The long wait begins... The first SBHT Prototypes have went to fab and parts have been ordered. There are a lot of untested sections in this design so build up of the first rev boards will be slow.
Just a sneek peak at what I've been slowing working on for the past few years. After building a number of test sub assemblies, filter testing, device selection flops, and lots of hours I've started routing the first prototype of a VHF Transceiver capable of TDMA operation at decent wattage.
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.
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.
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
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.
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.
I've started work on my ComboStar HF DSP based radio. Overall with a few hard to find parts, it's a great project to build. Assembly has been easy with a large selection of alternate parts on on the board. The BOM and schematic kept confusion thus far to a minimum. Big thanks to W4ZCB and SP5TAA for sending critical parts (Crystals and EEPROM). Mouser does sell a 16.67mhz but not in the package provided on the board. Thus far I have the DSP booting and awaiting more parts to complete the build. I completing my build with 805 size parts and hot air aides in getting everything straight. There are a few 603 exceptions such as LED's and in a few places I used 603's with parts I had laying around.
I've done about 98% of the board using mouser for parts sourcing. RFParts has the filter. Several members of homebrewradio provided critical crystals and EEPROM. Kitsandparts has magnetics and wire. The only items that were hard to come by seems to be the mini-circuits parts. I found a close match that pulse manufactures that I will try in place of the MCL 4:1 part (This likely won't work and W4ZCB was kind enough to send me an alternate). I was able to locate the amp on Ebay in small quantities. I've been assembling as parts arrive and testing voltage prior to setting any major components. So far so good and only a few mistakes that were easy fixes with hot air assistance.
DSP Testing the ComboStar. This is the first step in testing and be sure to check voltages prior to placing anything expensive. Also on the DSP be very careful as the pins are fragile. The technique I used was flux first, then tack a pad placing the part where you want it. You have to use very light pressure with iron to prevent bending pins. Ensure you have no burrs on the tip prior. If you evenly apply solder as you go down each row of pins you won't have to wick any excess. I've found that a continuous motion leading a bead of solder over the work does well with no or little cleanup.
More progress and DSP section is loading with Blinking LED. Just as a note for troubleshooting - No LED check LED orientation (You should have check voltages prior to DSP soldering). Solid LED - Check pF on crystal. Likely not enough capacitance = lazy clock. I used 22pF. Also for clarification to power DSP attach to DSP section and install jumper.
The OCXO section was tested and a nice clean output is seen. Any OCXO could be used in theory. The DDS input reference is 400mhz max and the IC has a 4x-20x multiplier. The schematics are for a 3.3v OCXO but this could easily be modified to work with several units. Assembly was straightforward but a heat-sink had to be made to fit in the board space. I drilled and tapped a hole to allow the heat-sink to sit off the board to stay clear of the components for the regulator underneath. A heat-sink is required as this part gets very hot. With the heat-sink shown the temps get warm to the touch but dissipation is well within the 317's spec.
Various Photos during the build.
Here a few screenshots of an IOS application I've been working on to allow IOS devices to communicate with external CAD systems. This particular integration is with TicketsCAD.
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.