FM Tuner Sensitivity & Selectivity:
Marantz 2275 specs only cite a MONO sensitivity of 1.9 uV [-109.2 dBm, 8.7 dBf]
(nothing mentioned re STEREO) and an Alternate Channel Selectivity of 80 dB:http://www.classic-audio.com/marantz/2275.html
Clearly a typo in the above table: "Adjacent" should be "Alternate", as in "similar" 2325:http://www.classic-audio.com/marantz/2325.htmlhttp://www.fmtunerinfo.com/receivers.html
Marantz 2325 specs claim 5.0 uV [-100.8 dBm, 19.2 dBf]
MONO for a (more or less)
listenable 50 dB SNR (ultimate is 70 SNR).
Unfortunately, Marantz specs don't say anything about STEREO performance,
although some "similar" units cite 35 uV [-83.9 dBm, 36.1 dBf]
for 50 dB STEREO SNR....
My 1971 Kenwood KT7001 design is "similar" with 4-gang tuner and crystal IF filters:http://www.fmtunerinfo.com/kenwood.html
Kenwood specs only say 1.5 uV [-111.3 dBm, 8.7 dBf]
IHF Sensitivity (MONO, 30 dB SNR)
(nothing re STEREO) and 90 dB Alternate Channel Selectivity, just slightly better than 2325.
Back in 1976, I brought my KT7001 to a Kenwood Tuner Clinic held at a local
Hi-Fi Convention....which was also demonstrating the "Earthquake" sound system.
Following are test results, per (non-Kenwood) techs (alas the 7001 died a few years ago):MONO:
1.6 uV for 30 dB SNR (IHF Sensitivity) [-110.7 dBm, 9.3 dBf]
2 uV for 50 dB SNR [-108.8 dBm, 11.2 dBf]
6 uV for 60 dB SNR [-99.2 dBm, 20.8 dBf]
73 dB ultimate SNR, MONO (1000 uV) [-54.8 dBm, 65.2 dBf]
0.14% Total Harmonic Distortion (1000 uV) [-54.8 dBm, 65.2 dBf]
0.9% THD at 50 dB SNR (2 uV) [-108.8 dBm, 11.2 dBf]STEREO:
4 uV for 30 dB SNR [-102.8 dBm, 17.2 dBf]
40 uV for 50 dB SNR [-82.8 dBm, 37.2 dBf]
140 uV for 60 dB SNR [-71.9 dBm, 48.1 dBf]
70 dB ultimate SNR, STEREO (1000 uV) [-54.8 dBm, 65.2 dBf]
38 dB STEREO separation at 1000 Hz
1.0% THD (1000 uV) [-54.8 dBm, 65.2 dBf]
1.0% THD at 50 dB SNR (40 uV) [-82.8 dBm, 37.2 dBf]
In the brackets, I converted uV to dBm (300-ohm) levels, presumably in
accordance with the OLD test procedure (cuz some didn't have 75-ohm).
I'm not sure whether FMFool uses 300-ohm reference or 75-ohm reference.
If FMFool is using 75-ohm, then add 6 dB to the above 300-ohm levels.
Modern FM Tuners use a NEW test procedure, with sensitivity in dBf (re 1 femtowatt),
which is the SAME whether measured across 75-ohms or 300-ohms.
Subtract 120 db from a dBf number to convert to dBm.
Lets compare a -85 dBm (STEREO, 50+ dB SNR) sensitivity level to your FMFool results.
All stations above the "grey" band "should" be receivable, presuming a 2 dBi Gain antenna.
Those stations in the grey band will be very difficult, esp. when they are within
two channels of a strong station. Marantz 2525 is much better prepared to
receive an station that is two channel positions away (next adjacent....or "alternate")
than the older tuners, which might only have 40-50 dB selectivity....vice 80 dB.
A directional antenna would help to suppress the stronger stations.FM Third Order Intermods:
You have three fairly strong local FM stations. Although I don't recall
seeing any overload tests on FM Tuners, fol. stations "MIGHT" be affected:99.5, 100.3, 100.5, 101.5, 102.1, 103.3, 104.1 & 104.9 MHz.
[I modified my DTV IMD Calculator spread sheet....]
Local stations on 99.5, 100.5 and 104.9 won't be affected cuz they're so strong.
W262AI on 100.3 and especially very weak WAEB-FM on 104.1 "MIGHT" be affected.
A directional antenna (with a rotator) could be used to reduce the signal
levels from the local stations to reduce the effects of intermod generation.FM Man-Made Noise/Interference:
Ultimately, whether you receive a particular station or not will probably depend on
the levels and characteristics of Man-Made Noise/Interference. The FMFool
(as well as TVFool) calculations do NOT include a guestimate for the widely varying
levels of impulse....and broadband noise emanating from ignition systems,
fluorescent lights, dimmer switches, brush-type motors, ad nauseum.....so YMMV....
A directional antenna can significantly reduce noise pickup from directions other
then the desired signal direction.....again, YMMV.....Comments re 300 vs 75-ohm Inputs:
In my KT7001, the 75-ohm coax input is DIRECTLY connected to the first
RF tuner stage whereas the 300-ohm input goes through a balanced
(floating input) to unbalanced Balun. Hence lower loss using 75-ohm input.
However in the earlier KT7000, there were two Baluns in parallel: one for 75-ohm
and the other for 300-ohm input, which had one of the "balanced" input leads
inexplicably connected to GROUND. Balun loss was probably about the SAME...
If you look inside any FM Tuner with a 300-ohm input, you are going to
find an internal Balun to convert from unbalanced to balanced, as well as
reducing the impedance for the RF input stage. The loss is probably 0.5 dB.
Hence, when using a 300-ohm impedance antenna, there is only ONE
(external) Balun to worry about if the Tuner has a direct connection on
the 75-ohm input (check your schematics). And for sure there will be
TWO Baluns in series if you use the 300-ohm input. FWIW, all of my
more modern AVRs only have 75-ohm inputs....which can be misleading
when spec numbers are STILL referenced to uV (across 300-ohm!!!).
Thankfully, they also state sensitivity in dBf, independent of impedance.
If you have an older FM Tuner that only has 300-ohm input, twin-lead
can eliminate the need for a (0.5 dB loss) Balun at the antenna, and
might have a slightly lower cable loss....but when it rains/snows the
loss of twin-lead increases, whereas coax does not:http://www.saarsham.net/coax.htmlhttp://www.avsforum.com/avs-vb/showt...php?p=16796125http://www.avsforum.com/avs-vb/showt...php?p=15969694