Field Day 2021 – Storms and Stations

This post is cross-posted to my general-purpose blog, jeff.glass/blog

Despite sunburns, shattered plastic, and a literal tornado warning, sunburns, I had a great time at Field Day 2021 this year.

My intention had been to head out to the northern Chicago suburbs on Saturday morning for some testing of the setup. My wife and I had purchased an annual pass to the Lake County dog parks in anticipation of the Fourth of July weekend, and our plan had been to drop her (and Winnifred, a very good dog) at one of these parks, go around the corner to a quieter, non-dog-filled local park, setup and operate for an hour and change, then pick the two of them up and head home. I’d charge my battery using an inverter in the car, grab some water and lunch at home, then be back out in a closer local park Saturday afternoon for a long operating session. And maybe, if I woke up in time, I’d pop back out in the morning to the park around the corner from my place for some grayline work on Sunday morning.

What Saturday should have looked like.

Chicago weather had other plans.

Tornado Warning including Chicago IL, Cicero IL, Berwyn IL until 12:15 PM CDT pic.twitter.com/v7zLSObdy5

— NWS Chicago (@NWSChicago) June 26, 2021

We spent pretty much the entire day on Saturday huddled indoors against a pretty fearsome storm, which including multiple tornado warnings, thunderstorm wanrings, flash flood alerts… it was a wild day. I did make it out once in the afternoon to run to the hardware store to work on an impromptu Magnetic Loop antenna project (more on that soon), but other than that, we were holed up with our poor frightened dog.

At least we have a sense of humor about these things

But like a breath of fresh air, Sunday brought cool(ish) clear skies, dry weather, and a rather perfect operating day by mid-morning. So I pulled the portable-rig back together and headed out to the originally-planned local park to catch the last few hours of Field Day.

My setup’s changed a fair bit in the last couple years (and will likely be changing again soon). Here’s what I was playing with on Field Day this year:

• Xiegu X108-G 20W Transceiver for SSB, CW, etc.
• Wolf River Coils “Mega Mini TIA” portable antenna, a stainless steel collapsible whip with a base-loading coil that sits on three removable tripod legs. WRC sells a wide variety of configurationsand sizes of this basic setup – mine is a 17′ whip with the larger (~14″) coil and 24″ tripod legs. It’ll tune around 80m to 10m, though of course on 80m it’s reeeeally short.
  • The antenna ships with three 10m radials, which attach to the tripod base with ring lugs. I added three 7.5m radials (1/4 wavelength on 30m) and re-used my 5m radials from the QRPGuys Tri-Band Vertical setup I had been using. Each set has a bullet connector on it, and a single ring-lug-to-three-bullet-connector squid attaches to the tripod
• The battery for the day was a TalentCell 12V, 6A, 8300mAh battery i picked up from Amazon. We used these batteries all the time in live theatre for their size and weight, and while I doubt that I’m getting the full 8300mAh from it (especially since the X108-G draws around 6A on transmit), it lasted me through a solid afternoon’s operating.
• I remounted my iambic paddles from their cast-iron base to a lighter plastic one
• I picked up an Autek VA-1 antenna analyzer earlier this year, which makes a great quick tuning method for the antenna. I played around with bringing my Nano NVA H-4 out, but it’s just a little too fiddly for regular field use.
• 25′ of RG8x from the radio to the antenna
• A camp chair and a portable picnic table make from easy ergonomic in the field
• Logging is pen-and-paper, for now

The setup in the park

I spent the first couple hours hunting and pouncing, mostly on 20m with a stint up to 15m. 20m was super-densely populated as usual; 15 less so, but still with some decent stations holding the band down. I made roughly 25 contacts in that time with some decent distance – Arizona, Florida, Arkansas, Pennsylvania..

At 1pm local time, Field Day hit 24 hours elapsed, which is the maximum operating time for home, mobile, and emergency operations center stations… but Class A (club) and Class B (1/2 op portable) were permitted to go to 4pm. And with the bands newly clearly of the massive home stations, I figured, why not call CQ for awhile?

WHAT A RIDE.

I held a frequency on 20 meters for roughly 75 minutes, during which I made 90+ contacts. Being the run station was an absolute blast – I’ve done such things at Field Days before, but never as a solo operator and never with my own personal station. Knowing there’s no logger to have your bag, just you and the airwaves and the piles of people calling… a truly great time. I know I won’t set any records for speed or quantity of contacts, but I had a blast.

