[R-390] (no subject)

Tue Jan 9 14:53:31 EST 2018

Hi

One of my “years back” ideas was to use (gasp!!!) an R-390A RF deck as the preselector 
for an SDR. After a bunch of back and forth with the SDR guys, it seems that this is not 
a real good idea. You can get at least R-390A levels of overload performance without doing 
it and you need fairly complex dither sources if you do use a tight preselector. 

Backing up a bit, even in the era the the 390 was designed, you *could* do better for selectivity
(both IF and front end). The point that is generally made is — what they did is plenty good enough
(in most areas of the design). I’d suggest the same is true when looking at an “improved” radio. 
There really isn’t a whole lot that I can point to on a 390 in terms of the front end being a limit over
the years. Yes, with a 1KW transmitter 3’ from the RX antenna, you have an issue …. in that case
move further away !!!

The same things that drove the rebuilds in the 60’s to improve stability apply at least as much today. 
A SDR of just about any type (even without a GPSDO) would be more stable. The same sort of issues
that drove the multitude of SSB adapters over the years also would apply to any upgrade. Neither one
of these “features” cost much in an SDR.  We could spend a number of years debating the virtues
of various fancy AM detectors. There have been a few times a fancy this or that helped. The other 
99.99% of the time, the stock 390 detector did just fine. There were a number of times it sounded
better than the crazy stuff. 

One of the most basic issues in terms of “good enough” or “how good” is the missing engineering
report. That’s where the data you really need is located. Anybody I’ve ever asked about it has 
returned a blank stare in response. The reaction was very much like the one you get when asking
questions about where a nuclear sub goes on a cruise ….. I don’t know of anybody who has spent
the time to really go crazy on a 390 trying to find what the issues are. They are pretty darn subtle ….
Were they classified? Did people simply not remember the super small stuff? Did it actually not 
matter at all? I have no idea. 

Lots of ways to spend a whole lot of time ….

