Hi Guys At the transmitter side, the complex base-band signal is modulated using a high frequency carrier, amplified and transmitted. At the receiver it is first passed through a bandpass filter to remove out of band noise, and then reverse processing is applied i.e. down conversion to base-band, matched filter, synchronization, equalization etc... The question will definitely sound stupid but are there any blocks between the antenna and bandpass filter? I recall something call hetrodyne receiver where the RF signal is first converted to IF. I tried to read on Wiki but got confused. Your help will be highly appreciated. Best Regards Chintan
A question on practical receiver
Started by ●September 23, 2010
Reply by ●September 23, 20102010-09-23
On Sep 23, 11:42=A0am, "cpshah99" <cpshah99@n_o_s_p_a_m.rediffmail.com> wrote:> Hi Guys > > At the transmitter side, the complex base-band signal is modulated using =a> high frequency carrier, amplified and transmitted. > > At the receiver it is first passed through a bandpass filter to remove ou=t> of band noise, and then reverse processing is applied i.e. down conversio=n> to base-band, matched filter, synchronization, equalization etc... > > The question will definitely sound stupid but are there any blocks betwee=n> the antenna and bandpass filter? I recall something call hetrodyne receiv=er> where the RF signal is first converted to IF. I tried to read on Wiki but > got confused. > > Your help will be highly appreciated. > > Best Regards > > ChintanYou forgot low-noise amplifier (LNA).
Reply by ●September 23, 20102010-09-23
On 09/23/2010 08:42 AM, cpshah99 wrote:> Hi Guys > > At the transmitter side, the complex base-band signal is modulated using a > high frequency carrier, amplified and transmitted. > > At the receiver it is first passed through a bandpass filter to remove out > of band noise, and then reverse processing is applied i.e. down conversion > to base-band, matched filter, synchronization, equalization etc... > > The question will definitely sound stupid but are there any blocks between > the antenna and bandpass filter? I recall something call hetrodyne receiver > where the RF signal is first converted to IF. I tried to read on Wiki but > got confused.Some things are better learned from books -- see if you can find a copy of the "ARRL Handbook", the equivalent from the RSGB, or Hayward's "Radio Frequency Design". The normal signal processing chain in a superhet is antenna -> preamp -> bandpass -> mixer -> narrow bandpass -> mixer -> baseband. The bandpass filter before the mixer is usually broad, to accommodate tuning and to keep costs manageable. The 'narrow bandpass' is the IF filter, which is as narrow as it needs to be (and how narrow that is depends on the service to which the radio will be put). -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
Reply by ●September 23, 20102010-09-23
On Thu, 23 Sep 2010 09:35:43 -0700, Tim Wescott <tim@seemywebsite.com> wrote:>On 09/23/2010 08:42 AM, cpshah99 wrote: >> Hi Guys >> >> At the transmitter side, the complex base-band signal is modulated using a >> high frequency carrier, amplified and transmitted. >> >> At the receiver it is first passed through a bandpass filter to remove out >> of band noise, and then reverse processing is applied i.e. down conversion >> to base-band, matched filter, synchronization, equalization etc... >> >> The question will definitely sound stupid but are there any blocks between >> the antenna and bandpass filter? I recall something call hetrodyne receiver >> where the RF signal is first converted to IF. I tried to read on Wiki but >> got confused. > >Some things are better learned from books -- see if you can find a copy >of the "ARRL Handbook", the equivalent from the RSGB, or Hayward's >"Radio Frequency Design". > >The normal signal processing chain in a superhet is antenna -> preamp -> >bandpass -> mixer -> narrow bandpass -> mixer -> baseband. The bandpass >filter before the mixer is usually broad, to accommodate tuning and to >keep costs manageable. The 'narrow bandpass' is the IF filter, which is >as narrow as it needs to be (and how narrow that is depends on the >service to which the radio will be put).Hi, cpshah99 might have a look at: http://www.arrl.org/tis/info/sdr.html [-Rick-]
Reply by ●September 23, 20102010-09-23
>Some things are better learned from books -- see if you can find a copy >of the "ARRL Handbook", the equivalent from the RSGB, or Hayward's >"Radio Frequency Design". > >The normal signal processing chain in a superhet is antenna -> preamp -> >bandpass -> mixer -> narrow bandpass -> mixer -> baseband. The bandpass >filter before the mixer is usually broad, to accommodate tuning and to >keep costs manageable. The 'narrow bandpass' is the IF filter, which is >as narrow as it needs to be (and how narrow that is depends on the >service to which the radio will be put). >Hi Tim and John Thanks for your replies. But I also came across a schematic which had AGC and ADC. So thats the reason I wanted to ask you guys what is a standard schematic look like? Regards Chintan
