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ICOM IC-R75 Communications Receiver

Image
ICOM's "triple conversion" IC-R75 Communications Receiver.
Many versions include the "Sync" circuit that is really worthless.
Also to my ears the audio quality in AM mode is fair at best even with a external speaker in use (can be improved, see text below).

Later samples (US versions marked as the IC-R75-12 and IC-R75-22 on it's outer box sticker) no longer offer the "Sync" function.
(N9EWO photo)


The IC-R75 tabletop HF communications receiver came into the Icom line back in 1999. Frequency coverage is from 30 hz right to 60 Mhz. This allows one to catch the 6 Meter amateur band as well. USA versions include a "Floor Brick" AC power supply. For most samples this will be a unregulated linear transformer, but in mid 2009 this was changed to a switching type supply (see below for more information on this subject).

The IC-R75 continues ICOM's trait of poor audio, but it's not as bad as the old IC-R71 "Distortion Beast". It's a muffled sound with the IC-R75. This "cloudy audio" ill is detected more so in the AM mode "super-wide" 15 Khz bandwidth. One can improve on this with 2 seperate internal audio modifications that can be done by
Kiwa Electronics in MN USA. However, from my own "before and after testing" this does NOT totally cure the problem either (when compared to the AOR AR7030's super good audio, the old Kenwood R-1000 does much better in the 12+ Khz bandwidth even after the mods). Important : One should have BOTH Kiwa audio mods done to help the audio, but at LEAST the "High Fidelity Audio Filter Upgrade" one. I have tested this in 2 steps, including before and after digital recordings, so I have experence with both of the Kiwa audio mods. The Sync detector is the other real stinker but Kiwa has a mild modification for that as well that sort of helps on this too (or not). More on the "Sync" topic from others below.

But overall it's a great tabletop set for the money even on the used market. Tuning knob even uses a optical encoder, so no cheap stuff here.

The set features "Twin PBT" (Pass Band Band Tuning) as used in many of Icom's Amateur Transceivers. The optional DSP is the same board that goes in other ICOM Amateur sets, so it's using the old AF type of DSP stuff. Rubber pushbuttons have been used, that seems to be the norm with ICOM these days. Of course this type of button may not hold up in years to come as air reacts to the plastic/rubber, and also the printing on these type of buttons can have a tendency to wear off . But I have not seen any groans on this over the years either (at time of writting).

Even in this price point Icom is using a 1 hz synthesizer. So you can tune AND DISPLAY razor sharp. No one else has ever come close in this price range with this super fine tuning step.

Alas, the linear "transformer" version of the AD-55 floor brick power supply (USA versions) is unregulated and provides way too much voltage even fully loaded (17.65 volts which is way over specs.). So the set runs super HOT as the internal voltage regualtor has to burn this excessive voltage off. Again, see my text below for more information on this.

Dave N9EWO
© N9EWO
Ver. 8.9

UPDATE's : Sync detection no more , "Icom IC-R75-02" (US version) gone. "AD-55S-12 Switching" AC Power Supply For Latest USA Production.

1. Back on October 16, 2006 we seen the IC-R75 listed with a revised FCC OET , and wondering what was going on here ? It turns out that the stinky "Sync" is no more with new samples sold starting in early 2007 ? The stock of the Motorola MC13022 Sync IC (this is a AM stereo chip) finally ran out. This IC has not been made in years, and for Icom to keep the receiver in production changes had to be made to this part of the circuit. The revised model is known as the IC-R75-12 (USA version, marked on the outer box sticker near the serial number). As we have made note here to this effect already, this is no real loss as the Sync was really worthless. UPDATE : Samples that include the new switching AD-55S-12 AC power supply are marked as the "IC-R75-22".

2. Observation that I discovered on the PUBLIC FCC OET web site. Perhaps there are additional "internal" changes that were been done with the IC-R75 as well in this update (this was unknown at time of posting) ?? We may never see the real story on this one I'm afraid ??

