Here a few measurements of receivers, using 500Hz filters.
MDS is a measure of sensitivity. -135dBm is 10dB more sensitive than -125dBm. This number doesn't matter very much in what you actually hear. The real test is if you hear a very noticeable noise increase when you connect an antenna to the receiver. If you hear an obvious noise increase when you connect an antenna instead of a dummy load, your receiver is sensitive enough! You should check sensitivity at the quietest time with the narrowest selectivity you use on every antenna you use.
Contrary to folklore and hyperbole, there isn't a receiver sold today that can dig into noise more than others on CW based on sensitivity or the use of a DSP or multiple DSP systems. The exceptions are:
If you read a review that claims a receiver made weak signals appear from nowhere, you better keep a wary eye on the rest of the review. It is possible for a receiver to be abnormally bad, but it is not possible for a receiver to work better than other properly working receivers based on sensitivity.
BDR is blocking dynamic range. This is the point where a strong signal either 2 or 10kHz just starts to make your receiver lose sensitivity. The bigger the number the better, ESPECIALLY at 2kHz spacing. The number you want here is probably around 80dB or more if you live in a reasonably quiet location and work weak signals on crowded bands. If you run two transmitters on the same band or have a neighbor who operates near your frequency, you almost certainly need more dynamic range. I'm in a very quiet rural location and have very directive antennas, and 80dB blocking DR suits my requirements just fine most of the time.
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.
Be aware the very good Drake receivers in the test below are essentially gutted and rebuilt receivers. They DO NOT use Drake mixers or amplifiers! Stock R4C's suffer from severe problems. See the notes!
Note 1: The FT1000MP has the same inherent problem as the FT1000 and FT1000D. A noise-blanker FET is left on even when the noise blanker is turned off with front panel NB and NB-W switches. This FET connects directly to the IF, and overloads when strong signals are present. Unlike the FT1000 and FT1000D, the front panel noise blanker level control affects the FT1000MP IMD performance. * is with the NB gain control fully advanced, ** is with the NB gain control fully off. In ALL cases the NB off-on switch is OFF!!
Note 1A: Yaesu copied the same basic NB from the FT1000D, and so this radio also has a NB problem even when the NB is switched off. This test was with NB gain menu set for minimum gain. The radio is worse when NB gain is increased in the NB gain menu.
Note 2: This is a MOSFET 2nd mixer R4C, aligned and in good shape but with no changes. This receiver is almost useless for weak signal CW work of any kind because of poor IM performance and filter blow-by.
Note 3: This is a tube 2nd mixer R4C, aligned and in good shape but with no changes. This receiver is almost useless for contesting or crowded bands because of poor IM performance and bad filter blow-by.
Note 4: This is the same receiver in note 2, but with the following changes:
Note 5: Gutted and rebuilt with solid-state double balanced high-level mixers. No vacuum tubes in signal path. Sherwood 600Hz roofing filter.
This page has been viewed times since revised on June 28, 2004