October’s POTA activation will bring us back to Winslow State Park on the flanks of Mount Kearsarge. This park has a huge picnic area that we have used in the past . I’ve personally talked to the ranger in charge so she knows us and she loves hams! The plan is to meet at the Winslow trail parking area this is at the end of Winslow House road also known as Kearsarge Mountain rd In Warner at 11 am on October 15th . Here is a link to a map detailing the area. In addition the route is well signed from the highway to destination so it’s an easy to follow drive.
You’ll also want to go to the NH State parks website to get a parking pass. Here is a link to The NH State Parks page where you can get that pass. In addition you’ll want to bring a fleece jacket and rain jacket, bug spray, sun block and a picnic lunch if you’d like. Also bring your HT if you have one.We’ll be at a higher altitude so you might like to get a few VHF/UHF contacts as well.
typical POTA setup
This is a POTA mentoring event so we will have multiple stations and antennas setup on different bands with a POTA coach at each one quite similar to a field day setup. If this is your introduction to POTA (Parks on The Air) fear not we can answer your questions and help you get on the air. All that’s needed is a willingness to learn. You don’t even need a ham radio license the coaches can be the control operator so bring an unlicensed friend!
If you have a mobile rig we will be listening to the N1IMO network of repeaters and 146.52 as well for chatting on our way up. If you have a GPS the physical address is 475 Kearsarge Mountain Rd. Wilmot, NH 03287. Make sure your GPS doesn’t try to default to another town. There are multiple towns in the area with Kearsarge Mountain in the name . If you have any questions email me and I can send more detailed instructions. It would be a good idea to email me anyway so we can get an idea of how many people to expect. My email is [email protected].
Recently, I was asked not only how I made out during the Nashua Area Radio Society’s Sep 3, 2023 Club POTA activation from Rollins State Park (K-2676) and Kearsarge Mountain State Forest (K-4918) (it’s a two-fer), but what the gear was that I used. So I decided to “pen” an article with some of the details.
The Box
Jay Francis, KA1PQK and I decided to put my go-box to the test in the field during this activation. It is an unassuming, little old “shack in a box”… although it is a large box… a large dayglow yellow box. So, maybe it isn’t all that little or unassuming after all. But I digress.
My unassuming go-box (the name plate in the center came from HamCrazy.com)
The go-box itself is built around Harbor Freight’s largest protective waterproof ABS case, the Apache 4800. Despite its size, the case lends itself to portability. I literally only need to grab it and my trusty modified Lenovo N23 Chromebook (more on that later) and head out the door. I’ve used this same model Apache case to ship photographic gear all over the country. It works exceptionally well at protecting my gear at roughly 1/2 to 1/3 the cost of a similar Pelican case. I like that, after all, I am a ham.
The go-box contains everything else I will need for an activation in any mode… SSB, CW, or digital. Altogether, the go-box weighs in at around 8 pounds… light enough to easily deploy to most places, but heavy enough that I don’t want to hike with it for a SOTA activation.
The Station
The Radios
The station itself is designed around a Xiegu G90 SDR Transceiver. The G90 is a 20w, all mode, 10-160m SDR radio with some incredible features for such a reasonably priced rig. It has a built-in antenna tuner that will match nearly anything you can throw at it, a (small but useful) waterfall display, DSP noise reduction, etc. The G90 is powered by a Talentcell rechargeable 12V 6000mAh Lithium-ion battery pack. While intended to charge cell phones via it’s 5v USB ports, the Talentcell has a very convenient 12v output port as well, and provides me with up to 2.5 hours of operating at reasonable output power for the radio.
For SSB, I use the stock Xiegu mic that came with the G90. Surprisingly, for a $450 rig, I have received several positive comments on audio quality! For CW, I use a CW Morse paddle. It is small, but hefty enough that it won’t move around the table when I am using it. As the G90 requires additional hardware for digital interfacing, I use a Xiegu CE19 digital interface kit connected to a Raspberry Pi 4b to allow me to operate FT8, RTTY, and other digital modes.
Finally, I have the Xiegu OEM CI-V USB cable that connects the radio to the Pi allowing for rig control and automatic frequency capture in the various software apps that I use. Xiegu radios use the ICOM CI-V protocols for rig control, which makes them (generally) easy to set up and use.
The go-box also contains a QYT dual band mobile FM radio, powered by an external battery. However, we did not use this radio on the activation.
The Antennas
All the RF is forced out of the radio into an MFJ-1899T portable vertical (which also lives in the Apache case when stored). The antenna attaches at the back of the rig to a right-angle connector with a PL259-to-BNC adapter on it. I also have a premeasured and marked counterpoise connected to the G90’s ground point that I deploy to improve the signal.
