SCCARC Meeting, Jan 17: Vertical Antennas
The guest speaker for the January 17 Santa Cruz County Amateur Radio Club meeting is Ron Skelton. The topic will be the Efficiency and Effectiveness of Vertical Antennas.
Holiday Luncheon 2019
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Everything should be made as simple as possible, but not simpler
By Dan Romanchik, KB6NU
“Everything should be made as simple as possible, but not simpler” is a quote attributed to Albert Einstein (https://quotationcelebration.wordpress.com/2017/01/07/everything-should-be-made-as-simple-as-possible-but-not-simpler-albert-einstein/comment-page-1/). Here’s one way to apply this principle in amateur radio, specifically to code practice oscillators.
A week ago, my friend, Paul emailed me:
“I am planning on teaching a two-hour introduction to Morse code to 14 girls ages 8 to 9 [[Paul’s granddaughteris a Girl Scout.]]. I plan on having the girls build a code practice device. I need your help in selecting a low cost buzzer and battery holder. Please take a look around and see would you can find. I would like to limit the power to one or two AA batteries.”
I replied that I’d be happy to help him with the demonstration, and offered the following advice:
“A while back, I built the QRPGuys’ K7QO Code Practice Oscillator (https://qrpguys.com/k7qo-code-practice-oscillator). It uses a CR2032 coin battery.
“Unfortunately, they don’t sell it anymore, but the assembly manual is still online (https://qrpguys.com/wp-content/uploads/2017/03/cpo_assy_012616.pdf). The assembly manual doesn’t call out specific parts, but here are some Amazon SKUs:
- B00J4BK0NS, Black 3V Electromagnetic Type Piezo Buzzer, 20 pcs/$6.58
- B06XF3K4NP, Coin Cell Button Battery Holder, 30 pcs/$9
- B008SNZUYC, 3 Pin PCB Mount Female 3.5mm Stereo Jack, 10 pcs/$5.40
- B071RMD6FD, 1/8″ 3.5mm Stereo Male Connector, 10 pcs/$7
“Batteries are available at the dollar store for about 30 cents each. So, you could do the whole thing for less than $5 for sure, even with a printed circuit board, which I would suggest that we do. Heck, if you ask nicely, the QRPGuys might even give us the artwork, or even better, have some boards still in stock. Even if they have neither, you should be able to get the boards in plenty of time.”
Later that day, Paul replied:
Thanks, Dan, for the information and making yourself available to help. I am just going to use a buzzer, key, and battery. The buzzer has a frequency of 400 Hz.
And this morning, he sent me this photo, noting, “FYI. Also sounds great.”
I think that this is as good an example of “Everything should be made as simple as possible, but not simpler” as there can be. I’ve volunteered to help Paul with his class. That will be fun, too.
Dan Romanchik, KB6NU, is the author of the KB6NU amateur radio blog (KB6NU.Com), the “No Nonsense” amateur radio license study guides (KB6NU.Com/study-guides/), and often appears on the ICQPodcast (icqpodcast.com). When he’s not trying to keep things as simple as possible, but not simpler, he likes to build stuff and operate CW on the HF bands.
JANUARY CLUB MEETING PRESENTATION: RON (W6WO): EFFICIENT VERTICAL ANTENNAS
Mark your calendar for the January 17, 2020 Santa Cruz County Amateur Radio Club meeting at the Red Cross Center (2960 Soquel Avenue, Santa Cruz). The meeting will begin at 7:30pm, with a brief business meeting, followed by a not-to-be-missed guest presentation by Ron Skelton (W6WO), an antenna expert, who will discuss efficient designs of vertical antennas.
DO YOU HAVE AN IDEA FOR A CLUB PRESENTATION?
Please contact Richard (K8SQB) <firstname.lastname@example.org> or
Becky (KI6TKB) <email@example.com>
2020 CLUB DUES ARE DUE!
Annual Club membership dues are due January 1 and can be paid at the annual Holiday Luncheon at Ming’s (Dec. 14).
