Cheap & Super-Portable Magnetic Loop antenna for 20-40 meters

Most of you know how much I enjoy playing with mag loops. I think I have something like 5 of them from different manufacturers, as well as my first one that I built myself. I showed a few photos of my homebrew baby on Ham Fun night a few months ago. My first contacts on 10 watts were to Maryland and then Hawaii a few minutes later on 17 meters from Morgan Hill. The really fun part about mag loops is that they don’t have to be hoisted high in the air. The two contacts I made that first day had the loop base about 2 feet above the grass in my front yard!

Just for fun, here’s a short clip of my Chameleon P-Loop in action. The station you’re hearing was 59 on 20 meters from Utah to Mississippi on my Yaesu FT-818 running 2.5 watts:
https://www.youtube.com/watch?v=mpmnCcrtKAo

Anyway, I know that some of you would like to try building a mag loop, but that it might be a little fiddly or require some tools you might not have. I just happened across this video from K6ARK, a SOTA guy that’s really into super-light, backpack-able radios and antennas, and he shows one that only weighs 8.5 ounces and can be put together easily without bending copper or aluminum tubing into a loop:

https://www.youtube.com/watch?v=Uz5ZKkxGDQ4

I thought this interesting (QRP power only) build might inspire you to try making one of your own. This one is not super-hard to make, doesn’t require any specialized tools, and packs away into a very small space. You might have to come up with some minor accommodations if you don’t have simple metal-working hand tools.

For example, the nice bracket that he made for the BNC connector could be replaced by simply cutting and stripping a piece of RG-174 or RG-58 coax and using a hose clamp to connect the coax braid to the ground point. Then solder or twist a simple 8 to 16 inch length of any kind of wire to the center conductor of the coax to make the “gamma” match. You can use either an alligator clip as shown, or even just another hose clamp to attach it to the main loop body. Just move the connection points around for the best SWR.

The little plastic switch box with the tuning capacitor is maybe a bit more of a challenge, but you can even substitute it with a 18-30 inch length of coax (for 20 meters), if you’re OK starting with just a single frequency/band. The capacitance between the shield and center conductor of the coax replaces the capacitors in the box. Just attach the shield to one side of the loop at the top, and the center conductor to the other side, leaving an insulator between the two ends of the loop. Something like a piece of scrap plastic, pvc, or even just a chunk cut from a soda pop bottle would work.

Leave the far end of the coax open, and measure your resonant frequency with a NanoVNA or some other wideband SWR meter. Snip the length of coax shorter a half-inch at a time until it resonates on the frequency you want. There–done!

I’m embedding a video by VK3YE showing this “coax-as-a-capacitor” method on his mag loop. You don’t necessarily have to make a big copper loop like this, or copy his tunable capacitor made of scrap pc board and a rubber band. You can just simply cut the open end of the coax a bit at a time as I mentioned.

The interesting thing about this antenna is that you can run a full 100 watts through it. Note just how low to the ground it is. That wasn’t just for the camera. I know some hams might think it’s impossible to get out with something this small and stealthy, but it really works!

As I’ve mentioned before, the only real downside is that mag loops are very narrow-banded, giving you only about 20-30 kHz of the band without retuning. Maybe the scrap pc board and rubber band kludge isn’t such a bad idea in that case. But…let’s say you’re really into FT8, or just want to join a daily net. This might just be your ticket! Stick it up in your attic and away you go…

Quick Links to Things We Covered on Tonight’s Net

Here are a few web URL’s to items we discussed on the 3/30/22 net:

Online tone generator–send DTMF over a radio or other device that doesn’t have a TouchTone pad:

https://onlinetonegenerator.com/dtmf.html


Source for SDR receivers and adapters for all sorts of uses:
https://www.sdr-kits.net/

Fully assembled little adapter boards for under $25 that you can add to your radio if it doesn’t have a built-in panadapter (waterfall) display). You would then connect this amplified IF output to an SDR dongle, add some free software on to your computer, and have a great display of what’s on the bands:

https://www.sdr-kits.net/Panoramic-Adaptor-Tap-Boards

Jack W6KRK and I bought these folding panels awhile back. Well-made and fold into something close to the size and weight of a laptop computer in a soft bag:

Amazon

George N6GWH bought these portable folding solar panels and likes them. They are about $50 less than the ones I bought, and have another 20W of power as well:

Amazon

Jehu Garcia’s YouTube page. He’s been one of my favorite instructors, as well as a source of parts, for building your own lithium batteries and battery packs. Be sure to also check out his VW Microbus that he converted to a full electric vehicle:

