SPECTRUM COMMUNICATIONS

ESTABLISHED OCTOBER 1978.

Partners; Mr A.J. Nailer HNC BA G4CFY, & Mrs J.R. Nailer

12 WEATHERBURY WAY, DORCHESTER, DORSET, DT1 2EF, UK.

Phone 01305 262250, Int 0044 1305 262250.

GAREX TVI FILTERS – 16 December 2011

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Update 20 November

The HPFS filter can be considerably improved by the addition of just one capacitor. All HPFS type filters henceforth will include this addition and will be designated HPF-3.

Update 10 November

The GAREX HPFS filter has been critically examined and the circuit and PC layout have been changed to produce a dramatic improvement in performance. The passband ripple has been reduced, the cut-off point is now sharper and the stopband is better than -60dB DC to 200MHz. It is now designated as HPF-450.

The GAREX HPF2 which was a 3 element high pass T has been converted into a bandpass filter by the addition of a 3 element low pass filter. It will now be more effective in reducing engine management noise interfering with car radios and will now reduce interference to domestic VHF FM reception. It is now designated BPF-100.

A new BANDPASS filter has also been designed using 5 element high and low pass Chebychev filters with a much narrower passband around the VHF FM broadcast band. The skirts are sharper and the lower stopband is now better than -60dB DC to 20MHz and -50dB at 30MHz and even -26dB at 50MHz. The upper stopband is only about -10dB at 144MHz but is better than -40dB from 250-1000MHz. This will be designated BPF-101. Final production PCB and case are not yet finalised.

HIGH PASS FILTERS

HPF-3 (modified HPFS). TVI filter and braid breaker with a passband above 450MHz. An additional capacitor improves the attenuation at 144MHz from -30dB to -46dB. It also reduces an unwanted return at 50MHz & -40dB to the noise floor at -60dB. Rejects signals from DC to 100MHz by 60dB. Passband ripple 450-100MHz 6dB. Price £12 plus £2 P&P. Quantity discount available.

HPF-450 TVI filter with a passband above 450MHz. Rejects signals from DC to 200MHz by 60dB. This includes HF, CB, 6m, 4m, 2m, 70cm, marine, & taxi. Passband ripple 450-100MHz 4dB. Price £15 plus £2 P&P. Quantity discounts available.

HPF-500 (or HPF-6) TVI filter with passband above 500MHz. Rejects signals from DC to 30MHz and from 100 to 200MHz by 60dB. Sharp skirt response falls from cut-off at 500Mhz to notch of -70dB at 420MHz. Seriously reduces interference from 70cm Amateurs and TETRA PMR. Price £25 plus £2 P&P. Quantity discounts available.

BAND PASS FILTER

BPF-100 with a passband of 80-120MHz to accept the VHF broadcast band and reject above and below this range. Particularly useful to reduce interference to car radios from engine management units. Available with car radio connectors or with TV connectors for use with aerial fed domestic broadcast receivers. Price £12 plus £2 P&P.

NOTCH FILTERS

These filters are designed to notch-out one specific band that is causing interference. They are available as NF14, NF21, NF27, NF29, NF51, NF70, NF145, and NF433. Other frequencies are available to order. Price £10 plus £2 P&P.

BRAID BREAKER

BB-1 is an RF transformer to be used on its own or in conjunction with any notch filter. Price £10 plus £2 P&P.

RADAR BLIP FILTER

RBF-1 is a tunable stub to notch out radar pulses from video cassette recorders. It is being evaluated for use on analogue televisions, digi-boxes and digital televisions. Price £10 plus £2 P&P.