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Re: [Discuss-gnuradio] Radio interoperability

From: Marcus Müller
Subject: Re: [Discuss-gnuradio] Radio interoperability
Date: Thu, 10 Oct 2013 14:53:37 +0200
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Hi Bijendra,

I'm under the _expression_ that Wayne has already supplied you with the idea of the AM tx flowgraph; it's your project, clicking together the flowgraph after his description is up to you ;)

Well, if you need full-duplex, you will need two independent RX and two independent TX radio interfaces, so you need to have two USRP sources, two USRP sinks, and connect everything correctly.

Again: AM Rx will always be noisy as long as you don't do stunts on the analog/physical side of your receiver; I haven't had a look at your GRC files though, so is it possible you don't low pass your received signal? AM transmission seldom have a bandwidth significantly higher than 3kHz; this is partly because usually analog AM receivers have quite narrowband RF filters, to avoid picking up a lot of noise. Since this is totally anti-software defined radio, the LFRX doesn't have such filters.
Get a filter, get a preamp, get a higher gain antenna. Do what you must do to get a cleaner signal.

Happy hacking,

On 10/10/2013 02:18 PM, Bijendra Singh wrote:
Yes, you got it right. Its a military equipment. Both of them are tactical radios one for HF and another for VHF. And I am trying to use my GNU as a relay platform. So could you please help me out in getting those flowgraphs. I've already attached .grc files of FM tx and rx, but couldnt find AM tx, and a noisy rx. Now I have to integrate them with one another, ie HF and VHF. What I'm suppose to do now?

On Thu, Oct 10, 2013 at 3:35 PM, Marcus Müller <address@hidden> wrote:
Hi Bijendra,
I, too, am confused.
So let's try to understand what you are doing here!

On 10/10/2013 10:39 AM, Bijendra Singh wrote:
Well it is a project I'm working on.
I am trying to receive an AM signal from HF radio
Yes, so receiving amplitude modulated audio on a carrier somewhere between 3MHz and 30Mhz (==HF)

which will be provided in the usrp source in my gnu
You want to capture that using a USRP and GNU Radio, I presume.
and will transmit a FM signal as output
Aaaaha! Second chain of operation! You want to simultaneously generate an FM signal

in the usrp sink which I'm trying to send it to the VHF radio.
And you want to transmit that using a USRP (the same USRP?) to another Radio receiver, that listens on a VHF carrier (30MHz-300MHz) then.
And vice versa.
Huh? Your radio receivers usually can't transmit, so that's confusing

I'm using CNR-900 VHF radio which freq range is 30 to 89.899 MHz and RS-HX radio which freq range is 3 to 30 MHz. When I tried the hf2vhf.grc file, it is working, but with noise. Same thing will be possible for VHF to Hf, I guess. And I'm stuck in this. Any possible remedies??

OOooooh ok... this is military communications, and I was under the impression we're talking broadcast Radio stations.
I must try to reunderstand now:
You're trying to set up a relay station, for someone with some kind of HF AM tactical radio to communicate with someone with a VHF FM tactical radio, right?
Anyway, Martin is right: Whatever you do, AM will always be noisy because it's AM, and unless you use laaarge antennas the HF signal on the USRP will most probably be strongly attenuated (1/2 wavelength of 30MHz is 5m...). So your SNR gets even worse.


On Thu, Oct 10, 2013 at 1:48 PM, Martin Braun (CEL) <address@hidden> wrote:
Hi Bijendra,

it's not quite clear what your question is.

A couple of things you might want to consider:

- AM is per se noisy. A commercial HF receiver would also have much
  better filters than you can achieve with an LFRX-only setup, so expect
  much noise here
- FM is much better with noise.
- You're not supposed to rx AM signals with an FM receiver.
- VHF and HF usually designate (separate) frequency ranges. So when
  talking about 'interoperability' between those, most people will be
  confused. Well, I am.


On Thu, Oct 10, 2013 at 12:58:06PM +0530, Bijendra Singh wrote:
> Hello every one,
> I'm working on a college level project to show interoperability between HF and
> VHF radio using GNU radio.
> My aims are listed below:
> 1)   To obtain FM transmitter and receiver waveform in GNU radio as flowgraph,
> so that i can communicate between laptop and VHF radio (In my case I'm using
> radio of the range 30-89.899 MHz)  :- This I have already achieved
> 2)    To obtain AM transmitter and receiver waveform in GNu radio as flowgraph,
> so that I can communicate between laptop and HF radio (In my case I'm using a
> HF radio of the range 3-30 MHz)    :- I was able to download a SSB receiver and
> it is functional but the noise level is high.
> 3)   To integrate Fm transmitter with AM receiver, so that one way communicaton
> is possible from HF radio to VHF radio. :- This I have already achieved, but
> with too much of noise and low pitch voice.
> 4)   To integrate AM transmitter with FM receiver so that one way communication
> is possible from VHF radio to HF radio.  I'm still lackung behind in this.
> 5)  To integrate both the 3rd and 4rth flowgraphs in a single flowgraph to make
> Hf and VHF radio interoperable from both sides.
> 6)  My GNU version is, I'm using two usrp's 1 for the HF with lftx and
> lfrx daughter boards and the other for VHF with basic trans and basic receive
> daughter cards.Also I'm using dipole antenna.
> &0 Please guide me. I'm here attaching some .grc file I have downloaded, and
> which are working in my GNU, but noisy( only ssb_rx is noisy and sstx1 is not
> working)

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Karlsruhe Institute of Technology (KIT)
Communications Engineering Lab (CEL)

Dipl.-Ing. Martin Braun
Research Associate

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Building 05.01
76131 Karlsruhe

Phone: +49 721 608-43790
Fax: +49 721 608-46071

KIT -- University of the State of Baden-Württemberg and
National Laboratory of the Helmholtz Association

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