SPECTRUM COMMUNICATIONS

Incorporating G2DYM Aerials & Garex Electronics

Aerials & Cables - 1 January  2017

  Please email or phone for a quote or to place an order by credit/debit card or for a Paypal money request. Purchase of several items is likely to make a saving on postage. Tel 01305 262250

Orders & quote requests to  jean@spectrumcomms.co.uk

Technical queries to  tony@spectrumcomms.co.uk

HOME AMATEUR AERIALS & CABLES TVI FILTERS
COMPONENTS LISTENER RADIO TEST EQUIPMENT CB RADIO BOARDS

        G4CFY Trap dipole HF (RX/TX)                        Slim-G TX & RX Aerial

        Inverted-L HF (RX/TX)                                      Nomad VHF/UHF (RX)

        1kW rated air-cored 1:1 balun                            Active Nomad VHF/UHF (RX)

        Flexi-whips VHF/UHF (RX/TX)                         Compact HF Active Aerial (RX)

        Mobile Whip Aerials VHF/UHF (RX/TX)         Active Wire Aerial (RX)

        Feeder Cable & Patch Leads                             Long Wire portable aerial (RX)

 

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 NEW LITE TRAPS for 10m, 20m, 40m, 60m, & 80m.  

Produced to satisfy the requirement for lighter weight traps.  Probably the lightest traps on the market weighing just 40gm (1.1oz), 51gm (1.5oz), 72gm (2.0oz), and 90gm (2.6oz) respectively.  The new design concept has made it possible to produce the long awaited 80m traps.  The maximum power rating is still to be determined but it might be greater than the epoxy potted traps.

Prices each 10m & 20m 27.50 each, 40m & 60m 30.00 each, P&P 4.50 extra. 80m 32.50 plus 5.00 P&P.

 

SPECTRUM LITE TRAP DIPOLES. These dipoles mark the next evolution from the original W3DZZ trap dipoles.  Since buying the G2DYM business in 2006  I have changed the trap potting compound, then the top wire lengths, then the end insulators and centre piece.  Then developed new multistrand low impedance feeder and now the design and construction of the Lite Traps without potting and with further modified top wire lengths. 

The low impedance twin feeder allows differential mode signals on receive and transmit to travel along the feeder without a measurable emitted electromagnetic field.  On receive identical noise is picked up on both cores giving almost no differential feeder noise at the rig.  It is so quiet using this feeder that at first you might think the aerial system is faulty.   

Supplied with 20m of twin feeder and a choice of 2.52mm or 62mm top wires.  Must be used with a 1:1 balun or balanced ATU in the shack.

Prices below including tracking and insurance.

 

 

 

 

 

 

 

 

An 80/40m Lite Trap Dipole in 6sqmm wire with 20m low Z twin feeder.

TYPE BANDS LENGTH 2.52mm  62mm
LTD40/20m 40 20 15m 52ft 136.25 148.50
LTD40/20/10m 40 20 15 10m 42ft 191.00 200.50
LTD60/40m 60 40 15m 80ft 147.75 169.25
LTD80/40m 80 40 17 15m 103ft 152.60 178.60
LTD80/60m 80 60 17m 112ft 154.50 182.60
LTD80/40/20m 80 40 20 17 15m 87ft  208.00 233.75
LTD80/60/40m 80 60 40 17 15m 101ft 218.50 243.50
LTD160/80m 160 80m 197ft 182.00 226.50
LTD160/80/40m 160 80 40 17 15 10m 170ft 236.00 273.50

 

SPECTRUM LITE INVERTED-L. These 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.

TYPE BANDS LENGTH 2.52mm  62mm 
LIL80/40m 80 40 17 15m 52ft 91.50 94.00
LIL80/40/20m 80 40 20 17 15m 44ft  106.75 116.75
LIL160/80m 160 80 17 10m 99ft  104.00 120.00
LIL160/80/40m 160 80 40 17 15 10m 85ft 121.50 143.75

Prices include tracking and insurance.

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BALUN 1:1 RATIO. 160 - 10 metres, air cored, 1KW rated. Low impedance balanced to unbalanced. For use in the shack in conjunction with 75/100 Ohm twin feeder. Price 40.00, carriage 5.00.

SWITCHED BALUN, 160-10m air cored, 1KW rated.  It includes switching to join the twin feedline wires so the aerial can be tuned against ground as a Marconi T.  This means the 80 to 10m trapped dipole can be loaded up on 160m, and the 40 to 10m trapped dipole can be loaded up on 80m. In some areas where noise level is high, switching the two feeders together to make a Marconi-T reduces the signal to noise ratio making  Ready built 50.00 carriage 5.00.

