RF Exposure Calculator

Probably should have brought this up on Tech Night. But we missed the opportunity. I need to keep an active sheet of all the crazy questions always popping into my head.

So why do we need an exposure calculator? Well, this bulletin kind of sums things up nicely. You should read it before proceeding. The FCC has adopted guidelines for RF safety, and let’s face it, as the FCC and ARRL continuously lowers the bar for the path to a license, and the hardware becomes more ubiquitous and available, any new ham with virtually no experience, can get a general license and then hook up a 1,500 watt linear in their bedroom with a square loop antenna over their bed with no real practical experience to clue them in that they just converted their bedroom into a microwave oven every time they key up.

Under new FCC guidelines operating stations will now be required to calculate RF exposure limits for stations. To make this easier for amateur stations, the ARRL now provides an online RF exposure calculator. To utilize the calculator, simply enter your peak envelope power (PEP), operating mode, and duty cycle. Many modern radios can tell you how much power you are putting into your antenna system. The calculator will then give you the minimum safe distance people must be from your antenna for safe RF exposure limits. You can print out or email the results and keep them with your station just in case someone with a badge shows up at the door (not likely), but it is certainly a good exercise for any Ham to to go through to learn more about the safety aspects of our hobby. We see things like antenna efficiency, propagation, and the like all the time. Everyone is always trying to make a better antenna. When is the last time you saw someone post the RF safety information for that same antenna, of for any antenna for that matter. Check it out.

By the way, my home configuration, =< 100 watts, and running digital modes, requires a minimum safe distance of about 3.5 ft or around 1 meter.

Talking About 10 Meters

In last month’s Tech Net, we talked quite a bit about the fact that 10 Meters has been open. In fact, Jack, W6KRK, told us that he had been able to check into a 10 Meter net being held by the Utah County hams earlier that evening, covering a distance of about 850 miles.

10 Meters is typically described as a daylight-only band that is more often than not closed. If we stop right there, we may not realize that we’re missing out on some big fun and possibly some very interesting contacts.

Another thing of great interest is that 10 Meters contains the only sub-band that allows Novice and Technician licensees to transmit data and SSB voice signals. This gives Techs a good chance to experience the fun and technical challenges of operating on the HF bands. Technicians have unlimited operation on 6 Meters and higher, but most of the time, those high-frequency signals behave more like a beam of light, where contacts can be made locally as long as antennas can “see” each other. There is more to it than that, but I’ll leave that description to be expanded upon in another post.

Being able to get a taste of HF operation, meaning operating in the shortwave bands from about 1.8 to 30 MHz, can be both exciting and challenging to a Tech who has not had any previous experience. When I say “challenging”, I don’t mean that it represents an unpleasant or insurmountable task, only one that is new and unfamiliar. You’ll have to decide on an antenna and transceiver to use, and also learn a bit about how signals on 10 Meters behave so that you don’t waste lots of time trying to make contacts when the band is not open.

Before we talk about antennas, radios and how signals bounce around the globe, let me briefly mention some of my own experiences with the 10 Meter band. On the net, I mentioned one of my favorites being a station from French Polynesia that came on 28.410 MHz, as I recall. I had a mobile station then (about 2010), and I was on 10 Meters only because I was checking the SWR of my antenna, a Lil’ Tarheel HP “screwdriver” antenna. This antenna covers 40 through 6 meters, and uses a motor to expose more or less of the internal inductor coil, tuning it to a particular frequency. In the earliest versions of these antennas, the motor from a battery-operated electric screwdriver was used because it was cylindrically-shaped and had high torque, hence the name “scredriver” applying to all motor-tuned mobile antennas.

Anyway, as I was checking my SWR on 10 Meters in the early evening, I heard this very strong S9+10 signal that I found was from French Polynesia. Interestingly, I couldn’t hear any of the stations calling him, but he was very strong. I gave him a call on my 100-watt Yaesu FT-857 transceiver, and he answered me on my first call with an S9 report! Cool! Interestingly, his signal persisted strong and clear until he finally said he was closing down for the night, at about 9:15 PM California time. Wow! That’s unusual, but not unheard of.

