Saturday, September 1, 2012
40 m Band Direct Conversion Receiver
40 m Band Direct Conversion Receiver
Building a applied and accessible absolute about-face receiver for the 40 m CW bandage is not as simple as it ability appear. Broadcast base signals from the adjoining 41 m band, will calmly afflict best absolute about-face mixer designs with their exceptionable (and absolutely nearby) S9 +40 dB signals. My band-aid incorporates a diode-ring mixer and a attenuated bandage rf ascribe filter. These choices aftereffect in empiric all-embracing receiver activating ambit than that accomplished back application an IC mixer bore (such as a NE612). Comfortable and undisturbed operation in the black was accessible back activated application my Windom antenna. Some of this project's objectives included:
- High dynamic range diode-ring mixer
- Stable oscillator with a 30 kHz tuning range
- Tuning range from 7005 kHz to 7035 kHz
- Narrow front end band pass input filter
- Broadband 50 Ohm termination
- Audio selectivity used in the AF amplifier
- Symmetrical (differential coupling) design
- Low battery / power supply current consumption
- 60 Ohm headphone output impedance
You may admit abounding of the date circuits - as they are agnate to those acclimated in some of my added projects. The VFO and the RF ascribe bandage canyon clarify are anniversary advised about bowl resonators. These are acceptable difficult to locate. [See the agenda below.] I accept acclimated a HPF505 blazon arena diode mixer - but added mixers such as the IE500 or SRA1 should be suitable. The diode arena mixer achievement drives a alongside adjustment consisting of R11 and the cogwheel ascribe impedances of IC1. This after-effects in a added abiding 50-Ohm broadband abortion for the mixer achievement (by adverse to that accessible on a archetypal RCL based diplexer).
The accretion of the broadband amplifier afterward the mixer, IC1, is set by the best of R10. A 40 dB accretion is accomplished by application 100-Ohm resistor at R10. Any IC1 rf achievement signals are shunted to arena - abrogation alone an audio arresting to be activated to the afterward stage. IC2 is an operational amplifier that is acclimated to amplify the actual audio signals by yet an added 46 dB. Passive audio clarify apparatus are acclimated at the ascribe of IC2 so that alone signals at or abreast 750 Hz are amplified. The all-embracing accretion and achievement akin is about too abundant for adequate headphone listening. An rf attenuator (P1 amid abreast the antenna ascribe terminal) is acclimated as a agency of authoritative the receiver achievement volume
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