My New Pedestrian Portable Backpack

Since my last article about the heat sink modification on my Icom IC-706 MKII, I have found the ideal use for the radio: backpack pedestrian mobile. This article will describe how I found the ideal backpack. How I made some additions to the backpack. How I mounted the radio, tuner, battery and antenna mount on the backpack. And finally how it worked when I strapped it on.

But to quickly recap the other article, the IC-706 had tendency to heat up and I wanted to do two things. I wanted to carry the radio in a portable pack and I wanted to eliminate the heat that had already killed it once. The other article told how I made the mod and now I will tell what that did for me.

The new heat sinks keep the radio case cool and I will assume the internal parts are just as cool. The backpack case that was designed for that radio still left me concerned about trapping heat in the radio so I continued to look for an appropriate pack and one that was cheap too. If I was going to fool around not knowing if it would work, I wanted to do it as inexpensively as I could. I started looking for a suitable candidate for a backpack mobile. After visits to different stores, i.e., Wal-Mart, Sports Authority, and others, I again went into Sports Authority to buy another product. I walked by the rack of backpacks and saw a metal-framed backpack on sale for a paltry $9. It was a junior model but looked like it had possibilities and the cost? Heck, maybe I lose that much hitting the slots in a year. So I splurged and took the thing home.

The pack fit okay and since I have expanded in places that I really don't like, I needed a way to keep the straps from slipping of my shoulders. I riveted a buckle strap across the front to keep the straps together and tried it on. It fit!! It was shorter than I would expect one to use when using it for the intended purpose but since I wasn't going to do that, it fit MY purpose perfectly. Now to find the parts I needed to make it a pedestrian mobile backpack.

The pack's metal frame has a small amount of shaping on the sides and across the back. I bought a piece of gray PVC and some bolts and nylon retainer nuts and set to work mounting an antenna mast on the pack. The PVC is 3/4" and was bent to follow the lines of the pack and bolted to the side using the nylon retainer nuts to keep it tight. I allowed the PVC to extend above my head about a foot so the antenna mount would be overhead and the dragging wire would clear me too.

I decided to try winding my own antennas. I bought a few bicycle flagpoles and tried winding double antenna lengths of wires on them. They worked after a fashion but not well. Without a tuner they were in a frequency that was well between the bands for amateur use at approximately 47 MHz. They would tune to any band I wanted but didn't seem to hear well. I built a short support mast for testing and tried to range test them. I used my mobile Hustler antenna as a comparison. I transmitted on the Hustler and set the field strength meter to maximum. I tried the home brew antenna that now named the "Red Top Antenna" just for a name in case they worked. They did, but not very well. I went back to trying different gages of wire, different lengths of wire and different tapers of windings. I tried the wire wraps in single and double wraps and the results remained dismal. The field strength tests showed they were well below even the mobile antenna. Even worse was the ability to hear. It COULDN'T!! I found a strong signal from a W6 station on the mobile antenna and switched to the Red Top antenna and the signal almost disappeared. -- So much for that idea, back to the idea room.

A few months back I read a story from another ham about using and tuning a dipole adapter with two hamsticks. I already had a full set of the regular hamstick type antennas. But I didn't like the idea of dragging wire. That was the next thing to work on. I used a small propane torch to heat the PVC and bend it in a small "S" shape to hold the antennas away from the backpack and my body. I figured on using the hamstick type of antennas and wanted to be sure they weren't going to hit me or the ground I walked on. Viola! What if I used the regular length antenna on one side of the adapter and the shorter one on the other side of the adapter and turned the setup vertical? NO dragging wire. A circular pattern and a 1:1 setup without a tuner. And they would work independent of a ground. The upper antenna would not be very high since the adapter would not need to be high since the shorter antenna was pointing down. I bought an adapter. Mounted it on the PVC and then tuned each antenna alone. They tuned to 1:1 and then when I mounted them both together, they stayed near that as well. I was happy to see that. I mounted the adapter vertically and tested the setup on 17 meters and 20 meters. It heard well enough that I heard a VP5 station on 17 meters the very first time I hooked everything up. The transmit was good and the hearing was EXCELLENT! I felt good again. That hurdle was cleared and now for the rest.

