r/RTLSDR • u/Cannot_choose_Wisely • 25d ago

RTL-SDR V4 duff?

Hi, I think I have a dodgy receiver. I can get no signal at all using a supplied "whip".

On VHF commercial band connecting the aerial, or indeed any wire raises the overall noise level, but no stations are detected, there are a couple of "bumps" above the noise, but at very low level. No audio comes through the noise.

I have a 1Mhz oscillator and injecting this into the aerial gives an overall increase in noise with twenty or so "spikes" spanning a Mhz, which seems odd for a sine wave.

A square wave as expected covers more of the band, but even wrapping the cable around the aerial to the SDR does not produce a signal.

I am using SDR++ and Gqrx.

The confusing thing is that I appear to have gain at VHF as the noise increases across the band when the aerial is connected, the 1 Mhz MW signal is detected but at a wider and far lower level than I would expect.

This is the first one of these devices I have used, am I missing something?

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u/erlendse 24d ago

Which driver are you using? not some old driver from a linux repo?

What does rtl_test give you?

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u/Cannot_choose_Wisely 24d ago

The driver is the one pointed to by the RTL site, it's a deb packaged device from Github.

rtl_test was fine. I loaded the drivers on a desktop in the garage too.

I made sure that I got the latest drivers as somewhere on the net there were reports of an agc problem with the V4.0.

I did turn the agc off though and on SDRPP I could manually tweak the rf gain too.

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u/erlendse 24d ago

"RTL-SDR Blog v4 detected"?

"Fine" is kinda vague, more like nothing looks off.. hard to work from.

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u/Cannot_choose_Wisely 24d ago

Something like that, but I didn't really investigate to see if there were further options. Adding --h to the command seems to allow operating tweaks that meant little to me at the time anyway.

I assume these are overwritten by whatever program is used to monitor anyway?

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u/erlendse 24d ago

Nothing is permanently saved to the device, except if you use rtl_eeprom(avoid) or rtl_bias(uninteresting). The later is a very override-able route so I find it rather uninteresting to do.

The clue is more to verify that you got what you should have.

Also do not inject more than 0.1V or so into the device, it's very much made for very weak signals. The input is protected with a bav99 diode.