I mentioned in my Field Day post from a few weeks ago that I was hoping to get out to a Parks on the Air activation soon, and this past Saturday, I made it happen!
Parks on the Air is an international program inspired by the ARRL’s 2016 National Parks on the Air event. While that program ended at the beginning of 2017, a group of invested amateurs set about booting up an independent, ongoing program in the style of Summits on the Air, Islands on the Air, World Wide Flora and Fauna, etc. The program engages two (overlapping) sets of radio operators: ‘Activators’ who set up portable, temporary operations in state and national parks and wildlands, and ‘Hunters’ who seek them out on the air from more permanent setups. Of course, you can make ‘park to park’ contacts and be a hunter and an activator at the same time.
The draw of this for me is, as I alluded to in the Field Day post – I love the energy of being in the middle of a pile-up. Even if these contacts have a more lighthearted and friendly feel than a rapid fire contest, being a desirable contact on the air is a really jam.
After attending the South Milwaukee Amateur Radio Club’s swapmeet in the morning, I headed back south to Volo Bog State Natural Area, a wilderness preserve in Northern Illinois.
The park surrounds a large natural mashland, with many miles of a loop hiking path, scenic overlooks and, importantly for radio operations, a picnic area. I did some scouting on Google Maps ahead of time, and guessed that the picnic tables would be far enough apart that I could find a quiet corner to operate in.
And indeed, apart from a few hikers and what looked like a field-trip just departing, the park was pretty quiet. I found a nice picnic table in the shade next to the marsh to set myself up.
My setup for the day was somewhat more powerful than my Field day setup, including:
A Yaesu FT-891 running ~70W SSB on 20m and 15m, with the included microphone.
A little powerpole Power Analyzer to track power usage from the battery
My classic Hamkey iambic paddle on its little plastic base
A paper logbook
Oh what fun was had! I made 98 QSOs in roughly two hours of operating – all but 4 of which were on 20m, the last few on 15m. The bands were all over the place. I had wild swings of propagation into the eastern seaboard and the Southeast; at one point, I had five consecutive contacts from the same corner of Northwest Georgia. But I also reached some ears out in the Southwest, and even a handful of stations out in Oregon and Washington. I also made 8 (I believe) Park to Park contacts with other operators out the in wild.
All in all, a tremendous day of fun and excitement, and I’m looking forward to getting back on the air in a park soon.
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.
Chicago weather had other plans.
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.
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:
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
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…
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.
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.
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 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!
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.
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!
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.
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.
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!
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 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.
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.
Having put up a basic wire antenna last week, I thought I might as well give it a spin over the weekend to see how well it might receive on the various bands I have access to. This being the weekend of the California QSO party, I figured there would be lots of big signals on the air to try to hear.
Much like when I first put the QST-49er on the air, I had much higher expectations for reception that for anybody else hearing me, but I was to be proved wrong. Using the ATS-4, my power output is about 3W on 80m, 40m, 30m, and 20m, and about 2W on 15m. I figured I would find the strongest calling stations that I could and use them as a gauge of where I was receive in signals from.
Much to my delight, the CW portions of both the 20m and 15m bands seemed to be filled with California stations calling “CQ CQP” (California QSO Party). Some of them S7, a couple over S9 even with my simple antenna. With no AGC, some signals were strong enough as to require me taking the earbuds partially out of my ears. With propagation and the antenna seeming to cooperate, I quickly looked up with CQP exchange (serial number and state) and responded to some of the CQs.
And do you know what? Not one, not two, but twenty-four different stations came back to my little QRP signal. Twenty Four! In the span of a Saturday afternoon (and one more Sunday morning) I increased my lifetime QSO count by almost %500, including my first 15m contact (K6LRN), my first 20m contact, and my first CA contact (both N6CK in Poway, CA). Here’s a map of as many contacts as I could grab Lat/Long data for, all up and down California:
One of Eric Guth’s guests on the QSO Today podcast (and I can’t for the life of me find who) expressed that the joy of radio sport for him was that he got a little spark of joy every time he made a new contact, and that contesting gave him that feeling hundreds of times in a row. While I didn’t hit hundreds of times, I certainly felt the rush of making contest contacts, fighting to be heard with other stations, the victorious feeling of finally being heard, the reward of persistence…. I could get into this radio sport thing.
