Question about Icom R75's filters in SSB mode

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GB46

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I'm a bit technically challenged when it comes to filter settings in the R75, so I simply go by trial and error and what my ears tell me.

My R75 is in mint condition; I have neither modified it (except for installing the DSP module), nor have I installed any optional filters since I bought it new in 2000.

Here are the filter settings I prefer for USB/LSB modes:
455K: 6
9M: 2.4

The audio in USB mode sounds fine with both twin pass-band tuning knobs centred (i.e. the normal setting), so why is there a lot less treble in LSB mode, so that I have to adjust the PBT to correct it?

If I use narrower or wider filters for SSB I notice the discrepancy there, too, but not as much.

By the way, I rarely use the narrowest filters for sideband, since I haven't encountered much QRM from adjacent stations lately, but 2.4 and 2.4 does occasionally help eliminate some background noise. Actually, the twin PBT feature is often much more helpful than the filters, anyway.
 

majoco

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IMHO you have noticed an effect which comes about when you use only one filter to cover USB and LSB.
Although the manufacturer likes to draw the bandpass graphs if his filter as being perfectly symmetrical either side of the centre frequency, they rarely are and the high frequency side tends to have a less steep slope than the low frequency side. See this nice pic from Universal Radio, probably gleaned from the manufacturers handout. ....
ICOM R75 Filter Options

When switched to USB, the carrier insertion is on the low frequency side and so you get some extended high frequency audio, but on LSB the carrier is on the high side so the high frequency audio is now cut off a bit. As you have found, shifting the passband a touch resolves the issue.

There's nothing wrong with the radio or your ears, in upper-class commercial radios they will have separate filters for all modes and don't change the carrier insertion frequency, other than a "clarifier" control. There aren't many people on LSB other than the hams below 9MHz and the odd Korean fishermen that are probably using ham rigs anyway - especially in the 80m band!
 

ridgescan

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My personal settings are as follows:
narrow-2.4/2.4
wide-15/2.4
I mostly use wide in SSB and keep the inner PBT set at about 1:00. This gives more dynamic range to both, while adding mid-highs to LSB and taking some from USB. I will use narrow on weaker stuff so I can work a signal with both PBTs.
You can also ride the RFgain down a bit to refine and kill some hash as well as hitting ATT and adding preamp1 to focus on smaller stuff. I love the R75 for all the ways one can refine signals.
 

GB46

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Thanks, majoco, that was a good explanation. Universal Radio's illustration is similar to the one about PBT in ICOM's user manual.

There aren't many people on LSB other than the hams below 9MHz and the odd Korean fishermen that are probably using ham rigs anyway - especially in the 80m band!
And CB'ers, too. In fact, from having listened to CB'ers in the past, it seemed that they preferred lower to upper sideband. A few of them seemed to think that if they used LSB they wouldn't interfere with a station on the same channel using USB. Not quite; it caused quite a mess, especially when signals were strong and when so many of them were overmodulated or sent through illegal linear amps! Of course, this was years ago, during skip conditions. CB here in western Canada seems absolutely dead. I haven't heard a signal on 27 mHz since 2002, even from truckers, and there are many of them in this area. Maybe it's different in the U.S.

Oops, sorry about getting sidetracked!
 

GB46

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My personal settings are as follows:
narrow-2.4/2.4
wide-15/2.4
I mostly use wide in SSB and keep the inner PBT set at about 1:00. This gives more dynamic range to both, while adding mid-highs to LSB and taking some from USB. I will use narrow on weaker stuff so I can work a signal with both PBTs.
You can also ride the RFgain down a bit to refine and kill some hash as well as hitting ATT and adding preamp1 to focus on smaller stuff. I love the R75 for all the ways one can refine signals.
Yes, I appreciate that flexibility, having used lots of receivers in the past. The best of them was an old Hammarlund SP-600 boat anchor with 20 tubes, but it was no match for the R75.

The benefit of reducing the RF gain can never be overstated; it works wonders, especially in my location, where I'm limited to an indoor antenna, making hash a huge problem.

Sometimes I shut off the AGC, too, which reduces the effects of fading, but I have to make sure to switch it back on if I plan to tune around the band a bit, or risk having my head blown off by strong signals. This happens very easily if I'm tuning around one of the ham bands, since there are a couple of local hams who are so close that they overload my receiver. I can always tell when they've come on the air, as I hear the AGC kick in and reduce the gain even when I'm nowhere near their frequency. One of them shouts into his mike and splatters pretty widely, but since I'm not a ham myself, I can't really contact him to let him know. Even ATT doesn't attenuate enough of his signal. As for the preamps, I usually keep them off altogether.
 

ridgescan

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Yes, I appreciate that flexibility, having used lots of receivers in the past. The best of them was an old Hammarlund SP-600 boat anchor with 20 tubes, but it was no match for the R75.

The benefit of reducing the RF gain can never be overstated; it works wonders, especially in my location, where I'm limited to an indoor antenna, making hash a huge problem.

