[UK-CONTEST] Bandpass Filters

[Ian White, G3SEK]

Jim Martin wrote:
>Just getting down to making a set for the SO2R set-up.  The design I have is
>from K4VX dated 1988 using a 3 pole Butterworth BPF.
>Couple of questions, is this still a good design to use or have other
>reproducible designs been published?

QEX, July/Aug 1999: 'Receiver Bandpass Filters having Maximum 
Attenuation in Adjacent Bands', by Ed Wetherhold, W3NQN (who seems to 
have been cranking out good filter designs forever).

These are single-band designs for 160m up to 15m. They use four toroids 
each, and have a flat passband combined with deep rejection notches 
(>60dB) on the next band up and down.

An earlier series of designs (QST, May and June 1998) included one for 
10m, but none of these has the notch feature.

> ( Ideally they would cope with 150w of
>RTTY but I suspect this would put the cost through the roof!)

All these filters are designed for at least 100W, to go between a 
transceiver and the amp or antenna. The QEX article is not specific 
about power, but it does mention "the typical 150W transceiver". Cost 
should be reasonable since they use mostly T94-size toroids and ordinary 
SM caps.

>Regarding suppliers, are there UK companies who will supply Amidon cores and
>other suitable components to the public?

Amidon are actually only a distributor in the USA - the manufacturers 
are Micrometals for the iron-dust toroids and Fair-Rite for the ferrets.

The cores you'd need are T94-2 for 160, T94-6 for 80 and 40, T94-17 for 
20 and T80-17 for 15 - four for each band.

The UK stockists I know of are Sycom (www.sycomcomp.co.uk aka Robin, 
G3NFV), TMP(?) in North Wales, JAB and Hands. However, I don't believe 
any of them stock the full range, and the ones you'd need are a bit 
uncommon.

A few years ago, I got some from one of the US distributors on the web 
who do of course stock the full range (I forget who, but could find 
out). That would probably be the best way to buy them. However, the bill 
for at least 20 toroids will mount up, so be prepared for being hit with 
an extra 30% or more in import charges.


-- 
73 from Ian G3SEK         'In Practice' columnist for RadCom (RSGB)
                            Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek