Browse Groups

• Re: [midatlanticretro] Re: Altair / Fool on the Hill question

(21)
• NextPrevious
• ... Experiment...see what happens beforehand and act accordingly ... my guess it ll have no measurable effect past a few feet. For example I found that it did
Message 1 of 21 , Mar 29
View Source
Evan Koblentz <evan@...> wrote:

>>> Plan B, build some shielding around your exhibit?
>
>I emailed Erik Klein (because he's done the demo) and he also suggested
>shielding around the exhibit.
>
>A quick Google search pointed me to simple directions for making a
>Faraday cage, but doesn't that have to be 360 degrees? Obviously my
>shield needs at least one open side. Can a cage work with one open
>side? Or is there a simpler way to make a shield?
>
>
>
>
>------------------------------------
>
>
>
>
Experiment...see what happens beforehand and act accordingly ... my guess it'll have no measurable effect past a few feet.

For example I found that it did not effect guitar amps thatwill were sometimes known to pick up police radio.

Set up the system get it working and position the am radio 2,5,10,20 feet.
--
Sent from my PDP 8/e.
• ... You are right to guess it needs to be 360 . These low frequency AM signals are like sound, they curve around objects to fill everything, vs high
Message 2 of 21 , Mar 29
View Source
--- In midatlanticretro@yahoogroups.com, "Evan Koblentz" <evan@...> wrote:
>
> >> Plan B, build some shielding around your exhibit?
>
> I emailed Erik Klein (because he's done the demo) and he also suggested shielding around the exhibit.
>
> A quick Google search pointed me to simple directions for making a Faraday cage, but doesn't that have to be 360 degrees? Obviously my shield needs at least one open side. Can a cage work with one open side? Or is there a simpler way to make a shield?
>

You are right to guess it needs to be "360". These low frequency AM signals are like sound, they curve around objects to fill everything, vs high frequency which works only "line of sight".

I would try using aluminum (window) screen.

Another option might be to use a small radio that can be placed right inside the Altair. Start the demo by lifting the lid of the Altair to show off the cool boards inside, place your radio inside, close the lid. Finish the demo by pulling out the radio (for those new comers that didn't see the radio going in).

If you like to do your own experiments, you can buy an AM transmitter from Ramseykits for \$35.

Or tune your AM radio to a local station and shielding it out.

:)J
• ... Ian and I found that the RF firehose coming from the Altair easily drowns out strong local AM stations. It also mostly overpowers FM stations as well, if
Message 3 of 21 , Mar 29
View Source
> Or tune your AM radio to a local station and shielding it out.

Ian and I found that the RF firehose coming from the Altair easily drowns out strong local AM stations. It also mostly overpowers FM stations as well, if the radio is really close to the Altair. We also found that angle of the antenna to the Altair matters, so presumably the source(s) of RF from the Altair have some degree of polarization.

Thanks,
Jonathan
• ... It wouldn t be a cage if you could get out! : ) Jack
Message 4 of 21 , Mar 29
View Source
>
> --- In midatlanticretro@yahoogroups.com, "Evan Koblentz" <evan@> wrote:
> >
> > >> Plan B, build some shielding around your exhibit?
> >
> > I emailed Erik Klein (because he's done the demo) and he also suggested shielding around the exhibit.
> >
> > A quick Google search pointed me to simple directions for making a Faraday cage, but doesn't that have to be 360 degrees? Obviously my shield needs at least one open side. Can a cage work with one open side? Or is there a simpler way to make a shield?
> >
>
> You are right to guess it needs to be "360". These low frequency AM signals are like sound, they curve around objects to fill everything, vs high frequency which works only "line of sight".
>

It wouldn't be a cage if you could get out! :>)
Jack
• ... Also, remember distance is your friend. unless there are directional antennas involved, signal strength is inversely proportional to the square of the
Message 5 of 21 , Mar 29
View Source
On 03/29/2013 08:34 AM, joshbensadon wrote:
> You are right to guess it needs to be "360". These low frequency AM
> signals are like sound, they curve around objects to fill everything, vs
> high frequency which works only "line of sight".
>
> I would try using aluminum (window) screen.
>
> Another option might be to use a small radio that can be placed right
> inside the Altair. Start the demo by lifting the lid of the Altair to
> show off the cool boards inside, place your radio inside, close the lid.
> Finish the demo by pulling out the radio (for those new comers that didn't
> see the radio going in).
>
> If you like to do your own experiments, you can buy an AM transmitter from
> Ramseykits for \$35.
>
> Or tune your AM radio to a local station and shielding it out.

Also, remember distance is your friend. unless there are directional
antennas involved, signal strength is inversely proportional to the square of
the distance.

