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Half duplex Full duplex?


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I see the upcoming Hackrf is half duplex, it can either send or receive, but not both at the same time.

I am completely new to this, so this could be considered a dumb question.

To get full duplex, can the $20 dongle take care of the receive part, with hackrf taking care of the send?

Or........would one need 2 Hackrf units?

Edited by xrad
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Depends on the range. The dongle only does 24MHz to 1850Mhz whereas the HackRF I believe can tune to in excess of 4GHz.

So your idea would work as long as you restrict your HackRF to dongle frequencies and of course you transmit on a different frequency than what you receive on.

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I see the upcoming Hackrf is half duplex, it can either send or receive, but not both at the same time.

I am completely new to this, so this could be considered a dumb question.

To get full duplex, can the $20 dongle take care of the receive part, with hackrf taking care of the send?

Or........would one need 2 Hackrf units?

Not a stupid question at all. This really all depends upon your needs. The main thing limiting you with the $20 dongle is the frequency range, and the bandwidth. I tested my dongle a few days ago and it got about 26MHz - 1.7GHz, with a bandwidth of about 250khz where as the HackRF goes from 10MHz - 6GHz and a bandwidth of 20MHz.

If you are only working within the frequency range and bandwidth range of your dongle then you can use just it and 1 HackRF, but I would personally use two HackRFs due to the larger bandwidth. Once I get my hackrf in I plan on using it to receive signals from geostationary satellites though (GOES) in the same manner I do with the NOAA satellites.

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Once I get my hackrf in I plan on using it to receive signals from geostationary satellites though (GOES) in the same manner I do with the NOAA satellites.

Interesting. And this is because of the bandwidth?

I always thought a low frequency band was used to get more range but a quick google found that for instance the Mars Orbiter transmit(s/ted) at 2298.525 MHz.

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Thanks Cooper and Sildaekar,

I intend to eventually get 2 hackrf's, it's just a large chunk of change (ie cash) at one purchase.

One more question, I am a bit concerned about the output, very low.....

I intend to get my amateur license and I will probably learn this as I go.

Since it is built the way it is........can the output be amped up for most frequencies with just one amplifier?, or is amplifying the signal based on frequency?

http://www.ebay.com/gds/A-Buying-Guide-for-Amateur-Radio-Amplifiers-/10000000177317515/g.html

http://www.ebay.co.uk/sch/Ham-Radio-Amplifiers-/163853/i.html?_from=R40&_nkw=ham+radio+amplifier

So a hamitup x2 and a linear or amplifier and hackrf x2.......would be ok to get me close to having a fairly decent ham set up?

I understand it would be better to get a used ham mobile unit if I intend to go ham, I'm just thinking out loud and trying to cover all the bases of what the hackrf can be used as.

I guess I should have called this thread......"Hackrf Questions" Maybe a mod can change it, I'm not sure if I can.

Edited by xrad
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Interesting. And this is because of the bandwidth?

I always thought a low frequency band was used to get more range but a quick google found that for instance the Mars Orbiter transmit(s/ted) at 2298.525 MHz.

Yeah, I want to check out the GOES satellites, pretty much the same as the NOAA's but they are geostationary so we can receive them 24/7 instead of waiting for that 10 minute window that comes twice a day :dry:

But...the GOES sats have a bandwidth of ~8.7MHz (well outside the range of my little dongle).

EDIT:

Missed where you were talking about the frequency. The reason we use low freqs to communicate long distances here on Earth are due to their propagation methods, they bounce off of the ionosphere very easy with little loss. However higher frequencies have a tendency to "punch through" it easier than lower frequencies. But there again, a lot more goes into it than just the frequency, you also have to look at polarization, transmitter power, sun spots, the time of day/night, etc etc etc....

Thanks Cooper and Sildaekar,

I intend to eventually get 2 hackrf's, it's just a large chunk of change (ie cash) at one purchase.

One more question, I am a bit concerned about the output, very low.....

I intend to get my amateur license and I will probably learn this as I go.

Since it is built the way it is........can the output be amped up for most frequencies with just one amplifier?, or is amplifying the signal based on frequency?

http://www.ebay.com/gds/A-Buying-Guide-for-Amateur-Radio-Amplifiers-/10000000177317515/g.html

http://www.ebay.co.uk/sch/Ham-Radio-Amplifiers-/163853/i.html?_from=R40&_nkw=ham+radio+amplifier

So a hamitup x2 and a linear or amplifier and hackrf x2.......would be ok to get me close to having a fairly decent ham set up?

I understand it would be better to get a used ham mobile unit if I intend to go ham, I'm just thinking out loud and trying to cover all the bases of what the hackrf can be used as.

I guess I should have called this thread......"Hackrf Questions" Maybe a mod can change it, I'm not sure if I can.

No problem man :) Yeah, I know what you mean, I plan on ordering 1 at the beginning of the month (payday), and I may get another down the line. I'm pretty sure it's the "most frequencies with just one amplifier" scenario but I could be wrong. I've only been experimenting with SDR for about 3 weeks now so I'm still new to it as well.

As far as the down-converter goes, I'm almost 100% positive that that is only for receiving, but HackRF goes from ~10Mhz - 6GHz so it should cover all of the bands, at least the ones that your technician license will cover (once you get it). Just throw in a decent amplifier between the Tx port on the HackRF and your antenna and all should be good.