I’m currently looking for a day to go out and do a Parks on the Air activation to recapture some of the rush of running a station. Really, what a joy. And I’ll have a couple of new toys to play with by then…

There’s lots of Parks on the Air parks in the Chicagoland area – I hope to be activating them soon!

73

A Portable 20/30/40m Vertical Antenna

This post is cross-posted to my more general-purpose nerdery blog, jeff.glass/blog.

Following the Forth of July, I took a few days off of work to recuperate from a grueling work project that we pushed over the finish line on the third. And what better way to relax in the wake of a heatwave than getting out in the beautiful, low-70’s weather and working on a new portable HF antenna.

From eBay listing

The heart of the antenna is an inexpensive ‘7.2m’ telescoping fishing pole, which can be had for less than $30 with Prime shipping or for less than $10 if you don’t mind waiting. The pole weighs about 10 ounces, comes with a small fabric sheath, and collapses down to about 24″. I’ve been wanting to try out something like this since I stumbled across VK3YE and his squid-pole setups awhile back – Peter’s also featured these particular poles in another video. Be aware, a pole called “7.2m” may not actually be 7.2 meters from end to end: check the listings carefully:

Note the difference between the “stretch” column and the “specification” column.

The length of the pole is enough for a quarter-wave vertical for 20m with some room to spare on either end. To allow for multi-band operation, I added a QRPGuys Tri-Band Vertical accessory to the bottom of the antenna. The piece is essentially just two loading-coils (in this case, iron-powder toroids) with slide-switches to short them out. The 20m configuration is a true quarter-wave vertical; one of the toroids is switched in series for 30m, and both are placed in series for 40m. Ultimately, not a complicated setup. While it would be easy enough to homebrew, the ergonomics of the switches, the hardware to attach the antenna wire and radials, and the clever PCB setup are enough to make it worth the $15 to just buy the darn thing. It even has little notches on the edges of the PCB for straps/ties/rubberbands to attach it to the vertical.

From QRPGuys.com

Tuning the antenna is straightforward: you cut a piece of wire (a bit long) for a 20m quarter-wave, and lay out four 10′ radials. Then, you bit-by-bit trim down the vertical element to resonate at the desired point in the 20m band. Then you switch in the 30m coil and compress/expand its turns without changing the antenna length to resonate on 30m. Finally, switch in both coils and adjust the second coil to resonate on 40m without changing either the antenna length or the first coil. Voila, a tri-band, base-loaded antenna.

Unfortunately, my antenna analyzer is old school, and doesn’t have a frequency readout. It’s an old MFJ-207 that I scooped up at the SMCC Hamfest in 2016, and while it does have a port to attach a portable frequency counter, I couldn’t find my cheapie one on the day. But I do have a nice Heathkit IM-2420 Frequency Counter with an internal OXCO that I scored an amazing deal on at a hamfest last year (it had an intermittent power switch). So, I attached the MFJ to the antenna, tuned its analog VFO for lowest SWR, walked inside without touching the dail and hooked it up to the frequency counter to see where the center frequency was. Repeat for say the upper and lower 2:1 SWR ranges. Trim the antenna a little, and repeat measurements. Once 20m is tuned, repeat with adjusting the coils for 30m and 40m. A fairly cumbersome process, but for three frequency ranges on one antenna, it was a half-hour project at most.

In the end, the antenna is less than 2:1 SWR across all of the 20m band, all of the 30m band, and all but the top 50 Khz of the 40m band.

I’ve glossed over the mechanical details of the antenna to this point – the base of the telescoping pole fits snugly-yet-easily into the a piece of 1″ schedule-40 PVC pipe. I bought a 5′ section from the local big-box store and cut off a ~10″ section to hold the antenna. I strapped two ground-stakes that I got at Hamvention this year to the bottom with a couple zip-ties and a couple rubber-bands. Finally,  I threaded a long 3/8″ eye-bolt though a matching hole about 2″ from the bottom of the pipe and secured it with a nut on either side – this acts as both a stop for the pole so it doesn’t fall out the bottom, and provides an easy hand- or foot-hold for pressing the stakes into the ground.

The finished antenna mount. It may be getting a coat of high-vis paint in the near future.

The setup for the radials was something I stumbled across by chance while buying the PVC pipe. Our local big-box hardware store was having a sale on these RECOIL Brand cable winders that are meant for headphones or charging cables or similar. I’ve found that they can almost hold four 10′, 24-guage speaker wire radials. This is solving the problem of wires-getting-tangled-in-a-bag that I’ve had with all my antennas to date. Thank goodness!

