Pedestrian mobile HF/VHF backpack

Counterpoise Length

How long is the counterpoise? The overall length including the "pigtail" that is attached to the antenna bracket is the appropriate length for the frequency based on Bonnie KQ6XA's research. Here are some excerpts from the Counterpoise_Radial_Length file provided by the HFPack group.

Counterpoise wire touching Earth

The problem of predicting or computing the length of a resonant wire gets more complex when using dragging counterpoises and very low radials or radial wires laying partly on the ground. Because of proximity to the earth surface, the wire needs to be shorter. Earth (soil) conductivity affects the resonance, so different soil types may require different length counterpoises. Generally, the more conductive the soil, the shorter the counterpoise.

Pedestrian dragging counterpoise length With broadly tunable whips (such as MP-1, mobile whips, etc)

I've found empirically that a pedestrian dragging counterpoise wire can be about 10% to 25% shorter than the standard quarterwave formula predicts, and the whip will usually tune to a fairly good 50ohm match. Insulated wire with low ohmic resistance should be used. For best dragging quality, Teflon or slick PVC-jacketed or oil-resitant multistrand wire is best. For safety while walking with a dragging counterpoise, some sort of slip-connector or an alligator clip should be used so that the connection will break apart if the wire is caught by a rock or vegetation.

KQ6XA's dragging counterpoise length by band

  |BAND| FEET | 
  |----|------| 
  |10m | 7.4ft| 
  |12m | 8.0ft| 
  |15m | 9.9ft| 
  |17m |11.0ft|
  |20m |14.0ft|
  |30m |18.5ft|
  |40m |26.3ft|
  |60m |34.3ft|
  |75m |45.4ft|
  |80m |49.3ft|

Pictures

Backpack

I am using a bass pro big country pack. I picked this backpack for it's external frame, hydration pack and because it fit me! The frame and padding are set up really nice. They do a really good job of letting air circulate around. I was really surprised when I felt a breeze come across my back while wearing it.

Antenna Mounts

I found some great brackets at a truck stop for mounting antennas. They are Barjan 300-306, "GM Models" prior to 1990 Mirror Mount. I did grind down the part of the bracket near to the pack.

One mount is configured with NMO so I have a lot of versatility with it. Using adapters can go to UHF or BNC F. Coax is terminated with BNC.

The other mount is standard 3/8-24 with a quick-detach stud. Connected a detachable counterpoise wire to one of the nuts on the mount.

VHF/UHF Station

I use a Kenwood TH-F6a mated with a Comet SBB-5 dual band antenna. The rig was an easy choice. The main factors were simultaneous dual VFO's, all-MODE recieve and excellent battery life. I can keep one VFO on a local repeater or simplex frequency. The other VFO can be monitoring 18.157.5 USB. So, then I don't drain the HF rig's battery in RX.

The antenna was a tough choice. In the end I went with a Comet SBB-5 because I like the black color with the pack, the height is just right, flexibility is good and I had one on hand. Why do I care about height for this antenna? As you wear the pack it is on the right side. I did this because typically a brush/trees that hang over the trail are lower on the outside. I'm going to see how this works out, but I will be very tempted to get one of the new Comet EX-510B NMO 6/2/440 antennas. It doesn't take much additional antenna on the F6a to really bring up the receive on HF.

HF Station

The Yaesu FT-817 is the rig that I use on the HF/50 side of the house. I use the homebrew vertical for the antenna.

Use the whip only for 6/2M operation ~55 inches.
Whip w/coil for 10m, 12m, 15m, 17m, 20m, 30m & 40M.
With the 9ft whip, 80M
With the 6 Meter whip and all of the coil bypassed the antenna is resonate in 10M band.
With all coil in good to 4.2Mhz.
With 9ft whip, good below 80M.

Antenna Construction

I used 1 1/2" PVC for the coil form. Female Spade QD's for the taps.
16 gauge wire
didn't calculate taps, evenly spaced at 10 turns.
Bottom of coil has 10 turns that are tapped at every turn, use this as "fine tuning" section.
Below fine tuning section is 3 turns.
The coil itself is right at 12". This means that there is a little bit of empty space after the coil then the caps.
Use vertical drill press to make holes for 3/8-24 TPI bolts in the flat end caps. Use lock washer and washer on inside of cap.
End caps were glued on. Then riveted. PVC is a soft material so it is not unusual for the rivets to want to pull through.

Counterpoise

I have a length of 14 gauge wire that has ring connector on one end and a female spade connector on the other. The ring connector is attached to the antenna bracket. The wire is routed down around the outside of the pack to where it terminates in the female spade connector. I then attach a counterpoise wire that has a male spade connector on the end. With this arrangement if the counterpoise gets hung up on something, it disconnects. Otherwise, the wire could pull on you causing you to lose your balance and fall. Not a good thing.

Now, the question becomes where to put the quick disconnect? Because of the way I have my wire routed I opted to put it a couple feet away from the bracket, past the end of the pack. My thought is to put the quick disconnect far enough out that you can easily reach back, grab the wire, pull the connector around in front of you and plug the dragging part back in. Saves you from having to take the pack off or from practicing to be a contortionist.

Also, take a piece of flagging tape and tie it to the part of the dragging counterpoise that is by the quick disconnect. Now when it comes unplugged you'll be able to quickly spot it. Optionally, use a brightly colored wire. But be prepared to have LOTS of people tell you, "you're dragging a wire."

Identification and Patriotism

I've also added a yellow ribbon (HFPack identification) to the VHF/UHF antenna. The yellow ribbon is also a traditional indicator of support for our troops. Thin, ribbed cloth type, melted the ends to keep from fraying.

On my HF antenna I added a US flag to the top. I used a flag that came on a round tube. Cut the top off the tube and again below the flag. Secured to the whip by putting zip-ties in place above and below the flag. HINT: wrap the zip tie twice and through itself to really snug it up! Now the flag waves freely when /PM.

Safety

When in an urban environment the ribbon and flag also serve as added visual attention getters. Especially handy when you're in hilly terrain. I sometimes find myself out during the twilight hours. For those times I have an LED flasher on the back of the pack. I also keep an LED flashlight in one of the pack pockets. Plan your route, follow your route, and make sure someone knows you're route and expected times. Pretty much your standard hiking/backpacking safety rules apply.

Be safe and have fun! 73 -- de Bryan, K0EMT