RF Combo

Description: The RF Combo (A3016) integrates three circuits designed to support the development of circuit boards for Stage Four of a subcutaneous transmitter. The printed circuit board maintains the same outline as the RF Tester (A3014). The SAW Oscillator (A3016SO) replaces the A3014SO, featuring unconditionally stable amplifiers and other enhancements while retaining the same dimensions. The RF Spectrometer (A3008C) has been updated to eliminate the ineffective self-calibration system of the previous model, replacing it with a local oscillator output connector for calibrating the spectrometer's local oscillator against a SAW Oscillator reference. This component also shares the same shape and size as the Data Recorder (A3007C). The Demodulating Receiver (A3016DR) replaces the A3014DR and incorporates unconditionally stable amplifiers in the RF input stages to prevent oscillations caused by the SAW filter outside its pass-band and by antenna cables. The IF amplifier is designed to withstand over-driving without damage. Attenuators are used between IF amplifier stages to enhance stability under limiting gain conditions, and a low-pass filter is added to the demodulated output to eliminate the second harmonic of the IF. A final buffer is included to provide a robust 50-ohm output. The SAW Oscillator (A3016SO) operates effectively, initially presenting challenges with narrow pass-band filters like the 868.4 ±1 MHz B3570, which was previously used with the A3014SO. However, the A3016SO functions well with broader pass-band filters, demonstrating stability and robustness. The circuit can be stopped from oscillating by physical contact, yet does not produce parasitic oscillations. The amplifiers maintain unconditional stability, and output power remains consistent even when bias inductors are removed. Coupling capacitors are substituted with solder lumps on either side of the SAW filter. A table of output frequencies for various SAW filters is provided, including the mixing of the A3016SO output with the 868-MHz A3014SO reference circuit, with frequency measurements taken using an oscilloscope. The output frequency of the A3016SO is reported concerning the reference frequency, resolving any ambiguities with the aid of a 910 MHz reference from the A3014SO. A comparative table for the A3014SO is also included, detailing the use of capacitors, inductors, and solder lumps for filter coupling. Both oscillators work with the AFS915S3 filter. The A3014SO was anticipated to allow for frequency variation between 902 MHz and 928 MHz through adjustments to its coupling networks, but only a range of 900-910 MHz was achieved. In contrast, the A3016SO provides frequencies from 896 MHz to 928 MHz. The A3014SO remains necessary for narrow-band SAW filter oscillation due to its less stable amplifiers. Replacing the ERA-3SM with a MAR-6SM amplifier does not affect circuit functionality or oscillation frequency with the B3563 filter, which reliably provides a 864-MHz output required for the local oscillator input of the Demodulating Receiver (A3016DR). A temperature sensor is attached to the A3016SO near the ERA-3SM and SAW filter, monitored with an A2053. Cooling the board with freezer spray reveals changes in output frequency, with the desired LO frequency exhibiting stability during thermal fluctuations. The frequency decreases by approximately 0.1 MHz/°C, which is minimal compared to the A3013 transmission frequency variation of ±4 MHz/°C. The output from the A3016SO is applied to the LO input of the ADE-2.

The RF Combo (A3016) circuit design is structured to optimize performance in subcutaneous transmitter applications. The integration of the SAW Oscillator (A3016SO) with unconditionally stable amplifiers ensures reliable operation within the desired frequency ranges while mitigating the risk of oscillation issues typically associated with narrower filters. The careful selection of components, including the use of solder lumps for coupling capacitors, enhances the overall stability of the circuit.

The RF Spectrometer (A3008C) has been redesigned to improve calibration capabilities, allowing for more precise frequency measurements. The elimination of the previous self-calibration system in favor of a local oscillator output connector signifies a substantial advancement in the performance of the spectrometer.

The Demodulating Receiver (A3016DR) incorporates robust design features to withstand variations in input conditions, ensuring consistent output performance. The inclusion of attenuators and low-pass filters further enhances the integrity of the demodulated signals, minimizing distortion and harmonics.