If that’s going to be an area of interest, I’ll need to practice a little more on my reception speed, especially when it comes to numbers. For this contest, I would often listen to the California station go through two or three other contacts to try to pick out the serial number he was on and his county before I’d make a call myself. My receive speed just isn’t high enough to go into a contact from scratch. But I’m grateful to all the ops who were willing to slow down and repeat themselves when asked. It made me feel very welcome as a new op.
In any case, my claimed score for this one was 1224 points, distributed like so:
I suspect my actual score will be much less than that. I know I botched a couple numbers early on, and even gave out the wrong number once (oh the shame). But even if I only get one point in the log, that’s good enough for a first time out.
Sometimes the simplest of radio work pay the biggest dividends. Last week, after a few weeks of hemming and hawing about it, I finally committed to putting up a longer wire antenna that allowed the possibility of using multiple bands. The 40m dipole I put up at the end of August has proved to be fine as a receiving antenna, but it suffers two key limitations. First, it’s obviously a single-band antenna (though I may try it on 15m as well). And second, situated as it is between two apartment buildings, I think I’m wasting most of my energy heating up the bricks rather than propogating energy out into the world. It’s also only ~10′ off the ground.
The new antenna helps with all of these issues. It’s simply a ~58′ piece of 22-gauge speaker wire strung from the office window out to a tree that sits in the apartment’s back yard.at its highest, the wire is maybe 20 feet up. While it’s a little visible in the alley if you’re looking for it, it blends in with the surrounding tan brick enough that I don’t think it’ll be noticed. I dropped a ~16′ piece of the same wire out the window to act as a counterpoise.
No, I swear, there’s an antenna running right through the center of this picture.
Like any random-wire, this one needs a tuner to be useful. I first tried using the ZM-2 tuner I got last Christmas. I sadly think I have a short in one of the variable caps in that tuner, which makes it non-functional for now. The MFJ-949e tuner did the trick though – I attached the long wire directly to the “WIRE” banana jack on the back, and the counterpoise to the grounding lug. The antenna tunes up better than 1.2:1 on 80m, 40m, 30m, 20m, and 15m. Which doesn’t necessarily mean it’s an efficient antenna, just that it won’t unduly stress my transmitters.
When I tuned the antenna the first time, I made myself a cheat sheet of the capacitor and inductor settings that gave me the lowest SWR on each band. I then taped this cheat sheet to the top of the tuner. This gives me a place to start when I need to retune for a particular band.
The same evening that I put the antenna up, I did a tune-through of the CW portions of 15m, 20m, 30m, and 80m. It’s really the first time I’ve been able to hear anything on a band beside 40m, so I figured a little exploration was due. I came across an S7 signal at 3.545 MHz calling CQ, and just for grins, I gave him a call. And he came back to me! Arthur, N8ART in Columbus Ohio, running an older rig into a dipole, if my copy was right.
Columbus is a little under 300m from my QTH in Chicago, so this was probably a single-hop contact, or really NVIS. But it represents my first contact outside of 40m, which is terribly exiting! The new antenna is already proving its worth.
This was also my first contact with a new transceiver, an ATS-4 which I snagged as a “tech-special” (i.e. broken) from qth.com and repaired. That process deserves its own write-up. I’m also using a second-hand Ham Key I picked up at Radio Expo 2016 in Belvidiere, an event that also deserves its own post. But really, I’m just too excited about the contact on a new band to try to keep these posts strictly sequential.
Up to this point, if I wanted to get on the air, I had three antenna options:
Walk 20 minutes to the lake, spend 15 minutes getting a 40m inverted-V set up in a tree, and hope I didn’t forget anything. This has been netting me good results, but is a bit cumbersome.
Set up the PHF40 loaded-dipole antenna on a tripod in the backyard. Also a bit cumbersome, and I’ve not had any success making a contact on that antenna yet. I suspect the efficiency is quite a bit down from a full size antenna.
Try the random-wire I’ve got strung up around the office.
While it certainly doesn’t feel like it in the August heat, winter is surely coming. In order to ensure I won’t have a long operating hiatus once the snow hits and going outside is impossible, this week I set about putting up a 40m dipole in an inconspicuous place.
I won’t share exactly where the antenna is mounted, but suffice to say all parts of the antenna are about 12ft off the ground – much more of a skywarmer than a DX antenna, I should think. I tuned this antenna the same way I did with my inverted-V, using just the MFJ-207 and a pair of snips.The antenna ended up being 31’6″ along each leg.
