[Premium-Rx] Premium RX Strong Signal Performance

[John Reed]

  ----- Original Message ----- 
  From: Carcia, Frank A. HS 
  To: 'John Reed' ; Premium RX 
  Sent: Thursday, May 29, 2003 12:34 PM
  Subject: RE: [Premium-Rx] Premium RX Strong Signal Performance

  Here is some information on the first IF (roofing) filters on some of these receivers:

  RA6793A:  Crystal, 16 KHz and 20 KHz BW, pre and post IF amp at 40.455 MHz.
  RA6772E:  Crystal, 16 KHz BW pre IF only at 35.4 MHz
  RF-590:  Crystal 20 KHz and 20 KHz pre and post IF amp at 40.455 MHz

  This has probably got a lot to do with it.

  Some other comments - 
  Notch filters.  I know I could construct one of these and add it to the receiver input.  What I was after was why some receivers do so much better and don't seem to need help like this, and what standard test would show this.

  Active whip:  I spent several months testing and constructing this accessory.  I tried MFJ and Dressler active whips.  Neither of these came close to eliminating second and third order products.  Dallas' whip however, does.  It consists of a high negative feedback U310 first stage followed by push/pull Norton amps.  I suppose I could string up a wire and try it, but I don't expect I would see any difference.  I think of the whip as a signal generator with a strong modulated signal and a close by weak modulated signal.

  John


      Hi John,
      I wonder what your first IF bandwidth is in Racals
      compared to the RF590? I have found the weak link in the Racal design is the second mixer when
  you are inside the first IF band pass. I wonder what  signal level the RX sees at 1450 KHz?
  I'm surprised about the RF590.  fc
    -----Original Message-----
    From: John Reed [mailto:jreed at alum.mit.edu]
    Sent: Thursday, May 29, 2003 1:30 PM
    To: Premium RX
    Subject: [Premium-Rx] Premium RX Strong Signal Performance


    I recently moved to a new location and discovered that there is a meduimwave broadcast station on 1450 KHz about 1/2 mile from my location with 5000 watts of power.  This has given me the opportunity to test various receivers in the strong field of this station.  For an antenna I'm using Dallas Lankford's Ultralinear whip with push-pull second stage.  There is a weak station on 1460 KHz and the test is based on how well this station can be heard.

    Here are some results, in order of best to worst:

    Racal RA6793A - good readability.  I used USB and manual AGC.  RF gain was turned down to give the best signal.

    Racal RA6772E - essentially the same performance as the RA6793A.

    WJ DMS-105R - more splatter.  I used 20 dB of input attenuation and the gain controls for best signal.  This receiver is single conversion so there is no roofing filter, also analog tuned so phase noise is minimal.  Still not as good as the Racals.

    NRD-525 - more splatter and noise than the above receivers.  This is not a stock 525.  It has the ESKA roofing filter and PLAM board with post IF filters.

    Harris RF-550 - Very noisy and splatter was bad.  Just pieces of the received signal could be made out.  USB was used, manual gain and RF and audio gain were adjusted for best reception.

    Harris RF-590 - about the same as the 550, but not as much signal made it through.

    I am surprised at the wide range in performance between these receivers.  The published specs don't indicate to me that much of a difference should exist.  I'm curious as to what specs would be most important in quantifying this test?

    John Reed


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