Re: [Repeater-Builder] Re: 455khz filter for Mastr II discriminator audio
At 02:55 PM 31/05/2008, you wrote: >Hello Ron, > >The audio emphasis for FM is a different issue. When I put the >discriminator output from the Mastr II receiver on a analyzer you can >clearly see a spike way out at 455khz which I believe is the IF >frequency in the receiver. > >This controller has a auto-squelch feature (it does not use a COS/RUS >line at all) and it listens for the presence of high-frequency noise >coming off of the receiver to control the squelch. When a nice, full >quieting FM signal shows up the high frequency noise goes away and the >controller will detect this and kick on the transmitter. > >This detection circuit is behaving poorly on the Mastr II because this >strong 455khz component is throwing it off and making it shut down the >squelch because it thinks there's a lot of high-frequency noise even >when the signal is actually full quieting. > >Running the audio through a 10 mH inductor tied to a 1000pf cap to >ground should cause it to roll off the very high audio frequency and >solve the problem but here's what I run into trouble, there's >thousands of parts out there that say "10 mH inductor" so I'm over my >electronics head now! > >Thanks, > >Mark Hagler >W7WMH Seattle - Just happened to be about to do the final tests on a Master II. Connected my HP 600el meter to Vol Hi on the squelch pot (convenient) and then tried to do a 20db quieting test. Took about 5uv to get it. The squelch opens at .2uv and the radio sounds clean at .5uv. Connected the scope to the Vol Hi and low and be hold, a band of noise. Noise you can't hear from the speaker. Squelch circuit works just fine. I don't have a spectrum analyzer so can't view that.. Tinkering with the scope, it appears to be random noise above the 3khz. (I can't hear anything any higher) It appears to be coming right from the discriminator. Various size capacitors across the audio line are ineffective unless you use a very high capacitance. When the service monitor is modulated with 1khz tone at 3khz deviation, on the scope it looks good... This is the first Master II I have worked on, but I have done several Exec II and the receiver is basically the same. The only thing I had to do with this radio is change the AS board. The one that came with it did not have the squelch components populated but had a external squelch board coupled into the IF. The AS board is out of a Master II UHF mobile. The radio was originally a General Mobile Radio unit on the JL channel. High side injection is used on the local osc. So it is back to the drawing board with this one. Cheers Doug
Re: [Repeater-Builder] Re: 455khz filter for Mastr II discriminator audio
At 6/6/2008 14:42, you wrote: >I checked yesterday and we are getting audio off the Vol/Squelch Hi >pin as most people do. We wired it up instead using the RUS signal >and a transistor and disabled the smrt squelch in the controller and >it's working like a champ! I don't recall ever seeing any 455 kHz at VOL/SQ HI, & my scope is good to at least 20 MHz. Perhaps there was some other oscillation or ground loop going on. RUS works fine on Mastr II base stations. On mobiles it can chop a bit of usable signal off of weak mobile signals if the fast squelch is left enabled; this is due to the fast decay coupled with a somewhat slower attack. Switching the COS feed from RUS to CAS solves the attack problem but the logic threshold voltage needs to be set just right for proper operation. Bob NO6B
Re: [Repeater-Builder] Re: 455khz filter for Mastr II discriminator audio
Willis, One point on inductors...they do have a frequency rating. This is because of the capacitance produced between the coil windings. This total cap and inductance can make the inductor become resonance and then start to look like a capacitor as one goes higher in freq. Same happens with capacitors. An inductor is a term for a physical component which has inductance, capacitance and resistance. Also since one often puts in a core to increase the inductance per number of turns the material the core is made of affects the inductance with frequency. Due to the sluggness of the core's reaction to AC/RF it might work fine at say 10 kHz, 60 Hz, but not at 400 kHz. This is why cores are marked with colors to ID them for various functions. For filtering 450 kHz one would probably not have a problem, but whatever you get make sure it will work at the freq you want. Going down in freq is not a problem so if spec'd to work at 500 kHz, 1 MHz, etc will work at 450 kHz. It might have more inductance, but not less. I think you are trying to seperate the audio from the 450 Khz. They are far apart so should be easy. At 450 kHz a 10 mH choke is over 28 kOhms. I would put say a 1000 pf cap on the load side of the coil also. This will produce a low pass filter with a high cut off much above the audio, but well below 450 kHz. 73, ron, n9ee/r Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome. On Wed, Jun 4, 2008 at 7:32 PM, Nate Duehr wrote: Willis M. Hagler wrote: I'm not terribly familiar with the nuts & bolts (so to speak) of the components so was unsure if the various styles of inductors all did the same thing and I was concerned once I looked and found what appears to be a pretty radical variance in size of available inductors all rated at 10 mH. Understand.. . the question still remains though -- are you connected to Volume/Squelch Hi coming off the MASTR II? There should be very little 455 KHz component there... I think... but there are other places to tap discriminator audio from... and we don't know from the other end of the keyboard here what your exact setup is... unless I missed that somehow too. (GRIN) Nate WY0X
Re: [Repeater-Builder] Re: 455khz filter for Mastr II discriminator audio
