1240MHz/1280MHz DIY Helix Antenna

Just finished with my helix antenna, designed for 1240MHz.
Used the helix calculator from http://jcoppens.com/ant/helix/calc.en.php.
Parameters were 1240MHz, 8 turns, 0.23 wavelengths.

My internal helix diameter is roughly 80mm with a coil spacing of 55.5mm. Wire diameter is 3.5mm/10mm².
Reflector size is 250mmx250mm. Center support is made from 6mm Balsa, soaked with epoxy resin.
For matching the IBCrazy wave trap method is used. Trap size is 30mmx15mm. See also http://www.rcgroups.com/forums/showthread.php?t=1377791

 


Controlling a FPV receiver tuner module

Ok Dan, here you go. 😉

A short summary of my attempts to control the tuner modules of widely spread 1.3GHz FPV receivers.

The description covers the receivers coming with two sets shown below:

1.3 GHz Wireless AV Receiver

The first one is a 23 channel receiver, the second a 4 channel only.

Both receivers are equipped with the same tuner module which uses a TA1322FN down converter. The tuner module is driven by a micro-controller via I2C bus. Details about the internal I2C bus protocol can be found in the TA1322FN datasheet.

The tuner module is set by a single 4 byte data frame in both receivers.
The following is an example from the 4 channel receiver setting the receiving frequency to 1080Mhz:

Data frame send to tuner: 0xC2 0x30 0xBC 0x8E

Split up in accordance with the datasheet:

ADDR   1   1   0   0   0   0   1   0   = 0xC2
                          MA1 MA0 R/W
DIV1   0   0   1   1   0   0   0   0   = 0x30
          N14 N13 N12 N11 N10 N09 N08
DIV2   1   0   1   1   1   1   0   0   = 0xBC
      N07 N06 N05 N04 N03 N02 N01 N00
CTRL   1   0   0   0   1   1   1   0   = 0x8E
           CP  T1  T0 TS2 TS1 TS0  OS

ADDR = tuner module I2C address
DIV1 & DIV2 = PLL divider
CTRL = PLL control byte

Band switch byte is not send and therefore not used.
From the control byte the PLL is set to:
– 50uA charge pump current
– normal operation mode & charge pump on
– reference divider 1/64 resulting in 62.5 KHz reference frequency

The divider is set to 12476. With the following math it’s possible to calculate the reception frequency:
fosc = 2 x fr x divider = 2 x 62.5 KHz x 12476 = 1559.5 MHz

To high? No, you must subtract the 1. IF with 480 MHz, so 1559.5 MHz – 480 MHz = 1079.5 MHz

The 23channel receiver uses a slightly different data frame 0xC2 0x30 0xC8 0x8E which results in a reception frequency of 1081 MHz.

For my tests I used a USB-I2C interface. The USB-ISS from robot-electronics.co.uk is very handy for this purpose and supports not only I2C but also other bus types.

VS2010 Source code for PC based MFC program is attached to this post. The program will just let you set the reception frequency in a range from 850 MHz to 2200 MHz.

FPV Receiver tuner control
FPV Receiver tuner control
TunerControl.zip
Version: 1.0
207.6 KB
692 Downloads
Details

1.3 GHz Wireless AV set – Summery

Here is a little summery about the following 1.3 GHz Wireless AV set:

1.3 GHz Wireless AV Set

I got mine from eBay http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=300405272136

The set was shipped with the following items shown on the next picture:

1.3GHz Wireless AV Set

Transmitter

Technical details:

  • Supply voltage 12V
  • Supply current 280mA
  • Output power >28.5dBm
  • Size 65x50x20mm
  • Weight (measured) 62g complete; bare PCB 10g
  • SMA antenna connector
  • 3.5mm 4 pin AV+power jack
  • Gain adjustable
  • One button control
  • 15 Channels

Externals:

Transmitter FrontTransmitter TopTransmitter Bottom

Internals:

Transmitter PCB TopTransmitter PCB Bottom

As you can see there is no extra shielding around the PCB. Heat dissipation is mainly done through the bottom side of the PCB.
Some details about the components:

  • Philips TSA5520 1.3 GHz universal bus-controlled TV synthesizer
  • Futjitsu FLU10 RF power amplifier
  • 24C02B EEPROM
  • uC marked JX903D ???

