ComboStar HomeBrew Since 2012…. What is next?

I built my first combostar/picastar back in 2012.  I’ve made several modifications over the past three years including adding a STM32 based embedded board to do FreeDV.  Many of the parts were difficult to get and even more so now.  I learned so much from its construction and the wealth of information from the homebrew group that I’d really like to see an update or maybe something entirely new.  The DSP used is very old in the design, the TFT controller parts are dated some aren’t made anymore.  Here is the short list of reasons to update or come up with a new design for a homebrew HF rig.

  • There are better parts for the GUI out.  Integrated graphics STM32F4 would be a great upgrade.  Maybe multiple screens and small OLEDs have come way down in price for adding addtional controls at low cost and ease of use.
  • The DSP could be replaced with a STM32 series ARM keeping it all on the same platform.
  • There are already improvements to the H Mode Mixer and maybe a direct conversion would possible now with some of the low cost TI frontends and low power/cost FPGA.
  • Codec2 is widely availible and there is no reason not to include not only this digital mode but a hardware platform that may run future digital modes.
  • Modularization of the GUI, RF sections etc.  I really like the idea of mounting the radio somewhere and the GUI/MIC elsewhere.  I would also like to see VHF/UHF modules that utilize all the work done on digital modes/GUI keeping the idea of a remote/even distributed GUI Head.





DRA818V + Minicircuits Low Pass Filter.

The DRA818V

I wanted something small and almost disposable for APRS tracking.  The DRA818V fits the bill but needs low pass filtering.   Some photos of the prototype boards and output floor while TX outside intended band.  The SMD filter works great, inexpensive, and makes for a nice package.  I used a Mini-Circuits LFCN-160+.  The DRA818V can be found on Ebay.  OshPark manufactured boards I designed in KiCad.

DRA818V Filter



METCAL Models, Tips, n Tricks

If you are in the market for a soldering station you can’t really go wrong with MetCal.  The are dependable and easy to repair should something happen.  Instant heating, well placed heat, and an easy to use hand piece are just a few of the reasons to use an inductive RF soldering station.  New stations have come down in price and units from Thermaltronics are compatible.

Big issues are if you haven’t seen one or not generally “in the know”, finding used units that are usable can be difficult.  First, to have a working, station you will need 3 main components.  Below is a list of recommendations about how to get everything together.  I’m sticking with the high end industrial models and not the smaller units.

Power Supply / RF Unit

RFG-30 – These are the oldest MetCal in this series.  Good units.  No auto-shutoff. Has one LED Light

PS2e-1  – These are the next version with Auto-Shutoff.  Please note that these were produced in 220V and 110V. You want a -1 or -01 unit for 110V. Has 2 LED Lights.

MX-500 – These are one release behind current.  They offer two outputs but you can only use one at a time.

Hand Piece

Any MX-500 Hand piece will work. MX-RM3E

Newer Metcal MX-H1-AV

Thermaltronics – SHP-1


You will want either the MetCal Stand or the Thermaltronics.  They have magnets built it to keep tip cooler when not in use.  SHH-1




OpenSource HT Part 2.

Prototype boards for testing the RF module along with provisions for a low pass filter have been sent off for manufacture.  I’m expecting to see these back in a few weeks.  In the meantime below are links to the Gerbers for the test board as well as Kicad Modules for making your own boards that use the DRA818V module.

DRV818V Image




OpenSource HT Part 1.

I’ve been looking at migrating some of the work I’ve done on my ComboStar build to VHF/UHF including GSMK and Codec2.  With 3D printed case, lithium battery, STM32F405, DRA818V/U, and a nice OLED screen I think its possible to build a DIY 1 Watt radio that support analog, FSK (APRS), and Codec2 GSMK.  I already have several working STM32 projects with successfully generating various modulations including GMSK, POCSAG and AFSK.  My first step is to play with the DRV818V module and see how difficult it is to implement.  From the datasheet I’ve included a low pass filter in this prototype which I should be able to prototype with my existing STM project board.


First successful Combostar w/STM32 Codec 2 test.

It has taken almost 2 years but I finally did a local test on 30 Meters of the modified combo-star radio with a STM32F4 based digital codec board running the last port I could find of Codec2. There is still a lot of work to be done packaging, winding the rest of the filters, and completion of the high power sections. Must of the time was spent on independent projects and assembly of the combo-star was quite a undertaking.  Although a hacked combo-star which I’m sure most of them are in the end given the home brew nature, I’ve got something now I can work with that is all integrated.  Eventually I’ll even have it in a ready to go box.

KICAD on Mac OSX – The easy way.

If you have trouble getting KICAD to build and haven’t checked out homebrew you might want to check it out. I try to keep a current tap for KICAD.

To install first install homebrew if you haven’t already:

ruby -e "$(curl -fsSL"

Then tap the KICAD homebrew script to build.

brew tap shaneburrell/homebrew-kicad
brew install kicad

To update/upgrade to the latest KICAD as often as you like.

brew update
brew upgrade

MendelMax 1.5 Build

I’ve been working on several stepper controller boards for other projects and I needed something small to do testing.  The MendelMax 1.5 was a good option so I’ve started construction.  These take a considerable amount of time to source all the parts and I purchased the majority from McMasterCarr and Misumi. Both have excellent service, website, and very fast shipping.

MendelMax Parts
MendelMax Parts
MendelMax Bottom Frame
MendelMax Bottom Frame
MendelMax Mostly Assembled
MendelMax Mostly Assembled