I have no test equipment to measure receiver characteristics, so this
just reports "what I heard" when installing the International Radio
(INRAD, formerly IRC) "FT-1000MP Background Noise Reduction, Sensitivity
Improvement Modification" by W2VJN (aka. 70 MHz amplifier mod), and the
K9AN CW audio mod (included in the IRC 70 MHz mod kit).
Summary:
First, I a did subjective, side-by-side comparison of two nearly
identical FT-1000MPs. Unmodified, both rigs sounded almost exactly the
same. Then I installed the INRAD amplifier mod in one, and compared
them again. The IF "white noise" was significantly reduced, and the
front-end sensitivity was improved a bit. Finally, I added the K9AN CW
audio mod. This dramatically reduces the CW audio response above a
certain pitch, making CW reception more pleasant. In sum, I think both
mods are well worth installing, though I may change my mind after I hear
how the receiver performs when there are lots of strong signals on the
band, as there will be this weekend during WPX CW.
Details:
(Best viewed with a fixed-pitch font such as Courier):
FT-1000MP "A" FT-1000MP "B"
(the control) (modified)
Serial No. 5N050201 5N050176
Factory Date (from menu 9-8) 951226c2 951225c2
Initial "r iF-GAin" factory
setting (from menu 9-1): 13 12
Post-mod "r iF-GAin" setting 9
A1-Pitch (adjust 3-5 to display) 450 Hz same
FrontEnd (8-4): Flat same
Freq: 28.200 same
Mode: CW same
Filter: 500 Hz Collins same
AF Gain: 12 O'clock same
RF Gain: Max same
Attenuator: 0 same
White noise level WITH NO
ANTENNA connected: very noticeable hardly noticeable
Audible front-end noise with NO
ANTENNA connected, and menu
9-1 reduced to 0. None very low
In other words, the mod increases the sensitivity of the front-end
(increasing the "low-growl" front-end noise), and then you can reduce
the IF gain (and its associated high-pitched white noise), by adjusting
menu 9-1. The documentation from INRAD claims the following measured
performance improvements (sorry, I have no way to verify these numbers):
Noise floor unmodified, tuned mode, 40 meters, 500 Hz filters -128
dBm
tuned mode, modified -132
Noise floor unmodified, flat mode, 40 meters, 500 Hz filters -135
flat mode, modified -137
Dynamic range improvement 1 to 2 dB
I believe these improvements are the result of allowing the front-end
noise to dominate the noise floor measurements, rather than the IF white
noise (hiss).
If you want to hear how much white noise will go away, just connect your
MP to a dummy load, put headphones on, and reduce the gain of menu 9-1
down to 9 or 10. Installing the amplifier board alone doesn't change
the white noise any, but it does allow you to adjust the IF gain down,
and this DOES reduce the white noise.
To access menu 9-1, power on the radio while holding down the FAST and
LOCK buttons. Then press FAST + ENT as usual, and turn the MEM/VFO CH
knob counter-clockwise until menu 9-1 is displayed. Then adjust the
main tuning knob and listen carefully.
If you can't hear any change in high-pitched white noise when you adjust
menu 9-1, then either your headphones or your ears are not sensitive to
high-end audio frequencies, and this mod is probably not for you.
Otherwise, listening to less white noise is bound to decrease fatigue
when operating for long periods.
After installing the mod and reducing the IF gain to 9, I listened very
carefully to lots of weak CW signals with both radios simultaneously
(the NCDXF beacons are great for this, see
http://www.ncdxf.org/beacon.htm). Did I ever hear a signal in one radio
that I could not hear in the other? In a word, no. I could always hear
the signal with both radios, but it was more pleasant to listen to the
modified radio. Did I occasionally use the built-in attenuator on the
modified radio to reduce the new "growl" of the front end? Yes, this
seems to "undo" the additional sensitivity added by the mod, making the
radio even quieter when super sensitivity isn't needed.
The IRC mod also seems to "help" the EDSP. In the modified radio, the
undocumented DSP feature I call "CW auto-peak" (MODE set to CW, CONTOUR
set to 3rd position, NR set to 1st position, EDSP on), sounds better,
with less artificial DSP noise, and more signal, than on the unmodified
radio.
Finally, I installed the K9AN CW audio mod, which is claimed to "cut the
high frequency hiss by 10 to 15 dB." I believe this mod makes an even
more noticeable receiver improvement, because it reduces all
high-pitched noise, not just IF hiss. But it only affects CW mode; SSB
is unaffected.
The K9AN mod reduces the high frequency audio response of the active
lowpass filter that the MP puts in-line whenever you switch the rig to
CW. To hear the audio filter at work in an unmodified radio, just press
SSB, then press CW, while keeping the bandwidth set to 2.0 or 2.4 kHz in
each mode. Hear the difference? CW sounds better, but you still hear
plenty of harsh high pitched bannd noise. The K9AN mod fixes this.
After installing the K9AN mod, the cutoff frequency of the audio filter
is made much lower (but not too low). The harsh noise of static crashes
really gets toned down, especially when you are using wide 2.0 or 2.4
kHz filters. Sure, if you try to listen to SSB or static crashes when
the rig is in CW mode, it sounds distorted (because you don't hear the
highs as well), but that's the point. CW signals still sound just fine,
even the high pitched ones, and the noise isn't nearly as hard on the
ears as it used to be.
In sum, I think both mods make the MP more pleasant to use. Assuming
they introduce no new front-end overload problems, I would recommend
them. After WPX CW this weekend, I'll let you know if I still feel this
way.
73,
Bob, N6TV
* K9AN installation note: In both rigs, C3015 was 0.015 uF (markings:
"153K"), as specified, but C3026 was 0.0068 uF ("682K"), not the 0.0066
uF value documented in the instructions. But since it was almost the
same value, I went ahead and installed the supplied 0.047 uF capacitor
across C3015, and it seems to work fine.
--
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