"Switching" AC Adapter to be included with future production of the Icom IC-R75 receiver (for USA samples). I see Icom obtained another update to the FCC OET (type acceptance) on July 28, 2009 for the IC-R75 receiver.
Click here to view the public FCC OET page. As I compare the 2009 updated owners manual (as seen on this FCC link) to the older manuals, on the "supplied accessories" page it shows a different AC Adapter and added switching regulator information on the bottom of that page. If you look close in the FCC test set up photo's (CLICK HERE) , you can see this new switching AC adapter in use !

Not sure if this means that Icom is finally addressing the excessive high voltage issue with the OLD AD-55 "unregulated" linear ac adapters with this new regulated switching type for all new samples (I discovered this over-voltage issue years ago, see below)
OR is it just that Icom's supplier just ran out of parts for the old AD-55's and have now switched to a lower cost switching supply (sic) ?? They may fix one problem and perhaps create another one at the same time (good old switching power supply noise).  But this is "very good" news as Icom must be planning to continue production of the IC-R75 for the foreseeable future.

UPDATE : The new included switching adapter model is the
AD-55S-12 (100-240 VAC 50-60 Hz , output 15 VDC, 2 Amps).

With at least the "High Fidelity Audio Filter Upgrade" done by Kiwa Electronics, it can sound 1/2 way decent too with the right external speaker. It's no AOR AR7030 either even after both of the audio mods, but AM mode audio is much improved (in wider bandwidths).

Dave N9EWO
© N9EWO
Ver. 3.6

A Simple Regulator Circuit For The Icom AD-55A Power Supply (Linear Transformer Version)
(for use with the IC-R75 ONLY!)

*** NOTE : I will NOT be held responsible for any info that is listed here ***
*** ALL DONE AT YOUR OWN RISK ! ***


Modified (USA 120 VAC version) Icom AD-55A "floorwart" power supply (transformer type).
Out of the box it supplies way too much voltage even loaded (17.65 volts in my testing) at a 1 amp current draw.
I added a regulator IC with a required heatsink and a few other parts in and on the AD-55A's existing case to make for cooler operation of the receiver.
The finished project is shown as above. A proper heatsink might take a bit of hunting for, this one I found at a hamfest (flea market).
It must sit near as shown, and only on this side of the supply. Be sure and read the warnings to this project below !!
(N9EWO Photo)

IMPORTANT NOTE : Be sure and read the update section above for the latest news with the included AC Adapter. This supply was changed in mid-2009 to a switching type , model number "AD-55S-12". The information below is NOT valid for the new version !!

Anyone in the USA who uses the Icom IC-R75 with the unregulated AD-55A "floor wart" power supply knows how hot the receiver's cabinet can get after a few hours in operation. Especially on the left side where the internal Sharp PQ30RV31 regulator / heatsink is located.

I measured the output voltage of the AD-55A power supply in a non-loaded state at approx. 21 volts. With the receiver on (loaded) it dropped down to about 17.65 volts. The IC-R75's input voltage is marked in the specifications as 13.8 VDC at 1.1 amps max with a ± 15 % tolerance. Hum, now that makes the recommended highest voltage at 15.87 volts maximum. Wow, the AD-55 exceeds that by almost 2 volts. No wonder the cabinet is so hot and of course creates stress for all internal components.

I feel that the AD-55A should have never been included with the IC-R75. Was this power supply was originally designed to work with the IC-R8500, a now discontinued Icom receiver ? This sets peak current requirement is DOUBLE what the R75's is, so would have a better chance to meet the voltage specifications (untested) ?

This was totally unacceptable to me and wanted to do something about it without having some large aftermarket 13.8V regulated power supply that was rated way over what current was required. Here is what I did to cure this problem and for some this will be very a simple project.

I came up with adding a few additional parts to the existing AD-55A that gives a clean regulated 13.8 VDC (or very close to it) output. More than enough current is still provided, the existing power transformer can handle that, no problem. One will have to be electronics handy to do this one however.

The "LM340K-12" IC is a 12+ fixed regulator in a metal TO-3 case. We add 3 diodes to float it's ground connection which increases (cheats) the output of the regulator very near the 13.8 VDC that we desire. Current rating on the LM340K is in excess of 1 amp, so OK here.

