The AlexLoop ($399.95) appears to be very well constructed, comes with a nice bag, and is 10-40 meters. The downside is that it is only rated for 20 watts. Still, given the amount of power Magnetic Loops put out 20 watts isn’t bad, especially if you are using it for portable. The price is very competitive, but given that I want to use my loop antenna for serious contesting in addition to portable operations, the MFJ 935B for me remains the leader.

The Alpha Antenna ($500.00), is another option. It too appears to be a well-made antenna and comes with a bag. It also comes with a small tripod. It is rated at 100 watts for 10-40 meters, and 20 Watts 40-80 meters. It is twice as much money as the 935B, but the advantage to it or the AlexLoop over the 935B is ease of use. The capacitors are smaller and lighter than that of the 935B, making them able to be supported by a small tri-pod. This however raises a very important question, given its larger and heavier size does the capacitor of the 935B perform better? I think the answer to this question determines which wins out, the MFJ 935B or the Alpha.

I think there is only one more antenna to consider, and that is the Ciro Mazzoni Automatic Magnetic Loop Antenna. It is one incredible Antenna, weighing an astonishing 44lbs is isn’t good for SOTA, but it is VERY well made, can be remotely tuned, is rated for 800 watts on 20-30 meters, and 300 watts on 40-80 meters. The rub is that it costs $2,479.99. That is a lot of bread, unless you consider the cost of the land required to erect a comparable 80 meter dipole!    

On Mon, Oct 19, 2020 at 12:17 PM Skip - K6DGW <k6dgw@...> wrote:
Jef points out a couple of advantages [and disadvantages] of small transmitting loops.  The circulating current will be high with any appreciable power.  The radiation resistance is in the milliohm ranges, and any resistance in the loop will dramatically lower the efficiency.  It is tempting to build a loop as an octagon with copper pipe since the fittings are readily available, however the added resistance in the soldered joints can be as much or more than the radiation resistance, cutting the efficiency in half or more.  Silver solder will ameliorate this a little, but a continuous length of copper pipe is much better.  The voltages across the tuning capacitor will rise dramatically with higher power, well into the kilovolt range, requiring vacuum capacitors.  Remembering that the RF current travels on the surface of the loop and is excluded from the inner region, the larger the pipe the better.

There are some decided advantages too.  The primary coupling mode for small loops is via the H-field and as a result, they tend to be insensitive to "ground" and surrounding objects so long as those objects have a permeability close to 1.0 ... I sit under my Alexloop which is on a tripod, and the tuning capacitor is just over my head.  There is little if any advantage to putting a small loop on a tower.  The loop is broadly bi-directional in the plane of the loop and the two nulls [orthogonal to the loop plane] are quite sharp.

Most loops use magnetic coupling, feeding the power through a smaller loop inside the main loop.  It is a resonant transformer, and the key word there is "resonant."  The loop must be operated exactly at resonance for power transfer to take place.  A 1:4 or 1:5 ratio between the diameter of the feed and main loops will provide close to a 50 ohm load to the transmitter.  The process is, 1) Bypass the ATU; 2) At low power, tune the loop for zero reactance; 3) Engage the ATU and let it find a match.  "Getting the loop close and letting the ATU match the rest" is a recipe for a very effective dummy load.  A phase detector is a real advantage, just tune the loop for zero phase difference between the voltage and current.  In fact, that's what is usually used for automatic, motor-driven vacuum capacitors on transmitting loops.

https://www.66pacific.com/calculators/small-transmitting-loop-antenna-calculator.aspx is one of many sites with small magnetic loop calculators.  Try a few designs out and you'll see that, at 100 W, you need to keep your distance! <K6DGW>






Re: Using a CB Antenna with an SDR receiver #antennas #elmer #howto #antennas #elmer #howto

Aaron K6ABJ
 

Thank you Skip for the link to the loop antenna radiation calculator.  I was looking for that, but couldn't find it! Are you operating your Alex Loop in a horizontal position so the null is towards you? Unless a person is operating from a second story or higher, as I understand its best to have a loop antenna in a vertical orientation. I am trying to picture your setup, and how I will do mine when I get a Magnetic Loop Antenna.

