Difference between revisions of "PTT and band switching"

Latest revision as of 14:48, 27 October 2022

In order to make the Portsdown transmitter integrated with transmit and receive systems, Pin 40 of the GPIO goes high when transmit is selected and the signals on pins 28 and 35 can be used for band switching.

Band outputs

These outputs are used to switch the LO filter and can be used to switch external filter and amplifiers.

Frequency Mhz	ATV Band	Pin 28	Pin 35
< 100 MHz	71 MHz	Lo	Lo
100 - 250 MHz	146 MHz	Lo	Hi
250 - 950 MHz	437 MHz	Hi	Lo
950 - 4400 MHz	23cms	Hi	Hi

Care must be taken to properly buffer these 3.3v signals from relay transients.

GPIO band decoder

As we only have 2 GPIO pins to provide 4 outputs, these outputs need to be decoded to provide an output for each band.

The Portsdown team have designed a simple board which can be either constructed on 0.1” perforated board (veroboard) or on a PCB - this can be home etched using the details below or blank PCBs are available in the BATC shop.

File:DECODE 4 Band instructions (2).pdf

File:Decode 4 Band Schematic.pdf

File:Decode 4 Band Perf Bd wiring.pdf

File:DECODE 4 Band Mirrored w SS.pdf

File:DECODE 4 Band Mirrored.pdf

File:DECODE 4 Band PCB Layout w SS.pdf

File:DECODE 4 Band Decode BOM 4bbom.doc

PTT steering

These band outputs can then used to "steer" the PTT line to the correct Power Amplifier using this simple relay and diode circuit - no PCB needed :-)

Tx Rx sequencer

We also recommend the use of a Tx / Rx sequencer to ensure your mast head relay has changed over and your expensive pre-amp is de-powered before you start transmitting. The sequence is as follows:

To go to Tx:

1) Turn off receiver pre-amp

2) Switch ant c/o relay to transmit

3) Apply power to PA

To go to rx

a) Turn off Tx

b) Switch ant c/o relay to receive

c) Apply power to pre-amp.

Many circuits and pre-built designs are available including this simple single chip design by Ian Waters G3KKD published in CQ-TV 125.

David M0YDH shows Ian's design in operation:- G8ADE RELAY SEQUENCER VIDEO and an updated version with extra relay for Portsdown PTT band switching..

W6PQL and W1GHZ have sequencer designs.

Summary of GPIO connections

As the Portsdown project has expanded in scope, so has demand for the GPIO connections on the RPi. Here is the latest list as of January 2018:

Pin No	BCM No	Wiring Pi	RPi Name	Primary Use	Secondary Use	DTX-1 Use
1	-	-	3.3v	-	-	EXT-DVLM
2	-	-	5v	-	-	-
3	2	8	SDA 1		-	EXT-SD0
4	-	-	5v	-	-	-
5	3	9	SCL 1		-	EXT-SD1
6	-	-	0v	-	-	-
7	4	7	GPIO 7	Keyed Streaming LED Indication	Transverter Select or incoming stream active	EXT-SD2
8	14	15	TxD	ADF5355 LE	Elcom LE	EXT-SD3
9	-	-	0v	-	-	-
10	15	16	RxD	Attenuator LE	-	EXT-SD4
11	17	0	GPIO 0	LCD Display	-	EXT-SD5
12	18	1	GPIO 1	Keyed Streaming or Keyed TX Switch	Hi to Stream/TX	EXT-SD6
13	27	2	GPIO 2	'Active' LED	Active Hi	EXT-SD7
14	-	-	0v	-	-	-
15	22	3	GPIO 3	Shutdown Button	Hi to activate	EXT_TSCLK
16	23	4	GPIO 4	LCD Display	-	-
17	-	-	3.3v	-	-	-
18	24	5	GPIO 5	LCD Display	-	EXT-PSYM
19	10	12	MOSI	LCD Display	-	-
20	-	-	0v	-	-	-
21	9	13	MISO	LCD Display	-	-
22	25	6	GPIO 6	LCD Display	-	-
23	11	14	SCLK	LCD Display	-	-
24	8	10	CE 0	LCD Display	-	-
25	-	-	0v	-	-	-
26	7	11	CE1	Touch Sensor	-	-
27	0	30	SDA 0	ADF4351 LE	-	-
28	1	31	SCL 0	Band LSB (D0)	-	-
29	5	21	GPIO 21	ADF4351 CLK	Atten and ADF5355 CLK	-
30	-	-	0v	-	-	-
31	6	22	GPIO 22	ADF4351 DATA	Atten and ADF5355 DATA	-
32	12	26	GPIO 26	I output	"Ugly" and RPITX RF output	-
33	13	23	GPIO 23	Q output	-	-
34	-	-	0v	-	-	-
35	19	24	GPIO 24	Band MSB (D1)	-	-
36	16	27	GPIO 27	IQ Filter LSB (D0)	-	-
37	26	25	GPIO 25	IQ Filter NSB (D1)	-	-
38	20	28	GPIO 28	IQ Filter MSB (D2)	-	-
39	-	-	0v	-	-	-
40	21	29	GPIO 29	TX LED and PTT Drive	Hi = TX	-

