signal reflections? on rtl sdr v4

[paul1945]

hello, i have a problem with sdr, namely when i connected a 3.5-52mhz longwire antenna, there appeared such dashed lines on the waterfall in sdr console v3.3, as if reflections of the broadcast station, rf gain is 29.7db
I have rtl sdr v4 Is there any option in the sdr console that allows to eliminate these phenomena?

[Max]

hello, i have a problem with sdr, namely when i connected a 3.5-52mhz longwire antenna, there appeared such dashed lines on the waterfall in sdr console v3.3, as if reflections of the broadcast station, rf gain is 29.7db
I have rtl sdr v4 Is there any option in the sdr console that allows to eliminate these phenomena?

Paul, it's a little hard to fully understand what you mean by "dashed lines on the waterfall". Can I firstly please ask that when posting screenshots you do so using the built-in Screenshot Tool as described here:

https://www.sdr-radio.com/screenshot

Do not edit/crop the shot as there is much useful information on SDRC at the screen edges which you have cut off in your shot. Also, always post it as an attachment (as you have done) and not an inserted picture so that we can see it in full detail. Please when you make the screenshot make sure to have the "Home" tab selected in the ribbon bar as it shows us all the gain settings for the RTL-SDR V4. Last request (although perhaps not so relevant to this specific case) have the RX DSP docked on the left of the screen so we can see these settings too.

So to comment on what I am seeing (and as a fellow owner of the RTL-SDR V4) this dongle is really a bare minimum for HF listening. It's superb value at the price, but that value means large compromise. One of those is that it's extremely easy to overload the front end of the receiver (and hence also subsequent stages). We cannot see if you have AGC on or off. You've got the waterfall zoomed right out and covering 1.5Mhz of bandwidth, which is too much to see any detail at this frequency, but even so, what I am seeing is a very overloaded receiver, and quite likely in and around the big broadcast AM section of HF in the 5-7Mhz region in the evening hours. If you try this on the RTL-SDR V4 at this time of day especially, there are many huge signals present within the front end of the dongle, and so you will see a large number (VERY large number!) of spurious responses which is what it looks like here. On a long-wire antenna (or any long antenna), with the RTL-SDR you need to start with the RF gain wound right down to 0dB, and most likely with the AGC OFF. Then have a tune around the bands of interest (zoomed in to see individual signals). Once you have found some likely genuine signal candidates, then you can try increasing the RF gain a bit, but it won't be long before you start seeing spurious signals popping up again.

As an experiment I just tried tuning around the same sort of area (actually the 49m broadcast band) on the RTL on my 80m EFHW wire and it's sort of OK up to an RF Gain setting of around 15dB. Anything above that and the display becomes rapidly overwhelmed with a mass of spurious signals exactly as I see with your screenshot. Truth be told I personally would very rarely use the RTL-SDR for HF listening, but with low gain settings I was actually quite surprised at how good it is even at this time of night (around 8PM in the UK). Lots of perfectly intelligible stations, also on the HF ham bands such as 40m/80m.

So the key is start off very low on RF Gain and slowly increase it if necessary (I did find it needed a bit more than 0dB) until you get sensible results with limited spurii. I found a setting for RF gain at 29dB far too high to get any worthwhile results at HF with the RTL-SDR. During daytime with less very strong signals you will probably get away with larger RF gains, bit largely pointless as most likely no more than 15dB gain setting will be needed hear what you want to hear. Any higher is probably inviting the overload issue at almost any time of day, from local MW broadcast stations for example.

Maybe give us a little more background and we can help further. For example, is this your first SDR? Are you sufficiently interested to upgrade a little? What are your main frequencies of interest? Do you have none-SDR kit, so what are your existing performance expectations?

Anyway, hope it helps a little.

Max

[jdow]

Max, his basic problem is expecting noteworthy receiver performance from an RTLSDR dongle. It is severely overloaded and generating spurious. His big antenna overloads it. Broadcast signals are way too strong for the poor little 8 bit RTLSDR dongle to deal with. An attenuator in the feed line will help some if the broadcast band signals are not too strong.. A much smaller antenna might help. A broadcast band notch or low cut filter might help. Combinations of those mitigations will help more.