Jeff piqued my interest in Magnetic Loop Antennas, and the more I have learned the more interested I have become. Being a high Q antenna, they have a VERY narrow bandwidth, but their OUTSTANDING efficiency, small size, and lack of need for a mast make these antennas VERY appealing to me. I have enjoyed learning about and researching Loop Antennas the last few days! These antennas wouldn’t work well in a contest for Searching and Pouncing, but if Running (which I prefer to do) it would do great!

Their extremely high voltage, current and non-ionizing radiation creates real safety concerns. These issues however are a good sign that the antenna will get me the DX I want! I will simply mitigate the safety issues by securely supporting the antenna and ensuring I and others maintain enough distance from it while transmitting. The challenge before me now is how do I get one!?

Building one is possibly the most affordable option, but sourcing a capable capacitor is a significant challenge! Building the loop using 3/8 inch flexible copper pipe would be a good material as it is relatively thick and could be made out of a single piece. Perhaps cut the ends using a dremel to create flat copper tabs to directly attach the loop to the capacitor.

MFJ’s products have significant workmanship/assembly issues, so I generally avoid MFJ, but they have three High-Efficiency Loop Tuners to choose from that would solve the capacitor sourcing problem. The only difference between the MFJ 933 ($209.95) and 935B ($249.59) is that the 935B includes an Antenna Current Meter. The MFJ 936B ($299.85) is like the others, but it takes up more space, includes an SWR Meter, a Current Meter, and adds 60 Meters. For me, I think the 935B is the best option. The nice thing about going with one of these as opposed to something else is that they are good for up to 150 watts, 10-40 meters, and I can make my own loop. By making my own loop I can experiment with various materials, can have a greater variety of loop circumferences allowing for greater performance and more bands, and I can roll the loop up for greater portability. I do however see two downsides to going this route: 1) The MFJ 1788 Super Hi-Q Loop Antenna ($559.95) comes with a loop that is an inch thick so would significantly improve performance over a loop I could make myself, and 2) The MFJ 1788 comes with a controller that allows the operator to tune the Antenna from afar, something that seems like a very good idea given the extreme voltage and non-ionizing radiation that occurs with these antennas.

The MFJ 1788 is rated for 150 watts, just like the loop tuners, but it is only good for 15-40 meters. Whether the efficiency of having a thicker loop would more than make up for the ability to have loops for each band, I do not know. Aside from the added cost, the other potential problem with the 1788 is that it relies on an electronic tuner and motor, which given that its made by MFJ could fail. Still, the ability to be able to tune the antenna from afar given the amount of radiation that is involved, if cost wasn’t a factor I think I would go for the 1788 over the 935B.

Other loop antennas that were considered: The AlexLoop ($399.95) appears to be very well constructed, comes with a nice bag, and is 10-40 meters. The downside is that it is only rated for 20 watts. Still, given the amount of power Magnetic Loops put out 20 watts isn’t bad, especially if you are using it for portable. The price is very competitive, but given that I want to use my loop antenna for serious contesting in addition to portable operations, the MFJ 935B for me remains the leader.

The Alpha Antenna ($500.00), is another option. It too appears to be a well-made antenna and comes with a bag. It also comes with a small tripod. It is rated at 100 watts for 10-40 meters, and 20 Watts 40-80 meters. It is twice as much money as the 935B, but the advantage to it or the AlexLoop over the 935B is ease of use. The capacitors are smaller and lighter than that of the 935B, making them able to be supported by a small tri-pod. This however raises a very important question, given its larger and heavier size does the capacitor of the 935B perform better? I think the answer to this question determines which wins out, the MFJ 935B or the Alpha.

I think there is only one more antenna to consider, and that is the Ciro Mazzoni Automatic Magnetic Loop Antenna. It is one incredible Antenna, weighing an astonishing 44lbs is isn’t good for SOTA, but it is VERY well made, can be remotely tuned, is rated for 800 watts on 20-30 meters, and 300 watts on 40-80 meters. The rub is that it costs $2,479.99. That is a lot of bread, unless you consider the cost of the land required to erect a comparable 80 meter dipole!    

