SPECTRUM COMMUNICATIONS

INVERTED-L AERIAL

These Spectrum Lite Trap Inverted-L Aerials are essentially half a trap dipole with the feedpoint at ground level.   Another way of understanding its operation is as a loaded quarterwave Marconi vertical with the radiating element bent over.

The aerial is fed via coax to a coupling box secured to an earth stake at the far end of the garden. There is then a near vertical section, as high as you choose, and the remainder is near horizontal back towards the house.   Because it is coax fed it is much noisier than the twin fed trap dipole.  To work efficiently it requires a good ground.  Supplied in 2.5²mm or 6²mm PVC covered wire and with the coupling box and U-bolts.

Prices not including packing or postage by Royal Mail.

BALUN 1:1 RATIO, Low Impedance 50R or 95R

This air cored balun is only a slight variation on that of Richard Holman G2DYM and 2 of them back-to-back give a flat response between -1dB points from 1.8-42MHz.  Experiments using toroidal cored designs by well known authors in Rad Com, such as the late Peter Dodd G3LDO, fail to produce anything like such a low loss flat response over such a wide range.  

The screen shot opposite of the back-to-back test has 0dB three divisions down from the top and each vertical division is 10dB.  The horizontal scale is 5MHz per division and you can just see that the response rises up near the white line on the left at about 1/5th of the first division (1MHz) and has dropped again to -2dB at the right of the 6th division across, that is 30MHz.  It continues at -2dB and rolls off again about 1/5th across the 9th division (42MHz).  That is for two Baluns back-to-back.

G2DYM rated the balun at 1kW but I had one fail at less due to thin enamel insulation so I switched to 3 different types of coloured enamel  It looks much nicer too. It might now survive 1kW again but I conservatively rate it at full legal power of 400W on SSB and 200W continuous.  It is to be used in the shack between the end of the 95 Ohm twin feeder and an ATU/RIG. Price £40.00, carriage £5.70

BALUN, 20 METRES OF 95R TWIN FEEDER & CENTREPIECE.

Here is a useful pack to help you make your own dipole or trap dipole. It includes the 1:1 Balun and 20 metres of 95R noise cancelling twin feeder and a centre piece.

Price £66.00 + £6.50 Tracked 24.

SLIM G TX & RX AERIAL. This is ¾ of a wavelength long at the manufactured frequency and achieves a gain of 1.8dBd, which is 12dBd (15 times) better than a 15cm rubber duck. The main element is fabricated using 300 Ohm twin feeder with a matching stub in a watertight housing 4" (10cm) long. There is 4m of coax cable with a choice of BNC, or PL259 connectors. Available for 2m (145MHz), or 4m (70.5MHz), or Air Band (118-137), or Marine Band (156-162MHz).  

This is a portable version of the Slim Jim described by G2BCX in PW April 1978. Actually the aerial described as a J pole is really a misnomer as it really is a squashed letter G, hence the new name.   The 156MHz version is 1.3m long, the 2m version is 1.4m long and the 127.5MHz version 1.6m long, and the 4m version 2.87m long. All fold down to 20cm. Weight is just 250g (9oz).Price for 2m, Airband and Marine Band, £20.00, 4m version £22.50, UK P&P £5.70, Tracked 24.

FLEXIWHIP FOR HANDHELDS   These are made using a nylon tube and are fully waterproof and rugged. Solutions have been developed to allow the aerial to be supplied with a wide variety of plug or socket connectors.  The maximum production length is 50cm, so for frequencies below 140MHz they are made as loaded quarter-wave aerials, and above that frequency they are full quarter wavelengths.

Flexi-whips can be custom manufactured for any frequency in the range 68-418MHz, and the 2m (144MHz)version is normally made and trimmed as a dual band, quarter wave on 144MHz and three quarter wave on 433MHz.

A loaded 4 metre Flexiwhip can be made 50cms long and is -6dB relative to a full length 1/4 wave whip. The loaded 4m Flexiwhip will give 12dB more gain (that's 2 S-points) than a 12.5cm rubber duck. Connector options are BNC plug, SMA plug, SMA socket, TNC plug, PL259.

NOMAD WIDEBAND PORTABLE SCANNER AERIAL 25-500MHz.The aerial element is made from 300 Ohm feeder configured like a Slim Jim, with modified stub matching to give greater operational bandwidth. It is intended to be portable but can be used as a permanent aerial in places where conventional wire aerials cannot be used. The overall length is 1.4metres with a matching stub housing 6" (15cm) long and folds down to just 25cm (10").  It is fitted with 4m of 50 Ohm coax cable with a BNC male connector as standard, but can be supplied with PL259.  For better reception of Air-band, 2m Amateur band or Marine-band use the Slim-G detailed above. Price £25.70 including UK P&P.  

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Version with Mains Adaptor £73.00 incxluding UK P&P.

LONG WIRE PORTABLE AERIAL. This thin wire aerial is ideal for discrete outdoor and indoor use.  It comprises 10m (32ft 10") of PVC covered wire together with a 1.8m length of thicker PVC wire with a crocodile clip to provide an earth. The two wires are joined to a short length of coax cable with a PL259, BNC or SMA connector. Your choice. The main element length has a natural 1/4 wave resonance on 40m (7MHz) so would benefit from the use of the RX SPC ATU to improve reception efficiency over the whole of the HF band.  Price £14.60 including UK P&P.

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