A few loose ends are worth it for the assurance that the wires won’t get tangled in transit.

It takes about 6 minutes to setup or tear down the antenna:

• The stakes are driven into the ground with a firm foot.
• The telescoping pole is unwrapped and placed in the base
• The antenna wire is unwound from the QRPGuys winder and tied to the tip of the telescoping pole with a small bit of cotton-wrapped nylon line (what we’d call tie line). The top section the pole is very flimsy, so I add a second tie to the next-largest section.
• The pole is pushed up to full height, taking the antenna wire with it, which leaves the QRPGuys rig hanging about 2′ off the ground.
• The QRPGuys rig is tied to the pole with another bit of tieline.
• The radials are unstrung from their winder, pinched to the ground terminal on the QRPGuys rig, and spread out.
• Run coax to a nearby table/seat/rock.
• Set up radio, battery, key, antenna, and logbook.

The antenna fully set up and freestanding.

Of course, my very first time away from home with the antenna… I forgot the radial wires. D’oh! I was way out in the suburbs, too. I wasn’t about to drive an hour home and an hour back for 4 bits of wire, so I first tried out the antenna with no radials (just the coax as a counterpoise). This worked alright – I picked up K2D in CT in the 13 Colonies event on the second call (this at 5W QRP with the ATS-4), but was having trouble with other contacts.

Since I planned to swing by the local Fry’s Electronics on this adventure, I decided to pause operating for a while and make that run. Mostly I was picking up parts for an amplifier project (more on that to come), but while I was there, I looked for solutions to my radial problem. I found a 10′ section of RJ11 phone cord with 4 wires for $1.69 – perfect! Back out in a new park, I stripped the wires out of their jacket, spread them on the ground, and tied them to the antenna’s ground terminal. Instant radials!

And such colorful radials too!

With the antenna back to spec, things really picked up – surely, being on 20m at sundown didn’t hurt either. I scooped K2A (NY), K2B (VA), K2H (MA), K2L (SC), and K2M (PA), as well as the 13-cols bonus station WM3PEN in Philly. Many of these I got on the first or second call, though K2L was a real struggle. There was a very patient operator on the other end though.

The 13 Colonies special operating event runs each year for a week around the 4th of July in the US.

I picked up a couple of other interesting stations along the way: PJ2/KB7Q out of Curacao (though the license gives away that he’s either an ex-pat or visiting), and CQ918FWC from Madeira Island (!) off the coast of Portugal. There were a number of these World Cup special stations on the bands this week as we close in on the finals. At 3800+ miles away, this was my best DX of the day, and a great proof of concept for the new antenna.

At QRP wattage ,this 3800 mile contact was made at 760 miles/watt.

Hear you on the air!

73

ARRL Field Day 2017 – QRP Portable

In contrast to my field day adventures last year, in which I hung out with the folks from the North Shore Radio Club and ran 100W on a K3S, this year I opted for a decided more small-scale approach. Using my ATS-4 receiver, I ran 3.5W CW on 15m, 20m, and 40m for about four hours Saturday afternoon in the lakefront park here in Chicago.

My antenna was a single 40-some-odd-foot wire hung from a tree, fed by my ZM-2 antenna tuner. I think when I built the ZM-2 last year, I goofed something up in the SWR circuitry – the built-in LED should go out at minimum SWR, but mine seems to be brightest at low SWR. To compensate for this, I brought along the MFJ-207 Antenna Analyzer I got at the SMCC Hamfest last year and used that to adjust the antenna tuner.

With the big analog, multi-octave dial on the front of the 207, I found it useful to first tuner the ATS to the desired frequency (say, 14.030) while attached to the antenna and adjust the analyzer until I heard the “WHOOP” of its signal generator in my headphones. With the frequency of the analyzer and receiver close to matching, I’d move the coax back from the tuner to the analyzer and adjust the ATU until the 207 showed lowest SWR. Reconnect the ATS, and away we go!

The MFJ-207 Antenna Analyzer covers up to an octave with a half-turn of the variable cap. Listening for its signal on a receiver made it much easier to find a specific frequency.