The temperature stability of the A3016SO is a critical feature, as it ensures that frequency outputs remain consistent under varying thermal conditions. This characteristic is essential for maintaining reliable communication in subcutaneous applications, where environmental factors may fluctuate.

Overall, the RF Combo (A3016) presents a comprehensive solution for the development of advanced subcutaneous transmitters, combining innovative design with practical enhancements to meet the demands of modern electronic communication systems.The RF Combo (A3016) is a combination of three circuits. Its purpose is to provide circuit boards for Stage Four of our subcutaneous transmitter development. The printed circuit board has the same outline as the RF Tester ( A3014 ). The SAW Oscillator (A3016SO) replaces the A3014SO. This new version uses unconditionally-stable amplifiers and othe r improvements. It is the same shape and size as the A3014SO. The RF Spectrometer (A3008C) replaces the RF Spectrometer ( A3008C ). This new version eliminates the poorly-performing SAW filter self-calibration system, and replaces it with a local oscillator output connector that will allow us to calibrate the spectrometer`s local oscillator with respect to a SAW Oscillator reference. It is the same shape and size as the Data Recorder ( A3007C ). The Demodulating Receiver (A3016DR) replaces the A3014DR. This new version uses unconditionally-stable amplifiers in the RF input stages, so as to avoid oscillations provided by the SAW filter outside its pass-band, and by antenna cables.

Its IF amplifier cannot damage itself when over-driven. We use attenuators between IF amplifier stages in the hope that these will guarantee stability in the face of limiting gain. We add a low-pass filter to the demodulated output to get rid of the second harmonic of the IF. We add a final buffer to produce a large 50- © output. The SAW Oscillator (A3016SO) works well. We were at first confused by it because it would not oscillate with any or our narrow pass-band filters, such as the 868.

4 ±1 MHz B3570, which we used to produce our reference frequency with the A3014SO. But the A3016SO does oscillate with filters whose pass bands are a few megahertz or more. And when it does oscillate, the A3016SO is stable and robust. We can stop it oscillating by touching the circuit, but we cannot provoke parasitic oscillations. The amplifiers are unconditionally stable. The output power remains unchanged if we remove the bias inductors. We substitute solder-lumps for the coupling capacitors on either side of the SAW filter. Below is a table of the output frequencies we obtained for various SAW filters. We mix the A3016SO output with our 868-MHz A3014SO reference circuit, and look at the IF with our oscilloscope. We give the A3016SO output frequency with respect to the reference frequency. When the sign of the frequency was in doubt (868+4 MHz or 868 ’4 MHz), we resolved the ambiguity with the help of our 910 MHz reference A3014SO.

For comparison, here is a simiilar table for the A3014SO. The table includes the use of capacitors, inductors, and solder lumps for the filter coupling. Both the A3014SO and the A3016SO oscillate with the AFS915S3. We expected to be able to vary the oscillation frequency of the A3014SO between 902 MHz and 928 MHz by adjusting its coupling networks, but we succeeded only in a variation of 900-910 MHz. The A3016SO gives us frequencies from 896 MHz to 928 MHz. Because the A3016SO won`t oscillate with any of our narrow-band SAW filters, we still need the A3014SO, with its unstable, oscillation-happy amplifiers to provide us with our ultimate ±1 MHz frequency reference.

When we change the ERA-3SM for a MAR-6SM amplifier, the circuit still works, and the frequency of oscillation with the B3563 does not change. The A3016SO with the B3563 filter gives us a reliable 864-MHz, which is the frequency our Demodulating Receiver`s (A3016DR) requires for its local oscillator input.

We attach a temperature sensor to our A3016SO, near the ERA-3SM and SAW filter, read it out with a A2053, cooled the board with freezer spray, and watched how the output frequency changed. We want our LO frequency to be stable as our circuit heats up and cools down. The frequency drops by approximately ’0. 1 MHz/ °C, which is negligible when compared to the variation in A3013 transmission frequency of ’4 MHz/ °C.

We applied the A3016SO output to the LO input of the ADE-2