Willis M. Hagler wrote: > I'm not terribly familiar with the nuts & bolts (so to speak) of the > components so was unsure if the various styles of inductors all did > the same thing and I was concerned once I looked and found what > appears to be a pretty radical variance in size of available inductors > all rated at 10 mH. Understand... the question still remains though -- are you connected to Volume/Squelch Hi coming off the MASTR II? There should be very little 455 KHz component there... I think... but there are other places to tap discriminator audio from... and we don't know from the other end of the keyboard here what your exact setup is... unless I missed that somehow too. (GRIN) Nate WY0X
Re: [Repeater-Builder] Re: 455khz filter for Mastr II discriminator audio
--- On Wed, 6/4/08, Willis M. Hagler <[EMAIL PROTECTED]> wrote: > From: Willis M. Hagler <[EMAIL PROTECTED]> > Subject: [Repeater-Builder] Re: 455khz filter for Mastr II discriminator audio > To: Repeater-Builder@yahoogroups.com > Date: Wednesday, June 4, 2008, 5:54 PM > Whoa, where did we get off on voters? > > I asked the question originally based on a conversation I > had with > Pacific Research. I'm using their RI-300e controller > which has been a > solid controller for me on several other repeaters, but > I've never > tried to interface to a Mastr II. With the particular > combination of > a Mastr II and the RI-300e "smart squelch" setup > I find the squelch > action is not working well at all. > > I spoke with Greg (Gregg?) on the phone and he said they > have had > trouble with 455khz coming out of the receiver and throwing > off the > "smart squelch". Their manual also mentions > this: > > http://www.pacres.com/support/manuals/ri-300%20user%20manual%20v3_11.pdf > > On printed page 12 (pdf page 20) it says > > If your discriminator does not > have adequate filtering for 455 kHz, you will have to > provide for this > filtering between the radio and controller. A 10mH > inductor in line with a 1000pF capacitor to ground should > work. You > may need to adjust these values according to the output > impedance of your discriminator. > > So I was proceeding down the path of a 10 mH inductor, and > the > feedback I really wanted from this group is what to do > about this > inductor as I see I can buy either a through-the-hole board > mounted > one that appears to look somewhat like a capacitor, or I > can get a > bunch of windings on a torroid core and make a choke. > I'm pretty new > at this so was asking more for advice along these lines. > > However, it's also very useful to know that the GE > Mastr II UHF > receiver shouldn't be outputting 455khz at all so > I'm still not sure > what the problem is. > > Thanks all, > Mark Hagler > > W7WMH Seattle > > As the Mastr ll does not have an output of 455 but around 9 to 11 MHz that should be a non issue. There is an inductor and capacitor to ground that should eliminate any rf comming out of the volume/squelch high pin that I assume that you are using.
Re: [Repeater-Builder] Re: 455khz filter for Mastr II discriminator audio
Willis M. Hagler wrote: > Whoa, where did we get off on voters? > > I asked the question originally based on a conversation I had with > Pacific Research. I'm using their RI-300e controller which has been a > solid controller for me on several other repeaters, but I've never > tried to interface to a Mastr II. With the particular combination of > a Mastr II and the RI-300e "smart squelch" setup I find the squelch > action is not working well at all. Ahh, sorry - my mistake. As far as the physical mounting properties of the inductor, that all depends on whether you're going to try to place the inductor/capacitor combo somewhere in the controller, somewhere in the MASTR II, or in its own "box" or similar. Nate WY0X
RE: [Repeater-Builder] Re: 455khz filter for Mastr II discriminator audio
> Since both you & Jeff asked the same question, I thought I'd > speculate. My question was rhetorical and tounge-in-cheek...I wasn't looking for an answer as I already knew it. > Noise squelches generally start with a HPF of some sort followed by a > detector & post-detector filter. The cutoff freq. of the HPF > should be > around 7 kHz, so it should have a fair amount of gain in the > 7 to 13 kHz > range, with nothing explicitly limiting the high frequency > response. I > think most RXs have a LPF shortly after the discriminator to > keep the 455 > kHz from propagating through the RX audio circuitry, but if > one were to > bypass this LPF for directly feeding a noise squelch & the > noise squelch > depended on upstream low pass filtering, it might behave as > you observed. Most radios have some kind of low-pass filter right after the discriminator like you said, and the squelch circuit usually starts out with a high-pass filter like you said, so the net result is the audio has been bandpass filtered before the detector. Although I have no dog in this fight, it seems to me that an aftermarket product should do similar bandpass filtering if that's what's necessary for it to work properly if it's designed/spec'ed to accept raw discriminator audio. The squelch circuit on a Micor audio/squelch board works properly when installed in a Micor repeater. If an aftermarket squelch circuit doesn't work right when connected to a Micor discriminator, it's not Motorola's fault... --- Jeff WN3A
Re: [Repeater-Builder] Re: 455khz filter for Mastr II discriminator audio
