ARRL Home Brew Challenge I
A 40 meter Tranceiver.
Initially built around the Fall of 2008, but put aside due to time considerations. Digital board, VFO, and IF Board were mostly complete, LCD and input button array were complete.
Assembled Digital, VFO and IF Boards, but set it aside after some unsatisfactory testing. Project was abandoned due to lack of time and frustration with some problems I didn't understand at the time.
Held a sort-of 'Make and Mend' month in November 2010 to clean-up and repair old proejcts. Took a deep breath and picked up the old project. Identified a number of mistakes in the build and inital testing setup. In addition, my debugging skills had improved over the period.
- IF Board is not actually grounded, but relies upon it's connections to PA. This is to reduce ground-loop conditions, but caused much strange behavior. It was fortunatate the board wasn't ruined.
- Not grounding the IF Board trickled down to the LM386-based speaker amplifier, causing all havoc with the IC, but not ruining it. Sounded like a loud square wave.
- The reason ground was brought from Digital, but not terminated on IF is that those pins were to be used as a shield. Added shielding on a number of critical lines - left off during the original build.
- Four (4) BS170 FET transistors are used on the IF board. The particular part I obtained was a BS170P - good quality, but a BS170P is in an 'E-Line package', which has a pinout exactly opposite from a BS170 - so all 4 of mine were backwards.
Anderson Power Poles are provided for either battery input or a regulated Bench Power Supply. Batteries are not so good on this project. Operation seems best when input voltage is between around 12.5 VDC and 13.8 VDC.
An additional power option is provided by a 2.5mm x 5.5mm jack which supplies a reverse-voltage protected LM350-based DC Regulator. Regulation is held to 13.8 on RX and around 13.5 on TX. A relay switches OFF the Anderson Power Pole input.
Enclosure is from an old, recycled Video Sync Generator - the type you might use in the 1960s or 1970s if your (old analog) TV reception was poor. (Click on any Photo to Zoom).
General Layout (Bottom is Front).
- [Top-Left] Serial I/F and colocated RX/TX Bi-Color LED Driver,
- [Left-Middle] Optional DC Regulator,
- [Center Bottom] Digital Board,
- [Center Top] IF Board,
- [Lower Right] VFO board and a small LM386-based Speaker Amp tucked in behind the front,
- [Upper Right] Final PA.
Note the copious use of RG-174 coax internally for shielding:
- VFO to Digital
- RX in from PA to IF Board
- TX out from IF Board to PA
- Mixer 1 and Mixer 2 from Digital to IF
- IRF510 IC to PA Board
- PA Output to Antenna
In addition, Mic Audio In, CW Keyer Input, and Audio Output are all shielded with shielded audio cable.
Final Notes - December 2010
Added a simple Microphone. Finally decided on a simple 1/4" stereo jack for that final connection. Tests fine when run to a dummy load near my FT-897D.
Added an externally accessible serial interface to the PIC, using notes given in the given in the ARRLHBC Yahoo Group's 'Builders Notes' files. And, since I ran out of 'free prototyping space', I incorporated on this board a Bi-Color (Red / Green) LED Driver. Taking it's signal from the RXTX line, this shows Green on power on (and during Receive), and Red during Transmit.
Items Added to the project included:
- An LM350-based DC Regulator board - this accepts 19 VDC / 4.9 A from a scrapped HP Laptop supply
- An LM386-based Audio Amp supplying about 1/4 watt for an external speaker if necessary.
- A TTL to Serial Interface board to allow reloading the PIC Microcontroller code via it's bootloader. Colocated on the board is a Bi-Color LED Driver using the RX/TX line as input.
- A Serial-Port PTT facility for use with PSK31. This was added to the TTL to Serial Interface.
Added a VOX for PSK31 to simplify the number of connections. And here's how it looks from 1320 miles away from Dallas. Thanks very much to VE3NOO for the screen cap and also for the QSO.