I still own my first (and only) mobile antenna: a CB antenna by CTE named "Dallas". It has been outside for many years and used seldomly until I dedicated it to my 10m beacon (pictures). One day I measured it with the MFJ antenna analyzer and discovered that it showed an horrible SWR, with a best 2.5:1 at 27.5 MHz. On 28.322 it was above 3:1 and unusable anywhere else!
So I opened it up. It's very easy: unscrew the whip part and slide off the plastic cover of the coil. Surprise surprise: it used a tapped coil of 15+3 turns (also called autotransformer). There is no visual damage to the coil and continuity tests showed zero ohms: no obvious damage to be fixed.
Since I am also looking for a 6m mobile antenna, I thought I might reuse the support for the base loading coil. Let's first try a quick fix for 10/11m: interrupt the tapped coil so that the antenna becomes a base loaded vertical:
A second run on the antenna analyzer made me smile: the resonance now moved to 28.8 MHz with 1.1:1 SWR after the 3m of RG58 coax. The antenna on the balcony fence is usable on the whole 10m band! :-)
What's next: measuring it on the car. Bandwidth might broaden a bit.
This is not really a homebrewing post, but I finally managed to get to use the stuff I built.
During a holiday in Toscana I could spare some 30-minute packs for radio activities. The shack was in the bungalow bedroom, on the bed:
FT-817 on the pillow, with earphones and homebrew CW paddle. Pencil and paper log, mobilephone as a watch. Hanging on the window a homebrew LC-tuner (my version of "ALT") with 5 switchable series inductances (0.5, 1, 2, 4, 8 uH) and 200pF swappable IN-OUT across capacitor.
The radiator was made of 12m of wire held vertical with a 9m fiberglass fishing pole, then 3 random counterpoises were laid on the ground:
This antenna tuned on all bands between 80 and 6 metres, including WARC. I had contacts on 80, 40, 20, 10 and 6, including some 2xQRP on 20 and 40m.
After the first few days I switched to battery power because the old laptop power supply was generating too much RF noise. Power has been 2.5W or less.
The 2600mAh pack gave about 3 hours of CW operations at 2.5W, with a 40/60 TX/RX rate.
Questions? Contact me via mycall at yahoo.com. You should know what "mycall" is...
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