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SLIM G TX & RX AERIAL. Manufactured for either 156MHz Marine band, or 145MHz 2m (Amateur) or 126MHz (Airband). This was previously called the GAREX JIMP and is essentially  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.   It is of a wavelength long on either 156MHz or 145Mhz or 126MHz and achieves a gain of 1.8dBd, which is 12dBd better than a 15cm rubber duck. The main element is fabricated using 300 Ohm twin feeder with a matching stub in a watertight housing. There is 4m of coax cable with a choice of BNC, or PL259 connectors. The 156MHz version is 1.4m long, the 2m version is 1.5m long and the 126MHz version 1.6m long and all fold down to 25cm. Weight is just 250g (9oz). Price 22.00 UK, 25.00 EU, 28.20 World.  EU & World tracking 5.50 extra.

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RECEIVE-ONLY AERIALS

NOMAD WIDEBAND PORTABLE SCANNER AERIAL 25-1300MHz. 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 receiving twin wire is 1.2m long and the matching unit is 18cm long. It is fitted with 4m of 50 Ohm coax cable with a BNC male connector. When folded up it is 25cm long and weighs just 250g. For better reception of Air-band, 2m Amateur band or Marine-band use the Slim-G detailed above. Price 22.00 UK, 25.00 EU, 28.20 World.  EU & World tracking 5.50 extra.  

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ACTIVE NOMAD WIDEBAND SCANNER AERIAL 25-500MHz. Now with a new MMIC amplifier giving a flat gain of 10dB from HF to UHF. Overall length 1.4m. Ideal for loft or portable use.  Includes 7m (23ft) coax cable.  DC/RF combiner box with provision for 9V PP3 battery, or external 12V supply.  0.6m patch lead with choice of phono, BNC, or PL259 connector for receiver. Price 48.00 UK, 55.00 EU, 59.00 World, including tracking. 

New version with Mains Adaptor 63.50 UK, 73.75 EU, 80.25 World, including tracking.

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COMPACT HF ACTIVE AERIAL, for receiving 500KHz to 30MHz. Ideally suited to permanent installation in marine environments and where other wire aerials would be unacceptable. It comprises a compacted element together with a wideband amplifier in a 420mm waterproof cylindrical housing together with an L mounting bracket and 7m length of coax cable with Belling Lee connector. The amplifier gives 21dB gain flat within 1.5dB from 680kHz to 30MHz.  There is an adapter to provide DC up the coax to the aerial and the RF out via a 1.2m length of coax terminated with BNC or Phono or PL259 connector. Also a red/black power lead to connect between the adapter and a supply of 12/13.5V with a current of up to 20mA. Price 50.00 UK, 58.00 EU, 64.00 World, including tracking.    New version with Active Aerial Mains Adaptor 69.00 UK, 79.00 EU, 85.50 World, including tracking.

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ACTIVE WIRE AERIAL. An active aerial for VLF to 30MHz and ideal for locations where an outdoor aerial is prohibited. The aerial is wire 5 metres long with 4 washers to allow it to be pinned to the wall or ceiling.  It comes with a mains powered wideband amplifier with 15dB gain, flat across the band. Also included is a 1.2m BNC to BNC, or BNC to PL259 patch lead.  Price 48.00 UK, 54.00 EU, 56.50 World including tracking. 

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LONG WIRE PORTABLE AERIAL for receiving 2-30MHz. It comprises 14m (46ft) of PVC covered wire together with a 2m 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 BNC connector.  Price 11.50 UK, 12.25 EU, 14.50 World.  EU & World tracking 5.50 extra.

Optional adapters BNC female to PL259 2.00, BNC female to SMA plug 2.80, BNC female to 3.5mm jack plug 1.50, BNC female to phono plug 1.50.

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ANGLER HF/VHF/UHF AERIAL uses the Long wire portable aerial section 14m long for receiving 100KHz 30MHz connected via a 'trap' to a wire VHF/UHF section 90cm covering 30 1300MHz. The feed end of the VHF/UHF wire is connected together with a 2m earth wire to a short length of coax cable.  The coax cable is terminated usually with a BNC connector but can be PL259 or BNC, your choice.  The earth wire has a crocodile clip to attach to a good earth point. Price 20.50 UK, 21.50 EU, 23.75 World.  EU & World tracking 5.50 extra.

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FLEXI-WHIPS FOR HANDHELDS

Short helical 'rubber duck' aerials are compact and convenient but are poor performers. The reduction of gain is close to the square of the shortening factor.  As an example, a quarter-wave whip for 70MHz should be about 1 metre long and the normal helical is only 12.5cm, the shortening factor is one eighth, so the reduction of gain will be about one sixty-fourth of a full size quarter-wave whip.  In radio terms 1/64 is equivalent to -18dB.

The FLEXI-WHIP on 4 metres can be made 50cms long.  The shortening factor is a half and the gain reduction is a quarter, or -6dB, relative to 1 metre whip.  Therefore the 50cm flexi-whip will provide about 12dB more gain than a 12.5cm helical.

