Accessories and Test Gear
A counter is probably the most useful addition to any rig! It has a single input channel that is normally fed from the rigs's VFO or circuits that generate the Local Oscillator signal.This much reduces the complexity (and hence cost) making it much easier to build. It shows just the important KiloHertz numbers of the input frequency - any MHz numbers overflow (normally) out of sight to the left! This means that it is suitable for direct conversion rigs, and for the simpler superhets whose IF is an integer number of MHz - as in all WE kits. It uses high efficiency small 0.3" wide by 0.5" high common cathode 7 segment LED displays with the least significant digit showing the units of KHz, and the top digit shows the hundreds of KHz. It uses low noise CMOS integrated circuits that count, store and decode the incoming signal for direct driving of the displays with all the advantages of low noise and only DC currents in the wires to the displays. For use with superhets, it can count either up or down, with remote DC control for multi-band options. It uses a crystal reference oscillator whose fundamental and harmonics are outside any amateur band. Input sensitivity is about 50 mV p-p at 10 MHz down to 100 mV at 35 MHz; the maximum input frequency will be normally be over 60 MHz. The PCB size is 50 x 80 mm; supply required, 7 to 22 volts. The 21 segment resistors are mounted behind the display or end-on at the logic PCB. The kit can drive the larger displays if required. The photo below shows the wiring between the displays and the three digit counter PCB - the kit to which this particular counter kit is attached, has two extra counting MHz drivers just out of picture! Extra MHz displays can be either hard wired, or made to count (under the control of the 3D logic PCB) by adding only two ICs. The basic 3D counter cost is 26 GBP. Extra MHz displays & resistors 1 GBP each, or two displays with 2 counting chips 5 GBP.
The Mk 6 version uses the same basic T match and bridge circuits as in earlier versions but with the variable inductor now formed from switch selected inductors. This approach is an easier way to make a variable inductor! The design has a resistive 50R matching bridge, a broadband RF transformer and the T configuration impedance matching parts. Power is limited to around 20W by the variable capacitors! When selected for tuning up, the resistive matching bridge will always present a safe load to the TX no matter what the load from matching parts and the antenna looks like! The bridge uses a high intensity LED for indication but can also work with a conventional meter or an S meter. When the bridge is out of circuit the LED responds to RF output voltage as applied to the matching circuit. The broadband RF transformer (on the white toroid) allows the matching section to work with balanced or unbalanced feed lines, and isolates the matching parts and antenna/feeder from the incoming unbalanced RF feed from the transmitter. The T matching section (two variable capacitors and the switched inductors) is very adaptable, dealing with load impedances from about 25 to 2000 Ohms over the frequency range 2 to 30 MHz. The main inductor comprises seven switch selected inductors wound on toroids - the inductance required can increase in steps of about 0.1 /uH in a near binary sequence up to a maximum of about 20 /uH; they are easily made single windings on T50-2 cores. For any particular band, feeder and antenna combination, usually only one or two (occasionally three) adjacent inductors will be selected which makes adjustment very easy by flicking probably just two adjacent switches. The price is 37 GBP.
The new High Power version has large heatsinks and uses IRF520 devices for about 15W out on 20m with 15v supplies while needing about 0.5W of drive for full output. 20m is intended to be the normal highest frequency band but on the lower bands, up to 30W is possible with about the same drive. The IRF520s really come into their own on higher supplies up to the maximum of 30v when 20W on 20m, or nearer 50W on 160m is possible (with care over heatsink temperature!) The design includes two TR relays so that it is only activated during transmission; these relays and the bias circuits are activated when you ground your push to talk line. Following the amplifier there is a single double Pi harmonic filter which is best built for your highest frequency band - when other filters are needed, they can be added externally after the amplifier. The size is 100 x 180 x 35 mm over the topside of the PCB. The price is 38 GBP.
This unit adds CW facilities to an existing phone transceiver. For the receiver, it has a humped 725 Hz low pass audio filter, which can be selected from the front panel switch (included) to reduce the rig's normal phone audio bandwidth to that desirable for CW. The filter is normally connected just ahead of the rig's manual or automatic audio gain control stage. For the transmitter, it includes semi break-in TR control from the key input (with about a half second delay before it reverts to reception) and is connected to the rig's PTT circuit. Closing the key also activates the separate adjustable level 725 Hz tone outputs (from an on board sinusoidal 725 Hz oscillator) that are fed to the receiver for RX sidetone monitoring, and to the TX's speech amplifier stages to make it transmit a steady carrier while the key is down. It is suitable for DSB or SSB phone rig's. The PCB is single sided, 50 x 80 mm, needing a nominal 12 volt supply. In the photo immediately above, it is the small PCB on the front end with two presets in the middle. The price is 19 GBP.
This unit provides audio derived Automatic Gain Control for receivers that have only a manual audio gain control. It is intended to be added immediately ahead of the rig's normal AFG control. It holds the audio output reasonably constant at about 250 mV p-p for inputs over about 15 mV p-p up to a few volts! It also has protection from the disturbing effects of noise spikes, which can lead to unwanted desensitization of the receiver. There are no extra front panel controls. When fitted, the rig's normal muting (during transmission) needs to be altered to instead apply muting to the input of the AGC kit, so as to allow a quick recovery on reverting to reception. The PCB is single sided 50 x 80mm and needs a nominal 12 volt supply. In the photo immediately above, it is the PCB on the side of the Tone RX. The kit is particularly suitable for RX's with simple audio output stages that can be prone to overloading on very strong signals. Builders say it adds greatly to the listening experience of rigs like the Rode! Price is 16 GBP.
This kit provides a simple approach for generating single band VFO signals on the higher bands where stability and chirp are a problem. It normally takes in a low frequency VFO signal from the main rig (eg a Culm) whose original oscillator has been altered to use either a 4 MHz ceramic resonator, or a VFO operating typically near 5 MHz, to give about 50+ KHz of tuning range; this is mixed in a SA602 balanced mixer (for least output harmonics) to suit the desired output band, with the crystal oscillator frequency being selected for the desired out band and variable input frequency. After the mixer, there are double tuned filters (the standard version allows for any single band in 20 to 80m group but others are possible) followed by an analogue amplifier to provide an AC signal biased at +2.5v DC that can directly drive the mixer and/or digital gates of the main rig. There are many options and please ask me about the intended use and frequency plan (additive or subtractive) before ordering to ensure the correct crystals etc. are available! The Sim-mix kit costs GBP 17.
Dual LPF kit
This unit provides a pair of extra low pass filters for a transmitter; they are selected by one or two relays depending on the application. If the rig only needs to switch between the two filters on this PCB, then a single relay is fitted in a one position; if the rig has three bands, with the filter for the middle band elsewhere on the TX PCB, and you wish to add to more filters for 3 band operation, then two relays in the alternative position are used as in the photo below. The standard kit has parts for any two bands in the 20 - 160m group, but other band combinations are possible by request. The unit does not need any power apart from that which activates the relays whose coils are floating so can be switched in either lead. The unit has a double sided PCB to make mounting easier. Size is 50 x 80 mm. Price is 15 GBP.
Walford Electronics Ltd.