Direct sampling & sub-harmonics

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Joined: Mon May 16, 2016 6:10 pm

Direct sampling & sub-harmonics

Post by Richard9026 » Mon Dec 26, 2016 1:46 pm

Hi !
I successfully soldered a wire to pin 1 of the rtl2832u chip of a cheap chinese rtl-sdr , i used a grounded soldering iron so i don't zap the chip
I'm receiving a lot of stations and some hams at night with the longwire antenna , but FM interference is a big problem , also there is a strong am station next to me , that appears on other frequencies .
Can a very strong signal fry the rtl.sdr ? especially that it directly enters the chip
How can i reduce the number of images ?
Are there some diy projects to improve the signals ?
I plan on making a fm trap ... z-fm-trap/ , I found some ceramic caps with the required values but i can't find a 0,35 mm wire

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Re: Direct sampling & sub-harmonics

Post by AD5NL » Mon Dec 26, 2016 7:54 pm

I doubt you will "fry" the unit unless you are sitting right next to a transmitter. You might temporarily desensitized it though.

The answer to your problem is mostly "filtering."

An FM trap might be a good first step. A good second step might be an HF low pass filter. And/or a high pass filter to cut out the AM broadcast band.

Remember also that the first filter in your RF chain is your antenna. Are you using a preselector or antenna tuner? That might be something to consider using if you can get one.

You might consider going to a local ham radio swap meet if there are any in your area. It is a good place to find parts and also talk to people with similar interests. If you are in the US the ARRL hamfest calendar website should point you in the right direction.

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Re: Direct sampling & sub-harmonics

Post by joe36 » Tue Dec 27, 2016 1:47 am

On the .35 MM wire. Just substitute something close. When you wind the inductors they will not be exact and some adjustment may be needed. There is a great series of videos on this page about characterizing filters
MARCH 11, 2015


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