I used a new battery setup for this outing – a 12V, 6000mAh TalentCell lithium-ion pack that I borrowed from work. I love this pack – a little less than a pound, charges from a wall-wart, and has a built-in barrel connector and on-off switch. There are also models with a built-in 5V USB charging port, for topping off cell phones and other devices on the go. While the ATS is designed to run at 12V MAX (not 13.8V), I found that the 12.2V the pack was putting out proved to be fine – it seems the limitation is in the heat dissapation from the BS170 finals, and running relatively low duty-cycle search and pounce that wasn’t an issue. I’ll be ordering one for my own use soon. (Or perhaps the even more compact 3000mAh version – the size of a deck of cards!)

The rest of the pack list included:

• A HamKey brand iambic paddle
• A golfball and a kite-string winder for getting the antenna wire into a tree
• A pair of Koss UR-20 headphones
• A small battery-powered speaker with 1/8″ aux input
• Variable DC and Coax jumpers
• A notebook and pen
• A folding camp chair.

All of the above fit into a small laptop bag, along with a few other tools and bits I didn’t end up needing.

The full field day setup, minus the antenna.

I managed 69 contacts, all QRP CW hunt-and-pounce, during my operating time – no tremendous DX, but I did hit a couple of rocky-mountain states and a plethora of sections up and down the East Coast. Final score was just over 1000 pts – that QRP multiplier really stacks up!

I also couldn’t have asked for better weather on the day – 72 degrees and slightly cloudy with a pleasant breeze. Simply stupendous.

Hear you on the air!

73

QST Forty-9er with DDS VfO

(Since this was originally posted, this transceiver has also gained a laser-cut faceplate.)

Long story short, I’ve got a new transceiver!

Back in March, QST magazine published an article about modding a cheap Forty-9er kit from eBay to incorporate a digital VFO. The original Forty-9er was a kit from the NorCal QRP club, a 40m transceiver designed to run on a 9V battery, hence the name. It, like many other kits, is based around an NE602 and an LM386. In the last couple years, cheap kits bearing the same name have been appearing on eBay, which bear only a scant resemblance to the original. The biggest difference is that where the original kit had a VXO attached to the NE602 mixer, the eBay kits are designed to be rock-bound to a single frequency. Perhaps this was the motivator for the QST article, to restore some frequency coverage to these fixed-frequency kits.

The Forty-9er kits from eBay – not a huge number of parts, but not a tiny kit either.

The process of using a digital VFO with an NE602 architecture is simple enough. Specifically, an AD9850 breakout board is used to provide the signal, and a small BJT amplifier increases the power output from the DDS chip. The oscillator power is adjusted to show about 300mV P-P in-situ. After the article was published, one of the authors, K2ZIA produced a limited run of kit boards, which include the amplifier and sockets for both the AD9850 board and an Arduino Nano to control the DDS over i2c.

The K2ZIA kit board, with attached Arduino Nano and AD9850 board. Image credit: K2ZIA

I purchased the breakout board, AD9850, Forty-9er kit, Arduino Nano, and a rotary encoder from a fellow ham, Justin AJ2Q, who had gathered the pieces but was focusing on other pursuits and wanted to pass the project on. Final assembly was pretty straightforward; there are a couple of mods that need to be made to the Forty-9er (specifically, replacing the oscillator crystal with an input for the VFO, and swapping the crystal input bandpass filter for a much-wider two-element bandpass filter), and connection made so that the Arduino can detect when the key is down and shift frequency. AJ2Q had already done most of this, so only some final tweaks and cleaning up some soldering were necessary.

The original Arduino code was designed to make use of a 16×2 LCD display to display the current frequency, as well as licensing information according to the 40m band plan. Since I’ve already been playing with an LCD display on another ongoing project, and since I wanted this to be a simple and durable bit of kit, I wrote a bit of code that instead flashes the current frequency in morse code on a panel-mounted LED. The display is triggered by the press of a button. The number of digits to display is configurable. I’ve found that just displaying the three kilohertz digits is plenty (I don’t need to be reminded I’m on the 7 MHz band every time, and I don’t need precision better than KHz for simple operating). As always, you can see the code on Github.

The internals of the transceiver. The two green perf-boards are an experimental audio filter to be documented later. The 40-9er board is bottom-left, the K2ZIA board is bottom right, and the small black board on the upper right is the rotary encoder mounted to the front panel.

