My lockdown project is a portable VHF/UHF satellite antenna for use with the motor home. The antenna uses plastic conduit for the boom, 8 elements on 70 cm and 5 elements on 2 metres, crossed. It all snaps together using plastic conduit clips and can be assembled and attached to a camera tripod in less than 5 minutes.
The normal split dipoles are fed directly with coax with some ferrite beads slipped on the coax to decouple it. I used a mini VNA and moved the 1st directors slightly for best match. SWR is about 1:1.3 at the band edges. SWR is just under 2:1 at 137.5 MHz with the gain down about 1db from 2m, so it’s probably useful for the weather satellites.
Since it’s for use in the motor home it needed to be versatile and therefore wide band rather than high gain. It has reasonably consistent matching bands and gain across both bands so will be effective for SSB simplex at the bottom of the bands and also the FM repeaters at the top of the bands. The idea is to use the app Look4Sat which includes a compass and elevation function for pointing the antenna. Just point the cellphone in the right direction (hopefully)
The next step is to make a lightweight az/el rotator for it utilising a couple of air conditioning actuators that I have in the junkbox.
Photo’s and words by Ian ZL3OF
Project 1:
I needed a simple portable RF sig generator for use as a crystal calibrator, to get receivers on the exact frequency. The final design uses an AD9833 DDS module, available from AliExpress, combined with an Arduino NANO. The frequency setting uses four linear pots with decade digits on the dials. Amazing frequency range – 1kHz to 9.999MHz! As well as sine, you can also have square or triangle wave output.
Project 2:
Originally I made this plywood case to house a Spontaflex shortwave receiver designed by Sir Douglas Hall. He was a commissioner and governor of some East African countries, and invented many innovative receiver deigns using just 2 or 3 transistors. Due to his African connections I thought it appropriate to add the elephant. The SW receiver became redundant, so I replaced the guts with some RadioTek FM radio modules. It roars again!
Project 3:
A variometer inductance found on the junk table was combined with an old slow motion drive, and enclosed in a clik-clak box for an outdoor installation under my 10 foot vertical rod aerial. A far better solution that switched tapped inductors.
Photos and words by Kelvin ZL3KB
