Trango VRX2550 2.4 GHz Video Receiver Experiments |
Overview
This is quick hack to allow a Trango Systems VRX2550 EaglePLUS 2.4 GHz video receiver to receive slightly out-of-band frequencies.
The stock Trango VRX2550 is a high-quality analog video receiver (FM with NTSC/PAL video output) operating in the standard 2.4 GHz license-free Part 15 band. These analog wireless video systems are getting to be a bit dated, but there are still alot of consumer wireless security and surveillance video systems which utilize the 2.4 GHz band.
Several commercial Unmanned Aerial Vehicle (UAV), and other drone-type aircraft, even use the 2.4 GHz band for their streaming video downlinks. It's possible to intercept these video feeds to help keep an eye on the watchers.
The Trango VRX2550 uses a common 480 MHz Intermediate Frequency (IF) for the input to the FM video demodulating circuits. This IF signal is derived by mixing the incoming RF signal within a Mini-Circuits MBA-25L mixer along with a synthesized Local Oscillator (LO) signal. A Z-Comm SMV1960L Voltage Controlled Oscillator (VCO) is used for generating the local oscillator frequency, and is tuned 480 MHz below the received frequency.
The Trango VRX2550 has a PIC controlling a National LMX2325 PLL synthesizer to determine the local oscillator frequency for each of the four channels. It's possible to reprogram the LMX2325 for your own receive frequency or to even replace the voltage tune line with something manual.
Trango Systems VRX2550 EaglePLUS
Channel Receive Frequency (GHz) Local Oscillator Frequency (GHz) VCO Vt (Volts) 1 2.413 1.933 2.529 2 2.432 1.952 2.691 3 2.451 (microwave ovens) 1.971 2.851 4 2.470 1.990 3.011
You can manually "tune" the Trango VRX2550's local oscillator frequency by replacing the LMX2325 synthesizer control line going to the VCO with a DC control voltage from an external potentiometer. By manually sweeping this voltage from 0 to around 4 volts, the Z-Comm SMV1960L will cover approximately 1.7 - 2.2 GHz.
The VRX2550 will then be able to receive anything between 2.1 - 2.6 GHz - sorta... There is, however, an input RF bandpass filter right after the VRX2550's antenna input, so any frequencies away from the filter's 2.45 GHz center frequency will be attenuated by 20 dB or more.
This on-board 2.45 GHz bandpass filter may be jumpered and external filtering used, along with any optional pre-amplification.
A horizontal video synchronization (15.75 kHz) detector and an automatic channel scanner will also be added to this unit. The video synchronization detector lights a LED when a possible video signal is detected, and the automatic channel scanner "hops" through the four channels about once ever two seconds so you don't have to manually toggle through them.
Pictures & Construction Notes

Internal overview of a stock Trango Systems VRX2550 EaglePLUS video receiver.
The audio/video/DC power connections come into the case via the weatherproof connections on the case's left.
The VRX2550 board can be powered from +6 to +12 VDC. The current draw is around 400 mA.

Overview of the Trango Systems VRX2550 EaglePLUS video receiver circuit board.
The antenna connection is via the right-angle SMA jack on the left.
The BNC jack is for the Video Output.
The white RCA jack is for Left Audio Output. This connection also provides the audio output when operating in monaural (mono) mode.
The red RCA jack is for Right Audio Output.
The Toggle/RSSI push button selects the receiver's channel. The four green LEDs indicate which channel (1-4) the receiver is tuned to.
The screw terminals are for the DC power and the alarm outputs. The alarm connections will not be used in this application.

Component overview of the stock Trango Systems VRX2550 EaglePLUS video receiver circuit board.
These units are very well designed and the receiver utilizes "proper" microwave receiver components.

There is a 2-pole Murata 2.4 GHz bandpass filter after the antenna input and a low-noise receive amplifier, which I believe is a MGA-83563 (or equivalent).
The RF input feeds a Mini-Circuit MBA-25L mixer. The receiver's local oscillator is based around a Z-Comm SMV1960L VCO and is PLL synthesized with a National LMX2325. Using a PLL circuit prevents the receiver's frequency from drifting.
The mixer's 480 MHz IF ouptut is common for these types FM video receivers and the video demodulation is done by a Zarlink SL1461.
Two Motorola MC13055 FSK receivers handle the audio and alarm code demodulation.

Alternate view.
Two EPCOS B801 480 MHz SAW filters clean up the IF output from the mixer.
This surface-mount SAW filters have a farily high insertion loss (20 dB or so) and replacing them with external filters could possibly increase the receiver's overall sensitivity.
The right audio channel uses a 6.0 MHz audio carrier and the left/mono channel uses a 6.5 MHz carrier. The alarm data is also on the 6.0 MHz carrier.
An Analog Devices AD8367 provides the Received Signal Strength Indicator (RSSI).

