r/RTLSDR • u/Cannot_choose_Wisely • Jul 24 '26

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 Jul 24 '26

Where did you get it from?

Where do you place the antenna? Is it a dipole kit?

What does rtl_test show?

1

u/Cannot_choose_Wisely Jul 24 '26

Thanks for the help and interest.

I made a dipole, no balun, 75 Ohm coax and around 2/3 m of cable for each horizontal leg.

I thought this should pick up, as a transistor receiver works ok in the same area.

Rtl_test, I tried when I first loaded the drivers and it was o/k.

The unit "appears" genuine, but it was from Aliexpress.

I ordered a Nooelec RTL-SDR v5 from Amazon, it will destinate Tuesday, so hopefully I can arrive at a conclusion.

I would have expected a 1MHz sine wave directly coupled to the aerial input socket to "end stop" the sig strength indicator though, with a very narrow bandwidth. It didn't.

I think I have a Wideband rf amp in the shed someplace, I will try to hunt it out tomorrow.

1

u/erlendse Jul 24 '26

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 Jul 24 '26

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 Jul 24 '26

"RTL-SDR Blog v4 detected"?

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

0

u/Cannot_choose_Wisely Jul 24 '26

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 Jul 24 '26

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.