The only 3 caveats I can think of are :

Number 1 :
You must use a larger "thicker case" heat sink (size as shown) to dissipate the heat as it will get way too hot without it.

Number 2 : Be sure and NEVER allow the output cable plug to touch the metal of the heat sink. The regulator must be isloated from circuit ground. If you are worried here, a 1.5 Amp fuse could be added to the output (along with a mica insulator on the regulator and TO-3 cover). Also be sure and use a dab of heat sink compound between the LM340K-12 and the heat sink as is the case with any power transistor. I would not use the TO-220 plastic version of this device, as I don't think the heat would dissipate properly.

Number 3 : Once you do this modification, DO NOT operate the IC-R8500 with it as it WILL overheat the regulator.

Placement of the parts is up totally to you. Except the heat sink needs to be mounted on the right side on the top of the AD-55's cabinet, that's on the output end/cable (see the picture above for the general idea and type). The heat sink does get a bit on the hot side after being on for a few hours, but not so much that I cannot touch it at all. The other parts I mounted on it's same internal PC board (I drilled a few additional holes). Again you will not be able to mount anything on top of the transformer end (at least not placing any screws at this end). Also the power transformer gets very hot after a few hours on, so another reason not to mount the heatsink at this end of the supply. I used the same output cable and plug of course.

While I was at it, to clear up any "hum" switching power supply diode issues, I added 4 "point 1" uf disc ceramic capacitors across the existing 3 amp power rectifier diodes. These spots are already marked and holes drilled on the power supply's board, but were never factory mounted on the AD-55 I modified.


This crude schematic shows what I added (in red) to the Icom AD-55A. Also see the parts list below.
(photo via N9EWO)

Sorry about the crude schematic above , but the parts in red is what I added, which includes:

1 LM340K-12 , TO-3 case, 12volt positive regulator IC
4 .1uf @ 50V disc ceramic capacitors
1 .1uf @ 35V Tantalum capacitor
1 10uf @ 50V electrolytic capacitor
1 100uf @ 25V electrolytic capacitor
3 1N4001 1amp power rectifier diodes
Large heat sink that will mount a TO-3 case transistor properly, but will still mount on 1/2 of the top of the AD-55's case.(see photo above for placement / size)
Mounting hardware for all / heatshrink tubing / 18~20 ga. hookup wire

I have tested this circuit in the AD-55A for many hours with the IC-R75 and has worked great and the receiver is much happier (runs cooler). I wanted to make this as simple as I could , with no adjustments, that gets the job done and still allows for placement in the existing AD-55A's case.

A final note: Again the power transformer in the AD-55A runs super hot. This is totally normal, but be very careful not to touch the transformer if you open the case up after it's been plugged in and operating the set for awhile. You could very well receive a burn !

Of course for those of you that are not handy with electronics or don't care to do modifications, forget about the AD-55 all together and just operate the receiver on a aftermarket "transformer type" regulated 13.8 volt power supply. I will also say here to stay well away for any switching type of supply (unless you like added garbage mixed with your signals). Add the overpriced and "now discontinued" Icom OPC-869 DC power cable (or just use the one off the AD-55A) for connection between the power supply and the receiver. I would purchase a 13.8 volt power supply good with at least a rating of 4~5 amps or more. Supplies with a larger current rating will have a larger heatsink for it's pass transistor(s) and will run cooler.

I hope this information was of intrest.

Sorry, I will be unable to offer any tech. help or retrofit services with any AD-55A's
.

Dave N9EWO
© N9EWO
Ver. 3.2


ICOM IC-R75 input from others
(these are a bit dated from 2000 or so)


Mike Moore from Canada has made a purchase of a ICOM IC-R75 than had it modified with the latest Kiwa Modifications. He notices distinct improvements and here are his initial impressions. Thanks Mike for the comments.

"The AGC fix and perhaps to some extent, the audio mod, really removes the distortion that, previously, was particularly noticable in the AM mode.  Now the audio is *extremely* clear and isn't easily affected by fading signals as it was before themod.  This modification is so good that the sync mod then becomes alot less important.  (I'm unsure as to how much is attributable to the AGC mod and how much is attributable to the audio mod.)  I tried feeding the audio into an Optimus PRO-X44AV speaker.  The audio was absolutely fabulous (although only average dynamic range). The sound was full and had a good bass.  Before the mods, with the external speaker connected, the AM distortion was so noticeable as to makelistening with an external speaker unpleasant.  Now, it is very pleasant."