 

The full schematic of the original Forty-9er as well as the necessary mods can be found on Farruk K2ZIA’s website. The only additional hardware changes I made were to wire an LED and a 1k resistor between Arduino pin 14 and ground for the LED, and an SPST button between Arduino pin 4 and ground to trigger the frequency display. Like the original code, depressing the encoder changes the tuning rate, though I modified the possible step values to be only 1000Hz, 100Hz, and 10Hz, in that order. 1KHz is useful for zooming around the band, 100 Hz is useful for tuning a specific signal, and the 10Hz step is mostly for resolving SSB/DSB/AM signals cleanly.

On the rear of the radio are the BNC antenna jack and the power pole power input. (Useful tidbit – a pair of connected 30A powerpoles fit neatly in the cut-out for a VGA connector!) I’ve yet to fashion a front-panel, so the connections on the Forty-9er board for a key and headphones are directly accessible.

I’ve had the rig out to the park a handful of times now, and it sounds good! Like my other direct-conversion NE602-LM386 experiments, the audio quality is great, but broad as barge, so selectivity suffers. The sidetone is clean, at around 700Hz, from the Forty-9er’s little BJT oscillator. I enjoy being able to tune up into the phone portion of the band and listen to SSB QSOs and nets and such, which provide a good sketch of current propagation conditions. Being able to quickly switch between tuning steps is helpful, as I tune around and try to find someone sending CW slow enough for me to keep up.

The top of the rig. Not fancy, but functional.

The only major limitation of the rig is that, with only a single-resonator input bandpass filter, out-of-band signals can get into the radio and cause interference. Specifically, World Harvest Radio WHRI, who maintain and 500KW (no that’s not a typo) transmitter in South Carolina, is often audible everywhere on the dial, which is distracting at best. A stiffer bandpass filter will be necessary soon. I’ve also been experimenting with a peaked audio filter to help with reception of CW, but that’s still experimental.

The unit puts out about 3 Watts, which proved to be enough to make my first CW contact and, over the weekend, my second. The gentleman on the other end this time was Gary N4PIR, who was running 5W on his FT-817 into a trapped vertical. I think a little afterburner would be helpful on my end, as we were definitely fighting QSB. But that’s a later project.

Hear you on the air!

73

First Encounters of the HF Kind

Today, for the first time, I reached out into the ether on HF, and had someone reach back! All with three Watts and a wire. I’m still in blog-post-debt for both field day and the new transceiver, but I’m just so excited, I’ll drop this in as quickie post for this evening. It’s not a proper QSO, but it’s as close as I’ve come yet.

(A small caveat – I’ve worked a couple field days, one with WVARA in Silicon Valley and now one with NS9RC in Chicago, but someone making rapid-fire contest contacts on somebody else’s very shiny K3 doesn’t feel like my contact, you know?… I’m still counting this as an emotional first.)

I had a 40m inverted-V thrown in a tree by Lake Michigan like I described in my previous post. I’d been listening an tuning around from about 7:45pm local time, throwing out the odd CQ, trying to tail-end some conversations without much luck. I’ve been hanging out mostly around 7.110-7.114 MHz, which are both a slow-code area and the area near the SKCC calling frequency, which seems to attract patient and friendly code operators. Finally, around 9:25pm, I heard a very, very slow “CQ CQ” right on 7.114 MHz. The call was from W4JWC, I suspect from a keyer – it was very slow and regular, and easy to copy. I shot him back a quick “W4JWC de KK9JEF,” and he came back! Still slow, medium-signal but with some serious fading.

Here’s the entire text of my first contact. I’m including it, not because it’s particularly interesting, because I think I’ll enjoy looking back on it later:

CQ CQ CQ CQ de W4JWC W4JWC K

W4JWC DE KK9JEF KN

KK9JEF DE W4JWC UR RST IS 539 RST 539 NAME IS JERRY JERRY QTH WIRTZ VA WIRTZ VA KK9JEF DE W4JWC K

FB FB JERRY NM HR IS JEFF JEFF QTH IS CHICAGO IL CHICAGO IL HW? HW? W4JWC DE KK9JEF KN

KK9JEF DE W4JWC QSB QSB SRRY SRRY DE W4JWC K

W4JWC DE KK9JEF YES QSB QSB UR RST 539 539 W4JWC DE KK9JEF KN

KK9JEF DE W4JWC QSB QSB SORRY QSB DE W4JWC K

The key thing to notice in all this is the Q-signal “QSB,” which denotes fading. In addition to dealing with general noise on the bands, both man-made and natural (including static-crashes from lighting), signals can also fade-in and out, just as if someone was playing with the volume knob. One moment the codeis loud and present, the next it just fades into the sonic underbrush. Frustrating, to say the least.

