manual at-9 xmtr

7/29/2019 Manual at-9 Xmtr

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AT-9

UHF SYNTHESIZED TELEMETRY TRANSMITTER

8/15/2006

Revised

05/2011

VLF / EENTEC1100 Forest Ave

Kirkwood,Mo.63122

Tel: 314-984-8282Fax: 314-984-8292

Web Site: www.eentec.com


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AT-9 Transmitter Manual

The AT-9 transmitter utilizes a commercially available, synthesized, UHF exciter combined with custom

circuitry to provide a low cost solution for FDM telemetry. A high efficiency buck converter provides a meansof adjusting the transmitters output power over a range of 100 mW to 2W. Output power remains constant over

an input voltage range of 12 to 14.5 VDC. Modulation distortion is extremely low, thus allowing the use of

multiple carriers with little or no intermodulation. Transient suppression is applied to the power and modulationinputs. With the addition of an optional quarter wave shorting stub installed across the RF output, the radio isextremely resistant to lightning damage.

Specifications

Type: Synthesized NBFM

Frequency Ranges: Specify 400-410.235 A band

410-420.235 B band420-430.235 C band

430-440.235 D band

440-450.235 E band

450-460.235 F band460-470.235 G band

Minimum Channel Spacing: 5 Khz

Frequency Stability: 2ppm, -30C to +60COutput power: 100mW to 2W adjustable

Output Impedance: 50 ohm

Harmonics: -58dB below carrierSpurious: -65dB or better

Audio Input Level: 1 Vrms for full deviationModulation Frequency Response: 300 -3500Hz

Modulation: True FM, no pre-emphasis

Modulation Input: 2K ohm, single endedModulation Distortion: 0.1% or better

Deviation: 5 KHz, internally adjustable with limiter

Operating Voltage: 12 V nominal (14.5 v MAX)

Operating Current: 75 to 430 mA (100mW to 2W)Size: 7" x 4" x 2"

Case: anodized aluminum

Operating Temperature Range: -30C to +60COperating Humidity: 0-95% RH (Non Condensing)

Controls: Power output (15turn pot)

Power and modulation mating connector: PT06-8-4S

Pin A: Power, Pin B Modulation Input, Pin C and D GroundAntenna connection: Type "N" (others available)

Specify desired operating frequency and power output when ordering so that unit will be properly tuned.

Frequency changes in excess of 200Khz require retuning in order to obtain best performance.


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Field Frequency Change

The exciter that forms the core of the AT-9 transmitter is frequency synthesized. The model # specifiesthe operating frequency range of the transmitter. Operation outside of this frequency range is not possible

without multiple component changes and reprogramming of the frequency synthesizer IC. Small frequency

changes on the order of 200 Khz can be done by changing dipswitch and or jumper settings, without retuningthe radio. Frequency changes outside of this range require retuning of the RF stages and resetting of the VCO

adjustment if the best performance from the radio is to be realized.

Base Frequency Table

Model# Frequency Range Base Frequency

AT-9-A 400-410.235 400.000 Mhz

AT-9-B 410-420.235 410.000 Mhz

AT-9-C 420-430.235 420.000 MhzAT-9-D 430-440.235 430.000 Mhz

AT-9-E 440-450.235 440.000 Mhz

AT-9-F 450-460.235 450.000 Mhz

AT-9-G 460-470.235 460.000 Mhz

In order to set the desired output frequency, first subtract the base frequency from the desired output

frequency. This gives the synthesizer programming frequency. It will then be necessary to close the appropriateswitches or jumpers to raise the transmitter above the base frequency. If the jumper and all switches are open

then the transmitter will operate at the base frequency. Closing a particular switch will increase the transmitters

frequency by the weight assigned to the particular switch or jumper. Note that the values are in a binaryprogression, so that you start by closing the highest valued switch or jumper that is less than or equal to the

synthesizer programming frequency calculated earlier. Once a switch has been closed remove the value of itsweight from the calculated synthesizer frequency and then close the next switch which is just less than or equal

to the remainder. Continue closing additional switches until the remainder is zero.

