I agree, and there are modfications shown on web sites for DRM software. 

In my case, I have home-brew radios so I can easily support wide bandwidths. 
Since I've got code to transmt and receive OFDM using FPGAs I should modify it 
for narrower subcarrier spacings and do wideband HF OFDM some day.

73,

John
KD6OZH

  ----- Original Message ----- 
  From: expeditionradio 
  To: digitalradio@yahoogroups.com 
  Sent: Thursday, May 03, 2007 22:22 UTC
  Subject: [digitalradio] Re: Wider Digital Bandwidth Filters - Hardware Mods


  > John kd6ozh wrote: 
  > For 20 kHz bandwidths you'd need a software-defined radio
  > like the SDR-1000 or Soft Rock 40 where all the signal 
  > processing is done in the PC. The T2 and R2 radios described 
  > in QST 10 years ago would also be ideal for this use as 
  > the audio filters can easily be widened. 

  Hi John,

  It isn't necessary to use an SDR. You can modify a standard hardware
  transceiver with wide bandwidth filters. It is simple. Obtain a new
  wide bandwidth filter of the proper bandwidth and frequency, such as
  25kHz bandwidth or 250kHz bandwidth. Install it in one of the filter
  options, or remove the original filter and install the new one. Other
  types of switching can be used as well.

  For transmit, tap into the balanced modulator directly with a high
  value series resistor, and run this directly to a shielded cable to an
  add a jack on the radio for it. This connects to the soundcard speaker
  output.
  For receive, add a small high impedance amplifier on a rider board
  inside the radio, and use a high value series resistor tapped into the
  product detector. Run this directly to a shielded cable to an add a
  jack on the radio for it. This connects to the line input of the
  soundcard.

  Bonnie KQ6XA



   

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