OK, here are the results of my quick bench measurements for whatever it's
worth. All receivers were on the same frequency (448.800 MHz). Signal
source was a Fluke/Philips 6060A sig gen locked to a rubidium reference
oscillator, modulated by 1 kHz AF at +/- 3 kHz peak deviation. The output
of the sig gen had a 10 dB pad on it for isolation -- all sensitivity values
below have already been corrected for this 10 dB offset. SINAD measurement
done on an HP 8920B using the speaker output of each radio (standard EIA
test method), AF PA terminated with an 8 ohm speaker, with a transformer in
parallel with the speaker to provide isolation to the test equipment. I
used the averaging function on the 8920B to help smooth out the inherent
variation in the SINAD measurement.
The commercial radios (Micor, M2, Delta) were tuned using the factory tuneup
procedure without a preamp in line, i.e. no optimization of the front end
tune was done to improve sensitivity when the preamp was added. RF patch
cables for all tests included a 4' piece of RG-400 with type N connectors on
each end connected to the sig gen. A short secondary patch cable (less than
2') with the appropriate connector on the other end (RCA for Micor and M2
receivers, UHF for Delta-S and Kenwoods, N for Icom, etc.) was connected to
the main 4' cable, either with the preamp serving as the connecting point of
the two cables, or a type N "barrel" was used when the preamp was out of
line. All commercial radios were the standard 450-470 MHz split models,
with no mods done to them. All sensitivity measurements are for 12 dB
SINAD. In other words, I did everything I could to make the test setup as
close to identical for all of the scenarios.
My goal here wasn't to determine which receiver/preamp was more sensitive
than another - even though I've shown resolution down to a tenth of a dB,
there is at least a few tenths of a dB of inherent uncertainty in the
measurements. SINAD readings fluctuate on a signal that noisy, even with
averaging, so you have to take the absolute values with a grain of salt
(i.e. any of the readings that are within maybe 0.5 dB of each other should
be considered "too close to call").
REPEATER RECEIVERS
------------------
GE Mastr II Rx
--------------
-116.3 dBm (0.34 uV) without preamp
-127.7 dBm (0.092 uV) with TE Systems model 4420N GaAsFET
-127.5 dBm (0.094 uV) with Angle Linear 448GNT PHEMT
Motorola Micor Rx
-----------------
-116.2 dBm (0.35 uV) without preamp
-126.3 dBm (0.11 uV) with TE Systems preamp
-126.6 dBm (0.10 uV)with Angle Linear preamp
GE Delta-S
----------
-117.9 dBm (0.28 uV) without preamp
-127.5 dBm (0.094 uV) with TE Systems preamp
-127.6 dBm (0.093 uV) with Angle Linear preamp
The simple average of the linear (microvolt) sensitivities WITHOUT a preamp
for the repeater receivers is 0.32 uV (-116.6 dBm).
The simple average of the sensitivies WITH a preamp is 0.097 uV (-127.3
dBm).
MOBILE RECEIVERS
----------------
Kenwood TM-732A (my bench radio): -121.1 dBm (0.20 uV)
Kenwood TM-731A (retired, collecting dust for the last few years): -123.5
dBm (0.15 uV)
Icom IC-45A (really old, but a workhorse in its day): -115.6 dBm (0.37 uV)
Kenwood TM-V7A (my most-hated radio): -125.0 dBm (0.13 uV)
Syntor X9000 (with internal preamp): -122.3 (0.17 uV)
As you can see, the repeater receivers with low-noise preamps out-performed
all of the mobile radios. Even if you throw out the relatively-deaf Icom
IC-45A, the repeater receivers beat the mobiles by a margin of anywhere from
1.3 dB to 6.6 dB. Personally I'd argue that the TM-V7A should be
disqualified too; it has to have the most intermod-prone receiver of any UHF
radio I've ever used.
Side note: for the heck of it, I also tried using the sig gen in the 8920B
when I had the Delta-S on the bench, and I got SINAD measurements within a
couple of tenths of a dB difference. I also wish I could have found an ARR
preamp and thrown that into the mix, I know I have one around here
somewhere.
I don't claim any of these tests to be indisputible either in terms of
absolute accuracy of the values, nor reproducibility by others. I'm just
giving you what I came up with. Run your own tests and publish the results
if you don't like my methods (or results :-).
--- Jeff
--------------------------------------------
Jeff DePolo WN3A - [EMAIL PROTECTED]
Broadcast and Communications Consultant
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