thru march9

June Meeting Date Change, June 14

and Speaker Announced

At the last board meeting it was decided that it would  be best to move the June meeting date up a week to accommodate Field Day activities.  Our guest speaker for that month, Ray Rischpater (KF6GPE), is agreeable to moving the date as well. Here is a bio and summary of his program for June 14:

The Automated Packet Reporting System (APRS) has seen a lot of use since its advent in 1984, and is the most popular digital mode on VHF today, providing real-time telemetry, position reporting, and messaging. A lot has changed since 1984, however — there’s an internet backbone for your traffic, satellites when you’re not within range of your local digipeater, and the possibility of working APRS using just a soundcard and PC, or with a stand-alone radio or your smartphone. In this talk, I’ll show you how to get started if you’re not already on the air with APRS, and maybe show you a thing or two you didn’t already know if you are!”

And the bio:

I’m a software engineer and author with twenty-five years of industry experience and sixteen books to my credit. Beginning with software development for mobile platforms, I’ve done work in several areas, including mobile, web services, building tools for mapping and geospatial engineering, and applying machine learning to geospatial processing problems. When not writing for or about software development, I enjoy writing, making music, hiking, and photography with my family and friends in and around the San Lorenzo Valley in central California. When I’m able, I also provide public service through amateur radio as the licensed Amateur Extra station KF6GPE.


Getting loaded (antenna-wise, anyway)

By Dan Romanchik, KB6NU

A couple of years ago, I homebrewed a “Cobra” antenna (https://www.kb6nu.com/yet-another-new-antenna-the-cobra/). It’s a doublet antenna, meaning that it consists of two elements connected to a center insulator, where it connects to a feedline. The unique thing about the Cobra antenna is that each element consists of three parallel conductors connected in series.

My antenna uses a lightweight, three-conductor rotor cable that used to be available from Radio Shack. The feedline is 450 Ω ladder line that connects to an antenna tuner to give me multi-band operation.

Connecting the conductors in this way is is supposed to provide “linear loading.” Somehow, running the conductors in parallel is supposed to increase the antenna’s effective length. My antenna is only 73-ft. long, but it easily tunes up on 80m.

The ARRL Antenna Book has a short section on linear loading. It says that linear loading is a “little understood” alternative to inductive loading that can be applied to almost any type of antenna. Furthermore, “…it introduces very little loos, does not degrade directivity patterns, and has low enough Q to allow reasonably good bandwidths.”

As I mentioned, I’ve been using this antenna with good results for a little more than two years now. When I first put it up, someone mentioned the concept of linear loading to me, but not being an antenna guru, I didn’t ‘give it much thought. About a week ago, though, I ran across a link to the page Short Ham Antennas for HF (https://www.hamradiosecrets.com/short-ham-antennas.html). That got me thinking about the topic again.

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This page describes a way to build a linearly-loaded dipole antenna with a feedpoint impedance of approximately 35 Ω. This allows you to feed it with coax instead of the ladder line that I use. The author uses 390 Ω ladder line for the elements. He says it’s commonly available, but I don’t think I’ve ever seen 390 Ω ladder line. You could probably use 450 Ω ladder line by adjusting the element lengths a little.

At that point, I started Googling. The next linear-loaded antenna design that I ran across is a design from M0PZT (http://www.m0pzt.com/40m-linear-loaded-dipole/). He built his elements from some sturdy wire and homebrewed spacers made from PVC pipe. He’s used this design for the 40m elements of a fan dipole covering the 40m, 20m, 15m, and 12m bands. Only the 40m elements are linear-loaded.

I also found a design for a linear loaded vertical antenna for 40m and 80m (https://www.qsl.net/pa3hbb/ll.htm). This antenna is only 7.736m, or 25.4 ft. tall. Of course, it requires a good radial system to work well, but it will work a lot better for DX than a low doublet or dipole.

Finally, there’s an eHam discussion on linear loading (https://www.eham.net/ehamforum/smf/index.php?topic=84418.0). Unlike a lot of eHam discussions, this one is quite civil. It’s worth reading if you’re interested in the topic.

So, if you’re thinking of getting loaded, errrrr, I mean loading your antennas, here’s a method for you to consider. It works!


 

Congratulations to Gary Watson, K6PDL

Congratulations to Gary Watson, K6PDL, for his volunteer communications workon our behalf.  For his work with County OES, Gary is scheduled to be recognized with a Outstanding Volunteer Award at the County Board of Supervisors meeting at 10AM on March 16th.  And Gary has just received his Certificate of Successful Course Completion for the ARRL’s advanced course, “Public Service and Emergency Communications Management for Radio Amateurs (EC-016).”  Gary is our first local ham to complete this training course.
Now Gary qualifies as Level 3 in the new 2019 national “ARES Plan.”
Thanks, Gary!
73, Cap KE6AFE

 

Notes from the CAKE meetingCAKE Crumbs for April 13 2019

Glen KG0T, Peter K6UNO and Ron W6WO met in comfort at the Abbey. The close-knit trio provided an opportunity for some intense discussions.

Glen is now well known for the breadth and depth of his knowledge in the field micro processors . The word “field” seems quite appropriate as they seem to be appearing like mushrooms. Glen brought seven types mounted on a breadboard and proceeded to describe how they compare in terms of speed, languages, ease of development and system software. The one item they had in common was their purchase cost being in single digit dollars. Ron commented that in his case the cost of programming labor would be prohibitive. Glen hinted that he was developing a presentation on uProcs to deliver at a future SLVARC meeting. Stay alert for details

Peter returned to a previous CAKE topic of software for printed circuit board (PCB) layout and fabrication. Peter showed a recent book on KiCAD -pro which is evidently a powerful well documented product. More details can be found on txplore.com and a PCB fabrication firm called OSHPark.

