[Hackrf-dev] interested in lower minimum frequency (LF range)

[Paul Connolly]

Sorry for the typo, i missed a couple of dots. It is the concept that is
important more so than the numbers I used.

Element 1 ,(360nF and 7*.*5uH)    
Element 2 ,(1.5nF and 1.8mH)
Element 3 ,(360nF and 7*.*5uH)


On 22/11/2015 20:11, Paul Connolly wrote:
> A spyverter would work (maximum power it could handle would be 200mW or
> +23dBm and the maximum that the HackRF One can TX would be 15dBm -
> https://github.com/mossmann/hackrf/wiki/HackRF-One#transmit-power ). A
> spyverter would normally map DC-60MHz to 120MHz-180MHz but it can work
> in reverse, just like a ham-it-up, 120MHz-180MHz to DC-60MHz. LF being
> 30kHz to 300kHz is a bit low for the ham-it-up, it was designed to
> convert signals in the MF and HF Bands (0.5MHz to 50MHz) to signals in
> the VHF Band (125.5MHz to 175MHz). The ham-it-up will work, but with
> more attenuation in the band that interests you (
> https://code.google.com/p/opendous/wiki/Upconverter ).
>
> You would still need a bandpass filter on the output before feeding it
> into an antenna to avoid spewing the DC spike (and other birdies) into
> the airwaves. So you would need to offset tune your signal away from the
> central DC spike, making sure that the DC spike is well inside the
> attenuation of the BPF.
>
> Lets say that you wanted to broadcast a AM signal at 100kHz with 9 kHz
> bandwidth.
> (ignoring any ppm offsets of the spyverter[or ham-it-up] and the hackrf
> clocks for now, it is something that you will need to deal with)
> So the signal that you want to TX would be at 120.100MHz(or 125.100MHz
> on a ham-it-up) on the HackRF One.
> And if the bandwidth was 8MHz on the HackRF and the centre frequency
> could be tuned to say 122.100MHz so that the DC spike would be 2MHz away
> from the signal that you want to TX.
>
> You sould  make a BPF circuit that sits between the spyverter(or
> ham-it-up) and the antenna - see below:
> You can make a reasonable basic bandpass circuit with 3 inductors and 3
> capacitors.
> (Random site found from a search for "bandpass filter calculator")
> http://www.changpuak.ch/electronics/butterworth_bandpass.php
> I gave it the following parameters:
> Center Freq. [MHz] 0.1 (100kHz)
> Bandwidth [MHz] 0.009   (9kHz)
> Impedance [Ω] 50
> Order [1-19] 3
>
> And it returned the following output:
> --- start of result ---
> Butterworth Bandpass Filter
> www.changpuak.ch/electronics/butterworth_bandpass.php
> Version : 10. Jan 2014
> ----------------------------------------------------
> Center Frequency : 0.1 MHz
> System Impedance : 50 Ohm
> Order of Filter  : 3
> ----------------------------------------------------
> Element 1 , Orientation : shunt
> C = 353677.651 pF, L = 7161.972 nH
> Element 2 , Orientation : series
> C = 1432.394 pF, L = 1768388.257 nH
> Element 3 , Orientation : shunt
> C = 353677.652 pF, L = 7161.972 nH
> ----------------------------------------------------
> Appendix : Prototype G values
> G[1] : 1
> G[2] : 2
> G[3] : 1
> --- end of result ---
>
> Approximate real component values can be substituted for the above, and
> it should still work well enough, but you should really test the circuit
> in a spice simulator to be sure of its frequency response.
> Element 1 ,(360nF and 75uH)    
> Element 2 ,(1.5nF and 1.8mH)
> Element 3 ,(360nF and 75uH)
>
> .11.2.2.33.
> ...........
>> ++-L-C-++>
> .||.....||.
> .LC.....LC.
> .||.....||.
> .GG.....GG.
> ...........
> .11.2.2.33.
>
> But if you are going to TX you should have a amateur radio license, in
> most countries you would learn everything that you need to know in the
> process of getting your license.
>
> On 22/11/2015 11:16, Dominic Spill wrote:
>> On 18 November 2015 at 13:40, Frank Ch. Eigler <fche at elastic.org> wrote:
>>> I'm interested in receiving and low-power transmitting with the HackRF
>>> at LF-range frequencies below, the 1MHz floor.  What are the limiting
>>> factors in the hardware or firmware that would impede transmitting a
>>> 100kHz AM signal?
>> The HackRF One transmit path passes a stream of complex bytes to two
>> DACs, then combines these two analogue signals and finally mixes the
>> signal up to the desired transmit frequency (in fact, HackRF shifts
>> the signal twice, but that's not important for now).  The hardware
>> limitations will be filters at the baseband and at the mixing stage,
>> which will filter out your LF signal.
>>
>> For this sort of operation I would normally recommend a ham-it-up
>> device[1], but even they only go down to HF/MF.  Perhaps other
>> upconverters are available, but I haven't seen any to recommend.
>>
>>> As I understand it, receiving is probably OK via decimation in software.
>> Have you tried this with HackRF One?  I would assume that you will
>> find the same issue with filters.
>>
>> Dominic
>>
>> [1] https://www.nooelec.com/store/ham-it-up.html
>> _______________________________________________
>> HackRF-dev mailing list
>> HackRF-dev at greatscottgadgets.com
>> https://pairlist9.pair.net/mailman/listinfo/hackrf-dev
>

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