The final antenna is resonant around 7.075 Mhz with an SWR of 1.2:1 at that frequency, with a 2:1 SWR bandwidth of 6.9-7.240 Mhz.
Currently, the feedline is just a piece of RG-58 sneaking in through a window into the apartment. Interestingly, the SWR at resonance shoots up to 2:1 if I bring the metal window-frame down to within about an inch of it. I should note that I’m not using a balun with this dipole, just the usual center-conductor-to-one-wire, shield-to-the-other setup, so it doesn’t surprise me that the coax is coupling to the window. I’ll need to set up some kind of non-metallic passthrough to block airflow with maintaining the antenna characteristics.
After a couple evenings of listening, all signs point to this being a workable antenna! The map below shows the stations that I’ve heard (not contacted) in the past couple evenings. The station in red is one that I was able to contact, but we were fighting QSB and couldn’t really complete the QSO.
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.
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.)
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 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 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.
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.
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.
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.
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.
Today, I received a package in the mail from a fellow ham who was getting rid of some gear. Specifically, he’d put together most of the parts to put an Arduino-controlled VFO on one of the cheapie Chinese Forty-9er kits, like Farrukh Zia did in a QST earlier this year (his kit is available online.) The package I received had the Zia board, an Arduino Nano, an AD9850 DDS module, a rotary encoder, and the Forty-9er kit itself, already assembled. I do want to someone assemble the kit as described in QST, but for the moment, what I’d really like to make is an antenna analyzer.
The scope of what constitutes an “antenna analyzer” is wide – from my rinky dink setup at the bottom end to 4-figure solutions at the high end. Really, what I’ve put together is andirectional coupler with 50-ohm terminations. The fancier analyzers will tell you not only the actual impedance of the antenna (or anything else on the output port), but also the magnitude (and in some cases the sign) of the reactive component of the impedance. Neat stuff! For my purposes, a simple Arduino-driven device that measures relative SWR will be good enough for my purposes. (Dan, KB6NU, has a helpful write-up of some of the mid-range options.)
I’ve been looking at K6BEZ’s plans for an Arduino-based analyzer for a long time – really, the key piece I thought I was missing was the AD9850 – and this seemed like a good time to give it a try.
I had an SWR Bridge Kit from KitsAndParts lying around, and I thought this would be a good time to put it to good use. The kit is simple directional coupler, with a couple diodes and capacitors in each line to hold a peak DC level. The coupler is meant to drive a pair analog meter movements.
To adapt this coupler for use, I first simply attached each output to the Arduino’s analog inputs. This went quite poorly – the charge building up on the capacitors on each side of the coupler has no where to go, and so rather than giving an instantaneous peak voltage, the analog readings just kept creeping up and up. A 68K resistor from each output to ground (facilitated by a small breadboard) solved that issue.
The main issue now is one of scale. The AD9850 Module itself puts out a little less than a milliWatt at most, deceasing with higher frequency outputs. The K2ZIA module has a little two-transistor cascade amplifier to help compensate for this, but that only pumps the output up to 14 or 15 dBm at 1 MHz, with decreasing returns at higher frequencies. Given that the directional coupler has a “single turn” (1 wire) pickup through the center of each toroid, and each toroid has 12 turns, we can surmise that less than 1% of the energy going into the coupler is being diverted to measurement functions. with the rest passing through to the antenna.
This low amount of coupling would normally be desirable, but this time, that means -5 dBm presented to the FWD measurement port, which just isn’t enough power to overcome the forward voltage of 1n5711 diodes in the coupler. (I measured mine to have a voltage drop of 0.323V. That’s which a $50 multimeter, so take it with a grain of salt, but that’s the order of magnitude.)
To temporarily overcome this, I hooked up my little BS170 board from the Si5351-Amplifier to the output of the K2ZIA board’s amplifier, which gives me about 4W output at 1 MHz (and decreasing above that). This gave me enough power to test the coupler (and the K6BEZ software), and both seem to be working fine. I’d like not to build another 5W amplifier just to use as an antenna analyzer, though, so once a shipment of 1n5711’s arrives from eBay, I’m thinking of just replicating K6BEZ’s detector circuit, using a resistive bridge and op-amps.