[Hackrf-dev] HackRF Questions (O.T. Powell Response)

[O.T. Powell]

As long as no signal from DC to 6GHz after amplification exceeds -5dBm.
https://github.com/mossmann/hackrf/wiki/HackRF-One#receive-power
The normal reason use use a LNA is to add a little bit more
amplification (to the noise as well as the signal of interest) to
compensate for the losses due to the signal passing through a long
length of coax cable.

***** RESPONSE **** Thank you sir!*

The ham-it-up does not have an amplifier so it will only add a slight
amount of attenuation from it's two filters, the LPF on its input and
the IF BPF on its output:
https://github.com/opendous/Upconverter1v3
Any signal that you loose from filters you will more than gain from by
what they are blocking. Just make sure then your antenna is optimal for
HF/MF frequencies.

***** RESPONSE **** Thank you sir!  Lamda = C / F to get the full wave,
then make a half wave dipole.  I was planning on making a half wave dipole
(quarter wave for each pole) and using my balun with this dipole.*

If you are using a LNB just be careful to isolate any power injection
required for its operation, from entering the HackRF. If you are using
an 22kHz LNB local oscillator selector tone, normally about 0.65 Volts
peak-to-peak sine-wave (~0dB), you would be safer if you added 6dB of
attenuation.

***** RESPONSE **** My LNB is a MMDS Down converter from China.  I
purchased this for a regular SDR, before I decided to buy the HackRF.  I
wanted to be able to receive at least 2.4GHz signals.  It has a L.O. of
1998 MHz and 39dB of gain.  I guess I can receive 8GHz signals if I use it
with the HackRF.*

***** RESPONSE **** How exactly is the correct way to add attenuation?   A
resistor?  *
*Or is there a parameter in the software I could use to attenuate?*
*I'm sorry for the questions, I don't fully have these concepts wrapped
around my brain yet and I'm still within my first few hours of experience
on software defined radio.*

***** RESPONSE **** Is a LNB the same thing as a MMDS Down Converter?  I
suspect they are not the same thing but the MMDS has a LNB incorporated
into it?  I have a bias-T (I think that's what you call it).  The
description is MMDS power supply and provides 18V to the LNB.  Maybe I'll
keep my MMDS and LNA and use them on my cheap SDR.  I'll probably keep my
HackRF stock for the most part, or until I learn enough to know what's safe
and won't damage my HackRF.*



> The HackRF has a LNA already incorporated, correct?  So would I see any
> benefit of running another one?
Most users leave the LNA in their HackRF off because it operates from DC
to 6GHz and is in front of all filtering. Without checking that there
are no strong signals nearby within the entire operating range you could
damage your unit. I suspect it is there for people living in RF
wastelands more so that people living in the RF junkyards of most cities.

***** RESPONSE **** When you say RF Junkyard, are you referring to an area
that has an absence or minimal RF signals propagating?*
*How do you turn the LNA off, it's a setting in SDR#, correct?*

The problem with adding gain is that you amplify the signals that you
want and also the noise that you do not by an equal amount. And if you
add too much gain you end up distorting the signals that you actually
wanted to see. You will get better results from adding a filter at or
near your antenna with a tiny amount of gain, than by adding more gain
at your receiver.
> Also, what's the best way to amplify a transmitted signal?
>
Please do not. First maybe get a ham license and, as part of the
process, learn all that would need to know before trying to turn up your
TX power.

***** RESPONSE **** I'm already studying for my HAM technician license.
I'm studying Electromagnetics & Wireless Communications in college right
now (I'm in the EE program).  Our curriculum is set up to prepare for the
FCC Certification/License.  This class is how I found RTL-SDR.  I've never
heard of them before I started researching antenna theory.  So now I have a
regular SDR, a SDR kit which requires a bunch of surface mount soldering.
It has two antenna things, one for HF, and one for UV RF.  I bought
probably 200 dollars worth from MCX to SMA to RP-SMA to F to BNC.  I also
have a LNA, a LNB, Ham it up converter in the mail, and a 9:1 balun in the
mail.  Just learning the proper way to use all this stuff will take some
time.  I have an ebook I think it's called SDR for the hobbyist.  I also
bought a Beofeng UV5 + radio so I can receive signals until I get my HAM
license, then I can transmit.  I should probably also get a GMRS license
along side my HAM license so that I can transmit on all frequencies.  As
long as I know that I'll learn how to safely amplify the HackRF transmitted
signal, that's good enough for me.  I also have a discone antenna for the
HackRF/SDR coming in the mail.  Additionally, I have a 2.4GHz 25dB Yagi
Wifi antenna coming in the mail.  I bought the wifi antenna for my Alfa
wireless adapter (for monitor mode in Kali Linux and war driving), but I
figure I can plug it into the HackRF to see how much I can pick up also.*

*I know more experience will answer a lot of my questions.  Thank you for
taking the time to read my hundred pages worth of questions.*







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-- 
*O.T. Timothy PowellEE Engineering TechM: 386.299.6991
<386.299.6991>otpowell at gmail.com*
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