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Picture: JM CHERRY
The ETEK model FR-4tr Readout was
designed as a companion frequency readout for amateur radio equipment
manufactured by R. L. Drake Company. Specifically, it is intended to interface
directly with the TR-3, TR-4, TR-4C and TR-4CW series of transceivers. When
interconnected with any of these units, the FR-4tr will provide both transmit
and receive frequency displays, even on units with RIT.
While intended primarily for use at a fixed station, the FR-4tr Readout can be
operated from mobile or portable power on all except the 10 meter band, since it
utilizes a high accuracy crystal controlled time base.
SPECIFICATIONS
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FREQUENCY RANGE (RF INPUT): 50 kHz to 50 mHz |
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SENSITIVITY: Better than 100mv-RMS |
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INPUT IMPEDANCE: 1.0 Megohm in parallel with no greater than 35 pf. |
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TIME BASE FREQUENCY: 3.579600 mHz |
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TIME BASE TEMPERATURE STABILITY: +-5 ppm, maximum in 20-30°C ambient |
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TIME BASE SETABILITY: +-2 ppm |
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GATE INTERVAL: 100 msec. |
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DISPLAY SCHEME: Non-flicker-last count held in memory |
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DISPLAY FORMAT: Six 7-segment red LED readouts (.3" high). LSD is 100 Hz. |
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POWER REQUIREMENTS: 105-130VAC, 60 Hz or 12VDC with user supplied dropping resistor |
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WEIGHT: 4-1/2 lbs. |
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CONTROLS: One three position switch OFF, COUNTER, READOUT (on back panel) |
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a) COUNTER-unit performs as a standard frequency counter |
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b) READOUT-unit corrects input for local oscillator offset and displays T/R frequency Even on unit with RIT. |
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CONNECTIONS: One RCA phono input (on back panel) |
OPERATIONS
Once connected to your transceiver as indicated above, the FR-4tr is ready to read out frequency. After applying power to the transceiver and to the readout bv placing the POWER switch in the up position, set the three position BAND switch in the proper position as indicated below:
BAND SWITCH POSITION
10 m Norm 15 m Norm 20 m 20 40 m Norm 80 m 80
Note that the readout will display a meaningless internal conversion number when the transceiver is
off or until it warms up.Theory of Operation
As indicated by the schematic diagram, Figure 2, your FR-4tr consists of four major sub-circuits. Each of these sections, the signal conditioners, time base, six decade counter and power supply will be discussed individually after a short section on the total system.
General
R. L. Drake transceivers utilize three distinct frequency mixing schemes in producing the desired transmit and receive signals. The particular mixing approach used at any given time is based on the amateur band selected. Each of these mixing arrangements will be discussed separately below:
| 80 Meters |
| 20 Meters |
| 10,15, and 40 Meters |
The transmit or receive frequency is simply the difference between 9.0 MHz (the receive i.f. and/or the transmit oscillator) and the PTO, since the crystal oscillator portion of the pre-mixer system is not used. Therefore, operation at the low end of the band corresponds to the high end of the PTO. As an example, the PTO would be at 5.5 MHz for operation at 3.5 MHz. (9.0 - 5.5 = 3.5)
The transmit or receive frequency is the sum of 9.0 MHz and the PTO. As in the case of 80 M operation, the crystal oscillation is not used. In this situation, however, operation at the high end of the band corresponds to the highest PTO frequency. As an example, the PTO frequency would be 5.5 MHz for operation on 14.5 MHz. (9.0 + 5.5 = 14.5)
The transmit or receive frequency is derived by first subtracting the PTO from the crystal oscillator and then subtracting 9.0 MHz from that result. As in the case of 80 M operation, the PTO will be at its high frequency end for operation at the low end of the band.
Note that the crystal frequencies used are 21.5 MHz (40 M), 35.5 MHz (15 M) and 42.5, 43.0, 43.6 MHz (10 M). As an example, operation at 21.5 MHz would utilize the 35.5 MHz crystal and the PTO at 5.0 MHz. (35.5 - 5.0 = 30.5), (30.5 - 9.0 = 21.5)
FREQUENTLY ASKED QUESTIONS ABOUT THE FR-4
Q: How does it hook-up? Do have
to modify my rig?
A: When used with any of the Drake R-4 or T-4X series of transmitters and
receivers, the FR-4 merely plugs into the injection jack, labeled INJ, on the
chassis of the unit. If, as is usually the case, you are using both the
transmitter and receiver in a transceive configuration, you will find it
necessary to unplug the INJ cable at one end and add a "Y" adapter
(such as a Switchcraft 330 FP1) in series. This will provide a tap for the FR-4.
In any case you must provide a short cable with a male phono connector on each
end. Note that there is no modification to the Drake equipment required.
Q: Once connected to my Drake "twins" will the FR-4 read both
transmit
and receive frequencies?
A: When the FR-4 is used with a separate transmitter and receiver its
reading will be based on the signal in the cable connecting the two units (the
injection cable). For this reason it will display both transmit and receive
frequency when either the transmitter or receiver PTO is in control. When the
mode switch is set to SEPARATE, however, it will read only t h e receive
frequency. This, of course, is not a concern to the user since he can check his
transmitting frequency by switching the mode switch to XMTR temporarily.
Q: Will the FR-4 provide accurate readout of auxiliary bands on my T-4X, R-4
station? Will it work with the FS-4?
A: The FR-4 will accurately display any frequency your rig can tune-in
fact, some users use junk-box crystals in the accessory crystal position to
create random 500 kHz band segments. Since the FR-4 takes both the crystal and
the PTO into consideration, it will always tell you exactly where you are. With
respect to the FS-4 synthesizer, the FR-4 will work fine since the synthesizer
is merely a substitute for the band selection crystals.
