Celebrating 44 years of activity on UHF by OE8FNK

The El Burrito Transceiver for 6cm (EB6)

is a really simple 6cm single-band FM/CW transceiver that is also
suitable for DIY, as long as you can handle the SMD assembly.
Updated Feb 28, 2023

El Burrito 6cm (EB6) is published in DUBUS 1/2023

What do you need for the El Burrito EB6 Transceiver?

"Consider bulding at least 2 El Burritos"
So you want to build a EB6 transceiver? First and most important, you need
a radio amateur in your area that you can connect with. The El Burrito EB6
is most usable if you find another amateur within 30km range, This might
work also with reflection. If you have a line-of-sight location available
the distance is no consideration, e.g. 95km is usually noise free in FM
as long as you use a 60cm dish as antenna. So the first thing in this
project is to find a partner. While contest operation is possible, the
usual "big guns" will rarely use FM mode and will not spend much time
on testing, so you need to find a partner station for testing anyway.

1st: One MAX2870 Module, see here on Ebay: MAX 2870 Module
or on Amazon: MAX2870 Module look for "MAX2870 Module"
The correct one is with a 2x5 pin connector, 2.54mm pitch.
Do NOT take the "Lora" makes.
max2870 module

2nd: One ESP32 Wifi Kit:
V2 and V3 works, available on Amazon and Ebay. ESP32 Wifi Kit V3
or look on amazon.com for "ESP32 Wifi Kit V3".
esp32 wifi kit 32

3rd: The PCB for the El Burrito EB6 Frontend is available at
OE8FNK Project page at pcbway.com
This makes sense if you want to make the PCB and assembly yourself.
Detailed description for ordering the PCB is at the project site.
Description for partitially assembled PCB will be available abt. mid March.
Currently El Burrito V0 and V2 should be listed, but often there it is not
listed for one day after an update due to the review process. Please be

el burrito eb6 frontend

4th:: The DRA818u or SA818u Transceiver Module (only receiver is used):
DRA818u or SA818u are available on ebay.

5th:: More SMD parts:
See assembly plan for rest of the parts. Most SMD parts are 0603 size.
el burrito eb6 assembly plan

6th: Software: You need the Arduino IDE with the ESP32 and Heltec libraries
installed. This ESP32 sketch for the complete receiver will be released by
end of March 2023, Sketch for testing the modules will be released before
March 15. Stay tuned.

7th: Stay tuned: Send me your email just subject "el burrito" and
I will keep you informed about important new software and new findings.
Email is:

8th:NEW: Collection order: DUBUS 1/2023 has still not arrived at
all subscribers. I will wait until March 15 for a collection order of the
partitially assembled El Burrito EB6 frontend V2. If you are interested,
send me an email, see above. This PCB will include all parts except the
DRA818u, which is easy to solder onto the PCB later. Shipping is only
possible within EU.

9th:NEW: FM Modulation. In order to provide FM modulation, the
small voltage out of the electret microphone is sufficiant for a 3kHz
bandwidth. This is seems small, but matches the DRA818U receiver.
The +3.3V comes from the FM pin of the ESP32.
El Burrito FM modulation

10th:NEW: Connections. The three modules need to be connected
together. The modules are ESP32, MAX2870 Module and EB6 the El Burrito
El Burrito ESP32 connections

Detailed Pin Description for the El Burrito EB6
6cm transceiver as seen from the ESP32 Wifi Kit 32:

Pin-goes to- description
13 - CE  - output, enables MAX2870
17 - rxa - output to EB6, enables TX // only TX or 
14 - txa - output to EB6, enables RX // RX can be high
27 - FM  - output, enables FM modulation = +3.3V FM
26 - (1) - future use
35 - det - input, from EB6, TX power detector voltage 
34 - MUX - input, MAX2870 MUX, can be Lock detect
39 - sel - Push Button "select" on the QEI (*)
38 - QA  - input, QEI A - frequency up (*)
37 - QB  - input, QEI B - frequency down (*)
36 - ptt - input, Push to talk (*)
2  - (2) - future use
17 - (3) - future use
5  - LE  - output, Latch data to MAX2870
18 - CLK - output, SPI Clock to MAX2870
23 - data- output, SPI MOSI to MAX2870
19 - sdi - not used, but belongs to SPI definition
22 - RD  - RS232 Txd output to EB6 DRA818u RD 
21 - TX  - RS232 Rxd input from EB6 DRA818u TD 

(*) the 2 capacitors at 36/37 and 38/39 on the ESP32
board must be removed.
11th:MAX2870 testing sketch: to test the connections
between ESP32 and MAX2870 a minimal sketch is available for testing
on GITHUB: github.com/OE8FNK