"The sync detector now works, ie. it maintains lock.  It whistles when gaining lock and whistles when it loses lock.  While testing it on a *very weak* station, it kept whistling/howling (before the mod, it seemed to make no attempt to gain lock).  With the dramatic improvement to the straight AM, it's now somewhat more difficult to find signals (with rapid fades) that would easily demonstrate the difference between the sync AM and straight AM.  Nonetheless, in the sync AM mode, audio and especially music appeared to suffer less from fading."

"The addition of the 3.8 kHz filter is just what the doctor ordered.  This is a perfect width for narrow AM/S-AM.  I tried it on Radio Havana, which had one sideband being interfered with. With sync AM, the 3.8 kHz filter and the inner PBT control turned to one side, the signal came in clear and sounded beautiful.  I had been considering buying another 3.3 kHz filter (many months ago, I had taken the one I had out of the R75 and put into the AR7030+) but with the 3.8 kHz filter installed by Kiwa, I have since changed my mind." 

"Also, the NR now seems to work better.  On this point, I'm not really sure if this is just subjective on my part or not.  Before the mods, the NR seemed to reduce signal and noise in equal proportions, rendering it rather useless.  Now it doesn't seem to attenuate the signal as much (or it seems to reduce the noise more) as it did before - actually making it useful. "

"Cheers! Michael Moore"


A few comments from Dan Blackburn on the IC-R75. I feel that IF a "Internal Power" supply is built correctly, no excessive heat or a cheap poor "buzzy" transformers...etc...it's better inside a radio. I hate Wall-Floor Warts !!!! The internal power supply in the JRC NRD-545 is a very nice one (not with later samples it appears), matched to the set perfectly (current vs heat) and is quiet as a mouse.

"I agree with many of the comments in the postings that have appeared so far, but I have a few things to add that I have found, from having owned two of these excellent receivers so far. First of all, I do not regard the receiver's external "brick" power supply to be undesirable. I have read several reviews and some of the comments in the postings on this site, which make mention of this." To me, an external power supply is VERY desirable for two major reasons: 1) It takes one of the main heat-generating components in any piece of electronic equipment, and moves it well-away from the sensitive circuitry inside the cabinet. This also helps remove potential hum and magnetic fields from the immediate vicinity of the receiver circuitry. 2) In the event of a power supply failure, it is only necessary to service the "brick" itself, rather than forfeiting use of the entire receiver during repairs."

"It should be noted that the external supply would likely be less failure-prone to begin with, as long as it is in a properly-ventilated location."

"Another observation I have made with regard to the R75's sync-AM function, is that it works MUCH better with signals which are lowered by the RF gain control. I have found that the sync circuit seems to be effective only on signals that "peak" below S10 on my bar-graph meter scale. In other words, by using the RF gain to suppress the signal level so that it only drives the meter to around S-7 or so, THEN engaging the Sync feature, the results are noticeably improved. Of course, the volume control must be appropriately increased due to the reduced RF signal, in order to maintain adequate audio levels, but this is a minor inconvenience. I have noticed that when the "S" character on the display is blinking, the sync detector is working and effective under the above conditions. When it is not blinking, the sync is not active and I further reduce the RF gain until it blinks on all but the received signal's peaks."

"I have also found that using Icom FL-257 and FL-223 filters, which produce 3.3 KHz and 1.9 KHz I-F passbands respectively, yield very good results and give the most available flexibility when selecting combinations for the many operating modes. For example, I have selected AM-mode filtering choices of 15/6 (wide), 15/3.3 (normal) and 2.4/2.4 (narrow) for most SWL activities."

"Finally, I have also found the R75's internal speaker to be somewhat less than adequate, so I use mine with the excellent Drake MS-8 external speaker unit. I have found the MS-8 just right for my listening preferences, and the speaker looks GREAT alongside the R75 with the receiver's tilt bail extended. I would recommend to anyone wanting to improve their R75's audio to give the Drake MS-8 a try."