I’m calling this my first HF “encounter” because I don’t think Jerry will have copied any of my information – typically, it seems, an HF contact or “QSO” involves the exchanging of signal reports (RSTs), names, and locations (QTH). Since Jerry didn’t get mine, I don’t think I’ll be in his logbook, and he isn’t officially in mine. But he’ll be remembered here, as the first key from the airwaves to respond.

Hear you, and hopefully talk to you, on the air!

73

Dipole Tuning and an Ugly Balun

So much has happened radio-wise in the past two weeks, and I’ve been quite delinquent in updating the blog. This post won’t even get to Field Day, nor my new transceiver, but I’ve got to start somewhere. So let’s get to it!

Using the MFJ-207 antenna analyzer I picked up at the SMCC Hamfest a couple weeks ago, I’ve now set up tuned, worked with, and taken down a 40m inverted-V four or five times now. Since space around my apartment is limited, I’ve been walking the 15 minutes out to the shores of Lake Michigan. The lakefront has ample trees and open space to erect an antenna without being too much in anyone’s way.

The first day I set up the inverted V was the most exciting, and went something like this. I took my dipole-kit out to the lake, which contains 200′ of thin nylon rope, a dipole center, a couple equal lengths of 18-guage speaker wire (35-ish feet each), two weights filled with rice to throw into trees, and three 8″ pegboard hooks. (The hooks make excellent ground-spikes to tie off the ends of the nylon rope. I picked up a bunch at Menards when they were on sale for 20 cents each.)

The good ole dipole center. No balun here, just wires from the center conductor and shield to either protruding wire.

In addition to the antenna parts, I’ve been taking along a small SLA battery and powerpole adapter, a 25′ bit of RG-58 Coax, a homemade “ugly balun” (see below), the MFJ antenna tuner, a radio, headphones, a pad of paper and a pen. The heaviest parts of the pack by far are the SLA battery and the the two coax items. I’ve also sometimes brought a portable camp chair so I don’t have to sit on damp grass… but lying in the grass in the summertime isn’t bad either.

The view over the lake just after tearing down the antenna for the night. I love the summer.

The process of putting up the antenna is straightforward. I unpack the kit and lay out the parts under a suitable tree. I throw one of the weights with a rope as high over a branch as I can, then tie the dipole center to the loose end of that rope. I lay out the two antenna wires roughly on either side of the center, and attach both wires, the ugly balun, and the coax to the dipole center. Once everything’s attached, I haul on the rope to raise the dipole center up as high as it will go, and tie the working end of the rope around a stake just under the center of the antenna. I walk the wires out as far as they’ll go (each now has maybe 5′ of nylon rope attached to the end), and tie them to stakes as well. The whole process takes between 10 and 15 minutes and is getting faster every time.

The first time I put up the inverted V was enlightening, to say the least. I attached the ends of the antenna wires directly to the ground stakes, and hooked up the MFJ tuner to the other end of the coax. The MFJ207 is essentially just a wideband oscillator with a 50-ohm output, with a built-in SWR meter. You tune across the frequencies of interest (in five separate ranges, see the MFJ 207 Manual for technical details) and read off the SWR on the analog meter. In this case, I was hoping to see a nice dip around 7MHz. Though that’s what the picture below shows, it was quite a process getting there.

The dial frequencies on the analyzer turned out to be fairly accurate, at least as measured with my cheapie Ebay frequency counter. The analyzer has an RCA port on the top next to the BNC specifically for frequency measurement.

The first time I put put the antenna, it showed a clear dip… but a little under 5 MHz! To be sure this wasn’t just an issue with the calibration of the analyzer, I plugged my cheapie Ebay 8-Digit Frequency Counter (“Cymometer”) into the frequency-measurement port on the top of the analyzer. It read 4.87MHz. Dang. My antenna was definitely too long.

As a starting estimate of how much to trim the antenna, I did a quite back-of-the-envelope calculation of how “electrically long” it currently was. Taking the speed of light to be roughly 3 x 10⁸ m/s and dividing by our resonant frequency of 4.87 MHz gives a wavelength of 61.6 meters, which means each quarter-wavelength wire of the dipole is about 15.4 meters long. To work on the 40m ham band (7.0 to 7.3 MHz here in the states), let’s say the antenna wants to be resonant around 7.1MHz. Similar math to the above gives a wavelength of 42.2 meters (surprise!), or about 10.5m per wire. By this math, the wires were about 5m too long.