On Mon, Oct 19, 2020 at 12:17 PM Skip - K6DGW <k6dgw@...> wrote:
Jef points out a couple of advantages [and disadvantages] of small transmitting loops.  The circulating current will be high with any appreciable power.  The radiation resistance is in the milliohm ranges, and any resistance in the loop will dramatically lower the efficiency.  It is tempting to build a loop as an octagon with copper pipe since the fittings are readily available, however the added resistance in the soldered joints can be as much or more than the radiation resistance, cutting the efficiency in half or more.  Silver solder will ameliorate this a little, but a continuous length of copper pipe is much better.  The voltages across the tuning capacitor will rise dramatically with higher power, well into the kilovolt range, requiring vacuum capacitors.  Remembering that the RF current travels on the surface of the loop and is excluded from the inner region, the larger the pipe the better.

There are some decided advantages too.  The primary coupling mode for small loops is via the H-field and as a result, they tend to be insensitive to "ground" and surrounding objects so long as those objects have a permeability close to 1.0 ... I sit under my Alexloop which is on a tripod, and the tuning capacitor is just over my head.  There is little if any advantage to putting a small loop on a tower.  The loop is broadly bi-directional in the plane of the loop and the two nulls [orthogonal to the loop plane] are quite sharp.

Most loops use magnetic coupling, feeding the power through a smaller loop inside the main loop.  It is a resonant transformer, and the key word there is "resonant."  The loop must be operated exactly at resonance for power transfer to take place.  A 1:4 or 1:5 ratio between the diameter of the feed and main loops will provide close to a 50 ohm load to the transmitter.  The process is, 1) Bypass the ATU; 2) At low power, tune the loop for zero reactance; 3) Engage the ATU and let it find a match.  "Getting the loop close and letting the ATU match the rest" is a recipe for a very effective dummy load.  A phase detector is a real advantage, just tune the loop for zero phase difference between the voltage and current.  In fact, that's what is usually used for automatic, motor-driven vacuum capacitors on transmitting loops.

https://www.66pacific.com/calculators/small-transmitting-loop-antenna-calculator.aspx is one of many sites with small magnetic loop calculators.  Try a few designs out and you'll see that, at 100 W, you need to keep your distance! <K6DGW>






Re: SFARC By-Laws Revision for Review 2020

Brian Gohl - AI6US
 

Please find attached the Rev8 SFARC By-Laws, which were approved by the board on October 9th and submitted for membership vote at the upcoming November 13 General Meeting to be held on online via Zoom.

Thank you for your review and input to create this document.

--
Brian- AI6US


Re: Using a CB Antenna with an SDR receiver #antennas #elmer #howto #antennas #elmer #howto

Skip - K6DGW
 

Jef points out a couple of advantages [and disadvantages] of small transmitting loops. The circulating current will be high with any appreciable power. The radiation resistance is in the milliohm ranges, and any resistance in the loop will dramatically lower the efficiency. It is tempting to build a loop as an octagon with copper pipe since the fittings are readily available, however the added resistance in the soldered joints can be as much or more than the radiation resistance, cutting the efficiency in half or more. Silver solder will ameliorate this a little, but a continuous length of copper pipe is much better. The voltages across the tuning capacitor will rise dramatically with higher power, well into the kilovolt range, requiring vacuum capacitors. Remembering that the RF current travels on the surface of the loop and is excluded from the inner region, the larger the pipe the better.

There are some decided advantages too. The primary coupling mode for small loops is via the H-field and as a result, they tend to be insensitive to "ground" and surrounding objects so long as those objects have a permeability close to 1.0 ... I sit under my Alexloop which is on a tripod, and the tuning capacitor is just over my head. There is little if any advantage to putting a small loop on a tower. The loop is broadly bi-directional in the plane of the loop and the two nulls [orthogonal to the loop plane] are quite sharp.

Most loops use magnetic coupling, feeding the power through a smaller loop inside the main loop. It is a resonant transformer, and the key word there is "resonant." The loop must be operated exactly at resonance for power transfer to take place. A 1:4 or 1:5 ratio between the diameter of the feed and main loops will provide close to a 50 ohm load to the transmitter. The process is, 1) Bypass the ATU; 2) At low power, tune the loop for zero reactance; 3) Engage the ATU and let it find a match. "Getting the loop close and letting the ATU match the rest" is a recipe for a very effective dummy load. A phase detector is a real advantage, just tune the loop for zero phase difference between the voltage and current. In fact, that's what is usually used for automatic, motor-driven vacuum capacitors on transmitting loops.

https://www.66pacific.com/calculators/small-transmitting-loop-antenna-calculator.aspx is one of many sites with small magnetic loop calculators. Try a few designs out and you'll see that, at 100 W, you need to keep your distance! <K6DGW>


The ABC's of Morse Code Operating

carl.wf6j@gmail.com
 

OK all you CW wanna bees and lovers… a book from CQ:

Begin forwarded message:

______________________________________________
The ABC's of Morse Code Operating 
By Ed Tobias, KR3E 

This small but solid guide is the perfect read for those interested in learning or improving CW operating techniques! 

