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remote antenna for DCF77 clock

B

Bernhard Kuemel

Jan 1, 1970
0
Hi sed!

Finally I finished my LASER clock which an analog DCF77 alarm clock
mounted on the ceiling and projecting a LASER beam around the room
at the wall as hour hand. But it turns out the signal is about zero
just below the ceiling :(( - measured with a DCF77 clock which
displays signal power from 0-5. Can I pick up the signal near the
window and route it with a coax cable to the clock? What antenna
should I use? Can I release the signal with an antenna, too, or
should I solder the coax into the clock? The clock has a ferrite
antenna. How about removing the ferrite antenna from the clock and
putting it via the coax cable near the window? Would the ferrite
antenna be a tuned antenna (resonating with a capacitor) and would I
need to retune it? Use some kind of terminating resistor?

Thanks, Bernhard
 
M

martin griffith

Jan 1, 1970
0
Hi sed!

Finally I finished my LASER clock which an analog DCF77 alarm clock
mounted on the ceiling and projecting a LASER beam around the room
at the wall as hour hand. But it turns out the signal is about zero
just below the ceiling :(( - measured with a DCF77 clock which
displays signal power from 0-5. Can I pick up the signal near the
window and route it with a coax cable to the clock? What antenna
should I use? Can I release the signal with an antenna, too, or
should I solder the coax into the clock? The clock has a ferrite
antenna. How about removing the ferrite antenna from the clock and
putting it via the coax cable near the window? Would the ferrite
antenna be a tuned antenna (resonating with a capacitor) and would I
need to retune it? Use some kind of terminating resistor?

Thanks, Bernhard

It depends, probably Yes or No.

Take a dayor two of relaxation.Post the problems on your web site,
with a bit more detail and a URL


martin
 
J

Joerg

Jan 1, 1970
0
Hello Bernhard,

The input circuit with the ferrite is usually a tuned circuit of pretty
high Q. Theoretically you could run a coax and consider the capacitance
of the coax as part of the tuning capacitor. But this will only work if
the coax is short and has less capacitance than what's in there now.

The 'proper way' is to build a tuned circuit with a pre-amplifier, then
run a coax to the clock. May need an additional DC wire to feed the pre-amp.

Simple question: Since you really only need the motor and gears where
you want the clock can't you just mount the rest of the electronics at
the window and feed the motor via a tiny cable?

Regards, Joerg
 
J

Joerg

Jan 1, 1970
0
Hello Bernhard,

Just one more comment. I would make a provision (catch plate or similar)
that nothing happens in case that laser hand falls off. It could shine
on a person or animal. Animals like dogs and cats won't know what it is
and stare at it which would can harm their eyes. Reflection in mirrors
might also be a concern.

Regards, Joerg
 
B

Bernhard Kuemel

Jan 1, 1970
0
Joerg said:
Hello Bernhard,

The input circuit with the ferrite is usually a tuned circuit of pretty
high Q. Theoretically you could run a coax and consider the capacitance
of the coax as part of the tuning capacitor. But this will only work if
the coax is short and has less capacitance than what's in there now.

Is 4 m short?
The 'proper way' is to build a tuned circuit with a pre-amplifier, then
run a coax to the clock. May need an additional DC wire to feed the
pre-amp.

Hmm, sounds like too much effort. Hmm, I once had an antenna preamp.
But I think I gave it away as it hadn't helped. The tuned circuit -
is that just a (ferrite?) antenna with a capacitor? I don't have
high tech tools here. Just a multimeter and I have measured
inductors resonating with a capacitor with my sound card, but not at
RF. Could I just adjust a variable capacitor for tuning until it worked?
Simple question: Since you really only need the motor and gears where
you want the clock can't you just mount the rest of the electronics at
the window and feed the motor via a tiny cable?

Good idea, but probably only with some extensive tinkering. There is
a light barrier going through holes in the gear wheels with the LED
and sensor on the PCB. That's for detecting the wheel positions. Not
sure if there are other problems.
Regards, Joerg

Bernhard
 
J

Joerg

Jan 1, 1970
0
Hello Bernhard,
Is 4 m short?

