the most fun $12 gadget ever- rtl2832+r820t USB software defined radio dongles

[dannyf]

Here is the funcube up converter.

It is almost perfect. Deadbug would be great.

[codeboy2k]

And here's a complete circuit with a 602, and a 100 MHz LO .

That can be simplified by either using an outboard oscillator (or a sig gen), or utilizing the built-in oscillator + the 100Mhz crystal -> which is actually quite rare.

Yeah, I didn't know why that circuit was using it's own LO circuit, the 602 just needs the external crystal. 

If I built it up I'd start with my sig gen as the LO anyway, and if I used a crystal on board , then I'd just use what I had and let the IF fall where it may, it's not important for this application, as long as it lands in the usable range of the dongle.

[codeboy2k]

Here is the funcube up converter.

It is almost perfect. Deadbug would be great.

It looks basically as we've described, diode mixer with filters. Simple.

Thanks for that.  good to have it in the forum as a reference too .
The site is back up for me now.

[codeboy2k]

almost perfect.  If it works as it is then good, but I'd probably want to add a bandpass on the IF output

[dannyf]

Either low pass or high pass alone would work.

Yes, otherwise, you can get mirror images of the stations.

[vk3yedotcom]

Yeah, I didn't know why that circuit was using it's own LO circuit, the 602 just needs the external crystal. 

If I built it up I'd start with my sig gen as the LO anyway, and if I used a crystal on board , then I'd just use what I had and let the IF fall where it may, it's not important for this application, as long as it lands in the usable range of the dongle.

One of the benefits of using an external crystal oscillator (instead of the internal one in the NE602) is you can filter its output so that only a 100 MHz signal is presented to the mixer. That lessens the chance of image signals causing interference.  As an example, I tried a downconverter using a 50 MHz crystal oscillator module with little filtering.  When I tuned the SDR to 101 MHz you could hear AM broadcasters at 1 MHz due to this lack of filtering (mixing occurring with the harmonic of 50 MHz). 

I would also be wary of using 100 MHz as a crystal frequency unless shielding is very good or you don't have strong local FM stations.  Breakthrough increases noise and lessens clarity of the HF signals you're trying to pick up.  And you can sometimes even hear the FM stations in wide FM mode whereas on narrow modes they just come up as noise that's not easy to tell as breakthrough. 

Depending on how low your dongle tunes an oscillator frequency of maybe 60 MHz, or maybe 110 - 120 MHz is probably ideal as signals in those segments (and 30 MHz above) aren't as strong or wide in bandwidth as FM broadcasters.

[janoc]

I would definitely give it another shot with a USB extension, some ferrites and another antenna. the PC noise makes the signals just fade into nothing and people think they are broken. And you don't even see signals. its some particularity of the fairly sophisticated internal tuner..

You mean the AGC turning down the gain when the front-end gets overloaded with RFI?

That's a bog standard feature in radio receivers 

[han]

I just Buy and test.
Quick setup:
1. Download SDR sharp (IMHO the best software for SDR)
http://sdrsharp.com/#download
2. Do not install any driver or software from the Dongle
3. Use zadig.exe from SDR sharp to install driver.
4. DONE

[vk3yedotcom]

I just Buy and test.
Quick setup:
1. Download SDR sharp (IMHO the best software for SDR)
http://sdrsharp.com/#download
2. Do not install any driver or software from the Dongle
3. Use zadig.exe from SDR sharp to install driver.
4. DONE

5. Set up a good VHF outdoor antenna (eg groundplane fed with coax cable >5m above ground) 
6. Start by scanning the FM broadcast band. 
7. Then experiment with other modes - eg NBFM on VHF/UHF and AM on airband.
8. Experiment with gain and AGC controls.  And filters and bandwidths.  Sometimes they will have a big effect.

[Shock]

Any dongle (usb tuner) recommendations with hardware comparisons (or links to these)?
Which models currently being sold have input protection, better crystals, compatible, superior antenna sockets, great usage flexibility?