Jehu Garcia on YouTube

Will Prowse has a great YouTube channel that has very informative info on batteries and solar systems:

Will Prowse on YouTube

WebSDR: Listen to Repeaters in Salt Lake City, and Make Other Fun Radio Links

The Northern Utah WebSDR receiver system has a unique feature that allows you to listen in on local repeater activity in the Wasatch Front area of Utah. Like the other WebSDR receivers, it allows you to listen to activity on the 1.8 to 30 MHz HF bands, but they’ve added another remote receiver for local VHF/UHF activity. This receiver is located southeast of downtown Salt Lake City, on the face of the mountains, about 600 feet above the valley floor. For those of you familiar with the area, it is near the entrance to Parley’s Canyon, where I-80 and I-215 meet. To get from the SLC Airport to Park City, you go right past this area.

Someone has taken the time to mark all of the repeaters that can be heard on the tuning ruler, so all you have to do is click on one of the little brown flags to move from one repeater to another.

NOTE: Before you go any further, if you use the Chrome browser, or any based on Chrome, make sure you remember to click the colored box above and to the right of the tuning dial that says CHROME AUDIO START or you won’t hear anything on any of the WebSDR receivers. Also, please know that if you click these links from an Android or iOS device, you may get re-directed to a different receiver page that might not have the same capabilities. Nothing wrong with your stuff, just a limitation of the design of these awesome receivers. In fact, I sometimes listen to 75 or 40 meter nets with my iPhone, so it works, just a bit differently.

Here are a few web links you can copy/paste (or just bookmark this page) that you can save into your web browser:

This is the 146.62 repeater, the busiest in SLC, and links to one in Park City

Here is the 146.76 repeater, also quite busy, and is my “home” repeater, covering Salt Lake, Davis and Utah (where I am) counties area.

147.12 repeater near our TV towers on Farnsworth Peak (named after Philo Farnsworth, the actual inventor of television), southwest of SLC. This repeater is part of a wide area network of RF-linked repeaters up and down Utah. It is called the Intermountain Intertie system, rivaling the famous Cactus Net for sheer coverage. It also covers southern Idaho (Boise, Idaho Falls), parts of Wyoming, Montana, Yellowstone Park, Flagstaff and Phoenix, AZ, and Las Vegas. Lots of activity here as well. Unlike Cactus, all may use it without fees or membership. Read more about it here

By the way, many of the WebSDR receivers allow you to make your own weblink that you can save or bookmark. It allows you to instantly go to a particular WebSDR receiver, frequency and mode. You can see how I did this by examining the URL’s in the links above. Or, for example, if you like listening to the NoonTime Net on 40 meters from about 10 AM to 2 PM every day, your link would look like this one below. Go ahead and click on these examples if you’d like. I made sure they work:

http://websdr1.sdrutah.org:8901/index1a.html?tune=7284lsb

Note the data after the question mark. Just replace the frequency in kHz with whatever you want, and then add the mode, such as cw, usb, lsb, fm, or am. That’s all there is to it. If you want to listen using a different WebSDR receiver, just use its URL, and add the same frequency and mode data at the end. Here are two more examples of the NoonTime net again, but listening first from the KFS receiver near Pacifica, and right below it is the same net, listening from Phoenix.

http://69.27.184.62:8901/?tune=7284lsb

http://w7rna.com/?tune=7284lsb

Easy, right? Here’s another hint if you’d like to monitor several frequencies or repeaters at once. All you need to do is start one receiver session by clicking one of the above, then open a new browser instance or tab, then either click another link or paste one in, then go. Note that sometimes opening just a tab doesn’t give you audio from both receiver instances at the same time, depending on your browser. It worked OK for my Chrome browser, but your mileage may vary, etc.

OK, here is one last bonus link. If you would like to practice listening to CW, here is a link to 7047.5 kHz. It is the ARRL’s station W1AW. Every day it sends plain text from a recent issue of QST magazine at varying speeds. Very good practice, but don’t freak out if you happen to arrive while it’s sending at 35+ WPM! Yeah, I can’t copy most of that either. If you look at the web link, note that I inserted the frequency as 7046.75 kHz to get to 7047.5. I don’t know why, but on CW, it’s 750 Hz higher. Maybe a quirk. I dunno. I’ll come back and edit this if I figure out why.

There you go–you’ve got lots of cool receiver power all over the planet for the price of…nothing. Can’t beat that!

What Are Those Weird Tones?