Interesting is the separate EEPROM. Obviously the channel and frequency configuration is stored inside. Seems that is the first transmitter with possibility to use customized frequencies. I need to find out 😉

The EEPROM is used only to store the selected channel. The channel will be read on power up and stored on new selection.

Channel Frequency [MHz] Power [dBm]
1 993 28.3
2 1020 28.4
3 1050 28.3
4 1060 28.2
5 1080 28.2
6 1100 28.0
7 1120 28.0
8 1140 28.2
9 1160 28.6
A 1180 28.7
B 1200 28.6
C 1220 28.3
D 1240 27.9
E 1256 27.6
F 1280 27.3

Harmonic Distortion:

1. 28.04 dBm @ 992.97 MHz
2. -13.51 dBc @ 1.99 GHz
3. -16.15 dBc @ 2.98 GHz

Receiver

The receiver is similar to many others coming with such wireless AV sets. You have two buttons to control the receiver, one to cycle channels and a second to store channels for auto cycle.

1.3 GHz Wireless AV Receiver

A very interesting fact: The receiver is rated for the frequency range 0.9 – 1.56 GHz, split into 28 channels!

Channel Frequency [MHz]
1 921
2 993
3 1022
4 1051
5 1062
6 1081
7 1100
8 1120
9 1140
10 1160
11 1180
12 1200
13 1220
14 1240
15 1256
16 1280
17 1300
18 1320
19 1340
20 1360
21 1380
22 1400
23 1420
24 1440
25 1460
26 1480
27 1500
28 1520

Internals:

1.3GHz Wireless AV Receiver

The quality of the PCB looks much better on this receiver than on others I have seen so far. A large spring washer keeps the tuner module in place 🙄 But it’s also the first one with separate video amplifier. By default the gain of the video amplifier is fixed. But there are pads to solder a potentiometer (2KOhm) to adjust video signal level. Very useful if you drive more than one video input in parallel from the receiver.
Some details about the components:

  • TA7176 IF Amplifier+FM  Detector
  • EEPROM 24C02B
  • Philips NE592D Video amplifier
  • uC without marking
  • 78M05 + 78M09 Linear voltage regulators

The tuner module is common standard but the RSSI output pin is missing. You need to solder one yourself, the PCB is already prepared. See picture below.

Level [dBm] 	RSSI [V]
-115		0,786
-110		0,784
-105		0,781
-100		0,771
-95		0,758
-90		0,789
-85		0,938
-83,5		1,000
-80		1,160
-75		1,382
-70		1,601
-65		1,810
-60		3,370
-55		3,570
-50		3,660
-45		3,710
-40		3,750
-35		3,790
-30		3,870
-29		3,940
-25		4,340
> -20		4,340

The tuner uses the common TA1322FN Down converter in combination with a TA8804F FM demodulator. A 27MHz SAW filter ECS-D479.5B is used in the tuner. (Should be replaced by a ECS-D480A with 17MHz)

Antennas

No idea here. These antennas are usually crap so I will not test them for VSWR. Better stick with an Yagi and the Inverted-V.

Conclusion

With some rework this wireless AV set has a big potential for hacking and customizing.

Due to the fact that frequency configuration seems to be stored in EEPROM on both transmitter and receiver one can use almost any frequency within the RF specs of the devices. (For example not only one legal frequency at 1280MHz).

A separate shielding box needs to be made for the receiver. 65g for the original one is a way to much to carry up in the air. Also heat dissipation can be improved this way.

All in all I think that’s a good set, good hardware potential and better quality than I have seen before.

Channel RX Frequency
1 921
2 993
3 1022
4 1051
5 1062
6 1081
7 1100
8 1120
9 1140
10 1160
11 1180
12 1200
13 1220
14 1240
15 1256
16 1280
17 1300
18 1320
19 1340
20 1360
21 1380
22 1400
23 1420
24 1440
25 1460
26 1480
27 1500
28 1520
Auto 1540

L/S Band Low Noise Amplifier

While ago I bought a low noise amplifier kit from Jim at www.w6pql.com. I’m going to try the LNA for FPV purpose on the receivers side between the antenna and the tuner module.

The LNA is set to work in the L- and S-band between 900MHz and 1300MHz. Althought it’s possible to configure the LNA for use in 13cm band (2.4Ghz) as well. See Jim’s page for details.

Some pictures and a gain plot:

Gain is ~15dB @ 1200MHz.