The GAREX FLEXI-WHIPS have a nylon cover 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 shortened 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.

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FLEXI-WHIP. Prices including carriage: Updated 25 August 2016.

Frequency band Length cm UK & EU World
68-88MHz loaded, 4m and PMR 50 24.00 25.75
118-137MHz loaded, airband 48 24.00 25.75
118-137MHz loaded, pilot airband 38 24.00 25.75
144/433MHz unloaded 1/4 & 3/4 wave 50 20.00 21.75
156-162MHz full length, marine band 45 20.00 21.75
300MHz full length, UHF airband 24 20.00 21.75
430-440MHz full length 17 20.00 21.75

Connector types, BNC plug, angle BNC, SMA plug, SMA socket, TNC plug, PL259, angle PL259, F plug, 6mm stud, 1/4" stud.

Note: 6mm stud suits Pye/Phillips PF45 and PFX.  1/4" stud suits MAXON, MOTOROLA & KENWOOD.

Flexi-whip for Wouxon KG699E 4m Handheld, 51cm long and supplied with SMA socket, 24.00.

Flexiwhip for ICOM E90 4m handheld, 51cm long and supplied with SMA plug, 24.00.

2m/70cm dual band Flexi-whip for Wouxon, 49cm long with SMA socket, 20.00.  

MOBILE WHIP AERIALS

2m/70cm DUAL BAND MOBILE WHIP.  This is a centre loaded whip with antiphase coil so the full 46cm length corresponds to 1/4 wave on 144MHz giving 0dBd (2.15dBi) gain.  The antiphase coil allows the top section to be in-phase with the bottom section on 70cm to provide 3dBd (5.15dBi) gain.  Robust and reliable ferrules connect the 17/7PH whips to the antiphase coil and the assembly is solid moulded in nylon.  The aerial is supplied with a hinge adapter, or a 3/8" UNF stud, or even with a PL259 and includes a protective plastic tip.  Price 24.00 including carriage.

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QUARTER WAVE WHIPS.  These are cut from 2.54mm diameter 17/7PH stainless steel to suit any centre frequency in the range 68 to 450MHz.  They are supplied with a hinge adapter, or a 3/8" UNF stud, or even with a PL259 and all include a protective plastic tip. 1/4 wave whips in the range 68-90MHz are two sections which screw together. Priced at 12.50 each including carriage.  1/4 wave whips 90-450MHz are single section and are 10.00 including carriage.

FEEDER CABLE & PATCH LEADS

TWIN FEEDER, 100 Ohm 2kW rated. 24/0.2mm cores individually polyethylene sleeved with an overall sheath of polyethylene. Loss only 0.04dB/m at 10MHz. Priced at 1/metre, postage at cost.  100m drum 92.00 including carriage. Making off to lugs with heatshrink 7.50. Replacement 20m length for full size dipole, with ends made-off 27.50, plus 3.50 P&P.  Replacement 16m length with ends made-off 23.50, plus 3.50 P&P.

COAX CABLES

RG213UBX; 50 Ohm. High quality with 7 strands of 20swg (0.035") plain copper centre core and plain copper braid with estimated 70% coverage.  Solid polyethylene dielectric with a 66% velocity factor.  Outside diameter 10mm.  Suitable for use with RG8 N type plugs and PL259/9.  1.60/metre + P&P at cost.

RG Mini 8; 50 Ohm. High quality with 19 strands of 22swg (0.011") plain copper centre core and plain copper braid with estimated 85% coverage. Low loss foam polyethylene dielectric with a velocity factor of 80%.  Outside diameter 6mm.  Uses plugs with 7mm braid entry, such as PL259/7.  Can be used with BNC plugs and also with RG58 N type if rear nut is drilled out 1/4".  80p/metre + P&P at cost.

RG58C/U; 50 Ohm. High quality with 19/0.18mm (26swg) tinned copper centre core and tinned copper braid with 90% coverage. Solid polyethylene dielectric with a 66% velocity factor. 100pF/metre, outside diameter 4.95mm. 60p/metre + P&P at cost. 100m drum 60 including carriage.

URM76; 50 Ohm. High quality with 7/0.32 plain copper centre core and plain copper braid 87% coverage.  Solid polyethylene dielectric with a 66% velocity factor. 100pF/metre, outside diameter 5.0mm. 65p/metre + P&P. 100m drum 65 including carriage.

RG174A/U; 50 Ohm.  High quality with 7/0.16mm tinned centre core and heavy braided tinned copper screen.  50 Ohm, 98pF/metre, 2.8mm diameter.  75p/metre + P&P at cost. 100m drum 60 including carriage.

PATCH LEADS; RG58C/U 0.6m (2ft) or 1.2m (4ft). 

