Simple Projects

All of these are suitable to demonstrate your skills for the Intermediate Radio Amateurs exam but see notes on the Ordering page!

The Rockwell

This is a simple Regenerative Tuned Radio Frequency (Regen TRF) receiver design for those just embarking on electronic construction projects; it is also suitable for Radio Club group building projects and as an introduction to short wave radio. You should be able to build it in a couple of evenings! It has two general coverage bands which can be chosen from MW or around 160m, and around 80m or 40m. These are chosen by alternative fittings for the four ready wound inductors.  Because it is a Regen TRF it is ideal for the powerful broadcast stations of the Medium Wave (and 'short' wave) bands, using Amplitude Modulation, which can be easily heard with a short aerial; so start by building it for the MW as a good confidence booster! Because it is a Regen TRF it can also copy the common modes of Morse, and phone Single Sideband. It has three controls - the Main tuning, and RF gain control and the Regen control. It uses four transistors arranged as an RF amp, the regen stage and two for the audio amplifier. The audio amplifier is designed specifically for modern 32R stereo phones which turn the RX on when plugged in and there is also very smooth control of the critical point of oscillation. The kit includes 5m of aerial wire for an initial 'throw-out' aerial which is usually enough for MW reception. The price is 19 GBP.

(The Rockwell below is an early model with a few extra holes for transmitter aspects since dropped!)

The Yeo Mk 2 DC RX

This is an entry level direct conversion receiver intended for serious communication use! It starts as a single band RX for any single band in the group 20 to 80m. The receiver stages have a double tuned RF bandpass filter that feeds into a JFET mixer with the Local Oscillator signal coming from its own separate Variable Frequency Oscillator (VFO) that runs at the desired band frequency; the VFO tuning is adjusted by the Main PolyVaricon control with a DC pot Fine tuning control acting on a tuning diode. With a suitable transmitter (such as the Isle), the Fine control can be automatically centred during transmission so that it can be used as RIT on either sideband to obtain the desired beat note. The mixer feeds an audio pre-amplifier (with phone bandwidths) followed by the AF gain control, or a narrow humped low pass audio filter for CW selected by toggle switch. The output of the AF gain control feeds the audio power amplifier which can drive phones or a low impedance loud speaker. It can be used in this form with a simple 'crystal' controlled CW transmitter like the Isle; however to avoid chirp when using a VFO that also drives the transmitter, you need to use the Mini Mix kit. This uses the Yeo's VFO (altered to near 5 MHz) for mixing with a crystal derived signal; followed by filtering for the desired band so that it can now provide VFO operation of the RX and TX. This combination can also provide the LO signals for 20, 40 and 80m reception with a Yeo Extra Bands kit - see the Intermediate section. The Yeo will also work with the Axe phone Double Sideband transmitter sown below. The Yeo needs a nominal 12 volt supply. The main PCB is 100 mm square with PCB front panel for the essential controls as shown below. The RX PCB is also drilled for a TR relay when there is not space for it on the TX PCB! The price of the single band Yeo Mk 2 is GBP 27, or with the Mini Mix kit the price is GBP 42.

 

The Isle CW TX

This is a 1.5W single band CW transmitter, that uses a crystal or, depending on band, a ceramic resonator for frequency control. The band can be any one of those in the 20 - 80m group. The kit includes a 3.58 MHz ceramic resonator for 80m which can be pulled over several tens of KHz down from the nominal figure using the on board trimmer. For the higher bands you have to use a crystal which means that the trimmer will then only have a very limited tuning range. The single band version is shown below with a single crystal, however there is space for three 'crystals' which can all be in the same band when using the single harmonic filter on the Isle PCB, see the Intermediate section. TR control of the aerial relay (assumed to be on the associated Yeo RX PCB) is semi-break in from the key and includes facilities for muting the RX. If wanted, the TX can be driven by an external frequency source such as the Mini Mixer kit instead of using 'crystal' control. The price for the single band version, including the 80m resonator, is 18 GBP; just add the extra crystals for 3 frequency operation. Standard QRP calling frequency crystals for 20, 30 and 40m are 2 GBP each.

 

 The Axe

This is the matching phone transmitter for the above Yeo Mk 2 RX for those who want to get on the air quickly with DSB phone. It is entirely compatible with other stations operating single sideband! It produces a peak output of 1.5W when used on a nominal 12v supply. It is normally for any single band in the 20 to 80m group. Frequency control is by the included ceramic resonator for 80m giving about 50 KHz coverage down from 3.69 KHz with the on-board trimmer; for the higher bands where ceramic resonators are impractical, you will have to use a crystal with a tuning range of just a few KHz - the prototype (with crystal) shown below is for 20m. Ceramic resonator or crystal control would be appropriate for a simple Yeo where its VFO is at reception frequency, but the Axe can alternatively be driven by an external LO signal derived from the Mini Mix kit when the Yeo VFO has been altered for that! This avoids the limitations of crystal control and gives you transceiver VFO control over the whole tuning range of the RX! A SA602 is used for the balanced modulator which then drives and AD8055 high speed op-amp. Because the gain through these stages vary with band, the single drive level preset has to be set for that band which means that the rig is limited to single band operation. The output stage is three BS170 MOSFETs operating in parallel - these are ideal for the LF bands and allows for the standing bias current required for linear operation! The standard Axe can also be used to drive the Linear amplifier for a nominal 10W DSB output. The output stage is followed by low pass harmonic filters and the control circuits include RX muting and control for the TR relay which would normally be mounted on the Yeo RX PCB. The Axe price is GBP 26; 7159 KHz and 14318 KHz crystals are available at GBP 2 each.

 


Site Navigation

Home Page, List, Intermediate, Advanced, Accessories, Ordering


Walford Electronics Ltd.