Direct Conversion Receiver Local Oscillator Frequency

[Ytwati]

Hello everybody I am interested in astronomy so I decided to make a radio telescope I took a long time to find I good one that I can make I am not making it exactly because i have to buy
a kit from internet https://stargazerslounge.com/topic/75170-basic-jupitersolar-radio-astronomy/ and i am not doing that. that kit is a sipmle direct conversion receiver using NE612 and LM386 and i am making one using NE612 and LM386
and my problem is i have receive on 20.1 MHz ( Jupiter radio noise ) and i have to make lower by using the Ne612 mixer so it can be in audio frequency 20 Hz to 20 Khz .
if i use a 20 MHz local oscillator then the 20.1 MHz signal will be 0.1 MHz and that is 100 Khz and it isn't in audio band so i can hear it or connect it to the computer sound card
i want to know what is the frequency of the local oscillator i have to use so the 20.1 MHz signal can be in audio frequency band. :?:

 

[Mityan]

If 20.1 MHz is this Jupiter radio noise central frequency, then you should have 20.09 MHz LO.
I doubt that you could find it. You should use frequency synthesizer to get any frequency you want.
Or, if you find a way to record this 100 kHz signal, maybe using a PCI-based board or something else, then you may make a second downconversion by software (multiplying by digital sine wave) and do with your signal all that you wish

 

[DeboraHarry]

A direct conversion receiver, sometimes called a homodyne receiver, has a zero IF.

If you want to receive 20.1 MHz and use a local oscillator of 20.0 MHz, then the IF will be 0.1 MHz and it will not be a direct conversion receiver. Instead it will be a superhet receiver. In a DC receiver, the IF is zero, and the LO runs at the same frequency as you want to receive.

Is there some good reason for wanting to receive 20.1 MHz. I don't know anything about radio astonomy, but the link you provided seemed to indicate 20.1 MHz was chosen as this is a quite part of the radio band.

Perhaps I am missing something, but I very much doubt it is possible to pick up signals from Jupiter on a half wave dipole on a simple direct conversion receiver, as described in the link you provided. If the author of that article thinks he is picking up signals from Jupiter, I believe he is wrong. But I'm the first to admit, I have never studied radio astronomy.

I would suggest you consult the professional literature on radio astonomy and Jupiter, and copy that article to /dev/null.

Deborah.

 

[godfreyl]

i have receive on 20.1 MHz ( Jupiter radio noise )

The exact frequency is not important. See this link and this link for some useful information about Jupiter radio noise.

Jupiter's radio emissions may be heard from Earth on frequencies ranging from about 14 to 38 Mhz. I suggest you pick a frequency between 18 and 28 Mhz for the greatest likelihood of success.

Aren't search engines wonderful? I'd never heard of Jupiter radio noise until 5 minutes ago, now I seem to know more about it than the OP.

 

[sky_123]

Also this rather old paper may help on astronomy receiver architectures(I've no knowledge in this area, I've only scanned through it, but looks interesting). Also maybe join this group, seems low cost, and they have a radio section.