Each pin on the RPi3 GPIO can be referred to in 4 ways: its physical pin number, the Broadcom I/O number, the Wiring Pi number or the name. Where possible, the Portsdown software uses the Wiring Pi driver and hence Wring Pi numbers in the code. The Broadcom numbers are referred to on the Willow Electronics GPIO breakout board.

For reference, here is the original Portsdown GPIO allocation chart, drawn up in early 2017.

@@ Line 45: / Line 45: @@
 [[:File:DECODE 4 Band PCB Layout w SS.pdf]]
-[[:File:DECODE 4 Band Decode BOM 4bbom.xlsx]]
+[[:File:DECODE 4 Band Decode BOM 4bbom.doc]]
 ===PTT steering===
@@ Line 80: / Line 80: @@
 David M0YDH shows Ian's design in operation:- [http://youtu.be/u4AeW-bPYxo G8ADE RELAY SEQUENCER VIDEO]
 and [https://www.youtube.com/watch?v=pUudd2GR63w&feature=youtu.be an updated version with extra relay for Portsdown PTT band switching.].
-If you prefer an elegant kit solution then you could try the [http://www.shortwaveradio.co.uk/tropic.htm. TROPIC sequencer from Shortwave radio.]This is listed at £11.50 but price is available on application. W6PQL and W1GHZ have sequencer designs.
+W6PQL and W1GHZ have sequencer designs.
 ===Summary of GPIO connections===
@@ Line 112: / Line 113: @@
 | 11 || 17 || 0 || GPIO 0 || LCD Display || - || EXT-SD5
 |-
-| 12 || 18 || 1 || GPIO 1 || Keyed Streaming or Keyed TX Switch ||  || EXT-SD6
+| 12 || 18 || 1 || GPIO 1 || Keyed Streaming or Keyed TX Switch || Hi to Stream/TX || EXT-SD6
 |-
-| 13 || 27 || 2 || GPIO 2 || Shutdown LED ||  || EXT-SD7
+| 13 || 27 || 2 || GPIO 2 || 'Active' LED || Active Hi || EXT-SD7
 |-
 | 14 || - || - || 0v || - || - || -
 |-
-| 15 || 22 || 3 || GPIO 3 || Shutdown Button || || EXT_TSCLK
+| 15 || 22 || 3 || GPIO 3 || Shutdown Button || Hi to activate || EXT_TSCLK
 |-
 | 16 || 23 || 4 || GPIO 4 || LCD Display || - || -
@@ Line 168: / Line 169: @@
 | 39 || - || - || 0v || - || - || -
 |-
-| 40 || 21 || 29 || GPIO 29 || TX LED and PTT Drive || - || -
+| 40 || 21 || 29 || GPIO 29 || TX LED and PTT Drive || Hi = TX || -
 |}