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This receiver was started in 2002 and used for my first ever QSO in March 2002. At that time it was just a collection of boards lying haphazardly on the workbench, but later I constructed the cabinet you see here, using aluminium angle, and aluminium sheet front panel, and 1/4-inch pine board. My original intention was to eventually develop this radio into a CW/SSB transceiver covering all UK amateur HF bands. However, there were many diversions along the way and I do not now consider it likely that I will do any further development on it. It remains an excellent 80m receiver, and has served well for many QSO's.
This project is featured in Chapter 6 (HF Receivers) of the 8'th Edition RSGB Handbook, published in 2005. Click here to download my article, which probably contains a more detailed description than anything else you'll read on this page hereafter.
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Construction uses the "ugly" method and the receiver is currently unfinished. See early photo right (Medium photo, 800 x 602, 67K, Large photo, 1493 x 1125, 186K), showing the receiver as used for my first ever QSO on 25-Mar-2005.
It uses an 80m bandpass filter from the GQRP webpage using two KANK3333. There is no RF amplifier, the filter directly feeds a FST3253 Tayloe switching mixer.
The VFO uses a 74HCT04 inverter chip, stabilised by a magnetically coupled Huff & Puff VFO from my Huff & Puff stabiliser page. I have replaced the internal oscillator of the 74HC4060 with the inverter gate oscillator which runs at 14 MHz (4 x freq, for the quadrature mixer). I have also now boxed the VFO and stabiliser using PCB board, and use a reduction dial (also my Father's).
Frequency measurement uses my homebrewed frequency counter mounted at the top right of the front panel. Top left is my homebrewed Panel-mounting clock for convenience in those long ragchews.
Following the mixer are NE5534 op-amps with gains of 33dB.
Then a lossless 8-column polyphase audio network, with varying resistor AND capacitor values according to a 1995 QEX article (see below). Components in the network are matched to 0.1%. Next are a set of unity gain OP27 op-amps.
One output of the network feeds four NE5534's as low pass filters (8 poles Butterworth @ 3KHz) and two NE5534 high pass filters (4 poles Butterworth @ 250Hz). For CW I can switch in my CW filter, and/or a 2-pole Butterworth op-amp filter as in the ARRL handbook. There is another NE5534 as a preamp giving 20dB gain, then a TDA2002 audio amp driving a 4-ohm 30W computer loudspeaker.
I have been unable to measure the opposite sideband to the limits of my measurement (just 40dB at the moment). At night here in the UK and with just a few feet of wire strung into the next room, I have listened in on an American 75m net: all participants were audible (armchair copy).
below left, the bandpass filter and tayloe detector. The Tayloe detector is clocked via a synchronous divide-by-4 counter (74HCT163). As yet I have made no attempt to adjust the 1K balancing resistors, since I have inadequate measurement equipment to detect the opposite sideband (my limit is -40dB and the opposite sideband is below this).
The polyphase network below middle is designed according to an article in QEX November 1995 (see below). The resistor and capacitor values for the columns are shown at the top of each columns. I used expensive 0.1% resistors from RS Components, and matched the capacitors in each column to within 0.1% using a 555 oscillator circuit and frequency counter, and adding parallel capacitance from the junk box until the oscillation frequency matched to the required degree.
The chart below right the theoretical opposite sideband suppression with the component values shown.
Tetsuo Yoshida JA1KO explained how to design a lossless polyphase network in the November 1995 issue of QEX, which can be downloaded below.
QEX Magasine, Nov 1995: Polyphase Network Calculation using a Vector Analysis Method, by Tetsuo Yoshida JA1KO (7 pages)
PDF (968 K)
Reproduced by permission of the ARRL.
The picture (right) shows radio G0UPL. The station is all homebrew and made up of this receiver together with:
One-valve 80m CW transmitter,
ATU and power/SWR meter,
Frequency counter,
Panel-mounting clock,
and a longwire antenna.
To the left here is an old station photo, before the rx was boxed
Medium photo, 800 x 413, 51K
Large photo, 1441 x 745, 137K).
Photos of VFO tuning dial and reduction drive mechanism
Click Here for some more pictures and details of the VFO and stabiliser.
Click Here for a bigger picture.
Tayloe Detector
How to surface mount a FST3253 chip (centre of photo, Click for larger size). I sawed off a small piece of single-sided PCB material and cut tracks in it with a sharp craft knife. Soldering the FST3253 must be done with a steady hand. The small board is glued to the main board and connections made to the larger tracks formed on the board.
A picture of the main receiver board, excluding the VFO. This picture was taken before the board was split into smaller modules that are now mounted in an aluminium frame (see photo at top). "Ugly" construction methods are used. Later I will put the different parts of the receiver in screened PCB-material boxes and beautify everything.
Top Left: unity gain OP27 op-amps follow polyphase network
Top Centre: 8-stage polyphase network
Top Right: 33dB NE5534 amplifier stages preceed polyphase network
Centre Right: +5V voltage regulator, Tayloe detector
Centre: CW filter
Bottom Left: Audio filtering. Switches control which filters are used. Speaker socket at left.
Bottom Centre: Audio power amp, and volume control.
Bottom right: Transmit/Receive switch, test oscillator (3.515 MHz), input bandpass filter
I have made a few response measurements of the receiver. With my current setup I can only measure down to -40dB. I am unable to measure the opposite sideband suppression which is below this, even with NO balancing adjustment. The CW filter response shown here is the phasing CW filter. I now also have the option of a 2-stage butterworth filter as described in the ARRL handbook. It is less narrow than the phasing CW filter. The SSB response is too narrow and I need to redesign these filters. Nevertheless it is quite comfortable to listen to SSB. The polyphase network measurements indicate the validity of the method described in the QEX article for acheiving a lossless network. NOTE: The Tayloe detector response is shown out to 100KHz while audio reponses are shown to a scale of 10KHz.
The HF receiver was later made operational on 40m in addition to the original 80m. This uses the same 14MHz VFO divided by 2 rather than 4. Because this results in quadrature with imperfect phase (due to non 50% duty of the 14MHz oscillator output), the opposite sideband suppression on 40m isn't very good.
Here are pictures of the most recent work on the HF receiver. These two "rack-mounted" shielded boards are rebuilds of the bandpass filter and Tayloe detector/polyphase sections of the circuit. They are made from unetched PCB and will also have lids, forming complete screened boxes.
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http://home.planet.nl/~niess153/Polyphase_networks.htm: An excellent information resource by W.J. (Pim) Niessen PA2PIM.
http://rubidium.dyndns.org/~magnus/synths/friends/gingell/: Original PhD thesis on polyphase networks by Mike Gingell. (Thanks to Magnus Danielson for providing this information).
