[R-390] R-390 Digest, Vol 106, Issue 23

jay golden jgolden577 at rochester.rr.com
Sat Feb 16 11:40:17 EST 2013 

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From: <r-390-request at mailman.qth.net>
To: <r-390 at mailman.qth.net>
Sent: Saturday, February 16, 2013 11:39 AM
Subject: R-390 Digest, Vol 106, Issue 23


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> Today's Topics:
>
>   1. Filters (quartz55)
>   2. IF Gain R519 (quartz55)
>   3. Re: Filters (Charles P. Steinmetz)
>   4. Re: Filters (Bob Camp)
>   5. Filters (quartz55)
>   6. Re: Filters (KA9EGW)
>   7. Re: Filters (rbethman)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Sat, 16 Feb 2013 09:41:08 -0500
> From: "quartz55" <quartz55 at hughes.net>
> To: <R-390 at mailman.qth.net>
> Subject: [R-390] Filters
> Message-ID: <18CB1FECF0CB454BA66FE40912ED2B07 at DAVE>
> Content-Type: text/plain; charset="Windows-1252"
>
> I could see someone making a DSP setup to replace the filter 'can'.  Not 
> me though.  It would be nice to incorporate the front panel dial with an 
> encoder so it could have variable bandwidth from .1 to 16KHz, just like 
> original only continuous.  I think that would sell if the price could be 
> down around $200.  I'd buy one, especially if I can't get the old filters 
> working.
>
> I'm assuming my coil windings are good since I'm measuring 50 ohms in and 
> out, it's just the resistance to ground that seems wrong, I'm hoping it's 
> just a matter of cleaning them up and re-assembly.  I may start pulling 
> the 4K apart today.
>
> Again, do I have to drill a hole in one of the end caps to keep from 
> blowing the thing apart while heating the end?  I'm going to wrap a wet 
> towel around the label to see if I can save it and take off the input end 
> (bottom) first.
>
> Also, is the ground lug on the end cap just soldered on, or can I use that 
> to pull with and what is this nubbin in the center of the bottom end?
> http://i251.photobucket.com/albums/gg287/DogTi/R390A/filterbottom_zpse5ba0910.jpg
>
> ------------------------------
>
> Message: 2
> Date: Sat, 16 Feb 2013 09:47:41 -0500
> From: "quartz55" <quartz55 at hughes.net>
> To: <R-390 at mailman.qth.net>
> Subject: [R-390] IF Gain R519
> Message-ID: <6BD27088ED7F435F996FA5328F7A771A at DAVE>
> Content-Type: text/plain; charset="Windows-1252"
>
> One of my IFs has a 50K in place of the 10K R519.  I put a 12K across the 
> terminals temp. Anyone know of a source for the locking style pot?  I 
> checked Fair Radio and didn't see any.  I'd like to keep it original 
> looking if possible.  I probably have a standard 10K pot.
>
> ------------------------------
>
> Message: 3
> Date: Sat, 16 Feb 2013 09:51:01 -0500
> From: "Charles P. Steinmetz" <charles_steinmetz at lavabit.com>
> To: r-390 at mailman.qth.net
> Subject: Re: [R-390] Filters
> Message-ID: <20130216145135.33FED11BA3F at karen.lavabit.com>
> Content-Type: text/plain; charset="us-ascii"; format=flowed
>
> John wrote:
>
>>Anyhow, you folks have my curiosity up about the software
>>requirements to do a DSP filter suitable for Collins mechanical
>>filter replacement.  Can some of you gurus point me to where the
>>math algorithms are defined?  Gotta be on the web someplace
>
> For the software, start with Hayward, et al., Experimental Methods in
> RF Design and then move to dedicated DSP texts.
>
> The software isn't the problem -- processing horsepower
> is.  Digitizing and manipulating 455 kHz with sufficient bit depth is
> still close to cutting edge.  Most DSP radios use a final IF in the
> 12-20 kHz range, and even that is taxing to process in real
> time.  This is not a job you can do with microcontrollers.