However, there are many factors that can cause an antenna’s resonant frequency to be lower than it would be in free space, and one of them is proximity to the ground. Not only was the antenna’s center only 6-7 meters feet above ground, but the ends of the antenna were literally touching the ground.  Given these factors (and the fact that while I had cut the wires longer than necessary, I didn’t think they were that much longe), I decided to be conservative in the my trimming. What’s more, I left the ground stakes where they were, and replaced the trimmed sections of wire with nylon rope. In other words, the angle of the inverted V didn’t change as I trimmed the wires, only the length of the wires themselves, and therefore the height of the ends above ground.

One end of the antenna – you can see the orange nylon rope staked into the ground at the upper left and tied to the antenna wire in the lower right.

With an eye toward being conservative with my trimming, and knowing that the math would have me trim 5 meters off the antenna in free space, I instead opted to trim 5 feet off each wire instead. This left each end of the antenna about 2′ off the ground, instead of touching it. After this brief surgery and re-attaching the nylon rope, the MFJ meter proclaimed the antenna resonant at 6.46 MHz. Now that’s better!

Another quick snip of 18″ on each end got the antenna resonant around 6.75 MHz, and another 15″ off yielded resonance at 7.097 MHz. For these measurements, I tuned the analyzer for lowest SWR, then measured the frequency with the frequency counter. In future, it seems like the dial measurements will be good enough for daily use, but for dialing in the antenna the first time, the frequency counter was very helpful.

The lowest on the trimmed antenna was around 7.097 MHz, neatly in the middle of the 40m US amateur band. Success!

To get an idea of the useful bandwidth of the antenna, I also swept the frequency up and down around the resonant point and took some frequency measurements. The antenna had better than 2:1 SWR between 6.922MHZ and 7.282 MHz. Pretty much all of the the 40m band, and certainly the CW portion that I plan to most immediately be working.

All in all, I consider the several outings this week to be great successes. The MFJ is surely worth the $15 I paid for it. I was battling some dodgy coax the first couple times out, which made it hard to take SWR readings without the needle jumping all over the place. A little Amazon order of some RG-58 fixed that. Now, I’ve got a working, tuned, successful antenna.

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One more thought: the so-called “ugly-balun” or air-core choke. Mine is simply 25′ of RG-58 close-wound on 10″ of 1.5″ PVC pipe, secured with zip-ties and duct-tape.

The “ugly balun.” It’s at least kinda pretty…

My understanding of its usefulness is still rough (and there is much information, data, and heated discussion about it), but here’s what I think I know:

When using a dipole without a proper center balun (that is, an actual transformer that forces equal and balanced voltages on the balanced side from a single voltage on the unbalanced side), the dipole essentially becomes a “tripole”, with the outside of the coax shield possibly becoming part of the antenna and carrying RF. I say possibly, because it will vary with the length of coax between the transmitter and antenna feedpoint. This is undesirable, because we’d like the antenna itself to be the radiating/receiving part of the system, and not be depending on the physical arrangement/length of the coax itself.

One solution would be to install a proper balun (sometimes called a voltage balun) at the center of the dipole. This forces the voltages to each leg of the dipole to be equal, thereby eliminating common-mode current on the outside of the coax. However, a choke can also reduce current on the outside of the coax. For this reason, the coke is sometimes called “current balun” or “choke balun,” though strictly speaking it isn’t a balun at all.

Here’s a quote from one of the links above:

A choke is not a balun in any way. It’s given that description, ‘balun’, because it can do something a balun can also do, get rid of unwanted currents (CMCs) on the outside of the coax feed line. It can’t transform from a balanced to unbalanced state.
– ‘Doc

There’s lots of other useful information in that same thread, which I find myself returning too and musing over. It seems, long term, that a ferite balun is really the way to go for choking off stray RF, but in the meantime, adding the air-choke to the antenna feedpoint does seem to help somewhat. I’ll continue throwing it in my pack and experimenting in the meantime.

Hear you on the air!

73

Wind, Antennas, and a First Portable Session

This week I had two radio firsts: trying to put together a halfway decent antenna, and a first portable operating session.

