Accessories and Test Gear

Three Digit Frequency Counter

This counter has been designed specifically for the Dipper (see below) OR as a tuning readout on simple rigs. Mechanically it is the same shape as the Dipper and uses a 50 x 160 mm PCB. For use with rigs, the displays are normally mounted on the front panel leaving a logic section of just 50 x 80 mm. Normally it shows the incoming signal as XY.Z MHz but, with wire link alterations, the resolution is increased to show the three KHz numbers of its frequency, so that the MHz part of any frequency over 999 KHz overflows out of sight. For use with a rig, the local oscillator signal is fed to the counter. These options make it suitable for general purpose test gear, such as a signal generator, or for simple rigs, both direct conversion or single band superhet rigs - provided their IF is a whole number of MHz. It will work up to about 50 MHz and can count either up or down which makes it suitable for additive or subtractive superhets. (For non-integer IF superhets, the easiest approach is to count a little of the rig's RF output.) It uses the same high efficiency small 0.3" wide by 0.5" high common cathode 7 segment LED displays and driving circuits as the full 5 digit counter - see below - hence has the same advantages. Price £35 or £74 with the Dipper.

This is the Three digit counter, with the display section attached to the logic part.

Five Digit Frequency Counter

Probably the most useful addition to any rig! It has two full (60+ MHz) input channels which are normally connected to the rig's VFO and CIO; these can be read individually, added or subtracted so making it suitable for additive or subtractive superhets with any IF, or for direct conversion rigs or test gear. The five displays show the MHz & KHz with a normal LSB of 1 KHz. This counter is recommended for multi-band superhets. It uses high efficiency small 0.3" wide by 0.5" high common cathode 7 segment LED displays; these are driven by DC signals from the electrically quiet CMOS counting logic using a crystal reference oscillator whose harmonics are outside any amateur band. The individual LED segment resistors are mounted immediately behind their display and are separate from the driving logic PCB. The high impedance input circuits have a typical sensitivity of 50 mV RMS at 20 MHz. PCB size 160 x 50 mm. The kit includes parts for one input buffer and suits all Somerset Range rigs. Five digits £49.

Antenna Matching Unit

This unit includes a resistive 50R matching bridge, a broadband RF transformer and the T configuration matching parts. Power is limited to around 20W by the variable capacitors! When selected for tuning up the matching controls, the bridge will always present a safe load to the TX no matter what the antenna looks like! The bridge uses a high intensity LED for indication but can also work with conventional meters or an S meter. When the bridge is out of circuit the LED indicates output RF voltage. The broadband RF transformer allows the matching section to work with balanced or unbalanced feed lines. The T matching section (two variable capacitors and a tapped inductor) is very adaptable, dealing with load impedances from 10 to 2000 Ohms. The inductor is made from a printed circuit flexible strap with switch selected taps for 10m upwards - for 160m there are toggle switched extra capacity and inductance. Price £32

This is the AMU:-

Dual Low Pass Filter and Pylle CW TX

These were both originally part of the large Upton project, which is no longer available. However I do have several Low Pass Filter kits and some Pylle CW transmitters. They are both on 50 x 80 mm PCBs.

The LPF kit contains a pair of relay selected 6 element 50 Ohm half wave low pass filters for removing unwanted transmitter harmonics. There are normally two relays, one to select each band, so that several of these kits can be cascaded for multi-band operation. Alternatively, a single relay can be fitted in a slightly different location to select directly between just two sets of filter parts, without cascading for other bands. The standard kit of parts allows either band to be selected from 20, 30, 40 or 80m using a combination of series or parallel connected capacitors, with the inductor values being changed by altering the number of turns on the powdered iron toroids. On request, parts for any other HF band are available. £19.

The Pylle is a 1.5W CW TX with full break in operation, a receiving RF amplifier, TR control, sidetone and muting; it is normally driven by an external LO source but can accommodate a crystal or ceramic resonator for single band use. It needs external low pass filters such as those above. The Pylle costs £24.

Linear Amplifier

This is a broadband design for any of the 1.5 Watt transmitters of Somerset Range rigs. Producing 10W on all bands, 20 to 160m on 13.8 volts, it can be used on the higher bands with reduced output. With higher supplies to 22 volts, it can produce appreciably more! By connecting it just after the driving rig's output transistor(s), it makes use of the rig's existing TR switching and low pass filtering, which reduces its complexity. The bias supply is also controlled from the main rig. The PCB is only 80 x 100 and has two 50 mm high upright heatsinks. It goes very well with the Fivehead - see photo there. Price £24.

Meter Kit

This kit is an optional extra for those rigs needing the facilities of a receiver S meter (based on an audio derived AGC circuit); and for the transmitter, it provides RF output and AMU matching indication. When used in the RX audio path, the AGC circuit provides extra audio gain of up to x20 for milliVolt signals and a stable audio output of 100 milliVolts p-p. The transmitter 50R resistive matching bridge is brought into circuit by a 'Tuning' relay which ensures that the TX will always have a safe load while adjusting your AMU. With the bridge out of circuit the meter indicates RF output voltage/power. Needs nominal 12 volt supply and can handle 20W with care! PCB size 50 x 80 mm. The RX section can be separated from the TX part. Price £24.