>
> But my previous question still stands -- once you have developed the
> DSP capacity to do the filtering, why in the world would you convert
> back to analog and put it through the 390A IF?  It would be plain
> silly not to have the DSP also handle AGC, passband shift, notch
> filtering, noise blanking, all-mode detectors, and synchronous AM, at
> the least.
>
> Best regards,
>
> Charles
>
>
>
>
>
>
>
> ------------------------------
>
> Message: 4
> Date: Sat, 16 Feb 2013 10:26:07 -0500
> From: Bob Camp <ham at kb8tq.com>
> To: "r-390 at mailman.qth.net Group" <r-390 at mailman.qth.net>
> Subject: Re: [R-390] Filters
> Message-ID: <10E49DE5-E640-4A91-9B2C-05F3DD419F82 at kb8tq.com>
> Content-Type: text/plain; charset=us-ascii
>
> Hi
>
> When I do them at work, the typical target is an FPGA. There are a variety 
> of approaches. In this case I'd probably do a CIC decimator down to 
> something rational, do the filter(s) as a FIR, and then a CIC interpolator 
> back up to 455 KHz. Run the A/D's and D/A's with a sample frequency around 
> 2 MHz or so. I would go with fairly high order CIC's and a filter or (more 
> likely) cascaded set of filters in the 1 to 2 K taps region. The internal 
> clock on the FPGA would be in the 50 to 200 MHz region so it didn't nuke 
> the radio to bad.  Its probably a pretty solid day or two to work all that 
> stuff out.
>
> You want the digital filter to be "better than" the existing filters in 
> terms of shape factor, and ultimate attenuation. That takes you out of the 
> cheap / dirty approach to some of this. You want at least 120 db (more 
> like 135). The parts you use will need to be pretty good. The filters 
> themselves would not be simple in terms of horsepower. You actually need 
> *less* DSP horsepower in the gizmo to run it into a PC than to put it back 
> out at 455 KHz. If you have a PC, you do all the real filtering there. You 
> also don't have the CIC interpolator and RF D/A. IF DSP done *right* has 
> it's own bucket of worms, they each need to be taken care of. That adds 
> complexity.
>
> Lots of details to work out. How big a front end filter ahead of the A/D 
> (probably a ceramic bandpass)? What sort of setup to use as a dithering 
> source (it's an IF, you don't have enough noise to dither adequately) ? 
> The board layout and enclosure would have to be *very* good to get the 
> isolation. Same is true of the power supply. The clock source would need 
> to be quite good to get the ultimate attenuation you are after. Since you 
> don't have massive decimation going on, the A/D would be at least a 16 bit 
> part (18 and 24 bit parts are out there). I'd bet on an 8 layer board, BGA 
> construction on some of the parts, and three passes to get a final layout. 
> Hopefully you can avoid 0.5 mm pitch BGA's.
>
> Tooling the custom enclosure, doing the board runs would need to be funded 
> somehow. By the time you are done, there's probably $20K in the "tooling" 
> bucket. That assumes somebody will do the pick and place for free on the 
> prototypes. Doing a production run probably involves fronting another $20 
> to 40K.
>
> More or less you have the same stuff as in a QS1R or something like it, 
> plus the front end filter, plus the RF D/A. Weather it is $1,000 or $2,000 
> when you were done depends on how many thousand a year you can sell and 
> how many years you plan to do it. Last time I saw scrap IF decks they were 
> below $200. For that matter one can eBay a whole radio for $500 and part 
> it out.
>
> As pointed out earlier by Charles, for the same money you can just tack a 
> SDR + PC on the radio and have a *lot* more features. Features creep is a 
> very real issue. The SDR + R-390 combo won't quite work right, since you 
> don't have much dithering on the A/D, but it will work.
>
> The whole point of "it won't quite work right" is the real issue. The 
> R-390(A or not) is a pure analog radio. What ever issues it has are analog 
> issues. Digital radios have their own set of issues, quite independent of 
> anything analog. As soon as you drop DSP into the radio, you bring all the 
> digital "stuff" along with it. You then have both the analog limitations 
> plus the digital ones. If you want to deal with digital issues, just spend 
> the same money on a full digital radio. That way you don't have to deal 
> with the analog issues as well.