I can give you many examples of contacts I’ve made on 10 Meters when the band appeared to be shut down. The usual thing to do is to tune around, and if you don’t hear anyone, set your dial to 28.400 MHz, the SSB calling frequency, and call CQ. Like me, you might be surprised to get someone calling you back! If I had just listened instead of calling CQ, I might have not made any contacts because everyone else was just listening also. So by all means, get on the mike and call if you don’t hear much.

Even in “down” times, when the 11-year sunspot cycle is at a low ebb, there are contacts to be made. Each year, from about May through September in the Northern Hemisphere, the band tends to open up, sometimes allowing even daily contacts. This will happen mostly from late morning through to early evening, but there are plenty of exceptions to that timetable as well, such as my hours-long connection to French Polynesia.

As we are now climbing up the 11-year sunspot cycle roller coaster, things are heating up on 6 and 10 meters. Especially if you are a Technician class ham with a shiny new HF transceiver, this is your moment! You can work the world when these two bands are open. 10 meters should be your “go-to” band right now, as it will open more reliably, possibly on a daily basis. 6 meters is a bit more tricky, relying most on what’s called E-Skip propagation. But when it’s open, fun things can happen as well.

Something else to listen for on both bands are the beacons. Hams have put up simple CW beacons all over the world, and they provide an easy means of telling when the band is open. Have a look at these two links to get you started with understanding how to listen for and identify what frequencies to use, and where the beacons are calling from:



Build a Super-Simple Radio, Get it on the Air, and Learn CW Along the Way

Tuna Can QRP Radio

One of our group is working on a very simple little one-transistor low-power 40 meter transmitter. No, the picture above is not it, although this is a fun little receiver kit you can build if you want to start with a simple kit.

Anyway, when he’s done with his little transmitter, he then faces his next hurdle: The dreaded CW monster!

The CW Monster!
Does that maybe ring true for you as well? Let me give you some encouragement, and maybe we can shine some light on the monster. You may find that he doesn’t actually bite, and is even friendly!

I’m re-posting some comments I made to Bob just tonight, and I thought I’d pass this along for you to consider:

When you get a simple radio put together, you might find that CW is your biggest challenge. I’ve always had a love/hate relationship with it–mostly love. The hard part, of course, is in getting started.

There are lots of QRP clubs around to offer encouragement and also even on-air schedules. I know I’ve mentioned the QRPARCI club on our net nights before. You may also find lots of encouragement in learning CW with the SKCC, the Straight Key Century Club: http://www.skccgroup.com/membership_data/opfreq.php

This page shows their “watering hole” frequencies. I’m listening to two SKCC members right now on 7055 kHz. They are going along at about 7 words per minute or less. The idea, of course, is to use a simple hand key instead of an electronic keyer, and to (usually, but not always) slow down. They usually call “CQ SKCC” and then exchange numbers and pleasantries. The two guys I’ve been listening to are in Florida and Rhode Island. I can hear them easily with my G5RV dipole antenna, so they’re probably running 100 watts. You don’t have to use QRP power levels if you don’t want to.

It’s fun to sit here and hand write each letter on the back of a piece of junk mail I received today as they send them. I get to think about other things for a moment, and then write down the next letter sent, etc. Very pleasant actually. Kind of like taking a slow ride through the back country roads instead of zipping down the interstate highway.

Anyway, just thought I’d pass that along to you. It’s always a bit intimidating to get on the air with CW for the first time. By the way, Jack, W6KRK, can be counted on as a helpful guy when it comes to CW. He just decided last year to dig in and re-learn CW. So if you can get him to take a few minutes on the air with you, it might help to get over the “first call” jitters. Oh wait–I could do that, too, from here in Utah! Just ask. I can be as sloooow as you’d like! We could try 20, 40 or 80 meters just about any time you want to try.