The IC-706 mobile mount was mounted inside the backpack near the top so the IC-706 would mount sideways and allow for airspace around it to help keep it cool. I also made wing nut screws for the mounting so I wouldn't need to carry a screwdriver to remove and mount the radio. I only used two screws in the upper side of the mounting since the bottom would be resting on the side of the mount and the upper screws would hold it securely. It also allowed room in the pack for some air to circulate and keep the radio from overheating. Now I am happy I used a low profile set of heatsinks on the radio.

I bought a LDG auto tuner with the internal batteries and placed that inside the pocket in the back of the pack. I cut into the rear of that pocket to allow the coax and tuner control cables to get to the radio. The coax cable to the antenna was fed into the larger pocket and then up the side of the mast to the dipole adapter. The coax cable from the IC-706 only needed to be about a foot long and was fed to the tuner. The tuner control cable was fed through the same hole as the coax cables and allowed me to tune the antenna from the remote head of the radio.

I have three 12VDC 7AHr batteries that I keep charged for the backpack use. I just place one in the bottom of the backpack and then use a PowerPole connector to allow me to connect and disconnect them quickly for charging. The batteries each weigh about six pounds so it doubles the weight of the backpack when a battery is placed in the bottom of the main pocket in the pack.

I found a small camera case with a shoulder strap and a hook and loop fastener that I could fit the IC-706 remote head into for carrying. The camera case can be attached to the cross strap I added to the backpack shoulder strap or I can carry it over my shoulder. Once I find a frequency to use, the remote head can lock the frequency and the camera case affords protection against knocks and bumps when walking with the backpack.

I didn't want to have the radio speaker on for the world to hear as I walked and I didn't want to carry a separate microphone and earphones. I bought a Heil single earphone headset called the Traveler with a microphone and that seemed to do well. I still had the radio speaker on and had to plug out the earphone jack so the speaker would be off. I made a 5-ohm resistered plug and that took care of the speaker when I used the headset. Now I can listen to the radio, control the frequency change without having to carry the remote head and talk using the PTT switch on the headset.

The only thing I that I wanted was some stiffer support for the backpack itself. The backpack material sagged into the radio from the weight of the battery and the tuner. It also limited the amount of airflow around the radio. I found some heavy wire clothes hangers and cut and fit until I got the stiffness in the pack I wanted and that allowed for more air space around the radio. I slid the heavy wire through the upper band of the backpack and put a frame in the inside of the pack and that gave the pack the stiffness that allowed room around the radio and battery. The whole thing with everything weighs about 20 pounds and being on a backpack for support, it isn't too bad to carry.

The ability to walk and talk to anyone anywhere in the world is intriguing. The fact that so many other hams are doing the same thing using commercially sold radios and military surplus radios says much for the future of ham radio. With the current tendencies for homeowners associations to limit the use of any radios and prohibiting the placement of outside antenna, this mode of hamming offers an exciting way to work the world and gain a sense of accomplishment in doing so. The field of hamming using pedestrian mobile has opened many new avenues for hams to get on the air. Look at these sites online: http://groups.yahoo.com/groups : HF Pack, MilPack and QMac-Users for more information.

After almost 40 years of hamming and just when I've thought there isn't much new to experience, along comes backpack mobiling. Try it. It will surprise you and maybe walking will be good for you.

Since I wrote this article for the World Radio magazine, I have purchased an Icom IC-703 and reinstalled the IC-706MkII in my vehicle. Now the battery will give me longer time to operate portable and I no longer need a separate tuner for the antenna since the IC-703 has the built-in tuner. I continue to use the Icom line of little portables with much success.

73,
Frank
KL7IPV

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