I started by putting together a center insulator a dipole antenna. There are many possible designs online, but I ended up making one with materials I’m familiar with. It’s made of a 1″ PVC cross, four PVC caps, three 1/4″ eye-bolts, some nylon lock-nuts, and panel-mount BNC connector. The whole went together in about half an hour. The PVC connections were surprisingly tight as a press-fit, but they and the eye-bolts are secured with lock-tite and sealed with hot-snot just in case. The BNC connector is soldered internally to a couple pieces of hookup wire, which you can see poking out the sides of the cross. The antenna wires themselves are simply tied to the eye-bolts and wire-nutted to the hookup wire.

The dipole center-support. This picture was taken after the fact, hence the pre-cut Nylon cord wrapped around it. You can see the two copper hookup wires poking out either end.

The dipole center, a 200′ spool of nylon wire, some “stakes” for securing the antenna to the ground (really, 8″ pegboard hooks, on sale at Menards!), some zip-ties, and a couple of rice-filled socks as counterweight all fit handily into this small plastic case I had lying around:

I live only about a mile from Lake Michigan and the beautiful lakefront park space that runs along the East side of Chicago. I figured with the sunny-but-chilly weather we’ve been having this week, the lakeshore on a weekday afternoon would be pleasant to work in and not too packed with people.

I couldn’t find a suitable table or bench close enough to trees to set up under, but then I spotted the convenient height of the sea-wall between the outer lakefront trail and the lake itself. I couldn’t have been any closer to the lake without getting my socks wet!

The operating position. There’s a little ledge just on the other side of this wall that was perfect for standing on.

I strung up a portable, homemade 40m dipole (wires cut in advance) as high as I could could into one of the nearby trees – I only got the center maybe 20 feet in the air, but that’s still better than the 8′ the random wire in my home office is. The ends are tied off to stakes near the ground. This made the setup more of an inverted-V than a true-dipole.

One of the antenna-wires staked off to the ground. You can see the black coax sloping from the tree to the operating position.

The antenna is fed from ~60′ of RG-58, running into a ZM-2 Tuner for matching, and then via a short RG-58 jumped into the Virgin Receiver. I also brought along the ardiuno-controlled, Si5351-VFO I’ve been working on to allow for the ability to change frequencies, as detailed in my last post. If I’m going to spend the time setting up practically in a lake, I thought it would be nice to actually scan the whole band. Since the VFO rig is still on a breadboard, I was quite spread-out over my little stony operating station.

Visible here: the coil of coax coming from the antenna; the Virgin Receiver, open to allow the VFO to interconnect; the breadboard with the Si5351 VFO on it; two separate 12V SLA batteries; some nice comfy headphones; and the large red cable-coiler I used to store the dipole wires (a bit overkill).

So now, the moment of truth – I hooked up the batteries, connected the receiver and VFO, did a quick by-ear tune on the ZM-2. I’ve never done something like this before – would it actually be better than my office random-wire? Was it all just a jaunt in the park? In short, would it work?

LIKE HECK IT WORKED!

Especially up in the SSB portion of the band, there were some stations that might as well have been on the other end of a phone call. (This, by the way, confirms that the Virgin can receive SSB and AM as well as CW.) In no particular order, I heard:

• N8KKR, KA9ZXN and others on the Hams for Christ net on 7.263 (330p Central, Monday-Sat). Not my personal bag, but they seemed a very pleasant bunch.
• W9DCQ and W4LWW having a nice QSO, between the two of them and some other operators I couldn’t quite copy.
• KG9O and KK4FZI having a friendly chat.
• Some other snippets of stations.

The listed stations alone include QTHs in Evergreen Park IL, Columbus OH, Middleton WI, Franklin TN, Grassy Creek NC, and Marion IN. None of them terribly far away in radio terms (the Tennessee locations is farthest at ~500 miles), but a great confirmation that the antenna was clear and working. With a height above the ground of less than 1/4 wavelength, the ideal dipole should have a high takeoff angle and be fairly omnidirectional, and that seems plausible based on results.

In sadder news, I seem to have broken some part of the WSPR functionality of my VFO in consolidating that functionality from two separate programs into one. 1W into the antenna and several repetitions netted be exactly zero receptions, either into this antenna or my office random wire. So it’s back into the code I go. While I’m at it, it would really be worth packaging up the little VFO into its own enclosure – having all those wires flapping about is a bit worrisome for transport!

All in all, a tremendously successful, if very chilly, day by the lake. Now that I know what I’m doing, I suspect it would be able to have the station set up and listening in about 10 minutes, and about the same for tear down. With the days getting warmer all the time, I’m sure I’ll be out there again soon.

Hear you on the air!

73