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Topic: Re: Portable Software Defined Transceiver (Read 15468 times) previous topic - next topic

Re: Portable Software Defined Transceiver

i have been toying with the idea too.

especially a portable unit, using a gumstix overeo and fpga it could be done but will be costly. gnu radio is a great software package.

if a second 24bit audio codec can be attached to the gumstix without to much trouble, it would reduce the need for a larger fpga or even possibly just the si570 and an cpld.

i have a few eagle files for layout purposes it should work well, there are some single chip I/Q demodulators that would work well.

i'd like to have the ability for vhf/uhf t/rx

Re: Portable Software Defined Transceiver

Reply #1
i am not totally familiar with the power consumption of the omap, however it can be used in the lowest power mode that is usable. reducing consumption, i'm not interested in a hand held unit, however a self contained small unit supporting vhf/uhf with 40/50wats output power would be ideal as a satellite transceiver.

i am familiar with all the aspects of software defined radio, and the trade-offs of using an audio codec for the adc and dac is acceptable and in many applications is overkill.

i did not mention all of the required components i'd use, at this point i'm only considering the size of the boards and total cost.

Re: Portable Software Defined Transceiver

Reply #2
in general this will be used for voice, an 192Khz audio codec will surpass any ax.25 speed commonly used.

5 watts output can do satellite, and is plenty of power for most vhf/uhf linear amplifiers, the PA would be on a separate board anyways.

the cost will be much higher than $200.

another way to do this is start with separate boards for the different stages, it can be configured and assembled for individual needs.

Re: Portable Software Defined Transceiver

Reply #3
the first step i would take is to test the demod chip with the i and q going into a sound card. using sma connectors for the rf and lo and standard 1/8 inch audio jacks for for the i and q

a breakout board for the si570 and whatever demod chip i decide to use would have to be made,

Re: Portable Software Defined Transceiver

Reply #4
the idea is similar to the softrock, but will use an ic specifically designed for demodulation, with integrated pga

Re: Portable Software Defined Transceiver

Reply #6
the idea behind using that part is reducing part count, i had planned on filtering the input depending on what band it is tuned to.

having a board with that on it and the local oscillator would allow me to test different filter options.

Re: Portable Software Defined Transceiver

Reply #7
sa long as it stays above or below the desired signal the software will "tune it out"

the beauty of software demodulation is there is room for an infinite amount of filters.

qsd does not demodulate the base-band so much as it encodes it to be demodulated by software

Re: Portable Software Defined Transceiver

Reply #8
unfortunately intermod will cause problems even if you run a $10k radio, imho it is something that will have to be dealt with when it happens, easiest way around intermod is to change frequency away from source. something i am ok with.

as this project will be mostly just for fun, and some educational value i am not in need of the cleanest rx section.

operating a qsd receiver (tayloe mixer) in the 2meter and 440cm bands is near imposible i have not seen any multiplexers that will switch fast enough. limiting the available selection.

Re: Portable Software Defined Transceiver

Reply #9
the only thing i have invested into this project is time, i'm not dedicated to any part yet.

reduced part count is important, if i can find a more suitable part that will work on those 2 bands ill probably use it.

otherwise if your familiar with the g59 project, shrinking the entire board and including an dsp/cpu is something else i'd jump in on.

Re: Portable Software Defined Transceiver

Reply #10
Cool info. I'm going to try to blog it. It would be great if you wanted to though ;)
Got a question? Please ask in the forum for the fastest answers.

Re: Portable Software Defined Transceiver

Reply #11
[quote author="jason"]There is a classic paper on the subject of receiver performance written by Robert Watson of Watkins Johnson available at ... l14_n1.pdf that goes into a lot of detail on this subject.  Until radios are 100% digital, it will be very relevant for anyone interested in designing high performance receivers.[/quote]
Unfortunately, this link is broken. The correct link is ... l14_n1.pdf

Re: Portable Software Defined Transceiver

Reply #13
Is there a kit or "PCB only" for this project?

Re: Roofing Filter

Reply #14
[quote author="jason"]An 8th order lowpass Bessel filter meets the requirements I set out above, offering 40dB of attenuation at 20KHz, rapidly increasing above that frequency while maintaining a linear phase response within the passband.

Here is the schematic of the low pass filter.  There are two identical filters in the design, one for the in-phase (real) channel, and the other for the quadrature (imaginary) channel.  I have attached a PDF copy of the schematic for those who wish to examine it more closely.[/quote]
It appears that you've implemented your 8th-order Bessel with 4 Sallen-Key 2nd-order filters in series. However, as noted in the blog, you have no feedback in the schematic, making it highly doubtful that the circuit shown in the schematic will work. Any chance you'll update the schematic or provide an explanation?