4 Band CW/SSB Receiver for the 160m...30m Band
In the past years I build some HF Transceivers. One project I found were the R1/R2 direct conversion
receiver of Rick Campell, KK7B. It took me one or two years until I start to built it in 2006.
However in a version of a 80/40m receiver by Dave Lyndon, AK4AA.
My assembly correponds in majority to the circuit of Dave. The LO Mixer from 1.7MHz to NF however is
the original R2 circuit of Rick. To cover additionally the 160m and 30m band I plan to add two
switchable converters. In the current stage the receivers works on 80m and 40m. For more details see
the pictures. The complete circuit is built in ugly construction style. From my point of view this is
the fastest way to get satisfying results in an adequate (...and limited) time. I do not describe any
circuit details as this is already done in the mentioned reports.
The following links give you detailed views on the receiver...
The VFO is tuned by 2 variable capacitors. The left one is for coarse tuning
the right one for fine. Below the RX frequency display is the band switch.
LO Mixer and LF Unit
When I start with the receiver I built first the LF amplifier
and the LO mixer. The assembly stage on the picture represent the R1 of Rick Campell, KK7B. The inductors
I used are not the TOKOs described in Rick's publication. The L's used are 10% tolerance inductors found at
at Reichelt Elektronik. This is my main source for standard electronic items.
LO Mixer with Diplexer
This is a detailed view on the LO mixer with the following Diplexer.
LF Filter and Amplifier 1
LF Filter and Amplifier 2
The LF finals are a complementary pair of BD240C/BD239C transistors. The LF Preamplifier LM387 is an obsolete device.
I checked some dealers and made a note in a ham forum. In fact, I still got one last item which was on stock at a small electronic shop...
Complete 1.7Mhz LO Unit
The 1.7MHz Unit with the additional Mixer/Diplexer. The phase shifting network is not assembled. In this stage
I check each Mixer/Diplexer with a 1.7Mhz input Signal. The 1,7MHz IF amplifier and the 1.7MHz BFO are
assembled on the vertical board. The Pot on the picture bottom is for the HF gain adjustment.
1.7Mhz LO and IF Amplifier
The IF amplifier is on the right the LO left. The LO is tuned by a small air variable VHF cap with
a 1:3 gear which I have disassembled from an old radio years ago...
Phase Shifter Board, blank
For the phase shifting network which performs the sideband supression I used a copper coated board.
For interconnections I used glued copper coated board pieces on the mainboard. The
separations were made with a sharp carpet knife. The distances are made according to the opamp
Phase Shifter Board, assembled
I used standard resistors which I have in my shack instead of the metal film precision
devices recommended. It is also possible to reach the defined values with its tolerances by parallel/seriell
connections of appropriate resistor values and measure it with an OHM-Meter before assembly.
This needs some time but at the end of the day it works great for me.
Input Filter/Mixer and VFO
The input filters for 80m and 40m are as described in Dave's article. The C's are in majority
SMD's. I bought a well sorted batch of them some time ago at E-Bay. Against the described VFO coil
of Dave I used a AMIDON T80-6. The turns are round about 50ea. I played around with the capacitors and
removed some single windings to get the right VFO span. That needed some time but finally
my span was 5.2MHz to about 5.65MHz, ok for me. After tuning the AMIDON toroid VFO coil I covered the winding wire
with some glue. The VFO works great. It needs about 10-15 minutes to stabilize. After this time it
is nice to use it for CW and SSB. May be I will sample the frequency deviation curve
and present it here...sometime
The frequency counter/display is a completely own developed unit of myself (wow !). On the one hand
the counter measures the VFO frequency and calculates the RX frequency by adding or substracting the
appropriate offset in dependence of the selected band. On the other it measures the BFO frquency
and displays the offset to the exact value of 1.7MHz. If working with a TX the frequency of the RX
can be tuned to the same as the TX and the offset for SSB or CW is adjusted by the BFO. I made a
small pcb material housing with the display mounted 15° in angle from vertical position. This is just
to get a better view on it when the receiver is in front on the desk during operation.
frequency counter circuit
The heard of the counter circuit is a ATMEL Atmega8 microcontroller. This controller involves a
16-bit counter which is used for the frequency measurement. The frequency to measure is divided
by 10 before it is routed to the timer input pin of the processor. The VFO frequency range of
5.2...5.7MHz is converted to 520...570kHz. In the software I set a fixed measurement time (the GATE time of the counter) to 100ms. Therefore, the 16-bit counter result is between
52000 and 57000 counted pulses for the VFO. As next an offset will be added/substracted in dependence of
the selected band. The cases when the result is a higher number as the max. 16-bit value is handled
by the software e.g. the RX display for the 40m and the 30m band. Below you find the assembler
code of this counter. Additionally the counter measures the BFO frequency. This is done in a
step by step order with the VFO frequency measurement. The microcontroller controls a input switch
which is constructed by a 74HC00 4xNAND TTL circuit. The processing of the BFO frequency corresponds
to the VFO frequency measurement process. An offset of 17000 leads to the BFO display result.
Assembler program code for the RX Counter/Display