Update

The G4CFY Trap Dipoles have been re-priced to take account of the work time required to make off the wire and feeder ends.  As a result the top wires are now cheaper and the feeder dearer.  Overall an aerial with feeder will cost the same.

The new Poundbury 70MHz Front End unit is now available and will feature in the June issue PW, on sale 10 May 2007. It works together with the Poundbury Main Board, the Portland VFO, and the Mixer-VFO to make a complete 70MHz SSB transceiver with 250mW output.  It can also be used with the TA4S3 amplifier to bring the output up to 25W.

The Link Receiver and Transmitter have now been post designed in accordance with the the requirements of ETSI EN 300 454-2 Part 2 Harmonized standard under article 3.2 of the R&TTE Directive.  The RSL Transmitter is currently being built and tested in accordance with ETS 300 447.   Account has also been taken of the facilities required of RSL transmitters in the OFCOM Engineering Code sections 2 & 4, and also the OFCOM RSL information document Section 9 Appendix II Technical Conditions.

The foregoing approach means that both Link and RSL transmitters will have the same construction format and again are offered in economy and rack mount versions.  Orders are now being taken for Link systems for delivery at the end of March.

G2DYM Update  The design equations show that the coax traps having a higher L to C ratio than used in the W3DZZ design need to be used with an inner wire length of 33 feet and an outer wire length of 19 feet 7 inches.  Some 2 feet shorter overall than as sold by G2DYM. Customers who have tried these lengths found that correct resonance occurred on both 80 and 40 metres.

I have found an article from Technical correspondence in QST August 1976 which gives the equations to determine the net inductance loading required for a trap at a defined position on an aerial wire.  The extensive equations have been tried and do agree very closely with the W3DZZ design of trap dipole.   A program has been developed to calculate top wire lengths and trap inductance and capacitance. 

Measurements of the inductance of the 7MHz coax traps reveal the inductance to be about 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 total capacitance to total around 42pF. 

Experiments with trap potting material have resulted in a choice of an epoxy compound designed for electronic potting and available in 500gm sachets.  It is slow curing but rigid and does not absorb water.  The dielectric constant is very close to that of polythene.  A batch of traps has now been potted using this material. 

During December I have been busy with manufacturing work and building new transmitter for Ireland for Clubs and Community work and Church broadcasts.  It operates on 27.6-27.99MHz 10W FM which is now an EU allocation for this purpose.  Also I have laid out a revised amplifier board for my successful range of Transverters.  This board now incorporates a relay used extensively in my other products.  The layout is an inverse of the previous one so that input and output wiring can now be run along the bottom of the case.

Update 7 December 2006

Poundbury Project.  A breadboard of transmit and receive preamps was built and tested.  It was fine on receive providing a low noise amplification with 20dB of gain.  The transmit side was stable and clean and produced 600mW output when driven with 400mV p-p from a signal generator.  When connected to the Poundbury, the maximum undistorted output from the Poundbury ring mixer was only 40mV p-p, so the transmit preamp will need to consist of two mosfet amplifiers followed by a BSX20 stage and then a 2N4427.  The overall gain of this is going to be so high that stability will be a problem.  At this time I am not sure if I can make it stable as a single board with a top side ground plane of if it will have to be split into two boards. The work unfortunately will not be done in time for the February PW but it is hoped to be in the March issue.

5 November 2006 On 30th October 2006 Spectrum Communications acquired G2DYM Aerials.  That business has 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 was unable to continue running the business. 

Together with manufacturing materials, tools, and moulds, we received a quantity of made up aerial wires for both full size and half size trap dipoles, and a quantity of 7MHz traps ready for potting.   Since receiving the stock we have been busy cataloguing it and going over all aspect of manufacture of the traps.  Also delving into my radio books and learning the theory of trap dipoles, and researching different types of potting compounds.

Stangely enough, during my employment with the ministry of Defence at Portland Dorset I spent 6 months in the Coils and Filters Section involved in potting transducers with epoxy resin.  That experience made me conscious that different types of potting compound and filler have wide ranging effects on the coils being potted. 

3 October 2006  The Poundbury project is attracting steady sales but with many clients wishing to opt for 10.7MHz IF for some unknown reason.   Unfortunately I am unable to supply the kit with 10.7MHz crystal filers as they are just not available World-wide at a price less than £99.00 !!  In the last week I have spent time developing a 6 crystal ladder filter for 10.7MHz. I now need to get a quote from overseas for a batch of crystals to fabricate my own filters for 10.7MHz.   Unfortunately they will not be as reasonably priced as the 9MHz filters.  They will also take at least 4 weeks to be manufactured.

DiBD & PW Projects

You may have noticed that my site now includes a new linked page DiBD & PW Projects to accompany the successful by-monthly Doing it By Design Series which has been running since March 2004.  This linked page also includes any stand alone projects which have also been published by me in the last two years.  These include the Whitcombe 4m converter, a Two Tone Tester, the Mellstock 4m 1W AM Transmitter, and the companion Mellstock 4m AM Receiver.  Now also the Portland VFO & Buffer.  The May issue of PW featured a Mixer - VFO unit to work in conjunction with a Portland VFO to create a local oscillator for a 4 metre receiver or transmitter with a 9 or 10.7MHz IF. 

Radio Remote Control Unit

Designed for use with track and field events requiring starting and stopping lights or indicators to be activated remotely from the command or control centre, to remove the need for extended cable connections. The system comprises encoder and decoder units which can be wired to suit most transceivers by plugging into the microphone socket at the transmit end and into the earphone or extension speaker socket at the receive end.  The encoder box is fitted with green and red large push buttons with large matching colour LED indicators.  The decoder unit has large green and red LEDs and an output to drive an external relay.  Both units run from 13.5V DC supplies and draw less than 50mA each.   Ready built and fitted with traditional jack or microphone connectors the complete package costs £160.   There may be additional charge for special connections to the radio equipment.

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