SCCARC ANNUAL DUES (Due January 1) Full Member: $25.00 Family Members: $6.00 for each additional member at the same mailing address Youth Members: $10.00 for full-time students age 18 or under Dues for new, first time members (not renewals) shall be pro-rated after April 1 of each year, as follows: • Reduced 25% between April 1 and June 30 • Reduced 50% between July 1 and September 30 • Reduced 75% between October 1 and December 1 After December 1, full payment shall be required, and dues shall be applied to the following year. Annual Dues are due January 1. Members over three months in arrears in the payment of dues shall be considered inactive, thereby relinquishing privileges in the Club.
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Membership dues may be paid securely online using the Donate button above, with PayPal or a credit card.
PLEASE NOTE: We appreciate the convenience of using PayPal to transmit funds to your Club. However, PayPal subtracts fees from each payment in the amount of 2.9% of the base amount plus $.30 per transaction. In order to keep your Club from losing money as a result of this convenience to you, we request that you include an amount equal to these fees in addition to the base amount of your payment. Example: To pay dues of $25.00, add $.73 + $.30 for a total of $26.03. We appreciate your cooperation.
Also, with your payment, please include a comment including your callsign or purpose of donation. Or, Membership dues may be paid with cash, or check (payable to Santa Cruz County Amateur Radio Club), at regular Club meetings, or checks with completed Membership Application Form may be mailed to the club’s mailing address: SCCARC PO BOX 238 SANTA CRUZ CA 95061-0238 Dues Renewals may be paid in these same ways. Thanks!
Getting Loopy – by John Keating AI6LY / November, 2019
How the hunt for the source of RF interference led to the realization that the resonant frequency of my small transmitting loop antenna moves inversely with ambient temperature.
Why I got interested loop antennas
In 2017 I experienced particularly disruptive QRM in the evenings on 40M. (See nasty bits recurring every 20 kHz in the panadapter image below). Based on rotating my HF antenna, I determined the source was directly south from my QTH. I had seen W0IVJ’s article, “Locating RF Interference at HF,” in November 2014 QST and decided to build the small receiving loop he described, pair it with a small shortwave receiver, and walk up and down the street.
I tried a few times to locate the exact source, but the antenna really didn’t have sufficient directivity to identify the culprit. So, just for amusement I tried to use it for transmitting. Predictably, the air variable tuning capacitor arced at low power – about 10W if I recall correctly – so I figured the whole thing needed to be scaled up. But first, I acquired a Pixel Technologies/DXE RF-PRO-1B receive-only loop to investigate claims about its directivity; it was interesting for the obvious lateral nulls, but I found its gain and SNR didn’t compete with my EX-14 tribander.
What is a “Magnetic Loop” antenna?
For quick background, a small transmitting loop antenna consists of a loop whose circumference is between one-eighth and one-third of a wavelength. It is essentially an inductor which can be resonated with a fixed or variable capacitor to form a high-Q tuned circuit. It radiates a figure-8 pattern in the plane of the loop, and exhibits deep nulls broadside. Reasonable performance can be achieved when operated at heights that are only a fraction of a wavelength – slightly more than one loop diameter – above ground level. RF current through the loop creates a strong magnetic field which, in turn, generates an electric field; hence, the name “magnetic loop.”
Over the course of many months, I home-brewed several loops using various sizes of aluminum and copper tubing before settling on a roughly 1 meter diameter radiating loop of half-inch copper tube, tuned by a large vacuum variable Russian surplus capacitor (see photo), all mounted on a PVC pipe mast. The 5-250pF 5kV variable capacitor has enough range to tune from 10 to 40 meters and sufficient voltage rating to withstand levels generated at transmit power up to about 300 hundred watts. The capacitor shaft is coupled to a gearhead reduction motor driven by a PCM speed controller whose low frequency control signals are multiplexed on the coax feed line. The feed loop is approximately 1/5 the diameter of the radiating loop, and there is an RF choke at its feedpoint. During early testing, I had to experiment with the vertical position of the feed loop to determine the location for optimum SWR, now typically 1.05:1. I also tried several different variable capacitors.
