Download VLF Designs specializing in Analog Telemetry Earthquake

RCV-***
SYNTHESIZED TELEMETRY RECEIVER
8/15/2009
REV 10/2012
VLF Designs
1621 Bella Vista Dr.
Jackson, Mo. 63755
PH 573-204-1286
[email protected]
RCV-*** Receiver Manual
The RCV-*** receiver utilizes a commercially available, synthesized, receiver module combined with custom
circuitry to provide a low cost solution for FDM telemetry. The receiver has been customized by replacing the extremely
narrow band crystal filters with a wider band monolithic ceramic filter. The 2nd IF ceramic filter has been replaced with a
linear phase response unit in order to insure very little distortion in the demodulated signal, thus allowing the use of
multiple carriers with little or no intermodulation. A 5 pole low pass filter has been added to the output to minimize out of
band noise from the receiver. As an option, the receiver audio output can be transformer coupled. Transient suppression is
applied to the power and demodulation outputs. With the addition of an optional quarter wave shorting stub installed
across the RF input, the radio can be made extremely resistant to lightning damage.
Specifications
Frequency Ranges: Specify Desired Operating Frequency
RCV-144
144.000-154.235Mhz
RCV-154
154.200-164.435Mhz
RCV-164
164.400-174.635Mhz
RCV-210
216.000-226.235MHz
RCV-220
220.000-230.235MHz
RCV-400
400.000-410.000MHz
RCV-410
410.000-420.000MHz
RCV-420
420.000-430.000MHz
RCV-430
430.000-440.000Mhz
RCV-440
440.000-450.000MHz
RCV-450
450.000-460.000MHz
RCV-460
460.000-470.000MHz
Type: Synthesized NBFM
Minimum Channel Spacing: 5 Khz
Frequency Stability: 2ppm, -30C to +60C
Modulation Acceptance: ± 30 Khz
Input Impedance: 50 ohm
Sensitivity: 0.35uV or better (12 db SINAD)
Selectivity: -50 db at ±25 Khz
Image Rejection: 60 dB
If Filter: 10.7Mhz Ceramic, 455Khz Ceramic
Frequency response: 300 -3500Hz
Distortion: 1.5% or less, 0.8% typical
Output Impedance: 100 ohm
Output level: 5Vp-p Maximum
Operating Voltage: 12 V nominal, 11 to 14.5VDC
Operating Current: 40mA Max 35 mA. Typical (depends on output level)
Size: 7" x 4" x 2"
Case: Anodized Aluminum
Controls: Squelch, Output level
Operating Temperature Range: -30C to +60C
Operating Humidity: 0-95% RH (Non Condensing)
Power and modulation mating connector: PT06-8-4S
Pin A: Power
Pin B: Audio output
Pin C and D: Ground
Antenna connection: Type "N" (others available)
Specify desired operating frequency and audio output level when ordering so that unit will be optimally tuned.
Field Frequency Change
The receiver that forms the core of the RCV-*** is frequency synthesized. A microprocessor
programmed at the factory is used to set the operating frequency. This microprocessor is installed in an 8
position DIP socket. Frequency changes of less than 500 Khz can be performed by simply replacing the
microprocessor. Frequency changes greater than 500 Khz are done in the same fashion but may require retuning
of the whole receiver for optimum performance. Two additional frequencies can preprogrammed into the
microprocessor when the radios are ordered. Selection of these frequencies is explained later in the manual.
If a frequency change is to be done in the field, first replace the microprocessor IC with one for the new
frequency. Then, retune VCO coil L1 to produce 2.0 ± 0.5VDC at TP1 , otherwise the lock range of the VCO
may be decreased.
If the frequency change is done on the bench and a communications service monitor is available, then,
the entire receiver should be retuned for optimum performance.
Telemetry Application Notes
The receiver manufacturers schematics and troubleshooting for the VHF version of the receiver are
provided as part of this manual. The UHF version is similar. Because this receiver can be used for many
different applications, not all of the manufacturers information will be applicable to the telemetry application.
The alignment procedure that follows should be used in place of any instructions from the receiver manual as
they pertain to the use of this equipment specifically in the context of telemetry applications.
Several modifications have been made to the receiver to make it usable with telemetry equipment. The
low impedance output amplifier components have been removed in order to conserve power. FL-4 is a wider
bandwidth ceramic filter, and all 4 crystal filter elements and their associated components have been removed in
order to minimize passband distortion. FL-5, the 2nd IF filter has been replaced with a linear phase version in
order to minimize distortion in the demodulated signal. C44 was removed to remove modulation de-emphasis.
R38 was changed to lower distortion.
Alignment instructions
Alignment of this radio is similar to any narrow band FM receiver once the synthesizer has been set up
properly. Follow the instructions for field frequency change if the radio operating frequency is to be changed.
Alignment should be performed at a nominal input voltage of 12.5 VDC.
Alignment of the radio should normally be done at the average temperature the radio will be exposed to.
For most applications, this is normal room temperature. However if the radio will only be used in a climate
substantially different, then the alignment should be performed at the average of the temperatures the radio will
be exposed to. This radio will inherently operate over a very large range of temperatures, however minimum
distortion may not be realized when the radio is operated near the extremes of its temperature range, unless
tuning is done under these temperature conditions.
RF Alignment Procedure
1.) Adjust L1 for 2.00 VDC between TP1 and ground.
2.) Connect a service monitor set to receive with the input cable draped near the radio. Set the service monitor
receive frequency to 10.7 Mhz below the receiver operating frequency. Adjust TCXO U3 to zero the first LO
relative to the service monitor.
3.) Set the service monitor to transmit at the receiver operating frequency. Set the modulation to 1KHz and the
deviation of the service monitor to 5 Khz. Connect the audio output of the receiver to the SINAD input of the
service monitor. Adjust the audio output for 1.0Vrms. Adjust the RF output level of the service monitor to
produce a SINAD level of approximately 10-12 dB. Readjustment of the generator output level may be required
as each stage is tuned.
4.) Adjust C29 for best SINAD value.
5.) Adjust C30 for best SINAD value.
6.) Adjust C21 for best SINAD value.
7.) Adjust C24 for best SINAD value
8.) Adjust C32 for best SINAD value
9.) Adjust C33 for best SINAD value.
10.) Adjust C31 for best SINAD value
10.) Repeat steps 4 through 10 until no further improvement is obtained.
11.) Set T1 to mid range. (tuning is not important without crystal filter)
12.) Set signal generator for full receiver quieting. (typically -80dBm) and adjust quad coil T2 for minimum
distortion.
13.) Optionally adjust U3 tcxo to minimize distortion. This will match the IF frequency to the output of the
mixer.
14.) Set receiver output to desired level (typically 1Vrms for 5 Khz deviation)
15.) Set service monitor RF output level to produce 12 dB SINAD level. Record this value as receiver
sensitivity.
Optional squelch set up
1.) Set generator to 0.3uV output and adjust pot to squelch receiver output then turn squelch pot CCW until
receiver just unsquelches
2.) Decrease generator output level to .2uV and verify that receiver squelches.
RECEIVER BASE LAYOUT
RECEIVER BASE SCHEMATIC