>
> Bob
>
>
> On Feb 16, 2013, at 9:14 AM, John Saxon <johnbsaxon at yahoo.com> wrote:
>
>> I am not as "savvy" as you folks when it comes to the electronics, but I 
>> am a "savvy" software guy who has done a lot of low-level, embedded stuff 
>> (including micro-coding on array processors for you old-timers out 
>> there).  I have a couple of home projects using microcontrollers and I 
>> enjoy playing with them.
>>
>> Anyhow, you folks have my curiosity up about the software requirements to 
>> do a DSP filter suitable for Collins mechanical filter replacement.  Can 
>> some of you gurus point me to where the math algorithms are defined? 
>> Gotta be on the web someplace :-)
>>
>> FWIW I currently have a 390 and a 390A.
>>
>> Thanks & 73,
>> John
>> K5ENQ
>> Pearland, TX
>>
>>
>> --- On Fri, 2/15/13, mlmccauley at att.net <mlmccauley at att.net> wrote:
>>
>>> From: mlmccauley at att.net <mlmccauley at att.net>
>>> Subject: Re: [R-390] Filters
>>> To: R-390 at mailman.qth.net
>>> Date: Friday, February 15, 2013, 8:23 PM
>>>
>>> Absolutely.
>>>
>>> I've seen those come and go. The concept is great, but the
>>> market is very limited, hence the cost.
>>>
>>> A savvy ham with the proper background could homebrew a very
>>> nice filter for a relatively cheap price. Soldering the
>>> hardware together would be a fairly easy weekend project,
>>> assuming you had a surface mount adapter board for the DSP
>>> chip. The software would take many weeks to write and even
>>> longer to debug.
>>>
>>>
>>>
>>>
>>> On 2/15/2013 8:05 PM, Bob Camp wrote:
>>>> Hi
>>>>
>>>> Thus the variety of outboard dsp filter boxes that have
>>> shown up over the years. Once you get them into production,
>>> the cost is high enough that there is a very limited
>>> audience.
>>>>
>>>> Bob
>>>>
>>>
>>> ______________________________________________________________
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>
>
> ------------------------------
>
> Message: 5
> Date: Sat, 16 Feb 2013 10:57:19 -0500
> From: "quartz55" <quartz55 at hughes.net>
> To: <R-390 at mailman.qth.net>
> Subject: [R-390] Filters
> Message-ID: <6B611F8E862A402FB90A75EE2A5AEF8B at DAVE>
> Content-Type: text/plain; charset="Windows-1252"
>
> That link to collinsfilter is for the old sytle.  Mine has no connection 
> from the top to bottom end caps.  Anyhow, I've got it apart.  Bottom came 
> off not to hard with the small butane torch, but the wires broke off while 
> removing the cap.  It's really hard to work fast and get it hot enough to 
> pull off easily.  The top end was a real problem since I was trying to 
> save the label and I wrapped a wet paper towel around the label.  It just 
> would not come off with the butane torch, I tried a heat gun and it 
> wouldn't even melt the solder, so I broke out the propane torch which was 
> much easier to work with since the butane torch I have to keep my thumb on 
> it and it's really hard to keep down.  Anyhow the top end came out with a 
> swoosh and pulled out the whole filter assembly with it.
>
> Don't know if I just have a mess right now? I'll clean it up and see what 
> I have.
>
> http://i251.photobucket.com/albums/gg287/DogTi/R390A/filterapart_zpseb3e20cf.jpg
>
> ------------------------------
>
> Message: 6
> Date: Sat, 16 Feb 2013 10:24:16 -0600
> From: KA9EGW <ka9egw1 at britewerkz.com>
> To: quartz55 <quartz55 at hughes.net>
> Cc: R-390 at mailman.qth.net
> Subject: Re: [R-390] Filters
> Message-ID: <511FB2B0.7020009 at britewerkz.com>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> If it is actually teflon, good luck trying to get it to melt.  Years ago
> when I was a Novice, WA9TIR told me [speaking in praise of
> Teflon-dielectric coax] "you can get that stuff glowing red and it won't
> melt".  Whehter he was exaggerating I know not.