AA5TB has a nice excel file that generated the following predictions for my design operated at 20m:
Bandwidth = 28.806 kHz (-3 dB points)
Efficiency = 28.806 %
Wavelength Percentage = 13.163 % λ
Loop dc Inductance = 2.407 μH
QL (Quality Factor) = 511.686
Total tuning Capacitor = 52.736 pF
Capacitor Voltage = 3306.179 V rms (at 100W drive)
Initial testing confirmed the expected high Q/narrow bandwidth characteristic; on 20m it was 23 kHz (3:1 SWR) and 13 kHz (2:1 SWR), with a measured Q of 744. The tuning capacitance of 49pF (nominal) was very close to the calculated result. Resonant frequency was very sensitive to changes in capacitance. So, when I set the antenna up for operation and saw a lot of drift, I suspected thermal effects and decided to investigate.
Characterizing the temperature issue
With the antenna set up in the backyard and tuned to an arbitrary point in the 20m band, I logged the resonant frequency and ambient temperature over a period of about 36 hours (without transmitting during that period). The data, shown in charts below, clearly indicate that resonant frequency varies inversely with temperature. On average, the change was about -1.6 kHz per degree F. The steepest rate of change was 500 Hz/minute which occurred at about 3PM on the second afternoon as the temperature declined from 82F with antenna in direct sun to 75F with antenna in shade. Given the robust construction of the copper elements, I attribute the drift to the glass-encased capacitor becoming a mini-greenhouse. I plan to perform additional testing with a shade on the capacitor, and also to find the impact on resonant frequency from transmitting at different power levels.
Thermal issues aside, is it a good antenna?
In limited daytime on-air testing, the antenna “did what it is supposed to do.” I QSO’d with a station in Hawaii whose signal was about four S-units weaker on the loop than on my EX-14 tri-band yagi. His signal dropped six S-units when I turned the loop broadside to Hawaii. There was little difference in band noise between the loop and tribander, not surprising since the noise level was very low on the day of the test. Band noise on the loop was two S-units higher when turned broadside (i.e., orientated for roughly North/South figure 8 pattern), while noise increased only about one half S-unit with the tribander aimed similarly, due to its front-to-back characteristics. In transmit, the signal received by the Hawaiian station from the loop was two S-units weaker than the tribander with both aimed at Hawaii. When I turned the loop broadside, the signal received in Hawaii was seven S-units lower than when the loop was aimed direct. Signal reports were measured during SSB phone exchanges on FTDX-3000 radios at both stations.
|Loop||EX-14||Loop vs EX-14|
|Signal received at AI6LY, RX direct||S-5||S-9||-4|
|Signal received at AI6LY, RX broadside||S-1||n/a|
|Signal received in Hawaii, TX direct||S-7||S-9||-2|
|Signal received in Hawaii, TX broadside||S-0||n/a|
|20m band noise, East-West||S-1||S-1|
|20m band noise, North-South||S-3||S-1.5|
There are many fine articles about small loop antennas. However in my reading I had not seen the thermal issue raised per se. TF2LJ has posted an interesting page on a DIY arduino-based stepper motor-driven autotuner for loop antennas, citing the high-Q as the cause for retuning the antenna if you move your operating frequency by more than a few kHz, but without mention of the temperature sensitivity. In email correspondence to me, VK5KLT made the amusing comment that not only does the small loop make an excellent ambient temperature sensor, but when placed horizontally it also couples to the proximate ground and makes an excellent ground moisture transducer / sensor as well….