"All in all, even with the cost of the added filters and MS-8 speaker, I believe the R75 to be a superior receiver, preferable in many ways to the more expensive Drake R8B, and with better coverage and cosmetics. Having owned two Drake receivers previously, as well as two Kenwoods and a Yaesu, I must say that the Icom R75 remains my hands-down favorite of them all."


A short comment from Björn Danielsson, Sweden on the IC-R75 .

"I have one since 1 week. And I am very satisfied with it so far.Yes it has 99 mem + 2 memories for scan edge. Is not 99 enough? I think it will be nice for me. Yes it can scan between 2 freqs and memory scan and on selected memories too like the R72 did. I can´t compare it to other radios execpt for my old Icom R72. And the R75 is much better than the R72. Better sound quality, almost noting background noise on the audio. The R72 had a lot of noise. The squelch is selectable between squelch and RF-gain or both at the same time. But I have RF-gain at max and only squelch on the squelch !! :-) If you buy one don´t forget to buy the DSP at the same time. It has Noise reduction and auto notch. I don´t know why they have it as option, it should have been in it at first."

Björn Danielsson, Sweden


A note from Johan Letterstål in Sweden on the Bandwidth scheme ..sounds like good news here ??

As for the bandwidth scheme:
The standard R75 comes with 15k and 2.4k in 9MHz 2nd IF and 15k, 6k and 2.4k in 455kHz 3rd IF.

There are one empty spare slot for both IF's. I've added a 1.9k narrow SSB filter in 2nd IF. Actually I'm considering stripping my R71, moving both the 2.4k 455k crystalfilter (Inrad FL44 substitute) and a 4k 9M crystalfilter to the R75. R75 gives you the ability to tailor each of the bandwidths (wide, normal, narrow) with any combination of 9MHz and 455kHz filters. Eg for AM I've choosed 15+6, 2.4+2.4 and 1.9+2.4 respectively.
Johan
(Thank You Johan for the information..Dave)


Johan Letterstål in Sweden with his promised comments on his new IC-R75 . Well it looks like the audio and Sync circuit both.."Stink"..oh well so much for wishful thinking. Want the best audio , looks like the AOR AR7030 is still the winner for audio. You can have BOTH of the Kiwa audio mods done to at least improve the IC-R75's audio. A Big "Thank You" Johan for the input.......Dave N9EWO

The following are my first impressions and comments on the R75 after about 10 hours of usage, including some comparisions with my other units, the AOR AR7030 (standard w NB/notch) and the Icom R71(w/o PLAM). The review is based on PURE LISTENING (BC-stations, mostly AM) and not any scientific A/B testing. The R75 is equipped with the optional DSP and a optional 1.9kc filter in 2nd IF. The antenna is an 8 m(27ft) random wire with coax-feed and balun. For specifications and technical details, please refer to the Icom US website (link below..) or other sources.

First look:
The R75 is small and light. The look and styling of the exterior is very nice although it doesn't have the robustness of the 7030. The buttons are the "rubber-type", but feels distinct and has a good "feedback". The main dial is ok, but the R71's big "free-wheel" is still superior. Also the solid metal knob of the 7030 has a better feeling. The other two knobs are quite small and I did have some minor difficulties to operate them (big fingers?).

{Good to hear that. I wish that AOR would have used optical encoders with the 2 smaller knobs. The AR7030's larger tuning knob is sort of like grabbing a greasy door knob....Dave N9EWO}

On the rear you will find the ordinary connectors for antennas, PC, recorder, speaker etc. "Why didn't Icom label them?" I asked myself, until I took a close look on the serial number label! The layout is shown there! The R75 has a traditional front panel with the "one control=one function" concept, compared to the 7030 which uses very few controls and a complex menu-system with lots of up and down toggling. The similarity to the "older brother" R71 is obvious in some cases and if you're a R71 user, the step to the R75 is a short step.

