- Ts 950sdx Serial Number Data
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million serial number on a TS-940 means that it was made in 1987 becuase they weren't made after 91 or so. Now the dillemma. The TS-940 has a serial range of 10 million (1989) during which some very significant changes were made to the design of the radiosuch as soldering in the eprom to eliminate erratic problems. First exposure to Kenwood's (at the time) flagship radio was through my friend Hank, KA8RZT (SK). He bought a second-hand rig in the early 90s, previously having used a TS-440SAT for most of his HF operating. The '940 was a capable, fully featured rig and it made a lasting impression on me. The TS-940S is supplied to operate from a 120V AC, 220V AC or 240V AC 50/60 1-IZ power source capable of supplying 510 watts or more. For units shipped to the U.S.A., the switch is set for 120 VAC with a 6-ampere fuse installed. For units shipped to European, Central, South Ameri- can, and African countries, the switch is set for. Apr 02, 2017 The product reviews glow with superlatives, and the field -proven performance shows that the TS-940S is 'The Number One Rated HF Transceiver!' 100% duty cycle transmitter. Kenwood specifies transmit duty cycle time, The TS-940S is guaranteed to operate at full power output for periods exceeding one hour 1 14.250 MHz. The Kenwood TS 940 is a dynamic radio transceiver for the serious amateur radio operator. It has many features, including the following: Interference reduction: Enjoy the combination of dynamic interference reduction circuits and a high range receiver for quality transmitter design to get your signal through. Coverage: TS 940 covers 160 to 10.
Home - Techniek - Electronica - Radiotechniek - Radio amateur bladen - Ham radio - An improved agc circuit
Add this circuit to your Kenwood TS-940S or TS-930S for DATA/RTTY reception.
Automatic gain control (AGC) circuits are used in receivers to adjust the gain of RF and IF amplifiers automatically. This prevents overdriving of the amplifier stages and maintains audio that's nearly constant with the varying strength of the input signal.
When propagation conditions are good, interference from atmospheric noise is minimal, and adjacent channel chatter from other signals is low, any AGC circuitry will provide satisfactory results for most modes of reception. However, when fading is prevalent, or atmospheric noise increases due to summer electrical storms and adjacent channel chatter builds up, it's important to improve the design of the AGC system. While even a well-designed AGC system won't take the place of an effective noise blanker, it will supplement the blanker and let you receive information you'd lose in the presence of adverse conditions.
I realize that many of you may question the efficacy of changing an AGC system like the one in the TS-940S. Since the system doesn't generate any clicks or pops and works satisfactorily for SSB, AM, and CW, consider that chang.ng it runs contrary to the old adage 'If it ain't broke don't fix it.' My question to you is: does it work well enough for data communications - RTTY, AMTOR, and packet? After a year or more of careful record keeping and diagnosis, I concluded the system wasn't effective enough. I found that nearly every case of an RTTY 'hit' or error in the copy had occurred on days when there was static from electrical storms. The major portion of the static was in the form of short duration noise pulses. While you might expect that -.such static errors would result from the addition of bits of data, most of the hits were caused by a loss of bits. I determined this by referring to the Teletypewriter Code and Garble Table.
I found these hits puzzling. If the receiver was blanking on or after noise pulses, why couldn't the blanking action be heard as it occurred? I reasoned that if the blanking action was of short duration, it could be 'seen' even though it couldn't be 'heard.' I connected an oscilloscope to the audio output, tuned the receiver to a vacant frequency, and watched the static pulses. I saw nothing of significance until I inserted a data signal using the 100-kHz calibration standard. I tuned the receiver to obtain a 2300-Hz audio tone and synchronized the scope to the tone. As I watched a static pulse, I could see the noise peak. But there was a loss of audio information immediately following the peak ,which lasted from 4.5 to 12 ms, depending on the position of the AGC switch. I found that the 'fast' position AGC was slower in recovering than the 'slow' position.
The data loss period is made up of the sum of three time intervals. The first is due to the duration of the noise pulse. The second is the circuit group delay (the time it takes the AGC to start to react to the noise pulse), which is about 1 ms according to Rohde.(1) The third interval is the recovery time of the AGC. When the total of these three intervals is an appreciable part of the length of time it takes for a bit to be sent, the bit is lost. The duration of the noise pulse is an act of nature and, unfortunately, uncontrollable. The circuit group delay depends upon the number of resonators, and varies inversely with the bandwidth. It can't be changed without making sacrifices. But you can modify the AGC's recovery time.
Once I understood the problem, I listened closely to the receiver and noted that the lag in AGC recovery immediately following the-static pulse caused a momentary quieting of the receiver. This, in turn, caused the loss of data bits. I decided that a reduction of the AGC's recovery time was required. It was necessary to come up with a reproducible test in order to work on the problem. I needed a test that would provide a pulse duplicating the effect of a static pulse on the receiver, so I wouldn't have to rely on electrical storms to measure my progress.
I devised the pulse generator shown in Figure 1. It has a 7.5-MHz crystal oscillator gated on for 2.5 ms at 2 Hz. The low pulse rate allows the AGC system to recover between pulses. None of the other parameters are critical.
Figure 1 - 7.5-MHz pulse generator.
U1,U2,U3 | 7400 |
Xtal | 7.5-MHz crystal |
RFC | 220µH |
The 7.5-MHz crystal came from my junkbox; the circuits are from QST(2) and The 555 Timer Applications Sourcebook with Experiments.(3) There's a broadly tuned circuit in the output which transforms the TTL voltage down to a usable value. I've provided outputs for the high and low level 7.5-MHz RF pulse and for the gate pulse. I built the generator on a Radio Shack perforated circuit board and mounted it in an aluminum box. I used a commercial 60-dB T pad attenuator with it to further reduce the generator low output.
The generator provided a calibrated 'noise' pulse, similar to a static pulse in its effect on the receiver when connected to the antenna input. I observed considerable rounding off of the pulse envelope with the oscilloscope connected to the output of the 8.83-MHz, 455-kHz, and 100-kHz IF This is to be expected in any transceiver with a narrow bandwidth similar to the TS-940S.
After I made my preliminary observations, I decided to make some changes in the AGC circuit and get some onthe-air experience. Details of the TS-940S AGC circuitry (reprinted with permission from the Kenwood Service Manual) are shown in Figure 2. I've found it convenient to think of this part of the AGC system as being made up of four 'sections' of related components. Table 1 lists the key components used in the various sections, along with their nominal functions.
An incoming IF signal provided at A of Figure 2 is rectified and doubled. A positive voltage is produced on the base of Q19. The voltage, which operates time constant sections 1, 2, and 3, comes from B and is established by setting the RF gain control. Current flows to 019 through R148 and R150. When the AGC is turned on, the drive to the AGC system at A sets the Q19 base voltage. This, in combination with the voltage from B and the drop through R148 and R150, establishes the collector current through 019. When 019 is driven harder by the IF signal (including noise pulses) Q19's collector goes down, dropping the voltage at the junction of R148 and R150. This causes the AGC circuits to react and lowers the AGC voltage at H to affect the transceiver's gain. The attack and decay of that voltage is determined by the components of the three sections.
Figure 2 - TS 940S AGC system.
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