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Receiver sensitivity
Looking at different manufactures units they are quoting their
receivers sensitivity as ..35uV at 12dB SINAD 1uV at 20dB SINAD -5dBu for 20dB SINAD Which of these values indicates the unit with the highest sensitivity and by what amount. Is there any easy way that a non technical can convert these values to a common denominator for comparison. beryl |
"beryl george" wrote in message
... Looking at different manufactures units they are quoting their receivers sensitivity as .35uV at 12dB SINAD 1uV at 20dB SINAD -5dBu for 20dB SINAD Let's convert the uV's to dBuV's first (= referencing all values in dB compared to 1uV). 0.35uV is -9dBuV 1uV is 0dBuV -5dbuV is, well, -5dBuV Now let's add 8 dB on both sides to get the same S/N ratio on the first line. This results in: -1dBuV at 20dB SINAD 0dBuV at 20dB SINAD -5dBuV at 20dB SINAD It is now clear that the last receiver requires the least signal to reach 20dB signal to noise ratio. Meindert |
Well done, Meindert!
I would only add that the differences in specified sensitivity among the three receivers would never be noticed in actual use. In fact, normal manufacturing tolerances are such that even on the bench, any one of the three could turn out to be the most sensitive. It is probably good to consider the three in the same sensitivity class. Chuck |
On Fri, 3 Dec 2004 20:25:26 +0100, "Meindert Sprang"
wrote: "beryl george" wrote in message ... Looking at different manufactures units they are quoting their receivers sensitivity as .35uV at 12dB SINAD 1uV at 20dB SINAD -5dBu for 20dB SINAD Let's convert the uV's to dBuV's first (= referencing all values in dB compared to 1uV). 0.35uV is -9dBuV 1uV is 0dBuV -5dbuV is, well, -5dBuV Now let's add 8 dB on both sides to get the same S/N ratio on the first line. This results in: -1dBuV at 20dB SINAD 0dBuV at 20dB SINAD -5dBuV at 20dB SINAD It is now clear that the last receiver requires the least signal to reach 20dB signal to noise ratio. Meindert That doesn't work. Receiver input level is not linear with sinad change. At the threshold (near 12db sinad) it takes very little signal increase for a large sinad increase. At a higher sinad level (near 20 db) it takes much more of an increase in signal level to make a small change in sinad level. Some receivers may not go much past 20 db sinad no matter how much signal is applied. Sinad is comparing signal noise and distortion. At low levels the distortion is very high. At 12 db it is around 33%. At 20 db distortion is about 12%. 30 db is around 3% distortion. The only way to compare is to measure all receivers at the same sinad level. You also need to know what the receiver bandwidth is too. If it is not the same on all receivers that will give different sinad readings. Also be sure they are operating in the same mode. Regards Gary |
Hello Gary,
You've posted some interesting information. I wondered about the inherent non-linearities and, of course, the deviation at which the SINADs were measured is not known, either. So the question boils down to whether modern VHF receivers for marine use are likely to have noticeably different sensitivity performance. As you know, SINAD is a measure of "useful sensitivity" and the noise plus distortion part of SINAD (rather than the signal part) is what is probably affecting the differences in VHF receiver SINAD measurement. Taking the issue into the realm of the real world, Icom quotes the following for their IC-F4GT/GS radios: 0.3 microvolts for 12 dB SINAD 0.79 microvolts for 20 dB SINAD The TK3160E UHF Transceiver reports similar results: 0.25 microvolts for 12 dB SINAD 0.63 microvolts for 20 dB SINAD These both work out to Meindert's results very closely. So we know that by assuming linearity, we are not necessarily wildly out of the ballpark. I'm not sure how you derived the distortion percentages you mentioned, but normally a receiver's distortion figure would be measured with an input signal on the order of 0.5 to 1.0 volt to ensure that noise doesn't affect the measurement. Under these conditions, a SINAD reading of 12 dB corresponds to 25% distortion, while a reading of 20 dB corresponds to 10% distortion. 73, Chuck |
"chuck" wrote in message
ink.net... Hello Gary, You've posted some interesting information. I wondered about the inherent non-linearities and, of course, the deviation at which the SINADs were measured is not known, either. The SINAD is measured with a single tone and the measured audio output is bandwidth limited with a filter with strict specifications, commonly known as as CCITT or P53 filter. So the question boils down to whether modern VHF receivers for marine use are likely to have noticeably different sensitivity performance. As you know, SINAD is a measure of "useful sensitivity" and the noise plus distortion part of SINAD (rather than the signal part) is what is probably affecting the differences in VHF receiver SINAD measurement. Taking the issue into the realm of the real world, Icom quotes the following for their IC-F4GT/GS radios: 0.3 microvolts for 12 dB SINAD 0.79 microvolts for 20 dB SINAD The TK3160E UHF Transceiver reports similar results: 0.25 microvolts for 12 dB SINAD 0.63 microvolts for 20 dB SINAD These both work out to Meindert's results very closely. So we know that by assuming linearity, we are not necessarily wildly out of the ballpark. Indeed. 0.63 vs 0.uV is 8dB, as well as 0.25 vs 0.63 mV. Meindert |
Meindert Sprang wrote:
I wondered about the inherent non-linearities and, of course, the deviation at which the SINADs were measured is not known, either. The SINAD is measured with a single tone and the measured audio output is bandwidth limited with a filter with strict specifications, commonly known as as CCITT or P53 filter. Hello Meindert, My comment about deviation referred to the fact the the EIA standard specifies that the signal generator deviation be at 60% of the peak deviation used for that service (if I recall correctly). While it is probably safe to assume that the peak deviation was the same for all three receivers, there is no way of knowing whether SINAD was measured using the specified 60% deviation. Chuck |
Lets hear nominees for the VHF rcvr hall of fame. Two votes I'd make are early
Motorola Modar, their 12 ch xtal controlled and the first full channel synth (can't remmeber model no. something like 55/75) . These were hot rcvrs and had GREAT intermod rejection, would work just fine in urban harbor environments where pager xmtrs would clobber all other marine VHFs. One other vote is an unsual combo, the Kenwood R 5000 rcvr with the factory VHF converter. Red hot sensitivity and low noise. Could actually hear comms that were unintelligable on other sets using the same antenna. |
"chuck" wrote in message
ink.net... Meindert Sprang wrote: I wondered about the inherent non-linearities and, of course, the deviation at which the SINADs were measured is not known, either. The SINAD is measured with a single tone and the measured audio output is bandwidth limited with a filter with strict specifications, commonly known as as CCITT or P53 filter. Hello Meindert, My comment about deviation referred to the fact the the EIA standard specifies that the signal generator deviation be at 60% of the peak deviation used for that service (if I recall correctly). The ETSI specifies a deviation of 12.5% of the channel spacing. I don't know what the EIA standard specifies. But indeed, one has to assume they were all measured using the same deviation. Meindert |
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