SPECTRUM COMMUNICATIONS

 

RX SPC ANTENNA TUNING UNIT Price £59.00 including carriage by Hermes.

The Receive SPC Aerial Tuning Unit is based on the Series Parallel Capacitor ATU configuration used for transmit matchers which prevents the circuit becoming a high pass filter with certain choices of tuning capacitors and inductances. It will work with long or short random wire aerials or with aerials fed with coax cable.  Unlike transmitting ATU's which must be low Q to avoid loss, the receive ATU should be high Q to enhance the signal as well as making the aerial resonant on the wanted frequency.  This high Q operation also reduces both unwanted signals and unwanted noise above and below the required band. It is provided with a single wire yellow terminal post for random wire aerials and with a single wire black terminal post for a connection to ground. Also an SO239 coax socket for a coax downlead.   Output to the receiver is via another SO239 coax socket.

 

The QRP TX SPC Aerial Tuning Unit is based on the Series Parallel Capacitor ATU configuration used for transmit matchers which prevents the circuit becoming a high pass filter with certain choices of tuning capacitors and inductances. It will work with long or short random wire aerials or with aerials fed with coax cable.  In this version the inductances are wound on toroids to provide high Q, small space, and low unwanted coupling.  Power handling will be limited by a 100V rating of the polyvaricon capacitors and the impedance of the antenna being matched.  By definition QRP means up to 10W SSB in the UK. With a random wire antenna presenting a high impedance at the required frequency the voltage when matched can be quite high and that is the limiting factor for this and all TX ATU's.  Indeed for really high powered transmission the variable capacitors are wide airspaced with flashover ratings in excess of 2kV. When matching to a low impedance antenna only a small amount of inductance is required to achieve the match.  Conversely with an antenna a bit short for a quarterwave (or resonant at a higher frequency than required) more inductance and less capacitance is required.

QRP TX SPC ANTENNA TUNING UNIT The ATU is provided with a single wire yellow terminal post for random wire aerials and with a single wire black terminal post for a connection to ground. Also an SO239 coax socket for a coax downlead.   Output to the transceiver is via another SO239 coax socket.  Price £85.00 including Hermes carriage.

 

VLF CONVERTER 100Hz - 100kHz PCB & Hardware kit £53.00.  Ready Built £72.00. Inc carriage.

This Very Low Frequency Converter operates from as low as 100Hz and up to 120kHz.  The conversion gain is; 100Hz 0dB (unity), 1kHz 0dB (unity), 10kHz 2dB, 50kHz 4dB, 100kHz 2dB, 120kHz 0dB (unity), 140kHz -10dB, 160kHz -20dB, 180kHz -30dB. The unit contains a 4MHz crystal controlled oscillator and a diode ring mixer (to cope with strong signals found in this region).  This means the output range will be 4.000100MHz to 4.100000MHz. At low frequencies the mixer becomes in effect a modulator so the inbound signal mixed with the carrier produces a carrier and two sidebands.  This means that the receiver can demodulate this as amplitude modulation if tuned to precisely 4MHz. At frequencies beyond the bandwidth of the receiver IF stages the mixed signal plus the carrier can be demodulated as a single sideband or CW signal.  It may be beneficial to use a CW IF filter if one is fitted to remove unwanted noise each side of wanted signal. The unit is powered from an alkaline PP3 9V battery (not included) and draws only 21mA.  It is housed in a plain diecast box 120x94x34mm.