The manual for the R75 is ok (but far from the excellent 7030 manual).Schematic is not included (not even a blockdiagram).{that stinks ...Dave N9EWO}

Usage:
The first thing that 'hits' you at power up, is the display. Large, clear and with a nice background illumination. All the settings of the receiver are shown on the display. Icom calls it a "function display" and that's what it is! I especially enjoyed the S-meter with its 'peak hold'. R75 really wins here. The method of selecting bandwidth seems to be taken directly from the R71. Each mode has three bandwidhts; wide, normal and narrow. Contrary to the R71, R75 gives you the possibility to combine the filters (15kc, 2.4kc, Spare in 2nd IF and 15kc, 6kc, 2.4kc, Spare in 3rd IF) for each bandwidth and mode. Eg for AM you could set 15kc+6kc, 15kc+2.4kc and 2.4kc+2.4kc for wide, normal and narrow respectively. The filter setup is very versatile and installing optional filters are easy. But, even this, I might still prefer the 7030 with its (up to) six filters and the excellent calibration feature. I lack a wider filter in either IF (2.8-3.3). The difference is very small, but points goes to AOR.

What about the twin-pbt? Again an heritage from the R71. The difference is that R75 uses two controls (a concentric knob) for moving lower and upper portion of the passband. Turning both controls togheter moves the entire passband. Works fine and it's much better than the R71 PBT. The 7030 uses one control and most importantly, shows the passband offset on the display. You see what your'e doing (aka WYSIWYG!).

Entering frequency with the keypad works fine, but Icom should have included a kHz button as well. To enter for example 15565 kHz, you have to punch 1 5 5 6 5 0 0 ENT or 1 5 . 5 6 5 ENT. Another ex: 1100 kHz would be 1 1 0 0 0 0 ENT or 1 . 1 ENT. Other settings (and there are a lot), such as tuning steps, beep level, cw pitch, dimmer etc, are done in a setup menu. Very user-friendly and easy to use!

The performance:
Audio: The R75 has a SMALL front mounted speaker (Icom US webpage calls it large!). The audio output and fidelity are ok and with headphones it's even better. I've not tested any external speaker. In general the audio is clearly better than the R71 (could it be worse?) but still not better than the 7030 (could it be better?). Distorsion shows up when using very narrow filters in AM, but that's logical and and could be remedied with the pbt. One way of getting nice audio is to use synchronous AM. Turning this on, the R75 will disappoint you! Honestly, I CANNOT hear ANY difference or improvement AT ALL! In fact, under certain circumstances, the s-AM will instead momentarly distort the audio! Very strange! Do I use it the wrong way or?...I suspect that Icom employs "carrier reconstruction" rather that "carrier replacement" for the R75 s-AM solution. The s-AM on the 7030 is superior and more versatile by all measures (even taking the disturbing low level heterodyne in account) The attack- and decay time for AGC fast and slow seems to be right and I'm satisfied with them. {This is bad news indeed on the Sync Detection Circuit....Dave N9EWO)

The optional DSP has two functions; noise reduction and automatic notch. The notch isn't operational in AM according to the manual, but that's not 100% true! Certain het's are reduced completely, others not. It seems to be some limitations within the passband (perhaps due to the notch being optimizedfor SSB bandwidths, not AM at 6kc). Well, it works to some degree. Compared to my MFJ-784B DSP, the MFJ is of course better and more aggressive in hunting and eliminating het's. The noise reduction works very well, also compared with the MFJ. The levelis variable between 1 to 15 (dB?) and at 5 the reduction is sufficient. As in any DSP, you will get 'echoing' or 'hollowness', when you increase the reduction level to maximum.

I would rate the R75 sensitivity as good and high enough for serious DX-ing. There are two preamps, +10db and +16dB, that works more and less over the entire spectrum (+16dB mainly used for 20+ MHz). Judging from S-meter readings and assuming that both S-meters are correctly calibrated (YES I know, this is not the right way) the R75 with preamp 1 equals 7030 w/o preamp on shortwave. With preamp 2, the R75 exceeds the 7030 with preamp. On mediumwave, the 7030 is better overall.

