Antenna60
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I’m developing a simple, five-frequency superhetrodyne receiver to operate between 2.5 MHz to 20 MHz in which the local oscillator crystals and whip antenna tuning circuits are selected (switched) using diodes. Here’s the problem:
The whip tuning circuit is comprised of a single variable capacitor with five fixed-value inductors, each in series with a BA277 "bandswtiching" diode. A single diode/inductor combination draws about 6 mA when ON (switched in). This works fine, but at and above 15 MHz, the BA277 diode significantly contributes to the series resistance of the inductor, inducing a 3dB "insertion loss" (as compared to the same circuit with the diode short circuited).
The BA277 datasheet indicates that at 6 mA and 100 MHz, the series resistance of the diode should be much less than 1 Ohm. No performance data is given for any other frequencies. My bench measurements indicate that at 15 MHz, the diode presents much more resistance than that (probably tens of Ohms). No surprise there.
QUESTION: The BA277 works OK for what I’m doing, but is there a bandswitching or PIN diode out there better suited for operation below 30 MHz?
-Dave
The whip tuning circuit is comprised of a single variable capacitor with five fixed-value inductors, each in series with a BA277 "bandswtiching" diode. A single diode/inductor combination draws about 6 mA when ON (switched in). This works fine, but at and above 15 MHz, the BA277 diode significantly contributes to the series resistance of the inductor, inducing a 3dB "insertion loss" (as compared to the same circuit with the diode short circuited).
The BA277 datasheet indicates that at 6 mA and 100 MHz, the series resistance of the diode should be much less than 1 Ohm. No performance data is given for any other frequencies. My bench measurements indicate that at 15 MHz, the diode presents much more resistance than that (probably tens of Ohms). No surprise there.
QUESTION: The BA277 works OK for what I’m doing, but is there a bandswitching or PIN diode out there better suited for operation below 30 MHz?
-Dave