Jay brought his portable vertical setup as well. It’s an MFJ 2286 portable 7-55MHz antenna on a Husky telescoping tripod. We switched antennas from the 1899T to Jay’s 2286 roughly halfway through the activation. Although I don’t have any empirical data, and my memory is like that of a 130-year-old, I recall that Jay’s vertical worked quite a bit better. No surprise, given that the 1899T is a true compromise antenna. But it does make Q’s.
View of the bottom of the go-box containing the radios and stored antenna.
The Computer
The Pi is powered separately from the radio’s power source by an Iniu 10,000 mAh 5v battery and can run for 6 or so hours on a single charge. As the Pi’s integrated audio hardware is insufficient for use with digital modes, I use an inexpensive Sabrent USB audio dongle which works nicely. For time synchronization, I either manually update the time on the Pi (as was the case on this POTA activation) or use a U-Blox USB GPS dongle connected to the Pi for a GPS time source. I did bring a new solar charger setup with me on this activation, but never deployed it.
The Software
The software on the Pi is a critical part of the entire solution, without which, the whole “shack in a box” concept goes out the window (ask me how I know this). At the base is the Raspberry Pi O/S, which I built from KM4ACK’s awesome Build-a-Pi solution. Although BAP is being replaced by 73 Linux, it is still an excellent quick deployment solution for a Raspberry Pi. The Pi contains a host of software applications that you would find in any shack, as well as some that are specifically EMCOMM related, and some that facilitate portable operation. I’ll go through what we used during the activation and leave the other details for a future article perhaps.
The Pi also has a hot-spot solution that auto starts when no known network is detected. The hot-spot is the real key to the overall shack-in a box solution though… but more on that later. For rig control, FLRig is my go to – it allows FLDigi, WSJT, and my logging program, CQR Log, to have connectivity to the radio. When operating SSB or CW, I simply fire up CQR Log and it starts FLRig, which connects to the radio, and I am off to the races. If I am instead operating digital using WSJT or FLDigi, I need only to tell CQR Log to start either program, and it seamlessly connects and shares QSO data (I say seamlessly now, not so much until I truly figured out how to integrate the software pieces… but that’s for another article too).
View of the top of the go-box case. All of the components are secured to the top by industrial strength Velcro fasteners. Some improvements were made post-activation to control the cables and wires better, and clean things up.
The “Other” Computer
Truly attentive readers may have noticed something missing though… a screen with which to view the Pi desktop. That’s kind of important. This is where the hot-spot feature of the Pi is really handy. It’s also where my Lenovo Chromebook comes into play. Although in reality, the Lenovo is no longer a Chromebook per se, but more of a “Linuxbook”. I removed Chrome from it and installed Debian Linux instead. There are videos on YouTube as to how to do this. It’s a great way to “rehab” an outdated Chromebook that cost $7 on eBay, and Linux is a great choice for portable ops as it is so much more flexible than Windows (in my opinion). I use the Linuxbook to VNC into the Pi and view the desktop. It is a slick solution that I admittedly copied from others. Any device with a VNC software app can be used, provided it can connect to the Pi’s hot-spot network (you do however need to know the password to the hot spot, which I now have written down). This includes Windows systems, iOS devices, Linux devices, Android devices, etc. In a real EMCOMM situation, that level of flexibility is nice.
The decision to include a Pi in the go-box was a simple one for me… having a preconfigured hardware / software solution with all of my apps in a single self-supporting enclosure requiring only a VNC capable device to operate it seemed like a pretty cool idea. So far, barring some experimentation and poor decision making by yours truly, it has proven mostly reliable.
Results
So, how did it do during the activation? We made 23 QSO’s running anywhere from 5 to 20 watts: 21 FT8, and 2 SSB. We contacted hunters all over the country… TX, OK, MS, NC, SC, IL, NH, GA, and even a DX station in England. Several park-goers stopped and talked to us about what we were doing, and we got to explain Ham Radio and POTA to a number of them. While it certainly proved a useable solution for the activation, I am constantly looking at ways to refine it and make it better and more “bullet proof”.
The “fully deployed” box ready for operating.
Here are some links to the various components of the go-box in case you are interested in more details:
With the exception of a 2m handheld and a temporary end-fed half-wave vertical[1] for use on 20m in the IARU CW contest, I have been off the air since July 2020. After assessing the rocky soil in the backyard, I have come to the conclusion that ground radials won’t be gobbled up by the lawn as they were by the St. Augustine Grass in Florida[2]. That’s when I decided to install a compromise antenna – one that does not require radials. Since I am apt to hang half-wave antennas for the top bands, I settled on the Hy-Gain AV-640[3].
The AV-640 is an 8-band antenna that, in addition to the WARC bands, adds 6m. Since I have not operated on the “magic band” for many years, it’s a nice bonus.