Some years ago when I was fiddling with my own version of rtlsdr.dll I implemented a pair of methods of HF reception. I played with it briefly. The performance was dismal and quite limited. And that was the end of my playing with the RTLSDR type dongle on HF. It does something there, which is remarkable. It does not work well enough to be useable except with very short antennas or an attenuator in the feed line to lower overall signal levels. If the measures above do not make it work well enough for him about the only solution is upgrading to a better front end. The AirSpy HF+ Discovery is expensive as a next step. But it is about as good as the best you can get, certainly good enough for most receiving sites. Few sites need a full blown 16 bits (or more) in the Analog to Digital converter.

I wish I could offer him a better solution but I've not played with any units between the RTLSDR type dongles and the AirSpy HF+ Discovery. (I do respect Youssef tremendously. I have no financial interest in his AirSpy series of products. I have a plethora of them dedicated to specific tasks. mostly VHF at the moment. My site is miserable at HF due to MANY local noise sources.)

{^_^} Joanne

[IK2NBU]

Dear Paul,

if you use a long wire + maybe a wide bande balun ... SWL result with a SDR RTL device it is not optimal, expecially on 5 MHz band.

Put a band pass filter on antenna or try to use a manual HF tuner.

73 Arnaldo www.ik2nbu.com

[KA1GJU]

Do yourself a HUGE favor, keep the RTL device for VHF/UHF work and purchase the Airspy HF+ Discovery. I have 10(?) on SDRC Servers all over New Hampshire, most on very long inverted L antennas, fed with long runs of RG11, RG6, 1/2"CATV hardline, etc to get them away from humans and their pesky QRM generating devices. You won't be spending so much time fiddling with controls to see/hear signals as you do with the RTL Dongle. Infact, the ONLY control I use is the Pre-Amp when I listen on 20M and higher. AGC remains on (high or low, doesn't make a difference that I can see/hear), ATT OFF, Visual Gain 0... it just works! You may have to slide the waterfall contrast slider (far right) to see the minutiae, but at least you will see it!
For the life of me I can't figure out why users put 30dB Visual Gain on my latest server, which has a VERY low noise floor. Yet when I connect, I find the Gains maxed out and ATT on and the noise floor is up around an S-9.

Here's a shot of the same frequency as heard/seen in NH this AM via one of my Airspy HF+ Discovery's, set for max bandwidth of 912kHz.

[Max]

Max, his basic problem is expecting noteworthy receiver performance from an RTLSDR dongle. It is severely overloaded and generating spurious. His big antenna overloads it. Broadcast signals are way too strong for the poor little 8 bit RTLSDR dongle to deal with.

{^_^} Joanne

Yes, that's absolutely true Joanne, as per my first reply to the OP. However, in defence of the RTL-SDR V4, following his post I've left it as my main receiver for a couple of days attached to my 132ft long wire. TBH I've been amazed by how good it is even at the frequencies shown by the OP, so long as the hardware AGC is left OFF and the RF Gain is backed right down to around 15dB. Then, for a $30 receiver, it really does give a very credible performance. Yes, not stellar, but amazing for the price.

I think it's always important for those who are new to SDR and particularly those who are new to the whole hobby and who may not want to spend big bucks to just try it out (which in my book is over $100!) to have an economical way to just get a flavour of SDR or the hobby generally. Anyway, just to restate, I have an RTL-SDR V3 and also the V4 and the V4 is a huge improvement over even the V3 and ditto over all the other RTL-SDR variants.

I also agree with Kriss. If you are new to the hobby and have a bit more than $100 to spend, then the Airspy HF+ Discovery is the way to go if HF and up to 144MHz ham band is your thing and can be had for a steal on the Black Friday deals. But keep the RTL-SDR for VHF/UHF.

If it's an HF transceiver you want, the Hermes Lite 2 is the way to go, and has an absolutely superb direct sampling receiver. All IMHO of course!

73 to all

Max