Within its pages you'll find:   
  • The secret of becoming a proficient CW Operator
  • Where and how to practice, practice, practice.
  •  Straight Key or Paddle?
  • Adjusting your Straight Key or Paddle
  • Keyers, Iambic Keying and Bugs
  • Contests, Events, DXing
  • Operating QSK
  • CW Filters
  • Signs, Signals and Procedures
  • Tips on Taking CW On the Road . . .  and much, much more!
Order your copy today!
 
6 X 9 Paperback - Only $15.95 
Shipping & Handling: U.S. & Possessions $3;  
CN/MX $5; All Other Countries $10.
  

Click here to visit CQ's Online Store!
 
CQ Communications, Inc,
CQ Communications, Inc., POB 1206, Sayville, NY 11782
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Re: Using a CB Antenna with an SDR receiver #antennas #elmer #howto #antennas #elmer #howto

Aaron K6ABJ
 

Much appreciated Jedi Master.

73

Aaron, K6ABJ

On Oct 18, 2020, at 7:07 AM, Jef Allbright <jef@...> wrote:


The small transmitting loop, often described misleadingly as the "magnetic loop" antenna, with a circumference under ⅓ wavelength (in some applications, under ⅒ wavelength) is a practical example of an antenna that sacrifices bandwidth in favor of good efficiency and very small size.

With proper construction, a small transmitting loop for HF can nearly match (and in some environments, exceed) the efficiency and radiation pattern of the standard half-wave dipole, but with an instantaneous bandwidth of only a few to several kHz (tuneable to operate anywhere desired within the band.) 

Because such a short antenna is very high Q, it will have very high circulating current, therefore it is imperative for efficiency that resistive losses in construction be kept extremely low, but if this done, the efficiency can be very high and nearly all the RF is radiated rather than dissipated as heat.

For more information on small transmitting loops, I highly recommend this writeup:  

For more information on the fundamental tradeoff between small size, efficiency, and bandwidth:

- Jef  N5JEF











 


See 






On Sun, Oct 18, 2020 at 1:40 AM Aaron Jones <aaron@...> wrote:
“I understand there is no free lunch, but I was unaware that one may choose two  of the three, desires, small size, efficiency, and bandwidth."

"Please tell me, Teacher, if I am willing to sacrifice bandwidth to obtain favorable efficiency and small size, what antenna(s) would be good for me?"

Aaron, K6ABJ

> On Oct 17, 2020, at 10:44 AM, Jef - N5JEF <jef@...> wrote:
>
> here is No Free Lunch, and for any antenna design one may choose two, but not all three, of small size, efficiency, and bandwidth."
>
> "But tell me, Teacher, what should I do?"


Re: Using a CB Antenna with an SDR receiver #antennas #elmer #howto #antennas #elmer #howto

Jef - N5JEF
 

The small transmitting loop, often described misleadingly as the "magnetic loop" antenna, with a circumference under ⅓ wavelength (in some applications, under ⅒ wavelength) is a practical example of an antenna that sacrifices bandwidth in favor of good efficiency and very small size.

With proper construction, a small transmitting loop for HF can nearly match (and in some environments, exceed) the efficiency and radiation pattern of the standard half-wave dipole, but with an instantaneous bandwidth of only a few to several kHz (tuneable to operate anywhere desired within the band.) 

Because such a short antenna is very high Q, it will have very high circulating current, therefore it is imperative for efficiency that resistive losses in construction be kept extremely low, but if this done, the efficiency can be very high and nearly all the RF is radiated rather than dissipated as heat.

For more information on small transmitting loops, I highly recommend this writeup:  

For more information on the fundamental tradeoff between small size, efficiency, and bandwidth:

- Jef  N5JEF











 


See 






On Sun, Oct 18, 2020 at 1:40 AM Aaron Jones <aaron@...> wrote:
“I understand there is no free lunch, but I was unaware that one may choose two  of the three, desires, small size, efficiency, and bandwidth."