The AV-640 arrived from the supplier in a box that was intact, but the first thing on the to-do list was to complete a parts inventory. That task was completed in, maybe, two hours. During that time, the parts, particularly small hardware, were separated into several Ziploc bags for easy identification later.
It turned out that there were a few pieces of stainless hardware and mounting brackets missing, and MFJ, with help from DX Engineering[4], replaced them in record time. Encouraged by the quick replacements, I decided to perform one last check before installing the antenna. Like any good homebrew tinkerer, I decided to open the Matching Network, Figure 1, to see what was inside and to make certain that nothing was broken. My curiosity was rewarded. I found that two wires had broken, thereby, separating them from the printed circuit board. There was also a Ty-Rap normally looped through the circuit board to anchor the toroid cores that had snapped. MFJ gave me the choice of repairing the unit myself which would have required complete disassembly, or a replacement assembly. I chose the latter.
Figure 1. Interior View of the Hy-Gain AV-640 Matching Unit. Please click on the image to enlarge it. A 1:1 current UNUN (right) for common mode rejection is followed by a 9T:20T autotransformer (left) for a turns ratio of 1:2.22. The black and white wires are connected in series. The black wire is the so-called “common winding”, while the white wire is the so-called “series winding”. The circuit board traces can be seen from the top. The matching unit arrived damaged with a black and a white wire detached from the PCB. The points of damage are circled in white. The broken black wire should be soldered to the PCB within the toroid. A Ty-Rap had also snapped. The 1:1 current UNUN is visible to the right.
Under “Theory of Operation” the AV-640 manual describes[5] the matching unit as a “broadband RF transformer” in one sentence and later on as a “4:1 toroidal transformer (voltage balun)”. Since the copper on the backside of the PCB is visible from the top, the wiring could be traced without removing the circuit card from the housing. What I saw was something that was a 1:1 stacked-core current UNUN[6] for common mode rejection followed by a stacked-core autotransformer having a 9:20 turns ratio (in Figure 1, the broken black wire should loop through the toroid and be soldered to the PCB within the core I.D.)
The schematic of the matching unit is shown in Figure 2. The autotransformer has a 9-turn (common) primary and a 11-turn (series) secondary. The black primary (common) winding of 9-turns is in series with the white 11-turn (series) secondary winding to form a 9:20 turn autotransformer. The voltage turns ratio is 1:2.22, whereas, the impedance transformation ratio goes as N2, or 1:4.93. So, the autotransformer transforms 50 ohms to 247 ohms. A shortened radial ground plane, lowers the impedance at the antenna base.
Figure 2. Hy-Gain AV-640 Matching Unit Schematic Diagram. Please click on the figure to enlarge it. A 1:1 current UNUN is followed by an autotransformer. Note that the left end of the UNUN is dotted. The coax shield is wound with the same sense as the center conductor to form a common mode choke. An autotransformer that follows transforms the impedance from 50 ohms to 247-ohms. Note that the left end of the autotransformer is dotted. The black and white windings are wound with the same sense. Point D is connected to point A to place the primary (common) winding in series with the secondary (series) winding. The antenna is placed at DC ground potential by an RF choke that serves to bleed static charge from the antenna. The autotransformer is AC-coupled to the antenna by a high voltage ceramic capacitor. The short (72″ long) ground plane radials, depicted, lower the impedance at the antenna feed point to one that is more easily accommodated by the autotransformer. Please note that the ground return for the autotransformer and ground plane radial combination is brought back to the input connector via the common mode choke coax shield that is wound around the ferrite core. The 247-ohm impedance match at the antenna feed point is a compromise match for the 8 bands. As a practical consideration, a remote antenna tuner should be located as close to the matching unit as is practical to remove standing waves from the transmission line.
We might also take a look at the voltages at the secondary of the autotransformer to see if they are reasonable. At 100W we expect to see 70.7 Vrms (100 Vpeak) under matched conditions at the current UNUN input. If we multiply this by the 1:2.22 voltage turns ratio, we have 157 Vrms (222 Vpeak) at the antenna terminal. These numbers increase somewhat for 1.5 kW to 274 Vrms (387 Vpeak) and 608 Vrms (860 Vpeak), respectively.
It has been shown previously[7] that these numbers may degrade by as much as the square root of the VSWR. Thus, for a VSWR of 3:1, we might expect these numbers to increase by a factor of 1.732, and so on.
The lossy ferrite used in the UNUN and in the autotransformer places limits on the continuous (key-down) operation of this antenna. This subject was discussed in other posts[8][9].
For these reasons, this antenna has been rated for operation on each band within their 2:1 VSWR bandwidths[10].
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