Bob

> On Jan 9, 2018, at 1:08 PM, Alan Victor <amvictor at ncsu.edu> wrote:
> 
> Putting a technical spin on this thread. 
> 
> It would interesting to see what it would take function and cost wise to duplicate or BEAT an R390A or comparable tube state of the art receiver. In particular, I would look at all the standard specifications as well as those that begin to encompass digital demodulation and see if this could be met with an R390A architecture; namely a continuous tracking pre selector receiver. You could consider up conversion and high performance 16 bit A-D converters and so on until you arrive at a comparable or better receiver. Just asking as I am in a breadboard stage of a variation on such as receiver. 
> 
> Alan W4AMV 
> 
> On Tue, Jan 9, 2018 at 6:39 AM, Bob kb8tq <kb8tq at n1k.org <mailto:kb8tq at n1k.org>> wrote:
> Hi
> 
> Well, I certainly would not debate the cost of the Hydrogen Maser one might
> (or might not …) attach to the system. :) The CPU side of things can be handled
> pretty well with one of a multitude of cheap “Raspberry Pi” like devices. The
> price more or less comes out to:
> 
> Board - $140
> Computer - $75 (board $35, display $40)
> GPSDO - $100
> Enclosure - $35
> 
> No, that’s not the whole thing, but it’s pretty close. It’s based on what you would
> buy today. Wait a few months and the details will change when the next this or that
> hits the market. Do the software with open source packages and there is no big deal about
> this or that outfit stopping support ….(and no cost for that side of it).
> 
> Indeed, R-390’s could be had from Fair a while back for $125 plus shipping.
> You still can find a range of prices even on eBay. What one sells for depends a
> lot on a whole bunch of things. There is no fixed price. I would not suggest to a
> new guy that $350 was his target budget for buying one though.
> 
> I’d say that it comes as no big surprise to anybody on the list that buying the radio
> is just the first part of the cash outflow. I can’t even remember all the bits and pieces I’ve
> accumulated to keep things running over the years. My guess is that the sun will
> cool to room temperature before there is a shortage of some (but not all) parts. …
> hmmm …just how many spare power transformers is a good number? …hmm…..
> 
> There’s only a fixed price on a project once you decide to stop doing it. Same is true
> of fixing up an old car or buying a used boat or just about anything else in life ….
> 
> Again, I’m by no means trying to talk people out of their R-390 project and into
> playing with SDR’s. From what I’ve seen, the “group” in each area is a bit
> different and each are very dedicated to what they play with. That’s great
> and it’s what makes it fun. I most certainly do not have any fond memories
> of playing with an SDR software stack as a kid. I also know a number of kids
> these days that would *much* rather play with tubes than sand. It’s not a one
> size fits all / this is fun for everybody kind of thing.
> 
> On the XYL side, none of this (SDR or R-390) is going to be a “living room” sort of thing.
> It’s a messy / dirty / fun / exciting project. Yelling nasty words at the dead circuit
> is *very* much part of the process. Tearing things down and putting them back
> together is part of either side of it. If you want a living room device, by all means,
> go for the $9,000+ super button machine. I have a few of them as well…. (though
> not the in the $9,000 category).Somehow I seem to play with the other stuff a bit more.
> 
> Bob
> 
> > On Jan 8, 2018, at 11:35 PM, Perry Sandeen <sandeenpa at yahoo.com <mailto:sandeenpa at yahoo.com>> wrote:
> >
> > Yo Again Dudes,
> >
> > My Learned Friens Wrote:
> >
> > Well, the ?gotcha? is that the alternative is no longer a $9,000+ super duper box. There are a lot
> > of sub $300 SDR alternatives out there.
> >
> > Yes the SDR can be sub $300.  The "gotcha" is that you also need a 27" monitor (minimum) $175, a good PC for $450, a better video card $185, Rb or GPS $200. A good backlighted keyboard $125 and a wireless mouse $30.  Less see Ahum...$1465 + tax.
> >
> > You forgot the XYL factor.
> >
> > XYL  What's that?
> >
> > You:  That's my new SDR radio.
> >
> > XYL:  What's that funny screen?
> >
> > You: That's a water fall disply of the radio frequencies I'm looking at.
> >
> > XYL:  Can I watch re-runs of I Love Lucy on it?
> >
> > You: Uh no, not really.
> >
> > XYL:  Well that doesn't seem like a good deal.
> >
> > You: Well it is as it's the latest technology.
> >
> > XYL: OK, Whatever
> >
> > You:
> > Locked to something good (an Rb or a GPSDO) they are way better than any of the ?old stuff?. Selectivity wise ? yup ? Dynamic range ? gulp ? take a look at the numbers. Sensitivity keeps getting better. If you live on planet Earth with normal noise levels and antennas, not much wrong with SDR sensitivity wise. Want to demodulate this or that weird signal? ? not a problem.
> >
> > Me: Yes but that's only if you need it. My point was maybe 90% don't
> >
> > You: Something new comes out next week? Download new software.
> >
> > Me.  If they are still in business and will it rus when MS does a forced update on Win 10?
> >
> > You: Price wise, less money than an R-390 on eBay. Yes, you will do a bit of this and that. You also will
> > poke a bit at than 390 ?
> >
> > Me: I just proved that is incorrect.
> >
> > Now, I'm not trying to sell anybody a SDR board or get them to toss out their R-390. Far from it actually.
> >
> > You: One is very much not the same as the other. Both are projects, they have different ends and stops on the way.
> >
> > Me: My original point.
> >
> > You: I?m just pointing out that there has been a lot of change in how you do a radio, even in the last
> > decade or so. If you are going to decide ?best? by the numbers (which I happen to think misses
> > a lot of stuff), it?s really hard to beat the newer SDR boards ?..
> >
> > Me: It depends.  You can't move a mouse as fast as you can twiddle the knobs.
> >
> > Me: You're forgetting the $9K ricebox and the XYL.
> >
> > Wife: What's that?
> >
> > You: That's my YIK 9000 Limited edition receiver.
> >
> > Wife: It seems to have a lot of buttons.
> >
> > You: Yes.  I think I counted 33, not including the multi-function ones.
> >
> > XYL: What do they all do?
> >
> > You:  They allow one to maximize the best possibility to hear the other guy.
> >
> > XYL:  Gee, and I thought my micro-wave was complicated.  Well good luck with it.
> >
> > Boat anchor scenario:
> >
> > XYL: What's that your doing?
> >
> > You: I'm restoring this antique R390A to it's original condition.
> >
> > XYL:  Wow, there's a lot of gears in there. Is is like a cars manual transmission?
> >
> > You:  That exactly describes what it does to the radio signals.  It was break-through marvel in it's time. Unfortunately there will never be another type of that radio again.  That's why I'm preserving it so our kids and grand-kids can see how far we've come.
> >
> > XYL: Gee, that's neat.  Good luck with your project.
> >
> > You: Thanks, I think it's going to be worth the effort.
> >
> > XYL leaves to watch TV and you get to do your radio stuff with her blessing.
> >
> > Regards,
> >
> > Perrier
> >
> >
> 
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