You probably will need to get a more "specialized" radio when you get further into ham, but I think the HackRF will be able to cover pretty much all of your bases until you are ready to dive into the deep end. This is one of the reasons I love the HackRF and can't wait to get mine...so much to do, so little time.

On a side note:

Another reason I can't wait to get my HackRF...McDonalds headsets (and other fast-food places) operate on public bands....would be funny to chime in and talk to them :tongue:

Edited by Sildaekar
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Hehehe. I can see it now. "Oh, almost forgot, can you also get me half a dozen burgers please!"

I'm actually interested in what they're saying at the movie theatre nearby. The staff there all carry radios. Same with one of the local DIY shops.

Once I know the frequency I could see myself assembling a jammer for that. It should be interesting to see how they handle such a situation...

But that's all just mischief. My main goal is to find a way to listen in on the police Tetra channel. Currently it's encrypted (TEA2 IIRC) which hasn't been broken just yet, but I can totally see that happening in the fairly near future, given the amount of work being put into it.

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Hehehe. I can see it now. "Oh, almost forgot, can you also get me half a dozen burgers please!"

I'm actually interested in what they're saying at the movie theatre nearby. The staff there all carry radios. Same with one of the local DIY shops.

Once I know the frequency I could see myself assembling a jammer for that. It should be interesting to see how they handle such a situation...

But that's all just mischief. My main goal is to find a way to listen in on the police Tetra channel. Currently it's encrypted (TEA2 IIRC) which hasn't been broken just yet, but I can totally see that happening in the fairly near future, given the amount of work being put into it.

Haha, that would be fun...just watch the laws, intentionally interfereing with another person's transmission is illegal, so you would have to be careful...also, monitoring freqs is completely legal but attempting to crack any form of encryption is illegal...just be careful ;)

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Yes, I was aware of that. They actually used that law to ban speedtrap detectors. If the signal used by speedtraps contained information you have a legal right to receive that signal and do with it as you please - the explicitly allowed exception to the rule which is formulated in a 'deny, unless' fashion. Since there is no information, you are wholly in the 'deny' part of the law which is why the detector was made illegal.

What's NOT illegal is for people to inform others of the location of known speedtraps. Quite early on, radio stations would include in their news update you get every 30 minutes an update on where they've been spotted by other listeners who phoned them in. These days there's also an app for it (obviously) which you can get for free via Apple's appstore. I'm sure they're in the play store aswell. The other brands... Peh, don't matter as nobody uses those. :smile:

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Oh wow, that sucks, they are still legal here in my state, I forget sometimes that not everyone is in the USA and some people have different laws :p

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"To get full duplex, can the $20 dongle take care of the receive part, with hackrf taking care of the send?

Or........would one need 2 Hackrf units?"

In my travels, I have not experienced a dumb question, but I have provided numerous dumb answers and stupid looks for increased dramatic effect.

Yes as Cooper points out, if the transmitted signal doesn't exceed the specifications of the receiver. But there is more to this.

For the purpose of transmitting, what information you plan to transmit (is this a broadcast for many people to hear or all directed to one receiver?) and how far will greatly effect what kind of amplifier you end up with. More to the point, which frequency you select and how far you are trying to go will dictate the type of antenna and how much power you will need. Which antenna you end up with will indicate what kind of power level you need to produce to over come path losses in the receiver(s). Which amp you buy will have some set of characteristics (some worse than others) that you will wish to filter out to remove undesirable by-products (stuff you don't want like harmonics and so on). Once you factor all those things together, you will improve your odds of being received successfully at the receiver, assuming the receiver isn't deaf, pointed in the wrong direction or turned off. For actual useful purposes, a typical 2 meter (144 MHz) radio with a 5 watt rating, using narrow band FM modulation can go miles on a stupid little antenna (as seen on TV) to a receiver with a higher location and a better antenna or preamp or both. That same radio talking to a similar radio at the same altitude can MAYBE go a mile.

Experiment first with 1/2 watt amps into a dummy load on the FRS band 49 MHz (or the 915 MHz) to characterize the amplifier first. If the output isn't very linear then try using the most narrow frequency usage as possible - be the ham - and see what you can do with the SDR receiver sticks and different antennas. If the amp has a flat and clean output, try different types of modulation (AM/FM/SSB/CW a.k.a Morse code or High Speed CW commonly referred to as OOK or On Off Keying). AM eats power to produce the carrier, FM will drive the amp class C = lots of heat. Single Side Band and CW are the most efficient but can make an amp go "non-linear" but only use power when information is sent. There are tons of books and articles to read on all this stuff but by far the most efficient method for moving data are the digital modes for brute force information transfer like OFDM (Orthogonal Frequency Division Multiplexing) which is a HUGE topic.

SDR is a white hot topic in numerous communities for one simple reason, the darn things are REALLY inexpensive and can do many things. I have talked to people on radio all around the world and through satellites. I tend to operate in big contests just for the fun of it but my passion is making things and then going out to try it and see if it blows up or works. I have been farting around with DSP for years and SO glad that others are jumping in on the SDR train. I'm just getting my arms around this stuff too. Maybe I'll find you on air some day, legally please. As we say 73 - KD6W

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