Contestia Signal

If you tune around the HF bands, you’ve very likely heard strange-sounding tones, squawks or beeps, and wondered what they are. Here is a link to a very well-done Wiki that gives you audio samples you can listen to, and a brief explanation of all sorts of different modulation types found on the Amateur bands to help you identify what you’re hearing:

https://www.sigidwiki.com/wiki/Category:Amateur_Radio


Items covered in our 1/4/17 Tech Net

In this week’s first-of-the-month Tech Net, we covered quite a wide range of Q’s and A’s, as well as some new and old laws on the books.

The first of those laws is the new California restriction on distracted driving and cell phone use that does not exempt holding an amateur radio mike or walkie talkie in your hand.  Nobody knows yet how this is going to play out, or if any hams are going to end up being pulled over.  Here is the paragraph taken from State Assembly Bill AB-1785 that defines what a “restricted device” is:

(f) For the purposes of this section, “electronic wireless communications device” includes, but is not limited to, a broadband personal communication device, a specialized mobile radio device, a handheld device or laptop computer with mobile data access, a pager, or a two-way messaging device.

I guess we would be caught under the “specialized mobile radio device”, but the wording, and even the definitions they provided, are so vague that I could probably be pulled over for talking into a corn dog.  And yes, they did exempt anyone operating as an emergency services person.

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Along this the above new law is a requirement that the restricted device be mounted to the dashboard.  One of our members reminded us of another law that is in effect that does not allow you to mount anything in the center of the dash, or on the low-center part of the windshield.  You must mount your GPS, phone, or whatever in either the right or left corner of the dash only.  The idea being that anything mounted in the center will obstruct your vision.

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Sugru is a neat, new product that just might find a use around your home or garage.  See it here:  http://www.sugru.com  It is a flexible, heat- and cold-resistant, grippy and moldable polymer that can do some pretty cool things.  After you mold it to the shape that you want, it remains flexible.  Easiest thing to do is to have a look on their website at the pictures and also videos that show some good ideas.  Aaron, W6TDR, brought it up and mentioned that he’s used it.  I have several sample kits of it, but I haven’t actually used it yet.  I also got a fun kit from them that includes some button magnets.  Oh boy!

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We talked briefly about using silicone grease (not silicon!) in RF connectors to displace water and to keep corrosion off of connector pins.  I am also reminded that I used a small tube of silicone grease on several rubber o-rings that I recently installed inside of my new water softener.  Avoid using silicone grease in very high-power RF, since you’ll get carbon tracking and flash-over, but for amateur power levels, that’s probably not a concern.  It is apparently OK to wipe silicone grease on the mating surfaces of RF connectors, and they will be protected from corrosion and presumably will wipe away from the points at which direct metal-to-metal contact needs to be made.  Remember that we are talking about SILICONE the polymer, not SILICON the soft metal that bursts into flames when exposed to a little moisture.  People constantly confuse the two in everyday speech.  Even those that should know better.  If you are ever having trouble remembering which is which, please refer to the “Rule of Two Valleys”:

1. SF Bay Area and Tech Capitol of the World:  Silicon Valley

2. Hollywood, full of “enhanced” actresses:  Silicone Valley

You’re welcome.

See here for further info:

https://www.w8ji.com/dielectric_grease_vs_conductive_grease.htm

http://lists.contesting.com/_towertalk/1998-09/msg00477.html

Dow Corning High-Vacuum Silicone grease comes highly recommended by some 2-way radio pros.  I have my own tube of it that will probably last me a lifetime.  Here is an Amazon link to it:  http://amzn.to/2hZEHAw

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A question was asked about whether DStar is becoming more or less popular, especially when DMR seems to be coming on strong.

My take (my opinion only, of course) is that DStar is declining in popularity, but truly DMR is experiencing explosive growth right now.  Some comparisons:

Even though DStar and DMR use the same analog-to-digital codecs, DMR’s has FEC (forward error correction) built into it, and there is much less “R2-D2” voice garbling than DStar when signal strengths get low.  In fact, because of FEC, DMR seems to get about 10-15% better range than even analog FM can do.  The only downside is that you’ll have to get your ear used to hearing band-limited, digitized audio.  This is the case for either DMR or DStar, BTW.

DStar is supported by one ham manufacturer, Icom, and has never caught on with any others.

DMR is a world-wide standard driven by the need to serve the professional 2-way radio crowd, so even though it didn’t hit the market until 2007, all sorts of radios and infrastructure are available for it now, driving down costs to $100 or so for an entry-level radio.  With DStar, I’ve always been annoyed by the “DStar tax” I would have to pay if I bought an Icom radio.

The best part of DMR for me is the wonderful volunteers that have set up several world-wide networks and charged exactly zero for the rest of us to join in.  There are tons of hams to talk to at any hour of the day.