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA
• ... Yes, I had that in mind too when I suggested putting the radio right inside the Altair box! Part of the demo is to show how it was done wirelessly, but
Message 6 of 21 , Mar 29
View Source
--- In midatlanticretro@yahoogroups.com, Dave McGuire <Mcguire@...> wrote:

> > Another option might be to use a small radio that can be placed right
> > inside the Altair. Start the demo by lifting the lid of the

> Also, remember distance is your friend. unless there are directional
> antennas involved, signal strength is inversely proportional to the square of
> the distance.
>
> -Dave

Yes, I had that in mind too when I suggested putting the radio right inside the Altair box! Part of the demo is to show how it was done wirelessly, but given the circumstances, it might need to go inside the box. Also, he will need to watch that an open Altair box doesn't interfere with his neighbor's demo.

But, things might just work outside of the box, if the radio is placed at the right position/angle.

I wish I had more experience with the Altair Radio Music. But I know the AM Radio antenna is based on a ferret stick, which should be directional. But, I think the interference really happens at the IF stage, which is further down the receiver circuitry. If that is true, you could remove the ferret stick antenna.

I'm sure the demo will sound good enough to get the point across. I just like the idea of opening the Altair Lid to show off the internals.

:)J
• ... Ferrite ... Ferrite loopstick antennas are very broadly directional. They have nulls off the ends but they re not terribly deep. ... Actually I d be
Message 7 of 21 , Mar 29
View Source
On 03/29/2013 11:46 AM, joshbensadon wrote:
>>> right inside the Altair. Start the demo by lifting the lid of
>>> the
>
>
>> Also, remember distance is your friend. unless there are
>> directional antennas involved, signal strength is inversely
>> proportional to the square of the distance.
>
> Yes, I had that in mind too when I suggested putting the radio right
> inside the Altair box! Part of the demo is to show how it was done
> wirelessly, but given the circumstances, it might need to go inside
> the box. Also, he will need to watch that an open Altair box doesn't
> interfere with his neighbor's demo.
>
> But, things might just work outside of the box, if the radio is
> placed at the right position/angle.
>
> I wish I had more experience with the Altair Radio Music. But I know
> the AM Radio antenna is based on a ferret stick,

Ferrite

> which should be directional.

Ferrite "loopstick" antennas are very broadly directional. They have
nulls off the ends but they're not terribly deep.

> But, I think the interference really happens at the IF
> stage, which is further down the receiver circuitry. If that is
> true, you could remove the ferret stick antenna.

Actually I'd be kinda surprised if the interference in question
happened at IF. Those IFs are typically 455KHz; you're much more likely
to get interference from higher frequencies than that in ~1~8MHz
microprocessor circuitry.

I've done it with a PDP-8; that interference comes from the
high-current pulses in the core memory subsystem if memory serves. The
interference there isn't at IF.

> I'm sure the demo will sound good enough to get the point across. I
> just like the idea of opening the Altair Lid to show off the
> internals.

I think it'll be great!

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA
• ... Well, it could be a Ferret, but I guess the little critter would likely run away. ... You d think they should be omni directional, but this is getting OT.
Message 8 of 21 , Mar 29
View Source
--- In midatlanticretro@yahoogroups.com, Dave McGuire <Mcguire@...> wrote:
> > the AM Radio antenna is based on a ferret stick,
>
> Ferrite
>

Well, it could be a Ferret, but I guess the little critter would likely run away.

> Ferrite "loopstick" antennas are very broadly directional.

You'd think they should be omni directional, but this is getting OT.

> Actually I'd be kinda surprised if the interference in question
> happened at IF. Those IFs are typically 455KHz; you're much more likely
> to get interference from higher frequencies than that in ~1~8MHz
> microprocessor circuitry.

Here, I will yield to your experience. I have never played with RFI Computer Music. Does the interference depend on where you tune your radio? If you are far away from your computer, does tuning your radio help bring in the signal? I'm sure there's lots to read about the subject, but playing is more fun.

:)J
• ... Hehehehe. I don t know, it might be patient. Ferrets like music, but I m not so sure they like RFI. Still, I can t imagine that wire wound around a ferret
Message 9 of 21 , Mar 29
View Source

> > > the AM Radio antenna is based on a ferret stick,
> >
> >   Ferrite
> >
>
> Well, it could be a Ferret, but I guess the little critter
> would likely run away.

Hehehehe. I don't know, it might be patient. Ferrets like music, but I'm not so sure they like RFI. Still, I can't imagine that wire wound around a ferret would make a very good antenna.

> Here, I will yield to your experience.  I have never
> played with RFI Computer Music.  Does the interference
> depend on where you tune your radio?  If you are far
> in the signal?  I'm sure there's lots to read about the
> subject, but playing is more fun.

It seems to work the best, further down on the dial, but "tuning" isn't really the word for it. The computer kind of splatters the whole band, so, really, you're trying to tune OUT all the other "interference", (like those pesky radio stations) so you can find a clear spot where the computer is stronger.

