MM0BSM
13th March 2005, 06:53 PM
ok dont want to hijack the other thread so will start here
{1} would it be possible to get 2kHz IMDR test done
maybe not this week but possible at a later date. This is a bit of stuff taken from another website
2kHz IMDR is most important
IMDR is intermodulation dynamic range. This is the single most important number when comparing receivers.
This is where two or more strong close-frequency signals mix and generate a new phantom signal or
multiple tones in a adjacent frequency SSB signal mix with themselves and make what sounds like splatter.
The measurement is made just at the point where the phantom signal level is high enough to interfere with
the weakest signal your receiver can detect. IMDR is a measure of how badly your own receiver causes
problems you might blame on other people. Bigger numbers mean better receivers. It is most important the
2kHz number be good. The 10kHz test number doesn't mean nearly as much, because almost any radio is good
enough at 10kHz or wider. Some number above 80dB is enough to stay out of trouble 99% of the time. If you
are in a noisy location, you obviously need less performance. 85dB keeps my receivers at the point where
poor quality external signals cause nearly all off-frequency problems. With 85dB IM3DR only a few of the
strongest stations cause my receiver to make its own internal problems.
MEASURING IMDR
Intermodulation dynamic range, or two-tone dynamic range, is measured by running two equal strength signals (from the low-noise oscillators) into the receiver with a certain test spacing. This test is equivalent to having two strong signals very near each other, with just the right spacing to cause a mixing product to fall on top of a noise-floor signal you are trying to copy. When the signal level of the mixing product is just audible above the noise floor, the ratio of the strong signals to the MDS (minimum discernable signal) becomes the IM dynamic range.
Poor IMDR performance shows up as splatter on SSB and as bloops, bleeps, and random musical thumps or phantom signals on CW
http://w8ji.com/receivers.htm
{1} would it be possible to get 2kHz IMDR test done
maybe not this week but possible at a later date. This is a bit of stuff taken from another website
2kHz IMDR is most important
IMDR is intermodulation dynamic range. This is the single most important number when comparing receivers.
This is where two or more strong close-frequency signals mix and generate a new phantom signal or
multiple tones in a adjacent frequency SSB signal mix with themselves and make what sounds like splatter.
The measurement is made just at the point where the phantom signal level is high enough to interfere with
the weakest signal your receiver can detect. IMDR is a measure of how badly your own receiver causes
problems you might blame on other people. Bigger numbers mean better receivers. It is most important the
2kHz number be good. The 10kHz test number doesn't mean nearly as much, because almost any radio is good
enough at 10kHz or wider. Some number above 80dB is enough to stay out of trouble 99% of the time. If you
are in a noisy location, you obviously need less performance. 85dB keeps my receivers at the point where
poor quality external signals cause nearly all off-frequency problems. With 85dB IM3DR only a few of the
strongest stations cause my receiver to make its own internal problems.
MEASURING IMDR
Intermodulation dynamic range, or two-tone dynamic range, is measured by running two equal strength signals (from the low-noise oscillators) into the receiver with a certain test spacing. This test is equivalent to having two strong signals very near each other, with just the right spacing to cause a mixing product to fall on top of a noise-floor signal you are trying to copy. When the signal level of the mixing product is just audible above the noise floor, the ratio of the strong signals to the MDS (minimum discernable signal) becomes the IM dynamic range.
Poor IMDR performance shows up as splatter on SSB and as bloops, bleeps, and random musical thumps or phantom signals on CW
http://w8ji.com/receivers.htm