Development of uhf spark-switched L-C Oscillators
Spark switched L-C Oscillator (LCO) transmitters have operated in the Low, Medium, and High Frequency Bands (10's of kHz to 10's of MHz) throughout the history of radio. In the 1970's they were pushed into the vhf Band by Moran, et al. By applying ultra-fast gas switching techniques and by overcoming spark gap losses the authors have operated LCO transmitters in the uhf (300 MHz to 3 GHz) region. Repetition rates >1 kHz with peak voltages >100 kV have been achieved. Uhf oscillators are inherently small because of the low inductance and capacitance required to generate ultra-high frequencies. This size constraint forces the device to operate at very high voltage in order to store enough energy to drive the antenna in spite of series switch losses and parallel corona and stray capacity losses. The spark gap must close in a time short compared to one half an R-F cycle for efficient switching; this equates to a few hundred picoseconds at uhf. The LCO output is a damped sinusoid of a few cycles duration. While the fractional bandwidth (3-dB bandwidth divided by the center frequency) can be 10% to 80% depending on the Q, it is much smaller than the bandwidth of UWB impulse sources (100% bandwidth with multioctave coverage). Compared to UWB, the narrower bandwidth permits the use of higher gain antennas which can efficiently increase the effective radiated power (ERP) over a given frequency range. The authors have constructed L-C Oscillators with center frequencies of 450 MHz up to 800 MHz. The Q of these oscillators varies from 6 to 8 for the 450 MHz device, down to 1 to 2 for the 800 MHz unit. Q is increased when a resonant antenna or antenna-reflector combination is added. Prototypes with simple fat-dipole antennas and small parabolic reflectors (8 inches [times] 20 inches) have radiated normalized electric field strengths of 30 kV/m at 1 meter (measured in far-field and extrapolated back to 1 meter).
- Research Organization:
- Sandia National Labs., Albuquerque, NM (United States)
- Sponsoring Organization:
- USDOE; USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 6386956
- Report Number(s):
- SAND-93-1280C; CONF-930616-2; ON: DE93015019
- Resource Relation:
- Conference: 9. IEEE pulsed power conference, Albuquerque, NM (United States), 21-23 Jun 1993
- Country of Publication:
- United States
- Language:
- English
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426000* - Engineering- Components
Electron Devices & Circuits- (1990-)