Maybe you could find some of our other friends to try, too. Building radios and then putting them on the air, at least for me, has been a lifetime passion. The “putting them on the air” part usually means CW for the simple gear, of course, and it can be tremendously satisfying when you make a contact with your little radio. Remember, too, that your first attempt does not have to be a full-on transceiver. A one- or two-transistor, crystal-controlled peanut whistle transmitter can be used just fine with your “big” HF transceiver.

New Stamps Pay Homage To Our Hobby’s Enabler.

This could be the kick you need to send out that stack of QSL cards you keep meaning to get in the mail. The United States Postal Service has issued the Sun Science “forever stamp” series honoring the primary enabler of the ham radio hobby, Sol. The series of stamps is printed with an embedded foil process which gives the images an extra shimmer. Designed by art director Antonio Alcala using colorized photos from our nearest star.

The forever stamp will always be equal to the current First-Class Mail 1 ounce price. You may order from usps.com/shopstamps.

Not Enough Hams on the Air? Have a Look

This is a snapshot of this weekend’s CW contest (CQ WPX) on 20 meters going on right now at about 7:15PM Mountain time. I was tuning around on the various web-based SDR receivers you’ve heard me mention many times on our Wednesday night net. I was impressed by the wall-to-wall CW signals as seen by the Northern Utah Web SDR receiver. Just a bit crowded, don’t you think?

Oh, and those semi-solid lines on the right hand part of the SDR window are the FT8 folks happily ignoring the CW contest below them. Everybody have fun!

The $50 Ham

I know what you are thinking. The $50 ham is that person in the group that buys a Baofeng for $30 and then 3 years later tries to sell it on Craigslist for $50. Or, thinks that 30 year old Kenwood, with the nice “patina” is worth original MSRP +30%. Nope. Not that guy.

The $50 ham is a series of articles by Dan Maloney over on Hackaday, one of my favorite sites on the interwebs for all things electronics and technology.

The series has several interesting pieces on WSPR, Digital modes, HF antenna building, dummy loads, and other topics for those ops on a budget, or just want to explore something new. Check it out!

Which Coax Did I Want Again?

How many ways is this question asked and answered? There are a gazillion articles on the topic. I have been reading. A lot. And here is what I have come to find…

Most of my coax has been RG8X, across the board. I didn’t really know much better, it is exceptionally cheap, and as far as I can tell, my signal is leaving my radio and exiting out through the antenna. So what have I learned…

For the average home amateur radio operator there are more options than just RG8x and LMR400. I know! Blasphemy! Like 90% of the conversations revolve around those 2, unless you are doing repeater work with the club and someone mentions Heliax or hardline. Well guess what. You should add a couple more.

RG-213 – Sort of the little brother of LMR-400 for HF. About 1/3 less loss than RG8X. But… if you are even remotely thinking about any kind of amplifier in the future, then RG-213 may be the cable you are looking for. Where RG8X is only good for around 400 watts in the HF bands, RG-213 can handle over 1,200 watts, easily. Is not as large and bulky as LMR-400, but is certainly larger than RG8X.

LMR-240 – Never heard of this before? If you are running portable, or insist on running RG8X, then you should also be considering LMR-240 and LMR240-UF. The “UF” is for ultra-flexible. With a 35% or better loss advantage over RG8X, in nearly the same diameter and flexibility, with almost 3 times the power handling, LMR-240 is a drop in, high quality replacement to RG8X. LMR-240 is also sort of in a sweet spot where for shorter runs, it also works well enough for UHF/VHF. For your Go-Kit cables, or field day setup, LMR-240 is a great option. I just used ABR Industries to order several LMR-240 cables and can’t wait to try them out. I will do a review in the near future.

