A Primer for a Portable PSK Station
PODXS 070 Club Member Rick N7WE suggested that I write up how I set up a portable digital HF station for grid activations, APE stations, POTA and SOTA activations. There are certainly as many ways to this as there are portable operators.
The most important thing is: just do it!
You can plan until the end of time and you will still forget stuff, break things and even fail to get there. But I’ve found that I learn something each time. Here is how I do it:
Above is a road map for the station. However, like any radio station the antenna is the most important thing. I usually use doublets because they are easy to set up, balanced in theory and can be used on a wide variety of bands with less loss than other designs.
Above is how I connect my speaker wire doublet to the tuner/transceiver. I once used a 1:1 balun to go from the coax to the speaker wire thinking that this would reduce the common mode current – or the current running on the outside of the speaker wire. I’ve since learned that a 1:1 current balun does not function that way on a doublet. The only thing to remember is that the feedline element can act as a radiating element on certain bands. The short run of coax to the tuner and the 3 foot coax from the tuner to the rig is usually long enough to keep RF out of the shack, but this is one thing to keep in mind. If things start acting strange, you may need to reduce power or stretch out the coax run.
I construct my doublets to be resonate on a desirable band, usually 40m or 20m. This allows me to bypass the tuner and the loss that the tuner introduces on that band. For all other bands I engage the tuner. I’m partial to manual tuners because they can usually match a much wider range of mismatches than auto tuners and they require no power to operate. The internal tuners in a lot of rigs have only what I would call “touch up” tuners in that are very limited as to what they can match.
To tune I unhook the rig and place my Rig Expert in place of the K3. I tune for the lowest SWR and return the coax to the transceiver. If I find myself switching bands a lot, I put a coax switch between the tuner and the rig, with the analyzer on the B side of the switch.
Speaker wire doublets are really easy to make. Just split the two wires to 1/4 wave of the desired band. Using an antenna analyzer trim the remaining feedline until you get a good match on the target band. Most of the other bands on all the higher frequencies should tune more or less easily.
Detailed description of making a speaker wire doublet to follow. Stay tuned…
I use a 30′ fiberglass mast from Jackite as my main support. I like this mast because it is very robust and, unlike carbon fiber masts, it is electrically inert.
I support the main mast with a heavy duty tripod I use for my job. I always try and flat-top the doublet as much as I can. I carry a bunch of brightly colored paracord that I can launch over tree limbs or attach to two other masts I carry.
I carry two 12 volt battery banks – a Bioenno 40 AH LiPO and the Yeti 1500. Gone are the days when I carefully lugged around two flooded-cell marine batteries. The Yeti 1500 does a really nice job of powering the laptop. Laptop power was always a problem before because the charger for my laptops needed 110v AC. The Yeti has that, but be forewarned: the power inverter is really noisy on HF. It pretty much makes the waterfall unusable. Unless you buy a very expensive inverter this will be an issue and you will need to charge the laptop while you not on the air. The Yeti avoids that by offering a USB C connection at 60 watts. This unit charges fast and lasts for days.
As far as the radio goes, I no longer use an interface. I do use an external sound card – an Asus Xonar U5. This is a high quality sound card that leaves the computer’s system sounds off the waterfall without having to mute them. It is very easy to adjust the Asus for maximum drive with minimal ALC/distortion.
The other thing that you might not consider but is important to me: a super sturdy table and a comfortable chair. REI makes a folding prep table that is really sturdy and has adjustable legs so it can be leveled easily.
The the last thing I carry is a case full of connectors, adapters, fuses, electrical tools, and anything else I can think of. I also have a toolbox with a Fluke multimeter, heat gun, soldering iron, electrical connectors, crimpers, cable ties, toroids, duct and electrical tape, heat-shrink tubing, a wrist rocket, wire, monofilament and 1.5 oz fishing weights. All this stuff is usually overkill but it fits in Whitedog the Tacoma. 😉
I hope that you have found this primer on my portable digital station useful. Much of what I have learned I gleaned from my much smaller Summits-on-the-Air (SOTA) backpack kits. Please feel free to contact me if you have any questions or comments. Portable operating is really fun and has the added benefit of fostering skills that may be very useful in large-scale disasters.
73 Eric KG6MZS
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