Yes. It depends on the capacitor that is in the circuit right now. Look
up the capacitance per meter of the coax you have. The higher its
impedance the less capacitance that will be per meter.
Hmm, sounds like too much effort. Hmm, I once had an antenna preamp.
But I think I gave it away as it hadn't helped. The tuned circuit -
is that just a (ferrite?) antenna with a capacitor? I don't have
high tech tools here. Just a multimeter and I have measured
inductors resonating with a capacitor with my sound card, but not at
RF. Could I just adjust a variable capacitor for tuning until it worked?

Yes, just a ferrite antenna. You can use a variable capacitor but they
are kind of large in that range. The sound card won't go that high. You
could connect a headphone via a capacitor to the output of the receiver
and listen to the clicks. Tune the capacitor and find out the points
where they disappear, then set the capacitance midway between these point.

You could also resonate the ferrite rod coil with a much large capacitor
on your sound card, then calculate the capacitance you'd need to get to
77.5kHz minus what the coax already has. That's just a little math. It
won't be precise since the receiver input will also have a capacitance
so you won't likely get around the tuning job. Also, most caps are 10%
tolerance or more.

Whatever you do make sure nothing can oscillate. That would possibly
render other DCF clocks inoperative and get you into trouble.

Regards, Joerg
 
M

Michael A. Terrell

Jan 1, 1970
0
Joerg said:
Hello Bernhard,

The input circuit with the ferrite is usually a tuned circuit of pretty
high Q. Theoretically you could run a coax and consider the capacitance
of the coax as part of the tuning capacitor. But this will only work if
the coax is short and has less capacitance than what's in there now.

The 'proper way' is to build a tuned circuit with a pre-amplifier, then
run a coax to the clock. May need an additional DC wire to feed the pre-amp.


A pair of simple LC power inserters will carry the power to the
preamp capacitively couple the RF at both ends, and use large chokes
with their SRF well below the RF signal to couple the DC at each end. I
also would put a three terminal regulator at the pre-amp to regulate the
voltage locally. I built a WWVB antenna about 10 years ago that has 8 v
P-P output to the receiver. It also has two tuned RF stages so very
little external noise gets to the receiver. I decided to us a 75 ohm
impedance so I could use waterproof "F" fittings and some of the RG6 I
had laying around.
Simple question: Since you really only need the motor and gears where
you want the clock can't you just mount the rest of the electronics at
the window and feed the motor via a tiny cable?

Regards, Joerg


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
W

Wolfgang Mahringer

Jan 1, 1970
0
Hi Bernhard,

Bernhard said:
Finally I finished my LASER clock which an analog DCF77 alarm clock
mounted on the ceiling and projecting a LASER beam around the room
at the wall as hour hand.

Cool! Pictures?
But it turns out the signal is about zero
just below the ceiling :(( - measured with a DCF77 clock which
displays signal power from 0-5.

Your problem is another one. One that has bitten me too :)
Your circuit emits disturbances (wire and/or fields) which
prevents a good DCF77 Signal reception.
I got around this using a little DCF77 Receiver Module (purchased
at Conrad). You only need a simple 3 wire cable to connect +3,3V,
Ground and the digital signal and put the module in a little
housing one meter away from the laser device.

HTH
Wolfgang
 
B

Bernhard Kuemel

Jan 1, 1970
0
Hallo Wolfgang aus Salzburg!

Wolfgang said:
Cool! Pictures?

Not yet ...
Your problem is another one. One that has bitten me too :)
Your circuit emits disturbances (wire and/or fields) which
prevents a good DCF77 Signal reception.
I got around this using a little DCF77 Receiver Module (purchased
at Conrad). You only need a simple 3 wire cable to connect +3,3V,
Ground and the digital signal and put the module in a little
housing one meter away from the laser device.

You were right :). It seems the magnetic field emissions from the
230->7.5 V transformer are the source of interference. The clock
worked at first when I had the trafo in the wall socket. The laser
did not make it fail then. But now the trafo is mounted with the
clock. I'll mount it a meter away and then we'll see. With
everything turned off the signal is at 5, actually.