To conclude, the antenna works. It is directional (for vertically polarised sky-wave signals arriving at very low elevation angles), and is generally insensitive to ground effects (since the ground does not form the “missing half” of the antenna). Due to the high-Q of the resonator, one must occasionally adjust the tuning to keep the SWR in an acceptable range as it shifts due to changes in humidity and temperature. The performance limitations and the necessity of retuning are the tradeoffs for utilizing a small footprint antenna.
November Meeting Recap
1) November Club Meeting Board Elections and Guest Presentation to a Full House!
The November 15 Club meeting was great fun, and brought radio operators and will-be radio operators from far and wide. The first item of Club business was to elect new Board officers, which occurred quickly. Here are the new officers that will serve for the next two years:
President: Becky Steinbruner (Ki6TKB)
Vice President: Richard Adams (K8SQB)
Secretary: John Gerhardt (N6QX)
Treasurer: Allen Fugelseth (WB6RWU)
Board Member: David Dean (N6DTH)
Board Member: Cap Pennell (KE6AFE)
Board Member (past President): Don Taylor (K6GHA)
Nate Preston (KM6THE)
Craig Harlamoff (N6SBN) (special interest in digital modes)
Duane Titus (K6TS)
Many thanks to Gary Watson (K6PDL) and Ned Rice (N6ZOZ) for serving on the Board for the past two years. We hope they will remain involved in Board discussions as important issues move forward.
A GREAT PRESENTATION BY ERIC SWARTZ (WA6HHQ) followed. Eric, owner of Elecraft, brought one of the new K4 Direct Sampling SRR HF transceivers that his company has developed and is currently taking orders for production. He brought a model to demonstrate the amazing technology and kept us all spellbound for the rest of the evening.
Open Shack (Its Better Than A Flea Market)
RON (W6WO) OPEN HOUSE AND EQUIPMENT SALE
Greetings to one and all, this is an invitation to an:-
Open Shack (better than a flea market) event at my home in Capitola
Saturday Dec7 from 10:00 AM to 4:00 PM
Pizza served for lunch at noon.
After 70 years of Ham Radio it is time for me to part with many Ham related items. Where possible I found the probable cost new then offer them at 50%.
In all cases I invite offers at What It’s worth to you the buyer.
Apache Labs Anan 100D an open source Software Defined HF Radio. The new owner will receive a 34 page professional test report on this specific unit $1,350.
I will send you a list of features via email if interested.
A SignalLinkUSB unit set up for K3 orKS3 is $75
Cushcraft R6000 HF vertical (20 to 6m) $225.
Astron 30A linear power supply $40
Alinco switching power supply 15v 5A individually adjustable $25
Diamond X200A VHF/UHF Base/rptr vertical $70. Mag-mount UHF /VHFvertical
FreeTalk wireless headset
50 Ohm 50 Watt Dummy load. N connector DC-8GHz $35
MFJ 281 ClearTalk loudspeaker RadioShack compact stereo loudspeaker
Many through-hole R L C components A 7×9” through-hole project board
Good collection of Surface Mounted components
Many lengths of coax. and several lengths of Al tubing- free
Collections of QST and QEX journals, various ARRL Handbooks and reference books
Fujifilm FinePix camera
Hustler mobile antenna, base, top plate and elements for 17, 15 and 10M $30
These are all in good shape, so hopefully my surplus will quickly become your treasure. Reasonable offers only please, of course no tax and shipment costs are involved. Sight unseen offers OK but I will send items only via a USPS Flat-rate carton.
Contact me by email if you have any questions firstname.lastname@example.org 831 477 1021
Please come and have some fun on Dec7
Addr 4220 Gull Cove Way Capitola
73 Ron W6WO
How to get “plugged in” to the amateur radio community
This morning, I found this email in my inbox:
Thank you for your website and great content. I passed the Tech and General tests on Saturday, and I will be taking the Extra exam in November. Your “No Nonsense” guides were very helpful.
