Front End


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FT1000MP Front End (Additional Info and Comments)

The K9AN mod consists of adding a 0.047 uF Mylar cap across C3015 on the audio board. It makes a very significant improvement. Run this test. Synch the main and sub receivers to the same CW signal. With the EDSP turned off and with 400 or 500 Hz filters installed, listen to each receiver separately. You will notice that the sub rcvr sounds much better than the main and has less hiss coming through. The difference is in the low pass filtering for each part of the radio. The main receiver is flat out to 1300 Hz while the sub receiver is peaked about 4 dB worth at 700 Hz and then rolls off quickly. Putting in the K9AN mod makes the main  sound the same as the sub. George, W2VJN

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).


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.


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 band 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. 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.
Bob (N6TV) pointed out that the INRAD documentation for  the FT1000MP CW-mode active-filter modification indicates that C3026 is 0.0066 uF in the radios that will benefit from the modification, whereas he found that his radio had C3026 = 0.0068 uF. This is apparently a minor typo in the INRAD documentation as my original description of the modification (see archives for December 1997) indicated  that C3026 was 0.0068 uF, as Bob noted. Steve K9AN




This site was last updated 08/27/07