At 6/3/2008 14:25, you wrote: >Willis M. Hagler wrote: > > > Well, I don't have many answers for you. I am new in this field and > > trying to learn and am sharing what I have heard from others who claim > > to have had this problem with a Mastr II. The gentleman at Pacific > > Research who manufactures the controller has write up on this in their > > manual but since I'm not the expert here I'm unable to tell if it's > > not applicable to the Mastr II without asking the question. > >Sitting here scratching my head... PR usually does good engineering >work, but I'd have to agree with someone else's recent comment. > >If their squelch circuit even looks at 455 KHz at all, I don't think I'd >use their squelch... you've probably done the right thing using a real >squelch line from the rig to "fix" the problem you were experiencing. > >Why would a squelch care about noise that's so high in the spectrum it's >RF Since both you & Jeff asked the same question, I thought I'd speculate. Noise squelches generally start with a HPF of some sort followed by a detector & post-detector filter. The cutoff freq. of the HPF should be around 7 kHz, so it should have a fair amount of gain in the 7 to 13 kHz range, with nothing explicitly limiting the high frequency response. I think most RXs have a LPF shortly after the discriminator to keep the 455 kHz from propagating through the RX audio circuitry, but if one were to bypass this LPF for directly feeding a noise squelch & the noise squelch depended on upstream low pass filtering, it might behave as you observed. Bob NO6B
Re: [Repeater-Builder] Re: 455khz filter for Mastr II discriminator audio
Paul Plack wrote: > Nate, you're usually on the money with your observations, but I have to > disagree here. I think I recall seeing "circuit descriptions" in service > manuals which mention low-pass filtering to keep ultrasonics out of > audio power amps. If you pick off a signal ahead of the audio PA in a > radio, this could be an issue. Yeah, understood... but this is a voter, and they're usually designed to pick off at the discriminator, which can be just about "anything". It would seem that even if you didn't filter right at the entrance to the voter, you'd want your squelch circuit to ONLY look at certain frequencies and you'd design accordingly. I totally understand what you're saying, I just think with a voter, it's a different thing than a controller. Nate WY0X
Re: [Repeater-Builder] Re: 455khz filter for Mastr II discriminator audio
Nate, you're usually on the money with your observations, but I have to disagree here. I think I recall seeing "circuit descriptions" in service manuals which mention low-pass filtering to keep ultrasonics out of audio power amps. If you pick off a signal ahead of the audio PA in a radio, this could be an issue. It probably wan't such a big deal back when most stuff was built with discrete components, but I was looking into using an LM386 audio amp in an ultrasound project a few years ago, and discovered it would make rated gain at 300 kHz. In short, if the IF frequency is passing from a receiver to a controller, I don't blame either manufacturer. The squelch circuit probably uses a simple high-pass filter. Anything more would be over-engineering for the application, so it's perfectly appropriate to address this through a recommended user mod. 73, Paul, AE4KR - Original Message - From: Nate Duehr To: Repeater-Builder@yahoogroups.com Sent: Tuesday, June 03, 2008 3:25 PM Subject: Re: [Repeater-Builder] Re: 455khz filter for Mastr II discriminator audio Willis M. Hagler wrote: > Well, I don't have many answers for you. I am new in this field and > trying to learn and am sharing what I have heard from others who claim > to have had this problem with a Mastr II. The gentleman at Pacific > Research who manufactures the controller has write up on this in their > manual but since I'm not the expert here I'm unable to tell if it's > not applicable to the Mastr II without asking the question. Sitting here scratching my head... PR usually does good engineering work, but I'd have to agree with someone else's recent comment. If their squelch circuit even looks at 455 KHz at all, I don't think I'd use their squelch... you've probably done the right thing using a real squelch line from the rig to "fix" the problem you were experiencing. Why would a squelch care about noise that's so high in the spectrum it's RF You don't mean 455 *Hz*, do you? Even then... that's also a sucky place to look for receiver noise. Something's wrong there... Nate WY0X
Re: [Repeater-Builder] Re: 455khz filter for Mastr II discriminator audio
Willis M. Hagler wrote: > Well, I don't have many answers for you. I am new in this field and > trying to learn and am sharing what I have heard from others who claim > to have had this problem with a Mastr II. The gentleman at Pacific > Research who manufactures the controller has write up on this in their > manual but since I'm not the expert here I'm unable to tell if it's > not applicable to the Mastr II without asking the question. Sitting here scratching my head... PR usually does good engineering work, but I'd have to agree with someone else's recent comment. If their squelch circuit even looks at 455 KHz at all, I don't think I'd use their squelch... you've probably done the right thing using a real squelch line from the rig to "fix" the problem you were experiencing. Why would a squelch care about noise that's so high in the spectrum it's RF You don't mean 455 *Hz*, do you? Even then... that's also a sucky place to look for receiver noise. Something's wrong there... Nate WY0X
RE: [Repeater-Builder] Re: 455khz filter for Mastr II discriminator audio
> I'll put it on the analyzer again and look but I'm pretty sure there's > a pronounced spike in the discriminator output up around 450khz. > There is, without a doubt, some unexpected high frequency noise on the > discriminator audio there that's throwing off the offboard squelch. Why in the world would any decent squelch circuit be looking at noise spectra out at 450 kHz anyway? Sounds like a design problem to me...