The only downside to both DStar and DMR is that they have a bit of a learning curve as a barrier to getting started.  You can’t just buy a radio and put it on the air 10 minutes later.  That’s where a knowledgeable ham friend who has been down that road already can be invaluable in getting you started.  Now, that said, let me offer some quick steps to help you at least get to the front door of the house:

  1.  Go to http://www.dmr-marc.net/ and click on “Register ID” in the upper right-hand corner.  You will be registering for a user ID, not a repeater.  On the bottom of the next page, click “User registration” and follow the prompts where they will validate you, making sure you have an active amateur radio call.  Within a day or two, you will get an email from them with your new 7-digit DMR ID number.  You will later program this into your DMR radio.  Note that you can also go back to this website later to see what you or your friends’ DMR ID’s are, or to find the name of the person whose only info that came up was his DMR ID. Here is a direct link to the database search page:  https://www.dmr-marc.net/cgi-bin/trbo-database/
  2. Buy a DMR radio.  Most of us locally have started with the TYT MD-380, and it’s just over $100.  If you have a TYT, you’re much more likely to find help with any questions you might have.  Most of us bought them on Amazon, such as this link:  http://amzn.to/2j199am
  3. Install the MD-380 programming software on your PC (available as a download after you sign up for their very good newsletter).
  4. Get one of us to email you a codeplug that you can program into your radio, and then you’re good to go!  We can also explain what a codeplug is, and how you can change it to suit your own needs.

Ham Radio 360 Podcast features local hams

George, KJ6VU, has a great podcast and accompanying web page with some interesting gear and DIY projects going on. They are presently doing a group build of a 1-30 MHz antenna analyzer based on the Arduino platform. Have a look and/or listen at www.hamradio360.com

 

I mentioned this on tonight’s tech net at 9 PM.  While you are perusing that website, have a look around at a few other very interesting things.  For instance, see George’s presentation from this year’s Dayton Hamvention, where he introduced the very handy portable end-fed antennas from his new company called PackTenna.

 

The presentation does a very good job of showing you how to wind some simple baluns (actually they are un-un’s) to get your 50 ohm feedline matched to the very high impedances of either a resonant, end-fed dipole, or a random-length end-fed antenna.  Or…you could buy one ready-made from PackTenna for $89.  If you go to www.packtenna.com and look around, be sure to read the QST magazine “test drive” of his antennas.  Highly recommended.

Anderson Powerpoles

powerpole05Lopping off the ends of the power connectors on your brand new gear may not sound like a good idea, but it probably is. Anderson Powerpole connectors have become the defacto standard for power connections in amateur radio. They are easy to connect, and come in a variety of amp ratings and colors. It is the power standard for ARES/RACES teams, and a quick, safe, way for hams to come together, and share power at an event or emergency. The connectors themselves are fairly inexpensive. But you will want to make a one-time investment in a proper Powerpole crimp tool. They are about $40-$50. Powerwerx has a great selection of Powerpole connectors and accessories. They also have an excellent tutorial page on how to make proper Powerpole connections. Check it out!

Switching Power Supplies

imagesWe need more power! Switching power supplies have been around for some time now. There are many options, features, and price ranges. Some have various power tap options, like CLA outlets, power poles, banana plugs, and basic screw posts. Other features may include meters, or voltage adjustment abilities. Since these are specifically marketed for amateur radios, many have RF filtering to help keep from impeding on your radio session. Some, not so much…

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Real Hams Drill Holes

radio-car1You all know “that guy” – The one with the UHF/VHF antenna (or antennas) stuck to the roof or trunk lid and wires trailing off to the side that go through a trunk, door, or window gap. The antenna maintains its death grip on the outside of the vehicle with the mysterious forces of magnetism, via a lip or edge clamp, or something that bolts to your roof rack. You wash your own car and drive a couple extra blocks to avoid parking garages. It’s all for the better you tell yourself. It is also why your significant other won’t let you touch their car.

I was “that guy”.  I also remember when I knew that it was time to no longer be “that guy”.

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Magnetic Microphone Mount

no_clipOne thing that seems to make amateur radio folks more squeamish than finding a bag of frogs under their bed is the subject of drilling holes in their vehicle. Drilling holes to mount radios. Drilling holes to mount antennas. Drilling holes to mount a microphone somewhere on the dash. Some of you drill holes for microphone clips, or purchase alternatives that clip onto an air vent, and some of you simply toss the microphone in a cup holder. Today, I am going to share my solution for making a magnetic microphone mount that does not require holes in your dashboard.

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