At a glance review, 1-5 (bad-excellent):
Price/performance: 5
Design: 5
Controls: 4
User friendliness: 5
Sensitivity: 4
Features: 4
Specific functions/features:
Filters: 3-4
Sync-AM: 2
DSP: 4
Setup menus: 5

Johan Letterstål, Sweden


Comments from James in Taiwan, edited from the "Newsgroups" .

I just got an IC-R75 after reading some reports both pro and con about the receiver. After using the receiver I found out that most of the cons were over rated. When using this radio keep in mind the price it cost. An IC-R75 IS NOT an IC-R9000 or anyother US$5,000+ radio. My IC-R75 is replacing my IC-R71A. The R75 is FAR BETTER that my R71A in all functions.

The size of the R75 is just right as it can be used as a portable receiver in a car without making any big changes. ICOM has choose to use hard rubber for the buttons and tuning dials. Some people on the net feel the hard rubber will get eaten away over time. I think there is some truth to this but under extreme temperture contidtions. The R75 is very light (My R71A was a ton!).

I must tell you that I put the DSP option in the radio and it works very well. The key to listen on the R75 is not to set the NR (noise reduction) level too high. If the NR is set too high you will get distortion at voice freqs. It a few cases I was able to masking / cover a voice completely by setting the NR very high. It's just a good ideal to set the NR to the maximum noise reduction level and not above.

The NB (Noise Blanker) is of great help. In some cases it kills more noise than my IC-R8500 with a DSP 599zx! I live almost under power lines and I night I get very bad bus noise fro the relay stations. With the DSP option the NB works very well (The NB doesn't work in FM mode).

I found the two level preamp VERY usefull in low signal conditions. Here in Asia we have to fight with noise a lot more that US or Europe based monitoring sites. In one case I was able to pull out a very low powered Mongolian station out between a radio station in Shanghai and Helongjiang in Northern China! I use the NR and ANF (Automatic Notch Filter) to peek the voice level of the announcer along with the TWIN PBT (Passband Tuning Controls) to adjust the level of IF to give me the maximum audio level ( this TWIN PBT wasn't a great help in AM mode but it did help!).

The memory bank space on the R75 is just too small. I don't know what came across the folks at ICOM by putting in ONLY 100 slots for programming. This is a major drawback. Because of the low memory banks I've started to use a PC control software to do large band scans. ICOM messed up here big time!

I found the scanning rate as fast as my R8500 and R7100 and the hit rate just as good.

The CW audio pitch adjustment also works well and saves me time when decoding via my external noise filter (Timewave DSP-599zx) The RTTY reverse mode helps me a bit when I screw up the MARK and SPACE signals. Also being able to select the RTTY shift helps when tunning a known RTTY signal.


Comments below from Gert Nilsson from Sweden on his IC-R75 . Thanks Gert for the input.

Some weeks ago I bought an IC-R75 with the 2.8 and 3.3 kHz filters and the DSP. Price around 9000 SKr = 1000$. We are some guys in Örnsköldsvik using 6 very long beverage antennas at a very quiet QTH. My friends have NRD 515, AOR7030+ and NRD525 receivers and I have made some tests. COMPARISON between R71E and R75 R71 with PLAM, 1024 memory board and some extra filters, attenuator below 1.6 MHz removed.R75 with DSP, 2.8 kHz filter in 9 MHz IF, 3.3 kHz filter in 455 kHz IF, AM band attenuator shorted out.These two receivers are rather similar, if you are used to the R75 you will enjoy tuning the R75. If you do not like the menus/remote control of the AOR AR7030+ the R75 is a receiver for you.

Sensitivity:My R71 is as sensitive as the AR7030, NRD515 and NRD 525. The R75 is even more sensitive. I have tried stations down in the noise and you definitely here them first on the R75. It has 2 different preamplifiers: Preamplifier 1 uses 2 JFET in parallel in a grounded gate configuration and I still have to se it crossmodulate. Preamplifier 2 can be used on all bands but it is intended for low noise operation above 20 MHz. It is an broadband IC amplifier with almost 20 dB amplification and very low noise, but it can not be used on crowded bands like the AM band during evening and night hours. It is perfect in a low signal environment. The specs for the R75 says 5.6 uV for AM below 1.6 MHz. With the attenuator removed it is very hot down to the lower frequency limit. ICOM has made a CP = Connection Point on the main board. If you short this connection point the attenuator is removed.The R75 has very quiet AF amplifiers, no broadband hiss like the NRDs which make readability of weak signals better.