"Please tell me, Teacher, if I am willing to sacrifice bandwidth to obtain favorable efficiency and small size, what antenna(s) would be good for me?"

Aaron, K6ABJ

> On Oct 17, 2020, at 10:44 AM, Jef - N5JEF <jef@...> wrote:
>
> here is No Free Lunch, and for any antenna design one may choose two, but not all three, of small size, efficiency, and bandwidth."
>
> "But tell me, Teacher, what should I do?"


Re: Using a CB Antenna with an SDR receiver #antennas #elmer #howto #antennas #elmer #howto

Aaron K6ABJ
 

“I understand there is no free lunch, but I was unaware that one may choose two of the three, desires, small size, efficiency, and bandwidth."

"Please tell me, Teacher, if I am willing to sacrifice bandwidth to obtain favorable efficiency and small size, what antenna(s) would be good for me?"

Aaron, K6ABJ

On Oct 17, 2020, at 10:44 AM, Jef - N5JEF <jef@...> wrote:

here is No Free Lunch, and for any antenna design one may choose two, but not all three, of small size, efficiency, and bandwidth."

"But tell me, Teacher, what should I do?"


Re: Using a CB Antenna with an SDR receiver #antennas #elmer #howto #antennas #elmer #howto

Jef - N5JEF
 

Joshua -

The three foot firestick will perform as a receiving antenna almost exactly the same as any three foot length of wire. A three foot length of wire without a ground plan will be most sensitive somewhere in the VHF region, depending on impedance matching.

Perhaps for further enlightenment:

"Tell me, Teacher, does the 3-ft Firestick have the Antenna-Nature?"

"The Antenna-Nature rests within all conductors, young padwan, ready to radiate or receive in proportion to electrical charge accelerated over lineal distance."

"But which is the True Path?  That of twists and turns of wire, or is it the Path through space of the superposition of fields of charge moving relativistically?"

"There are many Paths, padwan, and all are True within the appropriate context.  The aperture of the three foot Firestick is relative to its lineal length of three feet.  The electrical load as seen by the transmitter is as a 102 inch whip, but the coiling reduces its bandwidth.  Remember that there is No Free Lunch, and for any antenna design one may choose two, but not all three, of small size, efficiency, and bandwidth."

"But tell me, Teacher, what should I do?"

"Young padwan, keep in mind always your desired wavelength, then go forth and experiment!"

- Jef  N5JEF

On Sat, Oct 17, 2020 at 9:25 AM Joshua - KK6VHH <besneatte@...> wrote:
it's called a fire stick... about 3 foot long fiberglass pole with a considerable amount of wire wrapped around it and a spring base... like you see on 4x4s

being that it's SDR I can tune to and demodulate most any broadcasted signal... 

CB antenna is just sitting useless, so I am going to give it a try.

--
KK6VHH - Joshua

piratesinteepees.org
youtube.com/piratesinteepees


Re: Using a CB Antenna with an SDR receiver #antennas #elmer #howto #antennas #elmer #howto

Joshua - KK6VHH
 

it's called a fire stick... about 3 foot long fiberglass pole with a considerable amount of wire wrapped around it and a spring base... like you see on 4x4s

being that it's SDR I can tune to and demodulate most any broadcasted signal... 

CB antenna is just sitting useless, so I am going to give it a try.

--
KK6VHH - Joshua

piratesinteepees.org
youtube.com/piratesinteepees


Re: 2020 California QSO Party "CQP" -- Save the Date! #contest

Orion, AI6JB
 

Hey Everyone,

There is still time to submit your logs to the CQP.org website.  The deadline is Monday, October 26, 2020, 23:59 UTC.

If you worked the contest, for even a little bit, the Club can sure use your help.  Submitting your log is real easy: Simple as 1, 2, 3.  Step 1, follow this link:  http://cqp.org/logsubmit-main.html, Step 2, fill out the online form, and Step 3, upload your Cabrillo file.

If did your log by hand or used a spreadsheet, here are a couple of online utilities to create a Cabrillo file:  http://robot.cqp.org/cqp/cabmaker.html  or  http://www.b4h.net/cabforms/cqp_cab3.php 

When you submit your log to CQP, please credit "Sierra Foothills ARC".  Thank you!!

73
Orion, AI6JB