>
> if it's polyethylene, good luck keeping it from melting.
>
>
> On 2/16/2013 8:00 AM, quartz55 wrote:
>> I've got some 1/2" hardline.  Wonder if I could cut out enough teflon 
>> foam or whatever that dielectric is to use for the filter spacer?  Then 
>> how do you keep it from melting when soldering back together?  Or like 
>> someone said, use JB Weld.
>>
>> I've already sent the IF output (16KHz) to an SRA-3 mixer to mix the 455 
>> down to 12KHz and fed it into my soundcard, used 'Dream' to demodulate 
>> it.  I made up a 467KHz oscillator to drive the mixer. It seems to work, 
>> but is a pain to work with.  I couldn't seem to get the Radio Mondiale to 
>> demodulate, but then was not sure I had the signal.
>>
>> BTW I put the Fluke ohmeter on some of that foam used to put ICs into. 
>> It measures about 2Meg at 1/4" spacing, about 3Meg at 1".  Don't think 
>> that's a good solution.
>> ______________________________________________________________
>> R-390 mailing list
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>> Help: http://mailman.qth.net/mmfaq.htm
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>> Please help support this email list: http://www.qsl.net/donate.html
>>
>
>
>
> ------------------------------
>
> Message: 7
> Date: Sat, 16 Feb 2013 11:39:26 -0500
> From: rbethman <rbethman at comcast.net>
> To: r-390 at mailman.qth.net
> Subject: Re: [R-390] Filters
> Message-ID: <511FB63E.4000002 at comcast.net>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> Why do you think Teflon sheeting is approved for lining the inside of
> aircraft?
>
> It doesn't melt!
>
> "Most" hardline, older, uses ceramic "beads" to allow it to bend within
> the specified bending radius.
>
> HMMW Poly would probably do a very good job, is cheaper that teflon, and
> machines quite well.
>
> The pic I just saw from "this" filter "destruction" is just that. It is
> destroyed.
>
> The wires holding the stack of disks are broken.  Entirely too much
> force used.
>
> My $0.02 - YMMV
>
> Curry Longwave Products NOT available.  Sir Rippel posted this awhile 
> back.
>
> Perhaps putting out a LIST call for filters would have gotten a direct
> message from the small handful of folks that DO have excess R-390s and
> R-390As, AND modules.
>
> Bob - N0DGN
>
> On 2/16/2013 11:24 AM, KA9EGW wrote:
>> If it is actually teflon, good luck trying to get it to melt.  Years
>> ago when I was a Novice, WA9TIR told me [speaking in praise of
>> Teflon-dielectric coax] "you can get that stuff glowing red and it
>> won't melt".  Whehter he was exaggerating I know not.
>>
>> if it's polyethylene, good luck keeping it from melting.
>>
>> On 2/16/2013 8:00 AM, quartz55 wrote:
>>> I've got some 1/2" hardline.  Wonder if I could cut out enough teflon
>>> foam or whatever that dielectric is to use for the filter spacer?
>>> Then how do you keep it from melting when soldering back together?
>>> Or like someone said, use JB Weld.
>>>
>>> I've already sent the IF output (16KHz) to an SRA-3 mixer to mix the
>>> 455 down to 12KHz and fed it into my soundcard, used 'Dream' to
>>> demodulate it.  I made up a 467KHz oscillator to drive the mixer. It
>>> seems to work, but is a pain to work with.  I couldn't seem to get
>>> the Radio Mondiale to demodulate, but then was not sure I had the
>>> signal.
>>>
>>> BTW I put the Fluke ohmeter on some of that foam used to put ICs
>>> into.  It measures about 2Meg at 1/4" spacing, about 3Meg at 1".
>>> Don't think that's a good solution.
>
>
>
> ------------------------------
>
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> End of R-390 Digest, Vol 106, Issue 23
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