#HOW TO HOMEBREW SWITCH 8.1.0 PORTABLE#

Ideally I suppose you could pake up various 'test loads' with coils, capacitors and resistors and see if they match. I don't know how people test and calibrate ATUs. The VSWR indicator circuit has a small ferrite FT37-43 core, the primary of which is just a single wire passing through the middle.В It is constructed on veroboard. With a larger toroid, it may have been possible to get it all onto one core try a T80 or larger core and aimВ for 60 turns total if you wish to experiment. Because I couldn't fit all of the turns onto one core, a further 30 turns on a smallerВ T50-6 toroid is used to provide additional inductance if needed. Remember that the switch alnso needs to select the 50th turn, and the start of the coil (i.e. Most of the inductor is wound on a T68-6 (yellow) dust iron toroid core. There aren't many components involved, so cunstruction is simple.

with the unused turns shorted out, its behaviour was transformed. Mine did, at 21MHz it took a while to work out why it wouldn't load up on that band. Without that, the unused part can resonate. Make sure that the switch selecting the number of turns on the inductor shorts out the unused turns. There is a 'word of warning' with ATU design. After shopping around, the longest I could get was around 1.2m which you will realise has too small an aperture to be usable on HF (although it worked nicely on 2m, and could be matched on 20m and up). In keeping with the 'Wand' style ATU, I tried it out with a telescopic antenna. Particularly because of the latter, the power is limited to a few watts maximum.ДЄ simple LED indicating VSWR display is also used: the idea is that the LEDs light if reverse power is present, with one LED being more sensitive to allow 'nulling' of reverse power. An 'L match' ATU circuit is used, with a 12 position tapped inductor and 200pF 'polyvaricon' capacitor. The RF input is via an SO239 connector, which connects through a male-to-male adapter straight onto the back of the FT817. The ATU was designed to fit a 9cm x 3.5cm x 3cm diecast box. I liked the 'Wonder Wand' style of ATU, but thought I'd have a go at making my own.

There's no point having a small transceiver if you need to carry lots of kit to use it: so this was designed down to a size.

#HOW TO HOMEBREW SWITCH 8.1.0 PORTABLE#

This is a very simple ATU, designed for portable operation with an FT817.

How to homebrew switch 8.1.0