Re: [Repeater-Builder] Re: 455khz filter for Mastr II discriminator audio
Wjhat nobody seems to be pointing out is the simple fact that the Mastr II series does not normally use a 455 KHz IF frequency. It would have to be a special IFAS board with a second converter to get from the normal 11.2 MHz, or 9.4 MHz in low band and 800 MHz units, plus a very few that have a 10.7 MHz IF frequency. I have one of the latter boards, quite a bit different that the normal IFAS boards. So tell me just how you arrived at 455 KHz? A single conversion receiver using 455 KHz would be super prone to severe image problems. Please cite the exact location showing any Mastr II using a 455 KHz IF frequency? BTW, what schematics have you looked at for the Mastr II RX units? Wayne WA2YNE Mastr II repeater on 441.950TX On Sat, 31 May 2008 15:55:28 -0500, Willis M. Hagler <[EMAIL PROTECTED]> wrote: > Hello Ron, > > The audio emphasis for FM is a different issue. When I put the > discriminator output from the Mastr II receiver on a analyzer you can > clearly see a spike way out at 455khz which I believe is the IF > frequency in the receiver. > > This controller has a auto-squelch feature (it does not use a COS/RUS > line at all) and it listens for the presence of high-frequency noise > coming off of the receiver to control the squelch. When a nice, full > quieting FM signal shows up the high frequency noise goes away and the > controller will detect this and kick on the transmitter. > > This detection circuit is behaving poorly on the Mastr II because this > strong 455khz component is throwing it off and making it shut down the > squelch because it thinks there's a lot of high-frequency noise even > when the signal is actually full quieting. > > Running the audio through a 10 mH inductor tied to a 1000pf cap to > ground should cause it to roll off the very high audio frequency and > solve the problem but here's what I run into trouble, there's > thousands of parts out there that say "10 mH inductor" so I'm over my > electronics head now! > > Thanks, > > Mark Hagler > W7WMH Seattle > > > -- Using Opera's revolutionary e-mail client: http://www.opera.com/mail/ Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/Repeater-Builder/join (Yahoo! ID required) <*> To change settings via email: mailto:[EMAIL PROTECTED] mailto:[EMAIL PROTECTED] <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
Re: [Repeater-Builder] Re: 455khz filter for Mastr II discriminator audio
At 5/31/2008 13:55, you wrote: >Hello Ron, > >The audio emphasis for FM is a different issue. When I put the >discriminator output from the Mastr II receiver on a analyzer you can >clearly see a spike way out at 455khz which I believe is the IF >frequency in the receiver. > >This controller has a auto-squelch feature (it does not use a COS/RUS >line at all) and it listens for the presence of high-frequency noise >coming off of the receiver to control the squelch. When a nice, full >quieting FM signal shows up the high frequency noise goes away and the >controller will detect this and kick on the transmitter. > >This detection circuit is behaving poorly on the Mastr II because this >strong 455khz component is throwing it off and making it shut down the >squelch because it thinks there's a lot of high-frequency noise even >when the signal is actually full quieting. Perhaps this was covered earlier in the thread, but are you getting your discriminator output from VOL/SQ HI? I've never seen any significant 455 kHz at this point, yet it still contains all the high frequency unde-emphasized noise your outboard squelch circuit needs. Bob NO6B
Re: [Repeater-Builder] Re: 455khz filter for Mastr II discriminator audio
Mark, Could you describe EXACTLY where on the MASTR II you are pulling audio from and what type of audio (discriminator/pre-emphasized or regular/ de-emphasized) your voter is "expecting"? Like everyone else who's responded so far, I've never seen and "extra" audio from the IF of a MASTR II get through to anything following it in the receiver audio chain. A number of us are probably not responding because the troubleshooting and the problem your vendor decided upon, doesn't make any sense. -- Nate Duehr, WY0X [EMAIL PROTECTED]
