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

In article ,
(BOEING377) wrote:

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.

I'll second that vote for the Modar's. We still have a pile of those
rigs kicking around the North Pacific fishing fleet, and they are
coveted as if they were Gold. Unfortunatly there are VERY few techs
that still work on those, and the spare parts are getting fewer all the
time. I have a 55/75 with dual receivers in my house as a Limited Coast
Base Station, and it has the .0002 tolerance mod for Coast Station use.
They are one of the best VHF's, ever made. The SEA156 comes in a close
Second, in my opinion, I have one of those as well.


Bruce in alaska
--
add a 2 before @