Hack Chat Transcript, Part 4

A event log for Software Defined Radio Hack Chat

What's in your dongle?

Dan MaloneyDan Maloney 09/18/2019 at 20:400 Comments

RF will never cease to baffle me...

jmcservv1:15 PM
ah ok as for aerial i use a discone antenna buit from pipe fittings and stainless steel rods

Signals Everywhere/KR0SIV1:15 PM
Put it on a service monitor/sepctrum analyzer and feed a noise source into one side while changing the length of the open coax and you'll see the notch frequency change

Joyce1:15 PM
RF will always be magic to me :)

Signals Everywhere/KR0SIV1:15 PM

James Finch1:15 PM
@Dan Maloney I think it's like optics too... there's some wave particle duality think going on. :-)

What kind of bandwidth does a filter like that have?

Signals Everywhere/KR0SIV1:15 PM
There is always more to learn and I love it

Max-Felix Müller1:15 PM
It's amazing. I got the opportunity to get a basic look into it at university :)

James Finch1:15 PM
think = thing

Joyce1:16 PM
And I am glad to be able to practice RF

Joyce1:16 PM
and communications systems in general :D

Signals Everywhere/KR0SIV1:16 PM
@Dan Maloney I'm honestly not too sure, it's not a lot but it's enough that we've used them in commercial situations before to notch out a nearby interfering frequency on our repeater input

Well, I mean, a notch is a notch, right? Should be pretty tight, I'd think.

Signals Everywhere/KR0SIV1:17 PM
Yeah it's tight I just don't recall the exact bandwidth

James Finch1:17 PM
Read like a good scenerio to demonstrate in a video and/or write-up.

Signals Everywhere/KR0SIV1:17 PM
it'll notch out a 25khz wide FM signal so I'd say at least 30khz

Max-Felix Müller1:17 PM
Mathematically it's just the one frequency

Signals Everywhere/KR0SIV1:17 PM
I should measure it some time

James Finch1:18 PM
Maybe can incorporate into the RTL-SDR way cost effective toolkit as a way to measure? Maybe compare with a better performing device to see capabilities?

Signals Everywhere/KR0SIV1:19 PM
@James Finch you can use a noise source, RTL and an RF bridge

Signals Everywhere/KR0SIV1:19 PM
Planning to do a video on that too

@Signals Everywhere/KR0SIV - If I can put my $0.02 in and request a video on what you can do with an SDR and a digital scope to troubleshoot and design filters, etc. I think that's what you were mentioning before, but just wanted to plug for that. I'd find that super-useful

Signals Everywhere/KR0SIV1:19 PM


Tuning an HF Antenna with an Airspy, SWR-Bridge and Noise Source

Over on his blog Anders J. Ørts has created a good writeup showing how he used the combination of an Airspy SDR with SpyVerter upconverter, SWR-Bridge and a noise source to tune his HF dipole for the 40 meter and 20 meter bands.

Read this on

Oops - missed @James Finch while I was typing. Same thing basically

Signals Everywhere/KR0SIV1:20 PM
@Dan Maloney for sure, I want to do one filters and such, I may not have the work space to build a filter right now but I can take a ready-made cavity filter and tune that to show how the tools work

Sounds awesome!

Signals Everywhere/KR0SIV1:21 PM
It's crazy how much you can do with SDR these days

James Finch1:21 PM
Yeah... the Airspy HF+ with Spyverter looks good (maybe better in some freq ranges) compared to the SDRplay RSP1 and SV1AFN DC-55MHz upconverter.

Signals Everywhere/KR0SIV1:22 PM
Heh I feel like I'm going crazy sometimes, I honestly have more than 50 ideas I could rattle off right now for videos I want to do (and have parts to do most of them) it's just a lack of time that keeps them back sometimes

James Finch1:22 PM
@Dan Maloney We need the redundancy... it's like a survey without the website.

Signals Everywhere/KR0SIV1:22 PM
@James Finch Suposedly the RSP1 has true DB measurement which would be extra useful

James Finch1:23 PM
I still need to test mine out. Wound up working on outside projects.

James Finch1:24 PM
Wondering how the Spectrum Analyzer application performs also. The noise floor is great on those systems too.

