|
Details of our latest club construction project
MKARS80 (pronounced "em cars 80") 80M
transceiver
MKARS80 Yahoo group
http://uk.groups.yahoo.com/group/mkars80/
Progress summary
07th January 08: Kits now available to non member's.
30th June 07: Revised manual available below for kits supplied after
1st June 07 only
21st June 07: Second batch of kits now available
17th June 07: Parts for second batch of kits arrived, pending
kitting
13th May 07: Revised manual 14 pages increased to 26 pages
available from this page
9th May 07: Front panel image overlay, case drilling template,
pic program code available from this page
2nd May 07: Yahoo support group set up for MKARS80
http://uk.groups.yahoo.com/group/mkars80/ -NEW- added 10th July
1st May 07: Revised schematic and overlay available from this page
30th April 07: First kits available to members. Construction and user
manual 14 pages available from this page
18th April 07: PCBs procured and kit kitting imminent
25th March 07: Revised schematic and overlay added to web site (see bottom
of page)
19th March 07: Final prototype built and tested
1st February 07: Most components sourced by Steve G6ALU, enough components
for 25 kits
27th November 06: Presentation of MKARS80 project to members
1st November 06: First prototype finished
Background
Significant interest has been shown in the construction of Pic A Star
transceivers (see Pic A Star pages) by members of the MKARS, but for most the Pic-A-Star is either too
complex or too expensive project to take on. The MKARS 80 was designed for those
who would like to build and use the radio they constructed themselves; in the
design of this radio I have tried to balance complexity, functionality and cost
- most of all the radio must be usable.
Pictures of the first prototype and components for 25 kits
  
Pictures of final prototype (Track side and component side)
Brief specifications
- Frequency - whole 80M band by VFO
- Modulation - lower sideband SSB
- Power output - >5W PEP into 50 Ohm load
- Sensitivity - <1uV
- Audio output - > 0.5W
Basic description
The transceiver is based on a super-hetrodyne architecture using an IF frequency
of approximately 10MHz. The circuit is developed from the
BITX20 designed by Asshar Farhan,
however significant changes had to be made to achieve the required performance
on 80M.
To meet the cost target the radio has various "novel" features, these
include:
- Use of a low cost "polyvaricon" type variable capacitor for the VFO and
a large 10cm knob in lieu of a slow motion drive
-
Frequency lock circuit -
this is internal and consists of a PIC micro which measures the VFO
frequency and compensates for moderate drift, frequency range is approx.
1.5kHz which is sufficient to keep the radio on tune indefinitely if
operating conditions (temperature etc.) remain stable.
- Standard discreet 10MHz crystals in the 4 pole IF filter
- Single board construction without the need for inter-stage screening
- Low cost IRF510 MOSFET transistor as the RF output device
- Reverse polarity protection
Construction
A kit of parts will be
available which will contain the PCB, display and all components to be mounted
on it, not included are case, knobs etc. The target price is set at £35
including the display and £45 including case. To keep costs down the latest printed construction manual
and revision notes will only be available for download via the internet. It may
be possible to supply a paper copies for those without access to the internet
but a charge will apply for this extra service.
Construction has been made easier and more pleasurable by having when built
in its simplest form a completely "wireless" design, though the extra options
mentioned below will require a small amount of wiring as will an on / off switch
if thought necessary.
Full support will be given to any club member building the transceiver; as
most problems can be traced to poor soldering and wrongly identified components
a short lesson on correct soldering techniques and component identification will
no doubt be provided before construction commences.
Introduction to membership of the MKARS80 project at the club
 
In use
The MKARS 80 prototype has been in development use for about 2 months now, the
radio has been used many times including on the club net. I've found it very
pleasant and rewarding to use, as there is no AGC the RF gain has to be varied
fairly frequently to keep stations at a comfortable listening volume, one side
effect of this is the gain remains constant during pauses in transmission and
there is little back ground noise on a quiet band. A frequency lock circuit is
fitted as standard (see options below for details).
5 Watts of power doesn't sound much - during the radios first demonstration
someone quipped " There will be an award for the first person to get out of
Milton Keynes", this has easily been achieved and the club nets stand as
testament to this. It is quite possible to work into Europe and with the
frequency lock option installed I had a long QSO using PSK31 with an amateur in
the Czech Republic.
Options
There are several option planned some will be "built in" and others are simply
plugged in to the speaker and microphone sockets.
- The standard kit comes complete with frequency display module if this
feature is not required the display and associated components can be removed
from the kit and price adjusted accordingly.
- Future option will be an upgraded micro giving the feature of a battery
voltage readout and owners call sign / message on the display at start up.
The additional cost of this is estimated at £5
- LCD frequency and lock display - this is wired to the frequency lock
micro and shows frequency to the nearest 25Hz on the top row and amount of
frequency compensation applied on the bottom row.
- PC audio interface - Plugged into the microphone and speaker sockets
this module allows the PC to control transmit and receive switching and also
provides the required audio level change to enable PC driven modes; SSTV,
PSK31 etc.
Documents available
Important, please note the following regarding
overlay and template downloads:
After printing the PDF files confirm the measurements printed, if they
are incorrect make sure Acrobat printing is set to A4 paper and no scaling.
Construction and user manual
V1.1 for use with kits supplied after 1st June 07(Revised 1st June 07)
Hi res schematic diagram
V1.1 use your favorite graphics package to select required parts of the circuit.
Standard size diagram is included in the construction and user manual.
Construction and user manual
V1.0 for use with kits supplied prior to 1st June 07(Revised 13th May 07)
Front panel image overlay (issued
9th May 07)
Front panel reversed image
overlay (Issued 9th May 07)
Case drilling template (Issued
9th May 07)
Pic Program code (Issued 9th May 07)
Overlay (Revised 30th April
2007)
Block diagram
(now available in construction manual above)
Steve Drury G6ALU | 
