The FARS team has developed another useful Amateur Radio Project! This unit is based on surplus Bluetooth modules and provides a combined source, and level meter for the 13cm band. It can also provide test signals via harmonics for both the 10GHz and the 24GHz amateur bands.
This innovative project came from the golden rule of Ham radio “what else can we use those for?” Following a failed commercial project, a quantity of high quality WT12 Bluetooth modules became available. With the help of a very talented embedded software engineer, the VCO, PLL, PA & RX on-board the silicon yielded to software control and this project was born.
This page is also available as a PDF here.
This innovative project took the Construction Competition title at the Scottish Microwave Roundtable (GMRT) November 2017.
Kevin G3AAF accepting the Award along with the entry.
Bluetooth technology exists in every mobile phone, laptops, cars, and many more consumer technology items. The first generation Bluetooth modules were quite large (25mm *15mm) but size has been reduced in more modern parts. Bluetooth (BT) operates in a band almost 80Mhz wide, between 2402Mhz and 2480Mhz which is divided into 1Mhz channels normally used on a Frequency hopping (Gaussian Frequency Shift keying) GFSK basis.
Three power classes are available, class 1 at 0dbm, class 2 at +6dbm, and class 3 at +20dbm. The BT module in this project is class 2 type and enables the project to offer a conducted power to the SMA port up to a maximum of +4dbm.
The project software is loaded by a pre-installed boot-loader into a Freescale micro-processor. This provides a number of functions, controlled by a single rotary encoder with push switch, with a simple-to-use menu structure which is displayed on a standard 1604 LCD display. The signal output can also be keyed with entry of the desired text being intuitively available by means of a “rotate and click” menu editor for each character.MenusGenerateSweepModulateReceive
Four menus are provided in software for storing user settings, regularly used functions, and the software version. The integral boot-loader allows for software updates to be downloaded, and programmed with a standard USB to TTL lead, removing the need for any PIC programming hardware.
Applications in the Shack
Most surplus, low cost signal generators have an upper limit of 1Ghz. Even the relatively expensive Marconi 2024 stops at 2.4Ghz. Thus achieving continuous coverage of the 13cm band with generator & sweepers is difficult. Surplus Sweepers (HP, Wiltron etc.) are great to own, but have multiple plug-ins taking a huge amount of bench space, power and time to keep them working to specification….
Having a small 13cm source is therefore very helpful and amateurs have devised many ad-hoc ways to provide similar functions. Examples are the 13cm Comb Generators by G0MRF, re-purposed “brick” oscillators, and simple diode multipliers from RF signal generators.
This module provides continuous coverage from 2200 to 2750Mhz in 1 Mhz steps and will thus be a useful addition even to a well equipped shack.
A marker on 10.368Ghz (the 4 th harmonic of 2592 Mhz) can be devised by adding a BAT 15-04 or similar diode directly to the SMA output. This will provide an easily portable, low level 10GHz signal when operating /P, as well as enabling confidence checks on your sensitive transverter, LNA, antenna and rig in the shack.
The 9th harmonic of 2672Mhz can similarly be useful as a low-level 24Ghz marker on 24.048GHz. Stability in the transmit mode is respectable, considering the simplicity of the equipment. Typically a wander of +/- 250Hz is observed in the 13cm band (+/- 1KHz at 10GHz). The unit should be warmed up for about 20 minutes (and kept out of draughts!) to achieve its best stability.
The sweep function can be used in conjunction with a suitable Spectrum Analyser to view the response of a filter, or amplifier using the Max hold function.
Power supply requirements are 11-15V DC with a maximum demand of 70mA.
The power input is protected against reverse polarity & regulated down 7V for portable battery operation.
In transmit mode the module may be loaded into any output SWR without damage.
In receive mode the maximum permitted input level is +20dbm. The module may be damaged if this limit is exceeded.
It is not designed or intended to be used as, or replace a Local oscillator. Because the phase noise is not adequate, typically the Bluetooth phase noise specification is
<-80dbc/Hz @ 1Mhz offset, <-110dbc/Hz@2Mhz offset, <-120dbc /Hz @3Mhz offset. Spurious and Spurs are TBC Future Hardware /software enhancements ideas:
- Divide By 2 for 23cm band
- Multiply maths option in software
- Beacon only option Keyer kit, no Bluetooth module
- Software function to Auto flatten output power over frequency band
Current software Version: V0.18
Click here for the guide on Programming using Bootloader – Word Document
13CM Source by PA0BAT
Ideas are in the pipe line for a 3D Printed enclosure, but a case could be bought in, or found in a junk box. All that is needed is a small enclosure, with a window for the display, and few small holes need drilling for the rotary encoder, RF Output, Power, and anything else you want to include.
Such as Gerrard PA0BAT’s enclosure, with a plug in PSU, a Mod LED, and a PTT. The case is wedge shaped so the display is angled toward you for easier viewing. Nice work Gerrard.
Please send a photo if you have a 13CMS source, and have put it in a case. We’d be happy to show it here.
Roger GM4PMK sent us a picture of his