Reply by ●September 23, 20102010-09-23
cpshah99 wrote:>>Some things are better learned from books -- see if you can find a copy >>of the "ARRL Handbook", the equivalent from the RSGB, or Hayward's >>"Radio Frequency Design". >> >>The normal signal processing chain in a superhet is antenna -> preamp -> >>bandpass -> mixer -> narrow bandpass -> mixer -> baseband. The bandpass >>filter before the mixer is usually broad, to accommodate tuning and to >>keep costs manageable. The 'narrow bandpass' is the IF filter, which is >>as narrow as it needs to be (and how narrow that is depends on the >>service to which the radio will be put). >> > > > > Hi Tim and John > > Thanks for your replies. > > But I also came across a schematic which had AGC and ADC. So thats the > reason I wanted to ask you guys what is a standard schematic look like?No such thing as "standard receiver". All depends on the application requirements. The design of receivers is about as big science as the DSP. VLV
Reply by ●September 23, 20102010-09-23
Vladimir Vassilevsky <nospam@nowhere.com> wrote: (snip)> No such thing as "standard receiver". All depends on the application > requirements. The design of receivers is about as big science as the DSP.It seems that I am on some mailing list that I accidentally signed up for. Today there is one about new developments in SDR. The link is: http://i.cmpnet.com/rfdesignline/2010/09/807_ENOBS_pt1.pdf among others, it describes the use of new 12 bit, 3.6Gsps ADCs, and their use in SDR. Digitize the whole bandwidth and do all the filtering digitally. It seems we might be close to the point where it is antenna, RF amplifier, ADC, and then a medium sized FPGA to do all the processing. -- glen
Reply by ●September 23, 20102010-09-23
On 09/23/2010 11:50 AM, Vladimir Vassilevsky wrote:> > > cpshah99 wrote: > >>> Some things are better learned from books -- see if you can find a >>> copy of the "ARRL Handbook", the equivalent from the RSGB, or >>> Hayward's "Radio Frequency Design". >>> >>> The normal signal processing chain in a superhet is antenna -> preamp >>> -> bandpass -> mixer -> narrow bandpass -> mixer -> baseband. The >>> bandpass filter before the mixer is usually broad, to accommodate >>> tuning and to keep costs manageable. The 'narrow bandpass' is the IF >>> filter, which is as narrow as it needs to be (and how narrow that is >>> depends on the service to which the radio will be put). >>> >> >> >> >> Hi Tim and John >> >> Thanks for your replies. >> >> But I also came across a schematic which had AGC and ADC. So thats the >> reason I wanted to ask you guys what is a standard schematic look like? > > No such thing as "standard receiver". All depends on the application > requirements. The design of receivers is about as big science as the DSP. > > VLV >Yup. AGC is pretty common, although it isn't manditory. These days you'll often find an ADC, with more or less of the signal processing happening in digital-land, but it isn't manditory either. For that matter, a superhet isn't manditory -- you can have a direct conversion RX that goes straight from RF to baseband, you can have a regenerative receiver (self-oscillating or not) that demodulates AM or CW with a minimum of components, you can have that acme of Edwin Armstrong's twisted genius, the superregenerative receiver, etc. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
Reply by ●September 23, 20102010-09-23
glen herrmannsfeldt wrote:> Vladimir Vassilevsky <nospam@nowhere.com> wrote: > (snip) > > >>No such thing as "standard receiver". All depends on the application >>requirements. The design of receivers is about as big science as the DSP. > > > It seems that I am on some mailing list that I accidentally signed > up for. Today there is one about new developments in SDR. > > The link is: http://i.cmpnet.com/rfdesignline/2010/09/807_ENOBS_pt1.pdf > > among others, it describes the use of new 12 bit, 3.6Gsps ADCs, > and their use in SDR. Digitize the whole bandwidth and do all > the filtering digitally.This approach results in a combination of poor performance, huge power consumption and high cost.> It seems we might be close to the point where it is antenna, > RF amplifier, ADC, and then a medium sized FPGA to do all the > processing.There are few areas where the SDR approach is viable; in most cases good old analog is simpler, cheaper, smaller and better. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by ●September 23, 20102010-09-23
glen herrmannsfeldt <gah@ugcs.caltech.edu> wrote:>among others, it describes the use of new 12 bit, 3.6Gsps ADCs, >and their use in SDR. Digitize the whole bandwidth and do all >the filtering digitally.>It seems we might be close to the point where it is antenna, >RF amplifier, ADC, and then a medium sized FPGA to do all the >processing.SDR is valid for infrastructure but seldom the best way to design the highest-volume radio products (mobile handsets, WLAN devises, etc.) 12 bits may not actually be enough to remove a jammer that a superhet design can routinely filter out. Steve