Honestly, it works pretty well, all things considered. As long as the radio is *close* to the computer, and the cover is off, it works incredibly well. You don't have to go stuffing the radio inside the machine, or doing anything fancy. Yes, you can figure out exactly at which frequencies on the radio the signal should be strongest, and mess with directionality of antennas, or ferrets, but you don't have to. Just put the radio next to the computer and fiddle with the knobs until you hear the music. The Altair is an RF sieve. When I tried it, I could even hear the computer music on the FM band in spots (it was faint, and in the background, but there).

John even videotaped it when we got the program working on my machine:

So, yeah. RF music on S100 boxes works quite well. It really isn't that hard to do. At TCF, Corey entered the program into his system, and we put a random old AA5 radio I'd bought at the flea market area for a few bucks next to it, and it worked there too. We just set the radio next to the computer, with it's cover off, and had lovely RF noise/music playing loud and clear.

-Ian
• ... really the word for it. The computer kind of splatters the whole band, so, really, you re trying to tune OUT all the other interference , (like those
Message 10 of 21 , Mar 29
View Source
>
> It seems to work the best, further down on the dial, but "tuning" isn't
really the word for it. The computer kind of splatters the whole band, so,
really, you're trying to tune OUT all the other "interference", (like those
pesky radio stations) so you can find a clear spot where the computer is
stronger.

Wonder what a beat frequency oscillator would do for this kind of RF
noise.
• ... Nicely done! ... Ahh, someone else who knows what an AA5 is! You rock. -Dave -- Dave McGuire, AK4HZ New Kensington, PA
Message 11 of 21 , Mar 29
View Source
On 03/29/2013 03:27 PM, Mr Ian Primus wrote:
> John even videotaped it when we got the program working on my machine:

Nicely done!

> So, yeah. RF music on S100 boxes works quite well. It really isn't that
> hard to do. At TCF, Corey entered the program into his system, and we put
> a random old AA5 radio I'd bought at the flea market area for a few bucks
> next to it, and it worked there too. We just set the radio next to the
> computer, with it's cover off, and had lovely RF noise/music playing loud
> and clear.

Ahh, someone else who knows what an AA5 is! You rock.

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA
• ... There s an idea. I don t think the ferret would like it much though. I don t have ferrets, but I have cats, perhaps I can try it with one of them? Stay
Message 12 of 21 , Mar 29
View Source
--- In midatlanticretro@yahoogroups.com, Mr Ian Primus <ian_primus@...> wrote:
> > > > the AM Radio antenna is based on a ferret stick,
> > >   Ferrite
> > Well, it could be a Ferret, less the little critter run away
>
> Hehehehe. I don't know, it might be patient. Ferrets like music, but I'm not so sure they like RFI. Still, I can't imagine that wire wound around a ferret would make a very good antenna.

There's an idea. I don't think the ferret would like it much though.
I don't have ferrets, but I have cats, perhaps I can try it with one of them? Stay tuned! (My cats are looking at me, not amused).

> John even videotaped it when we got the program working on my machine:

Very cool! Thanks for the video.

> So, yeah. RF music on S100 boxes works quite well. It really isn't that hard to do. At TCF, Corey entered the program into his system, and we put a random old AA5 radio I'd bought at the flea market area for a few bucks next to it, and it worked there too. We just set the radio next to the computer, with it's cover off, and had lovely RF noise/music playing loud and clear.

Here's an idea. Get 2 Altairs to play dueling banjos (or Altairs).

:)J
• ... MARCH does have two of them...
Message 13 of 21 , Mar 29
View Source
>> Here's an idea. Get 2 Altairs to play dueling banjos (or Altairs).

MARCH does have two of them...
• ... I want to see a video of them playing dueling banjo s!
Message 14 of 21 , Mar 29
View Source
--- In midatlanticretro@yahoogroups.com, "Evan Koblentz" <evan@...> wrote:
>
> >> Here's an idea. Get 2 Altairs to play dueling banjos (or Altairs).
>
> MARCH does have two of them...
>

I want to see a video of them playing dueling banjo's!
• ... Not really; the EMI is very broadband. There are usually parts of the tuning range where it s stronger and/or more clear. And playing is DEFINITELY more
Message 15 of 21 , Mar 29
View Source
On 03/29/2013 03:16 PM, joshbensadon wrote:
> Here, I will yield to your experience. I have never played with RFI
> Computer Music. Does the interference depend on where you tune your
> help bring in the signal? I'm sure there's lots to read about the
> subject, but playing is more fun.

Not really; the EMI is very broadband. There are usually parts of the
tuning range where it's stronger and/or more clear.

And playing is DEFINITELY more fun. :-)

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA
Your message has been successfully submitted and would be delivered to recipients shortly.
• Changes have not been saved
Press OK to abandon changes or Cancel to continue editing
• Your browser is not supported
Kindly note that Groups does not support 7.0 or earlier versions of Internet Explorer. We recommend upgrading to the latest Internet Explorer, Google Chrome, or Firefox. If you are using IE 9 or later, make sure you turn off Compatibility View.