[SECC] Fwd:W8JI RE: FT1000MP

[W4OC@aol.com]

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In a message dated 12/2/01 6:46:19 PM Eastern Standard Time, 
owner-secc@contesting.com writes:

<< Hi Ken,
 
 >       Also, for those of you who own FT1000MPs, has anyone made tests
 >       on the change in signal to noise ratio on 160 meters with the
 >       radio receive front end in the "tuned" and non "tuned" position
 >       menu settings? I made some tests this morning listening to local
 
 The overall selectivity of a receiving system determines the noise 
 window, not the front end gain. The only exception is when 
 overloading and clipping in stages with noise, which would be 
 devastating to working anyone of any strength at any time!
 
 Changing from a 500HZ filter to a 250 Hz filter of the same shape 
 factor will improve CW signal S/N by exactly 3dB when it is limited 
 by broad noise.
 
 Adding a 3kHz filter in front of the receiver instead of a 300kHz filter 
 won't change a thing, if you are using 500Hz filters in the IF.
 
 Removing gain, assuming nothing is saturating with noise and the 
 receiver is quieter than the noise floor of the antenna, will make no 
 change at all in S/N. 
 
 >       line noise and a friend 30 miles away. With the additional gain
 >       of the front end device inserted the line noise is S7 and the
 >       station is S9.A S/N of 12DB. When the Front end amplifier is
 >       removed the line noise decreases to S4 and the signal of the
 >       other station is S8. A S/N of 24db. This is an effective S/N
 >       improvement of 12 db with the front end removed on 160.
 
 The test is not really meaningful. The FT1000MP, like virtually all 
 other receivers, is nowhere near 6dB per S unit as you move down 
 on the scale. It also does not have good resolution. As a matter of 
 fact, most receivers are "designed" to be 5dB per S unit, but few of 
 them come close below mid-scale on the meters. 
 
 My FT1000D is about 5dB per S unit near S-9, and gradually 
 changes to about 1dB per S unit at S-3. My FT1000D is about a 
 10dB change from S-6 down to S-1!!!!
 
 It is not useful to use S meters to measure dB changes, unless we 
 are positive we are in a linear and properly calibrated part of the 
 scale! No matter what we do, we should always use a step 
 attenuator and set the S reading to the same amount, and read the 
 change in the attenuation needed to produce the same exact S 
 meter reading. Or we could use the step attenuator to calibrate the 
 meter, understanding it will hold true ONLY for one set of 
 conditions.
 
   
 73, Tom W8JI
 W8JI@contesting.com 
 
  >>


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