CAR ANTENNA -- GP 144 Mhz -- * * * * I K 4 D C S * * * *

GP CAR ANTENNA FOR 144 Mhz

 
Yes, I tried another!
After many and fruitful experiments carried out on various HF bands with antennas linear load, I wanted to try what effect it could have
144 Mhz band.
Of course, nothing in particular: a simple car antenna to 1 / 4 wave.
Already an antenna for this band and 'short, but with the linear load shorten a little ', just 30%.
The calculations are always the same, already seen at the antenna dipole for 30/40 meters appeared in CQ of November 98, and commissioning work is simple.
We assume that we have already done the calculations for the band interests us and that they gave us as a result physically long antenna 36 cm!
We will divide the measure into two parts, which will be physically two sections vertically, and measure the value we add linear load.

The antenna consists of a single elongated rod of iron diam. 4 mm threaded. I used the threaded rod for so doing are able to use the same support that I had for the magnetic base with the attack of the antenna to 1/4 wave piercing and threading head of a bolt diam.6. mm.
Let's recap: So, our rod will be long total cm. be folded cm. 18 to form our loads, which will the measures contained in the plan, ensuring that the top antenna appears to be the remaining 18 cm.
> To fold the linear load, I used the system builders when they have to prepare the frames for the cast in concrete.

Let me explain: knowing what we fold the load, not is nothing but plant 2 nails on a plank of wood to size needed and continue to work while paying attention to the millimeter.
All tests of the prototype were made on a piece of wire diam.3 mm iron, and malleable and easy to work, and for calibration of that I used a mammoth electric into which I have scroll a tip to find the resonance in the band wanted.
I should point out, however, that as with antennas on HF, even here I had the same result: the calculations made and implemented, the antenna already sounded to 143,800 Mhz, so nearly band.
By adjusting the antenna base for connection to your support, whether it is magnetic or is fixed on the hood of the car, remember that the same will be part of the total length of the antenna.
Maybe you find the antenna resonant at 142 MHz, but there problem: just shorten the tip of 2 (two) mm at a time until
you onto the desired band.

The shape of this antenna will seem ridiculous, but I assure you that comparison of a 1/4 classic has a yield of about more half S point,
both in reception and transmission.
I know for a fact that surely the antennas work great commercial better and are also dual band, maybe shorter, with greater yields but
since we are being tested HOME MADE, comparison antennas mentioned above, a positive difference in my have it: it costs just 20 minutes of work and 2 €. of rod, if you already have a recovery support thrown in some corner of your cellar.
The robustness of the stylus will be in proportion to its diameter, so you see use of unobtrusive measures, but workers who can not bend
in the presence of speed exceeding 130 kilometers per hour (for both was test my antenna).
As regards the bandwidth, then you will be amazed.
The instrumentation used for the development of the antenna was a grid-dip meter of the MFJ. This is all !