Portable radio in summer: Test of the JPC-7 antenna

Hello, my name is Marco, DD6FM and today I am writing a report about my experiences with the JPC-7 antenna. Finally summer is here and the temperatures are rising. For me as a radio amateur, who prefers portable radio, the most beautiful and important season. Unfortunately, May is windier than average at the moment, which sometimes makes it not so easy to set up my mast somewhere. Today is Monday, fantastic weather and almost no wind. So I take the opportunity to test the antenna. Let's go ... I drive to the vineyards, where I know a nice place to sit and have a bit of a view at the same time.

The great thing is, I'm in a Castle on the Air and I can still activate a little bit, too. The antenna comes in a variety of designs. This one is the dipole version, then it's also available as a vertical radiator, there's then a ground spike with it and a mantle wave barrier, which is a slightly different design. The mast used here, however, must be purchased separately and is not included with the antenna.

Let's take a look at the contents of the carrying case:

  • 1 x Dipole centerpiece with NPT 1/2-inch thread.
  • 2 Mutliband coils
  • 2 dipole arms, consisting of 4 aluminum tubes
  • 2 telescopic rods, stainless steel
  • 2 copper connectors
  • 1:1 balun with PL connector
  • 2 fixing screws
  • Tripod adapter
  • Carrying bag
  • Velcro tape
  • Assembly instructions (EN)

The antenna is a shortened, rigid portable dipole for the bands 40m to 6m for a maximum transmit power of 100 W. When assembled, the dipole has a span of 6.56 m, disassembled it is only about 35 cm transport length with a low weight of 1.8 kg.

The booms on the center section can be mounted in different ways. Either screw them directly left and right into the center section and thus use the antenna as a horizontal dipole or mount it in a V-shape with the two connectors. The bands are then set on the coils, two markings for 20 and 40 m are already present.

It is an advantage to make notes about the coil settings, or I took photos of which tap I have to set the slider. The fine adjustment is then simply done via the telescopic rods. An analyzer is recommended. My experience is that once you have gone through all the bands and written down all the information, the SWR is relatively correct and you can also fine tune it with the SWR meter on the radio. This may save you from having to lug around another device. If one is on the way with the car, this is of course no problem. But since I'm also often portable in the woods, sometimes every gram counts. Today I will set up the antenna classically as a horizontal dipole. With me I have my Yaesu FT-100.

The setup is relatively fast and possible without tools. With some wind it is recommended to brace the mast slightly. I do that quite simply with three ropes, which I put into the ground with the help of pegs. With the small mast I use here, this is sufficient.

The thread on the dipole center section is an NPT 1/2 inch thread. Here you may have to improvise a bit beforehand and build an adapter if you don't have a suitable mast with the appropriate thread.

There is relatively little to explain about the setup, you simply screw on two dipole arms to the left and right of the center section, then comes the coil and then the telescopic antenna. In the following I will give a few explanations of the individual bands, describing the SWR curve.

10m band

Let's start with the 10m band. Here we use only the telescopic antennas left and right of the center section. So neither the coil nor the dipole arms are screwed on. The fine tuning is done by moving the telescopes a little bit together, always left and right in equal parts. I always take the first thick telescope part seen from the end of the coil.

12m band

Here we use now for the first time left and right two dipole arms each and then the telescope antenna. We leave out the coil here as well. We push the first element of the telescope almost completely in here.

15m band

So, now we install the coil. Directly after the two dipolar arms on the left and on the right comes the coil and then the telescope all the way out. We put the coil on the second tap seen from the outside and push in 1 telescope 50%.

40m band

Here we take now the inner red marking of the coil. Again, I had to push in one more element 50%.

Of course, these are all approximate values, everyone has to experiment for himself. But you quickly get the hang of it. You also have to experiment a bit with the antenna height. That also decides a bit about the SWR. All in all, I'm very satisfied with the antenna, I was able to make 67 QSOs in 45 minutes.

For anyone who wants to be portable QRV somewhere in a small space very quickly, this is ideal. Especially for such small short activations near a castle or the like you are quickly on the air.

I hope to hear you at a portable activity. It's a lot of fun and you can achieve really big ranges even with very small outputs. I experience that again and again at my activities, where I am only between 5 and 10 W.

73 de DD6FM - Marco

Many thanks to Marco for the nice report. One more note about the NPT ½" thread in the antenna center section. This is a common thread.

We have the following masts with NPT ½" male thread in our delivery program:

But even if it should not be these professional masts - a broomstick or a painter's pole will do. The thread of 18 mm does not quite fit. But for use on vacation on the farm it is enough.

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