Phono to phono:  Phono to TV:  Phono to PL259:  0.6m 4.50. 1.2m 5.00.

BNC to phono:  BNC to TV:  0.6m 5.00.  1.2m 5.50.

PL259 to PL259:  PL259 to BNC:  BNC to BNC:  0.6m 5.50.  1.2m 6.00.

Prices include P&P.  For longer lengths add 60p/metre and additional postage at cost.

G4CFY/G2DYM aerial development history

On 30th October 2006 Spectrum Communications acquired G2DYM Aerials.  That business had run for exactly 30 years selling Trap Dipoles mainly to the Amateur Radio fraternity.  Richard Benham-Holman G2DYM the previous owner had just had his 84th birthday and due to failing eyesight so was unable to continue running the business.  

The G2DYM Trap Dipole.  This was based on the W3DZZ trap dipole design using a 7MHz dipole comprising two inner sections of 32 feet each, with 7MHz traps then a further 21 feet 7 inches beyond each trap.  As standard it was supplied with 70 feet of 75 ohm twin feeder.  A 1:1 balun was then used to convert to the unbalanced feed of the transceiver.

The G4CFY Trap Dipole.  Design equations show that the coax traps have a higher L to C ratio than used in the W3DZZ design and need to be used with an inner wire length of 33 feet and an outer wire length of 19 feet 7 inches to resonate in the middle of the UK amateur bands.  This is 2 feet shorter overall than as sold by G2DYM. The trap potting compound and trap frequency accuracy are significantly improved. As standard the full size dipole is now supplied with 20 metres of high quality multistrand 100 Ohm twin feeder, and the half size aerial is supplied with 16 metres of high quality 100 Ohm feeder.  

Chronology

In 25 January 2007 I have found an article from Technical correspondence in QST August 1976 which gave the equations to determine the net inductance loading required for a trap at a defined position on an aerial wire.   These equations were tried for the W3DZZ dipole and gave the correct wire lengths for the middle of the American amateur bands.  A program was then written to calculate top wire lengths and trap inductance and capacitance.

Measurements of the 7MHz coax traps revealed an inductance of 12uH.  The effect of connecting the inner from one end back to the outer at the other end effectively shorts out the inner to outer capacitance at low frequencies.   At 7MHz the isolating effect of the intervening inductance allows the capacitance to total around 42pF.  The equation run for the coax traps and UK amateur bands showed the G2DYM design to have the aerial top wire inners 1 foot too short each, and the outers to be 2 feet too long each.

8 August 2009. The twin core single strand low impedance feeder was liable to fracture at the cable grip on the centre-piece.   It was also difficult to make-off and required time consuming work with sleeves, glue and heatshrink.  No multistrand low impedance twin feeder could be found Worldwide, so I designed my own feeder.  It is made using twin cores of 24/0.2 individually sheathed in polyethylene then with a solid moulded outer sheath of polyethylene.  The solid construction avoids water ingress and it has good flexibility.  When measured it revealed a characteristic impedance of 100 Ohms, which was a bit higher than intended, but still acceptable. 

The close spaced cores ensure virtually no differential noise pick-up.   It is typically 0.5dB per metre quieter than wide spaced feeder and coax.  On transmit the signal in the cores is equal amplitude but opposite in phase and cancels out any emitted field, thereby minimising TVI.  All but one person who has purchased it have been really impressed with its construction and performance. It must be used in conjunction with a 1:1 Balun.  Characteristic impedance 100 Ohms, 2kW power handling, 0.04dB/m loss at 10MHz (much the same as solid dielectric coax), weight 27gm/m. 

5 October 2009. New traps were perfected for 14.15MHz for use with a half size dipole. Top wire lengths were calculated and several aerials were sold using those length.  Results were very encouraging but resonance was slightly higher than desired.  Addition of 4 inches to each inner brought the resonance into the middle of the bands.   The total length is now 54 feet.

26 March 2010.  A new version of the 1:1 Balun is now available. It includes switching to join the twin feedline wires so the aerial can be tuned against ground as a Marconi T. This means the 80 to 10m trapped dipole can now be loaded up on 160m, and the 40 to 10m trapped dipole can be loaded up on 80m. Using an aerial in Marconi-T configuration requires that the twin feeder is well away from support masts and has no long run close to ground. 

20 October 2014. A new design of trap was developed with a lighter tube as well as small and lighter winding.  This was now enclosed in an adhesive heatshrink with low dielectric constant and good heat characteristics.   It is possible that this design will radiate heat from the winding better than the previously epoxy potted trap.   New versions for any frequency are now relatively easy to produce and initially I have produced traps for 28.5MHz, 14.175MHz, 7.1MHz and 3.65MHz.  The new L-C ratio of these traps requires different top wire lengths than previously used and the popular 80m trap dipole now is 104ft 6" which is 1ft 6" shorter than the former version.