Mini Mixer kit

This is a smaller and simpler version of an earlier kit. It not even fully occupies the 50 x 80 mm PCB! It has two main uses; firstly for mixing local oscillator signals such as needed by the Brendon or Brent on higher bands, and secondly to act as a receiving converter. It has a SA602 mixer with crystal oscillator followed by a buffer stage, and a double tuned RF filter using toroids and trimmers. For crystal mixing LO applications, the off board VFO (eg in the Brendon/Brent) is connected to the mixer which then feeds the RF filter to select the wanted mixer product. For receiving converter use, the aerial feeds the RF filter which then feeds the mixer and outputs to the main receiver. The standard kit includes parts for all bands 20 to 80 of the RF filter; the crystal is chosen to suit either the external VFO or the receiver input band - these would often both be 80m. The kit can easily be used with other crystals and RF filter frequencies. Remember you need to define the application when ordering! Price is £14.

CW Kit

This adapter kit adds CW facilities to either a DC, double sideband or superhet phone rig. For the RX, there is a switchable humped low pass filter centered on 750 Hz; for the TX there is a 750 Hz sine wave oscillator with keyed outputs for injection into the speech amplifier and RX audio stage for sidetone. Semi break in TR control is included. Size 50 x 80mm. It can also be used as a morse practice oscillator. £19

Variable Bandwidth Filter

This is a specialist audio filter for CW reception; it is intended for fitting after the product detector and before the rig's main gain control - manual or automatic, but can also be used after an existing RX. The centre frequency is fixed at a nominal 725 Hz but the bandwidth is adjustable from about 500 Hz down to 100 Hz depending on the setting of the bandwidth control, which is a board mounted shafted preset that can be easily changed to a front panel pot if required. This is a bandpass design as opposed to the simpler low pass audio filters that are often used for CW; furthermore the voltage gain of the circuit does not alter dramatically with the bandwidth. It is unity at the wide setting but as the bandwidth is decreased, the gain increases to about x 2 at the narrowest setting - this helps to lift the wanted signal right out of the noise and leave the unwanted signals well suppressed without the need for any other gain adjustments. The input impedance is high and the output is suitable for driving either the normal 4K7 manual gain control, or series connected Walkman type 32R phones when the filter is to be used outboard of an existing RX. The size is 50 x 80 mm and runs off a nominal 12 volt supply. No special test gear is required. The price is £19.

Speech Processor

This kit increases the average output level of an audio signal from a mike by clipping off the excessive signal peaks. As it is the peak signal which determines the maximum allowable drive to a phone transmitter, by lowering the peaks in proportion to the average level, a higher average output level can be attained with an associated increase in intelligibility under difficult conditions. The kit works by modulating a 5 MHz carrier which is then clipped, the resulting harmonics (of 5 MHz) are filtered out and then demodulated back to audio. It is set up easily without special equipment and has a preset for a compression control which can be changed to a normal pot if preferred. It can be used with any make of rig - requiring only signal connections to and from the normal mike socket. It uses a single sided 50 x 80 mm PCB working on nominal 12 volts. Price £24.

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Audio Amplifier

This is a general purpose audio power amplifier; it can be used with the Product Detector kit to form a specialist DC receiver as in the Upton project, or for boosting the output of a headphone output receiver, or acting as a low power AM modulator. It has a low level pre-amplifier with a gain control (preset with shaft/knob) between the amps. Both amps have a bandwidth of about 3 KHz; the pre-amp voltage gain is x20, the output amp x50. On 12 volts, the power amp will deliver a peak power of 1.5W into 8R or 4W intermittently on 22 volts. The pre-amp input is suited to the output filters of the Product Detector kit low impedance dynamic microphones. When used as an AM modulator, it will need a suitable transformer - consider using a small mains one! PCB size 50 x 80 mm. £14.

Test gear

Two items of general Test gear are still available. The first is a pair of separate 10 dB broadband HF RF amplifiers for use in nominal 50R systems - shown on right in the photo below. The second item is a switched low power 50R attenuator having steps of 1 dB up to a maximum of 20 dB. Both are on 50 x 80 mm PCBs and are £19 each. The power meters have all gone!

Two Tone signal source

This kit comprises two sine-wave audio oscillators that can be used singly as a source of audio test signals or together as a pair of unrelated tones for accurate setting up of single sideband transmitters. The two fixed frequencies are nominally 725 Hz and 1590 Hz. A three position slide switch allows either oscillator run separately or their outputs to be combined. The outputs (approx 1 volt) are balanced with a preset using an ordinary AC multi-meter and then a further optional resistor is added to bring the level down to about 10 millivolts - a bit higher than most modern microphones, with actual output level being set by a further shafted preset. This low level signal is input to the transmitter under test while the RF output is monitored with an oscilloscope. The presets can easily be changed to normal potentiometers if required. Size is 50 x 80 mm on a single sided PCB. It can use a 9 volt battery (to avoid hum loops) or nominal 12 volt supply. Price £19.

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