Selectivity:The R75 has 15 kHz filter in the 9 MHz IF ahead of the Noise gate, then follows the other 9 MHz filters, 2.4 kHz and one optional. Third IF has 15 kHz and 6 kHz filters with 450 kHz center frequency (very cheap Murata filters) and a 455 kHz Murata CFJ455K5 2.4 kHz in other receivers but just 2.1 kHz in the R75. Any mode can use 3 different settings: narrow, normal and wide and you can choose yourself. The only limitations are that you can not use the 455 kHz filters in the S-AM (more about that later). Selectivity is very good. My 3.3 kHz filter has very steep shirts.

Passband tuning:The PBT of the R71 adjusts the width of the filters, if you do not have a wide extra filter in the 9MHz IF or bypass these filters. The R75 has twin PBT with 2 concentric knobs. If you turn both the same amount in the same direction you just move the passband, like the Drake receivers or the 7030. You can move it +/- 1.29 kHz in 15 Hz steps. If you turn one of the knobs or turn the knobs in different directions you can tailor the bandwidth and move the position of the passband simultaneously. With the 2.8 + 3.3 kHz any bandwidth between 1.5 and 2.8 kHz is possible. This is similar to the NRD535. I think the PBT works great. It works best with the optional 455 kHz filters.

Frequency control:The R71 has 10 Hz, 50 Hz (when tuning fast), 1 kHz and 1 MHz steps. The R75 has fine tuning of 1 or 10 Hz, coarse tuning selectable 0.1, 1 , 5, 6.25, 9, 10 12.5, 20, 25 and 100 kHz and band tuning in 1 MHz steps. You can have different steps in all modes. Tuning accuracy:The R71 tunes in 10 Hz steps and a has 10 Hz accuracy if you have PLAM and learn to count the marks on the tuning control. The R75 tunes and shows 1 Hz. The only indication of correct tuning is by ear so I would say 10 Hz is a realistic accuracy. My R75 shows the correct frequency at 500 kHz but is 15 Hz high at 30 MHz. I have not tried to correct this.

Stability:The R71 drifts about 60-70 Hz from turn on. The R75 drift is within 10 Hz.AM/S-AM:Of course much better audio in the R75, but I can't see any major difference between AM and S-AM. Icom uses a Stereo IC to restore the carrier. Not close to PLAM. In fact the R75 sounds so good in USB/LSB I always receive AM stations in the SSB mode with 2.8 or 3.3 kHz filters. The DDS is very clean and the audio is very clear and open in SSB. If you have 2 or more stations on an AM channel it is much easier to separate them with the R75. I think ICOM should try another solution to synchronous AM, preferably with a small lock in range. If I have 2 stations 50 Hz apart I can lock on either of them with the R71 PLAM which functions very good.

Noise blanker:The NB works fine on impulse noise on both receivers. The R71 NB is adjustable the R75 is not. The R75 NB also distorts strong signals (when it is not needed).

DSP:The NR can be adjusted between 0 and 15. A setting of 3 to 5 works fine, but I personally think it is a disappointment. When you press the NR button it sounds very good when the noise drops a lot but in fact all audio get weaker so the difference is just a few dBs. Still it can make the difference when signals are very weak. Like all kind of DSP the sound is a little strange to listen to. The ANF, the automatic notch filters, is quite good and eliminates most heterodynes, very easy to use.

Crossmodulation:No problems unless you use the Preamplifier 2 on crowded bands .

Not so good:The concentric knobs for the Twin PBT are not very easy to use with big fingers like mine. The pressure needed to push a button is a little to much. I like the R71 much better.

Recommendations:If you like to tune to hard to get stations on crowded bands I think an extra filter in the 455 kHz IF is a must. If you have to compromise I think a 2.8 kHz filter is a good compromise. At 50$ the DSP is clearly worth the money. If you are a BC DX-er you should try to remove the attenuator. If you have troubles with local stations it is very easily restored to the original.


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