Signals Everywhere/KR0SIV1:25 PM
The analyzer software is hit/miss sometimes

@James Finch - Basically I'm too cheap to buy a legit spectrum analyzer but I still want the capability

Signals Everywhere/KR0SIV1:25 PM
There is one for the RTL that does 'okay' but I prefer the SpectrumSpy software

Signals Everywhere/KR0SIV1:25 PM
I'll be using an AirSpy for my videos on filters/antenna tunning just because the software available is better

Signals Everywhere/KR0SIV1:26 PM
@Dan Maloney Welcome to my life lol :)

James Finch1:26 PM
SpectrumSpy... I'll have to read into that. Is that what comes with the AirSpy?

Max-Felix Müller1:26 PM
Thank you @Signals Everywhere/KR0SIV this was all very interesting and I can't wait to get home and continue playing with my RTL SDR:) But for now I have to go. Bye

Signals Everywhere/KR0SIV1:27 PM

Signals Everywhere/KR0SIV1:27 PM
I was lucky enough to get one of these though

Signals Everywhere/KR0SIV1:27 PM
@James Finch yes it comes with the SDR# software/airspy

James Finch1:27 PM
Yeah... @Dan Maloney I was all over the web find ways to hack the FFT option to use on the TDS-520 and TDS series of oscilloscopes.

Signals Everywhere/KR0SIV1:28 PM


Spektrum: New RTL-SDR Spectrum Analyzer Software

Recently a reader of, Pavel wrote in to let us know about a new program called 'Spektrum' which he has written. Spektrum runs on Windows and Linux and turns an RTL-SDR dongle into a spectrum analyzer in a similar way to rtl_power GUI front ends and RTLSDR Scanner.

Read this on

James Finch1:28 PM
The RFExplorer and RTL-SDR wasn't cutting it at the time. I could only do so much with microphones and Spectrum Lab and am still planning to invest in a better microphone.

Signals Everywhere/KR0SIV1:28 PM
That's what could be used with the RTL

Signals Everywhere/KR0SIV1:28 PM
It works but finiky

James Finch1:28 PM
Spektrum is handy... that's what I've used with the RTL-SDR.

Signals Everywhere/KR0SIV1:29 PM
Not a bad application by any means but I'll probably still use spectrumspy over it given the choice

Signals Everywhere/KR0SIV1:30 PM
I use it in this video where I was playing with a cheap ADE passive mixer

Mike Walters1:31 PM
a HackRF & qspectrumanalyser is a nice option too. i was recently using it with a near-field probe set for some EMC pre-compliance work

James Finch1:31 PM
I didn't even realize SpectrumSpy is bundled with the somewhere in 2016 and later SDR# downloads:

Signals Everywhere/KR0SIV1:32 PM
@Mike Walters VERY true! Wow how did I forget that one, it was the first thing I used

Signals Everywhere/KR0SIV1:32 PM
iirc @James Finch it's also bunled with adsb software or at least used to be

James Finch1:33 PM
Does qspectrumanalyzer work with RTL-SDR's also?

Here is a reference for the record:

Signals Everywhere/KR0SIV1:34 PM
There is one dedicated for the HackRF too that works alright, it sometimes causes the HackRF to lock up on re-tune but you just re-plug it and it's fine

IRC1:35 PM
[Arsenijs] will have to try that one again - IIRC last time I tried that spectrum analyzer, it just segfaulted on me all the time.

Mike Walters1:35 PM
yeah, qspectrumanalyser works with RTL-SDR too. the nice thing about using it with HackRF is the tuning speed - it sweeps at ~8GHz/s

Signals Everywhere/KR0SIV1:35 PM

Signals Everywhere/KR0SIV1:35 PM
50mhz - 6GHz iirc and it scanned like no tomorrow

anfractuosity1:35 PM
wow, that sounds amazingly fast!

Signals Everywhere/KR0SIV1:36 PM
I used HackRF spectrum analyzer to find my cell phone signal

Signals Everywhere/KR0SIV1:36 PM
Too much bandwidth can be a henderance sometimes but other times... it's exactly what you need to find something odd over a swath of bandwidth

Signals Everywhere/KR0SIV1:36 PM
for this ability alone I'll always have a HackRF