I do have a question, though. How do I stay current on what’s happening in the ham world?For example the CQ WW SSB contest was this weekend. How do newbies know this kind of thing? How do we find local or regional hamfests and other events?
This is a great question. Like any special interest, it can seem daunting to get plugged in (pun intended) to the community. Here are a few of my suggestions:
Join the ARRL (http://arrl.org/). The American Radio Relay League (ARRL) is really the place to start for information related to amateur radio.QST, the ARRL’s monthly magazine, includes news about upcoming contests and ARRL-sanctioned hamfests. It also reviews new amateur radio products and provides a wealth of technical information.
In addition to QST, the ARRL publishes many email newsletters that members can subscribe to. For example, Contest Update is a biweekly newsletter that not only lists upcoming contests, but also includes tips on operating contests. The ARES E-Letter is a monthly public service and emergency communications newsletters. There are also email newsletters for ham radio instructors, those interested in DX, legislative matters, and satellite operation.
Join your local club. While the ARRL will help you keep abreast of amateur radio news and events nationally and internationally, if you want to know what going on in amateur radio in your area, you should join your local club. To find clubs near you, go to http://www.arrl.org/find-a-club.
Visit the WA7BNM Contest Calendar (https://www.contestcalendar.com/). This contest calendar has become my go-to resource for any and all contest information. This site provides detailed information about amateur radio contests throughout the world, including their scheduled dates/times, rules summaries, log submission information and links to the official rules as published by the contest sponsors. Its features include an 8-Day calendar, a 12-Month calendar, and separate calendars for state QSO parties, CW contests, and QRP contests. You can also get a weekly e-mail of contests taking place in an 8-day period (Monday through Monday), as well as a list of contests scheduled for the next week and a list of log submission information for recent contests.
Ham radio blogs. Blogs are also a good way to keep up with what’s going on in amateur radio. I like to think that I do a good job of covering what’s going on in amateur radio, but, of course, I can’t do it all. That being the case, you might also want read other blogs. Other amateur radio blogs that you might want to check out include:
- The K0NR Radio Site (http://www.k0nr.com/wordpress/)
- QRP–When you care to send the very least (https://w2lj.blogspot.com/)
- Everything Ham Radio (https://www.everythinghamradio.com/)
There are a bunch of other good ones out there. Find the ones you like and subscribe to them, so that you get a notification when new items are posted.
Mailing lists. Mailing lists are kind of old school, but if you have a special interest, chances are that there is a mailing list for it. For example, I own an Elecraft KX-3, so I subscribe to the Elecraft KX User Group mailing list (https://groups.io/g/Elecraft-KX/). Many amateur radio mailing lists are migrating to the Groups.io. To find a list, just click on the “Find or Create a Group” link at the top of the page. I just did a search for “amateur radio” and found 910 different amateur radio mailing lists.
Podcasts and videocasts. Podcasts are also another great way to stay up with amateur radio. I’m partial to theICQPodcast (http://icqpodcast.com/) because I am on the panel once a month. The podcast not only includes a discussion of what’s new in amateur radio, but also a feature, which digs a little deeper into a particular topic. Other great podcasts are Ham Radio Workbench (https://www.hamradioworkbench.com/), and Linux in the Ham Shack (https://lhspodcast.info/). Internet video shows that are worth checking out are Ham Radio 2.0 (https://www.livefromthehamshack.tv/), Ham Radio Now (https://www.hamradionow.tv/home), and Ham Nation (https://twit.tv/shows/ham-nation).
This is by no means an exhaustive list. If you have an amateur radio information resource that you find particular helpful, please let me know.
Dan Romanchik, KB6NU, is the author of the KB6NU amateur radio blog (KB6NU.Com), the “No Nonsense” amateur radio license study guides (KB6NU.Com/study-guides/), and often appears on the ICQPodcast (icqpodcast.com). When he’s not trying to keep up with ham radio, he likes to build stuff and operate CW on the HF bands.