Jumper E6 to E7 5.120 Mhz

SW1 2.560 Mhz

SW2 1.280 Mhz

SW3 640 KhzSW4 320 Khz

SW5 160 Khz

SW6 80 KhzSW7 40 Khz

SW8 20 Khz

SW9 10 Khz

SW10 5 Khz

For example; assume the desired output frequency of an AT-9D is 438.675 Mhz.

Subtract the base frequency of 430.000 Mhz.

This makes the synthesizer frequency 8.675 Mhz.

Installing jumper E6-E7 removes a frequency term of 5.120 Mhz, leaving a remainder of 3.555 Mhz.Closing SW1 removes a frequency term of 2.560Mhz leaving a remainder of 995 Khz.

SW2 can not be closed because it would remove more than the remaining frequency.

Closing SW3 removes a frequency term of 640 Khz leaving a remainder of 355 Khz.Closing SW4 removes a frequency term of 320 Khz leaving a remainder of 35 Khz.


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SW 5,6,7 can not be closed as they would remove more than the remaining frequency.

Closing SW8 removes a frequency term of 20 Khz leaving a remainder of 15 Khz. Closing SW9 removes a

frequency term of 10 Khz and leaves a remainder of 5 Khz. Closing SW10 removes a frequency term of 5 Khzwith a remainder of 0.

If a frequency change is to be done in the field, first measure and record the VCO voltage at TP1 towithin 10 mV. This voltage is nominally 2.0 VDC at room temperature. This voltage will change as a function

of temperature and switch settings. It is important to retune VCO coil L1 after the frequency adjustment has

been made to produce the same voltage at TP1 as recorded prior to the frequency change, otherwise thedeviation sensitivity of the transmitter may be changed.

If the frequency change is done on the bench and a communications service monitor is available, then,

the VCO coil will be set to produce 2.0VDC at TP1, and the deviation of the transmitter can then be checked

and reset during the remaining tuning process.

Telemetry Application Notes

The exciter manufacturers schematics and troubleshooting are provided as part of this manual. Because

this exciter 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 exciter manual as they pertain to the use of this equipment specifically in the context oftelemetry applications.

Several modifications have been made to the exciter to make it usable with telemetry equipment. The

input amplifier gain was reduced to unity and pre-emphasis has been removed by removing C49. This is doneso that deviation is not proportional to frequency and so that higher level inputs, typical of telemetry systems

can be used. R6 was decreased from 100k to 51k so that excessive rolloff at higher frequencies will not occur.


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Alignment instructions

Alignment of this radio is similar to any narrow band FM transmitter once the synthesizer has been setup properly. Follow the instructions for field frequency change to set the synthesizer dipswitches and jumpers

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 willbe exposed to. This radio will inherently operate over a very large range of temperatures, however maximumpower efficiency may not be realized when the radio is operated near the extremes of its temperature range

unless tuning is done under these temperature conditions. Additional power efficiency improvements of 5% or

so may be obtained.

RF Alignment Procedure

1.) Adjust L1 for 2.00 VDC between TP1 and ground.

2.) Connect a wattmeter to the output of the radio.

3.) Always operate the radio with a 50 ohm load. At high power levels the output amplifier may be damaged by

either a short or an open load condition.

4.) Adjust C25 for maximum output power.




8.) Adjust C43 and C44 alternately for maximum output power.

9.) Adjust C45 and C46 alternately for maximum output power.

10.) Repeat steps 4 through 9 until no further improvement.

11.) Adjust power adjustment R3 for the desired output power

Deviation adjustment

1.) Apply a 1Vrms 1Khz low distortion sine wave between pin B (input) and pin C (gnd).

2.) Connect an oscilloscope (or distortion analyzer) between the high side of R35 and ground. Turn R26 CWuntil clipping is noticed on the peaks of the sine wave. Back off R26 very slightly. Then adjust deviation pot

R35 for a deviation of 5 Khz on a service monitor.


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manual at-9 xmtr

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