Peter asked how Ron’s VNA exercise was pr proceeding. The best way to respond is to quote Lao-Tzu (a 6th century Chinese philosopher and writer). “The further one pursues knowledge- the less one knows” In this instance all was going well until my home-brew short circuit calibration standard was measured giving the result of 0.0007 Ohms. A value of 0.007 would have been cause for celebration as it indicates a precision needed to make accurate ESR measurements- however one extra zero seems unealistic and suggests all is not well.

Glen posed one of his insightful and deceptively simple questions -”what makes a VNA the instrument of choice for measuring impedance ?”Leaving aside the question of accuracy my best answer is that it combines all the needed elements of a programmable signal source having precise frequency and phase , a vector voltmeter, phase sensitive detection, analog-digital conversion and digital signal processing together with a comprehensive graphical user interface.That said even high-end   Rhode and Swartz VNAs have trouble measuring capacitor ESR.

A VNA provides the same degree of dynamic range, precision and upgrade potential which makes a SDR the choice for Amateur communications. The VNA I made was designed by true experts N2PK and G8KBB who have a high regard for entry level users while satisfying the professional demands of others. Our conversation included some terminology relevant to VNA measurements such as reflective loss and dissipation loss .

At his point in time I would like to inform all readers that I am about to leave the area for my annual trek to GA and KY with a possible side trip to the UK ( while it stillhas the U ) with an open ended return date, most likely in August

73 all round Ron W6WO

 


30th Annual Strawberry Fields Bike Ride

Volunteers Needed

We are looking for volunteers for the 30th annual Strawberry Fields Bike ride from around 8:00 am until the around 15:30 (depending on the shift) on Sunday, May 19th.

Operators novice & experienced are invited to join us! If you’ve never participated in a public service event, this is an easy one. We provide safety and situational awareness for the race at four rest stops.
If you can make it, please let me know so I can provide a count of available operators to the race director.

Please reply with: *Name: *Call: *Email: *Phone: *Favorite assignment (if any):
*Did you sign up on the website?:  *T-Shirt size:
(There is no guarantee of T-shirts or if we’ll have the correct sizes but let us know anyway)The event organizers are asking that we also sign-up on the Strawberry Fields site:  https://cyclistsforculturalexchange.redpodium.com/strawberry-fields-forever-xxx-volunteers-2019 . Under “Volunteer Team” select “Radio”. If you sign up on the website please let me know.

Feel free to forward this if you know someone that’s interested but may not be on the reflectors.
For more information about the event browse to https://www.cyclistsforculturalexchange.org/sff

Thanks & 73
Dan  N6RJX


CAKE notes for March 23 2019

No two days are exactly alike at our rendezvous of The Abbey and today it was conspicuously empty. All the usual “heads down in their laptops” were missing, end of final’s apparently. Ron W6WO was joined by Glen KG0T, Fred KJ6OOV, Kerry K3RRY and John N5HPB. At the previous session John amazed us by describing the 3D printer he was building, today it was a laser engraving machine.  This involved constructing a high current DC supply comprising a bank of diodes and power resistors all meticulously designed and constructed as we have come to expect. For hard-to-find parts John spoke highly of Anchor Electronics and Excess Solutions in San Jose. Anyone interested in joining Ron for a field trip??

We had more conversation about PCB layout software including the ability to deal with a variety of components from edge mounted SMA connectors to 0.65 mm parts. Contact Ron if you are interested in such very small capacitors. Fred showed an ARRL book on oscilloscopes which seemed to have most to say about “vintage”analog equipment. However a digital scope from Rigol was described with an attractive price of $350. Fred suspects that with relevant software this scope may become a spectrum analyzer.
A youngish fellow came up and asked if we were Radio Hams (are we so obvious?) then introduced himself as Nick a software engineer involved with geographic data and was familiar with APRS. Nick lives up in the hills so we alerted him to the SLVARC and informed him of their meeting place and time. Fred spent much of our session giving Nick a concentrated tutorial on Amateur Radio and on digital modes in particular. Good work Fred.

 Ron posed two mystery items one was the meaning of this string of characters ATC: 100C101JW2500X.  John identified it as an American Technical Ceramics TC100 series 100pF capacitor with a specific tolerance, needless to say this can not fit on a SMD component. It may take some time to realize that either a resistor or capacitor marked as 100 has a value of 10 and one marked as 101 has a value of 100, 102 a value of 1,000  etc. My XYL also has problems with the amount of zeros in a number !
The second mystery was the meaning of the term “Negative Dissipation” which came up in Ron’s  measurement of very small values of the Equivalent Series Resistance of capacitors. One of his measurements had a negative value. Resistors only positively dissipate power, hence the mystery.  Errors introduced in calibration and measurement techniques are known to cause a negative value. This is fully described in an excellent Impedance Measurement Handbook published by Agilent Technologies aka  Keysight. This is available online at https://literature.cdn.keysight.com/litweb/pdf/5950-3000.pdf section 5-6 . Hint don’t attempt to copy the full 140 pages as many include unprintable labels, at least by my PC/Printer combination.

 Here’s wishing you a better information to noise ratio in all you do.

Ron  W6WO