Sometimes I shut off the AGC, too, which reduces the effects of fading, but I have to make sure to switch it back on if I plan to tune around the band a bit, or risk having my head blown off by strong signals. This happens very easily if I'm tuning around one of the ham bands, since there are a couple of local hams who are so close that they overload my receiver. I can always tell when they've come on the air, as I hear the AGC kick in and reduce the gain even when I'm nowhere near their frequency. One of them shouts into his mike and splatters pretty widely, but since I'm not a ham myself, I can't really contact him to let him know. Even ATT doesn't attenuate enough of his signal. As for the preamps, I usually keep them off altogether.
For the most part, me too, but preamp1 can be effective when used in ATT mode because ATT kills most of the noise to begin with, then preamp1 brings some receive power back with better S/N ratio. Preamp2, I concur, is useless overkill.
BTW also what I use is S-AM mode but I ride RFgain down with it till there is a balance between reduced RFgain and S-AM; I.E. at a point where the "S" goes solid when the signal is at its strongest. This method allows S-AM to perform its function of hanging onto fade best as possible without the annoying "pop" S-AM suffers. You wind up with a more consistant signal copy with fade under control.
Great capable rig the R75.
 

GB46

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BTW also what I use is S-AM mode but I ride RFgain down with it till there is a balance between reduced RFgain and S-AM; I.E. at a point where the "S" goes solid when the signal is at its strongest. This method allows S-AM to perform its function of hanging onto fade best as possible without the annoying "pop" S-AM suffers. You wind up with a more consistant signal copy with fade under control.
Well, your R75 must either have been released later than mine, or maybe you have installed a mod for it, because my S-AM mode does absolutely nothing. If I detune the signal far enough I do hear the pop and can see the S flashing, but it has no actual effect on reception of the signal. I've read complaints by others about that. Some have installed mods, but I haven't bothered, mainly because most of my listening is in SSB mode.

Using MultiPSK (for receive only) I also monitor RTTY, CW, amateur JT65 and USCG weather fax, all of which seem to work best with the receiver set to CW mode. In fact, I no longer switch to RTTY mode. Anyway, that popping sound you mentioned caused by S-AM losing lock is very familiar to me, because I once had a Sony ICF-2010, so I know what you're talking about. Still, when I finally got it locked in with the Sony it was so effective that I often didn't notice any fading at all.
 

ridgescan

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You have much more experience navigating the R75 than I do as I never dabble in RTTY/CW/JT65 etc. I just surf the dial for fun. But I should have mentioned what you likely already know, that there are separate filter settings within S-AM you can set. Mine for S-AM are:
open-15/6
narrow-2.4/6
wide-15/15
the S-AM mode is most effective for me in "open" 15/6 filter setting; N-narrow naturally is too narrow in AM; and W-wide can be too hashy on fade. Plus I run the rig on a pretty fidelic Boston center channel speaker that I removed the crossover from, so possibly the S-AM can be more detected by my ears through this combo.
 

GB46

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You have much more experience navigating the R75 than I do as I never dabble in RTTY/CW/JT65 etc. I just surf the dial for fun.
Well, I'm not a ham, just an experienced SWL. I, too, use the radio just for fun, but once I had downloaded MultiPSK and finally learned how to use it, I started exploring those other modes more frequently. The accuracy and stability of R75 makes it easy to decode them. I prefer listening to voice transmissions, but am hearing less and less from international broadcast stations these days, at least in the English language. The only other language I can understand is German, but I haven't heard Deutsche Welle for a very long time.

Of course, there are lots of powerful signals from English language evangelist stations on there, and one can often hear the same tirade from the same speaker on many different frequencies, often outside the established bands, but that's not my cup of tea.
 

ridgescan

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Well, I'm not a ham, just an experienced SWL. I, too, use the radio just for fun, but once I had downloaded MultiPSK and finally learned how to use it, I started exploring those other modes more frequently. The accuracy and stability of R75 makes it easy to decode them. I prefer listening to voice transmissions, but am hearing less and less from international broadcast stations these days, at least in the English language. The only other language I can understand is German, but I haven't heard Deutsche Welle for a very long time.

Of course, there are lots of powerful signals from English language evangelist stations on there, and one can often hear the same tirade from the same speaker on many different frequencies, often outside the established bands, but that's not my cup of tea.
Grandpa Stair is everywhere! And his transmitters punch through where others don't even try regardless of conditions. Not my thing either that doomsday crap. They keep trying that stuff and we keep living.
Luckily I can still hear quite a few English BCs from BBC, VOA, Africa, China, Vietnam, Romania, Canada, etc. plus WTWW Lebanon, Tn. is pretty cool with the old school hits and country and HAM radio talk shows. Plus it's kinda fun to listen to Alex Jones on 4840 in the evening. When he loses it I can't help but LMAO.
Plus I like listening to hams at night ragchew-the R75 sounds so good in SSB. You can pick up a lot when they talk technical stuff.
 

GB46

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Not my thing either that doomsday crap. They keep trying that stuff and we keep living.
Yeah, an evangelist once promoted his book entitled "1975 in Prophecy". According to him, we shouldn't even be here today, since doomsday was supposed to have happened in 1975. Guess we must have dodged some bullets.:roll:

I like listening to hams at night ragchew-the R75 sounds so good in SSB. You can pick up a lot when they talk technical stuff.
Yes, the R75 really shines when it comes to SSB; in fact, I think that's where it performs the best. I listen to hams, too, but it can be frustrating when I can only hear one side of the conversation. Even though they may be at equal distances from me, the other ham has probably pointed his beam towards the other party and away from me. Then there's also the problem that I often tune in a ham when he's either in the process of signing off, or turning it over to the other guy, whom I can't hear.

As good as the R75 is for monitoring amateur CW and digital modes, the transmissions there are usually much shorter, especially during contests, so I've had to speed up my reaction time to click on the signals in MultiPSK's spectrum display as soon as I spot them. The CW signals are often so close together that they can all be heard at once at different pitches, even with the narrowest filters, so I wind up doing lots of clicking. ;)
 
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