How to Operate Pedestrian Mobile

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Joined: Wed Nov 16, 2022 5:27 pm

How to Operate Pedestrian Mobile

Post by w0rw »

How to Operate Pedestrian Mobile

It is really exciting to operate on HF while you are hiking into your favorite back country area.
Operating “Pedestrian Mobile”, which I will call “/pm”, is a very challenging and rewarding activity, especially using QRP. It is difficult to explain "/pm" to hams in foreign countries, so sometimes I tell them that I am operating ‘Back Pack Mobile’ or ‘Walking Mobile’. You won’t have to look for trees to support your antenna anymore; you will look for trails without trees.

Let’s start out with the options of which radio to use. You will probably want to use one you already have. You just need to configure it for trail operation. You will need to find a nice backpack (Like a military ALICE Frame Pack) or shoulder carrying bag (Bergen) that can hold your radio with its battery, an ATU and maybe a keyer. The easier it is to get everything together in one bag, the easier it will be to use and the more you will use it.
A radio that draws low power on receive is essential.
QRP SSB on a short whip is a real challenge in low sun spot minimum years. Soon it will be very easy to work DX on 10 meters with low power, but 20 Watts is really the minimum needed for successful SSB/pm these days on the lower bands.

CW has great advantages (as QRP’ers know). QRP/pm is easy, but you will have to be able to copy CW in your head and start sending CW while walking. This will force you to copy words and not letter by letter.

PSK/pm and RTTY/pm works well but the duty cycle is much higher. The NUE-PSK modem can be used without a computer of keyboard for these nodes.
Good Backpacking Radios
I use the military PRC319 backpack radio. It is set up for /pm right out of the box and can transmit SSB as well as CW. It can put out 5 watts or 50 watts. But at 50 watts CW, the battery won’t last long. It weighs 25 pounds, which is a bit heavy for a backpacking radio, and only operates on fixed frequencies.
I have worked 210 DXCC entities with this radio on a 10 foot whip.
The PRC319 can be seen here:

Another one of my favorites is the Elecraft KX1-4 transceiver. This great little radio will work on 80m, 40m, 30m, and 20m. The KX2 and KX3 are even better and everything is built in.
There are also hams using lots of other radios like the FT817, IC706 and Penntek TR-35 that are popular.
I use a 10 foot whip with a center loading coil. The whip is attached to the back pack frame for backpack radios, or I use my shoulder sling whip mount for shoulder bag radios and hand held radios like the KX1.
The loading coil is usually about 3 or 4 feet above my head. My loading coil is wound on a nylon Fram fuel filter. Whips longer than 10 feet are harder to hike with.
The antenna will also require a counterpoise, which I call a ‘drag wire’. The drag wire length should about 10% less than a quarter wave length. The drag wire should have a break-away connection, like a banana plug. On 14,000 foot mountain tops I always use a shorted quarter wave stub for a drag wire to protect the input of my radio from precipitation static. I never use a drag wire longer than 30 feet, because it gets a little too hard to handle (drag).

The simplicity of tuning with an automatic tuner is a perfect fit for /pm work. The tuning is done once and not retuned unless you walk over different terrain, like snow or salt water. The radio should be connected to the tuner with coax but the whip is connected to the tuner with only a single HV wire. The counterpoise wire goes directly to the tuner ground.

Before you take the rig out for the first time, set your rig up on a wooden step ladder and tune your antenna/drag wire with an antenna analyzer or for maximum on a field strength meter. This will make sure you are getting those few watts out into the ether, and may prevent harm to some of the simpler rigs which need to see 50 ohm impedances.

This is a good opportunity to ditch those heavy SLA’s. Newer LiIon cells provide /pm operators with twice the energy and half the weight of a NiCad pack. I don’t use Li Poly packs because they are a bit harder to handle. I use Sony hard carbon LiIon cells. The new A123 Lithium Iron Phosphate cells are excellent too.

You will probably have to procure a new LiIon charger too. I have been using for my LiIon cells and chargers. BuddiePole also has LiFePo4 battery packs. NiCad’s and NiMH’s are still popular cells, but tend to weigh a bit more for the same amount of portable energy.
As they say in real estate, location is everything. The best places to operate are on mountain tops and ridges. Deep valleys are not good. I have had the opportunity to operate /pm from National Parks, Beaches, inside volcanoes, on the Colorado Trail and the on the Santa Fe Trail. These /pm locations will generally be free of power lines.

There can be dangers to /pm, if you don’t exercise a little care. Possible problems are RF burns to the hand or ear, lightning, joggers, horses, coyotes, bears, etc. I was approached by a bear once as I was working Estonia on 20 meters at midnight with my KX1.

The good news is that all kinds of interesting things can happen to you. Once while I was walking down the street at night, operating on 80 Meter CW, I noticed a house light blinking on and off. It was me! I was tripping some SCR lamp inside the nearby home.

Don’t let older people get near you when you are transmitting until you make sure they don’t
have any implanted medical devices, like a defibrillator or pace maker.
You can check your RF Safety on the RF Safety calculator at
Don’t operate near low power lines or during lightning storms.

See you on the trail.
Paul Signorelli, W0RW/pm
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