Overview of the four channel indicating LEDs and the Toggle/RSSI push button.
These will be removed and panel-mounted for convenience.

Solder-side view of the LEDs. The have tiny 220 ohm resistors for current-limiting, but you may want to remove these so you have a bigger pad to solder to.
New 220 ohm resistors will added externally.

Overview of the voltage regulator components and PIC microcontroller.
The ten test pads can be used for tapping the board's +5 VDC, ground, video output, and left/right audio outputs.
Pin them out with an ohm meter. The square pad should be the video output.

Overview of the voltage tune line on a stock Trango Systems VRX2550 EaglePLUS video receiver circuit board.
This line controls the tuning voltage to the Z-Comm SMV1960L VCO. Switching in a potentiometer to vary this tuning voltage from approximately 0 - 4 volts allows you to manually tune the receiver over a (slightly) wider frequency range.

Scrap off the solder resist with an X-ACTO knife and cut the trace as shown.
The exposed trace going to the right is connected to pin 6 of the LMX2325 PLL.
The exposed trace going to the left is the voltage tune line for the SMV1960L VCO.
A relay will be used to switch between PLL and manual tuning for the SMV1960L VCO.

Drill a small hole in the PC board and route two #30 wires as shown.


Overview of the circuit board for the automatic channel scanner and the 15.75 kHz horizontal synchronization frequency detector.
For the automatic channel scanner, a TLC555 timer is configured in an astable operation with about a 2 Hz pulse rate. This then controls a relay in parallel with the Toggle/RSSI pads on the receiver's main board. This simulates pressing the Toggle/RSSI about once every two seconds.
Avoid faster channel scan rates, as it can take a moment for your video monitor to detect a valid video signal.
For the sync detector, a LM567 tone decoder is configured to detect a signal at 15.75 kHz. The center detection frequency is set by a high-tolerance 10 kohm resistor and 6800 pF capacitor. You may have to slightly tweak the value of the resistor to get the center frequency near 15.75 kHz. You can verify the LM567's detection frequency by monitoring the LM567's pin 5 with a high-impedance frequency counter. The detection bandwidth is just under 1 kHz.
The white relay is used to switch between PLL and manual tuning. The use of a relay is to avoid additional capacitance which could prevent the PLL from locking.
The 220 ohm resistors are for the new panel-mounted channel indicating LEDs.

Completed internal overview.
Try to keep the manual tuning wires as short as possible. You can use a multi-turn potentiometer for better frequency resolution in manual tuning mode, but you'll probably soon find it to be tedious. Slowly tuning a single-turn pot seems to be the least finicky.
The stock audio RCA jacks and video BNC jack where removed. New jacks were panel-mounted to the side of the case.

Alternate overview.

Completed overview with a matching Trango Systems AD2500-10 2.4 GHz patch antenna mounted on top.

Overview of the panel-mounted controls.
The banana jacks provide the DC power.
The RCA jacks are for the audio and video outputs. These outputs are at the standard "line levels." The impedance of the audio outputs is 600 ohms (unbalanced) and the video output is 75 ohms (unbalanced).
The manual tune 10 kohm potentiometer is on the left.
The red switch is for DC power.
The yellow switch enables the automatic channel scanner relay.
The green switch enables the manual tune relay.
The black push button is in parallel with the stock Toggle/RSSI switch on the receiver board.

Overview of the panel-mounted LEDs.
The four green LEDs indicate the receive channel and the red LED is for the video sync detector.


Household Data Systems (HDS) professional-level wireless video surveillance system. Complete with a fake pole-pig transformer housing and a $22,000 dollar price tag. The "1800" and "2500" in the model numbers most likely refers to the frequency bands they operated at. The Motorola HT most likely handled the camera pan/tilt/zoom controls.
TRON-Tek (tron-tek.com) still exists today. The "400" and "450" may refer to the 400 MHz UHF band.
Commmon wireless video carrier frequencies:
1710 - 1850 MHz 1990 - 2110 MHz (Part 74/Broadcast) 2200 - 2300 MHz 2402 - 2483 MHz 2450 - 2499 MHz (Part 74/Broadcast) 4400 - 5000 MHz 5250 - 5850 MHz 6875 - 7125 MHz (Part 74/Broadcast)
The audio subcarriers can be at 4.83, 5.8, 6.0, 6.2, 6.5, 6.8, or 7.5 MHz.