PackTenna Mini – SOTA Friendly Antenna

March 22, 2016

Last year I designed the PackTenna portable HF antenna system and showed it off at Dayton.  Nick, N3WG, and I made a bunch of antennas and they all sold out.  We got a lot of feedback from users and it was all very positive.  Given all that, we may make another batch later this year.  In the mean time…  we wanted to make an even smaller, SOTA friendly antenna so we came up with the idea of a “PackTenna Mini”.

20m end-fed version
20 Meter End-Fed Version

The design is a combination wire winder + matching circuit + antenna wire all in one little package you can toss into your backpack.  When I operate in the field, I want something that is quick to set up and quick to put away that is also fairly robust.  The PackTenna Mini fits the bill.

The antenna wire is 26 AWG copper clad steel wire with a great “silky” jacket.  This makes keeps the weight and bulk down while delivering a very strong antenna element.

There are two versions of the “Mini”.  There is a 9:1 UNUN version that is designed for use with radios that have an internal antenna tuner, like the KX3.  This version would use a length of wire that is not resonant on any band.  29′ works well if you need to keep it short.  It also matches up nicely with the PackTenna telescoping mast.  With this type of antenna, the feed point impedance is somewhere in the 500 ~ 1500 ohm range depending on the length of wire and the frequency you are operating on.  The 9:1 transformer brings the impedance down within the tuning range of the radio’s internal tuner.

The second version of the “Mini” uses a matching transformer with a much higher transformation ratio, around 50:1.  This is ideal for an end-fed half wave antenna.  Sorta like the trailing wire antennas used in the old air ships but our version is fed with 50 ohm coax.

zeppelin

The feedpoint impedance of an end-fed half wave is up in the 3000 ~ 5000 ohm range so the matching transformer needs to have a high ratio to bring it down much closer to 50 ohms.  With the end-fed half wave version of the “Mini” and about 31′ of wire, we can get a 1.2:1 or better SWR on 20 meters without a tuner !  It is also fairly broadband since it’s a full size antenna.  You can make it work on any band with the right length of antenna wire.

Here is a picture of the first prototype of the Mini configured as a half wave end-fed feed point.  You can see that in this case the antenna was a perfect match at 14.208 MHz.  You can move the resonant point of the antenna just by adding or snipping off a few inches of wire but it’s less than 1.7:1 across the whole band.

miniproto    mfjtuner

My favorite bands to operate while portable are 20m and 40m.  So I added a loading coil to the end of the wire and was able to get it to work on both bands.  I used a 3″ piece of 1″ diameter PVC and about 50 turns of 26 AWG magnet wire.  In addition to the coil, you have to add another 5 or 6 feet of wire off the end.  This makes the antenna less than 40 feet long and works on both 20 and 40.  I still need to figure out the optimum lengths but the initial experiments worked well.

coilside    coilend

The winder is made from 2mm thick FR4 PCB material.  The board is in a “figure 8” shape to allow you to wind the antenna wire on either side.  Little holes give you a convenient place to lace the end of the wire through to keep it from unraveling when you are all packed up.  There are multiple holes for paracord or bungee cord if you want to mount it to something.  You can also connect a wire element to the top banana jack and use the S-clip as a strain relief or to one of the bottom banana jacks for a ground radial or counterpoise.

ptminivert    ptradial

At the end of the wire element, there is a plastic “S-clip”.  This is a super useful gadget because you can thread the antenna wire through a few holes providing a secure connection to the clip and it makes it really easy to trim the antenna length to the perfect length.  I have used these clips for many things including guy line tensioners.  They are a real multi-tasker.

sclip     sclipside

It was a lot of fun designing the Mini and we will bring some to Dayton this year.  I will be giving a talk on portable HF antennas and the design of the PackTenna Mini on Saturday at 2:15 PM.  If you are at Dayton, stop by and say hello !

No Comments

Comments are closed.