Check out the stats here: https://www.universal-radio.com/catalog/cable/coaxperf.html

Spider Antenna – Circa 1985

On the heels of the Wolf River Coil DIY tripod rebuild, comes the Spider Antenna. Invented and patented at the time by Fred Smitka, K6AQI, out of California, the Spider Antenna was created and sold in the early 80’s. It is by design a mobile antenna designed to take advantage of the ground plane a vehicle can provide. But since I had just reworked my tripod for the WRC, I made a few adjustments so that I could also connect the Spider Antenna and take advantage of the radials I had already created for the WRC. And it works! Sort of. More on that in a moment…

Where the WRC is a bottom loaded vertical, the Spider Antenna is a top loaded vertical. This blast from the past was picked up in a Craigslist buy several years ago. I was looking to upgrade a dipole from my then G5RV Jr. When I arrived to purchase a DC-CC fan dipole I was greeted with a pile of various antennas. There were a couple of wire dipoles, a rigid Cushcraft D3 20-15-10 rotatable dipole, what looked like at least a pair of “chimney sweep” MFJ antennas with all manner of missing parts, and maybe one other antenna worth of parts I never did figure out. But, there was also a cardboard tube that contained this odd looking antenna system that is known as a Spider Antenna. The seller was more than happy to see the entire pile leave. Their trash became my treasure.

So what is this thing? In simple terms, the Spider antenna is a top loaded vertical. Unlike the coil antennas we are accustomed to seeing, where you have 1 coil, and then you tap the coil for the band you wish to operate on, the Spider Antenna has a 5′ metal mast, with a fitting at the top for up to 4 individual coils. There is a separate coil for each band. The coils come in bands 80-10. The one catch is that 80, and 40, can only go on top. So you cannot for instance have 40 and 80 on at the same time. But you could do 40, 20, 17, and 15 if you like, or whatever combo you wish. What was really cool about this find was that it was a complete set of coils for 80-10 meters. bands!

To tune the antenna, over each coil is a ferrite that you slide up or down the coil until it is resonant where you want it within the band. As the bandwidth can be a bit narrow on 40/80, you will have to adjust to which end of the band. What is also remarkable is that after 36 years, this antenna still seems just fine. The antenna is rated to easily be able to handle 200 watts. And I even found a review online from Gordan West that claims he ran a Magnus 800 watt amplifier through the Spider Antenna and it worked just fine.

The entire antenna is of quite high quality construction. Normally, as we have experienced, plastic coatings break down over time. The materials on the Spider Antenna have held up very well. Each coil is of rigid fiberglass construction.

Setting it up in the back yard and using my Nano VNA, I was able to bring adjust each coil in just a few minutes. I hooked up my KX3, but was only on battery so output power was quite low, but I was able to receive quite well. I will have to connect to the TS-440 and do an A/B test and post an update.

QRZ.COM New Logging!

Have you checked out QRZ.Com’s logging features lately? They have come a long way in the past year or so. Did you know you already have an account as an amateur radio licensee on QRZ.com? Well you do! You should check it out. Create your logon, and there are all kinds of goodies there from current news, forums for sharing tips, discussing new hardware, and even a swap meet for selling new and used equipment. There are always interesting things to read.

But what has truly improved over the past about 18 months is their logging feature. I now pretty much do all my logging directly into QRZ. Even with things like FT8, I have the software set up to directly send the log update into my QRZ log. I also have my LOTW set up so with 3 clicks of the mouse, I can upload all my current session QSO’s to LOTW, and then a couple days later, with 3 more mouse clicks, retrieve all my LOTW confirmed contacts. You should really check it out!

Look Ma! I’m on Facebook!

I finally took some time to straighten out the social media plugins and made some changes on the Facebook accounts. The interaction systems are kind of convoluted. For instance, you cannot just syndicate to Facebook groups. There are “steps” and they typically are not free. But you can syndicate to a page. So the After the Net Facebook group is being retired. And there is now an After the Net page instead. So be sure to stop by and hit the “Liked” button so you get updates in your feed. Articles written and published here will also automatically now be posted to the FB page. So we can use this format for longer how-to’s, reviews, and other technical discussions, but still promote to a wider audience on Facebook.

I will try to keep things here more up to date, and also to take advantage of the scheduling capabilities to space things out a bit. But If you would like to contribute to our local amateur radio community and write articles or share other information, please contact me. We can get you set up with authoring access!

Ray – N6DZK