I would never have thought that a 50 Hz trafo could interfere with a
77,5 kHz receiver, but I guess it induces voltage in the antenna
which distorts the DCF77 AM signal.

The signal is also 0 near the trafo when I turn off the laser.

Bernhard
 
M

Michael A. Terrell

Jan 1, 1970
0
Bernhard said:
You were right :). It seems the magnetic field emissions from the
230->7.5 V transformer are the source of interference. The clock
worked at first when I had the trafo in the wall socket. The laser
did not make it fail then. But now the trafo is mounted with the
clock. I'll mount it a meter away and then we'll see. With
everything turned off the signal is at 5, actually.

I would never have thought that a 50 Hz trafo could interfere with a
77,5 kHz receiver, but I guess it induces voltage in the antenna
which distorts the DCF77 AM signal.

The signal is also 0 near the trafo when I turn off the laser.

Bernhard


Are there any capacitors across the diodes in the power supply? If
not, it will generate a lot of RF garbage.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
J

Joerg

Jan 1, 1970
0
Hello Michael,
A pair of simple LC power inserters will carry the power to the
preamp capacitively couple the RF at both ends, and use large chokes
with their SRF well below the RF signal to couple the DC at each end. ...


That is the really elegant way but at this low frequency you need rather
large chokes that must not saturate at the DC current the pre-amp draws.
In Bernhard's case a few feet of extra wire might be easier. Unless it's
visible, then I'd go for your version with DC over coax. In the US we
can run cables through the hollow ceilings or through attic. In Europe
that is much more of a challenge since the usual ceiling is concrete.

Regards, Joerg
 
J

Joerg

Jan 1, 1970
0
Hello Bernhard,

Heed Michael's advice about the diodes. They create lots of harmonics
otherwise. A few thousand pF are usually enough. Also, transformers
broadcast any noise that rides on the line. Noise from those energy
saver bulbs, TVs, laptop power supplies. A filter in the line going to
that transformer might also help.

Regards, Joerg
 
M

Michael A. Terrell

Jan 1, 1970
0
Joerg said:
Hello Michael,

That is the really elegant way but at this low frequency you need rather
large chokes that must not saturate at the DC current the pre-amp draws.
In Bernhard's case a few feet of extra wire might be easier. Unless it's
visible, then I'd go for your version with DC over coax. In the US we
can run cables through the hollow ceilings or through attic. In Europe
that is much more of a challenge since the usual ceiling is concrete.

Regards, Joerg


I built my antenna before NIST upped the transmitter power and built
the new antennas at WWVB so it was designed to be mounted on a side arm
on a 40 foot TV tower. It is a three foot square, 3/4" copper pipe
Faraday shielded antenna that I wound the wire inside the pipe after all
the joints were soldered. I used a polystyrene cap and a small trimmer
to tune it. It still has the prototype preamp in it, I never did get
around to laying out and ordering a PC board for it. I had a bag full
of chokes made for low frequency tone detectors for old tube type pager
radios and they were perfect for the job. The pre-amp uses less than 50
mA, so there was no problem with saturation.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
J

Joerg

Jan 1, 1970
0
Hello Michael,
I built my antenna before NIST upped the transmitter power and built
the new antennas at WWVB so it was designed to be mounted on a side arm
on a 40 foot TV tower. It is a three foot square, 3/4" copper pipe
Faraday shielded antenna that I wound the wire inside the pipe after all
the joints were soldered. I used a polystyrene cap and a small trimmer
to tune it. It still has the prototype preamp in it, I never did get
around to laying out and ordering a PC board for it. I had a bag full
of chokes made for low frequency tone detectors for old tube type pager
radios and they were perfect for the job. The pre-amp uses less than 50
mA, so there was no problem with saturation.

Wow, you must yield a heck of a SNR out of that after they beefed up the
transmitter. I can barely receive it here in the office (California).
The clock only works on one wall and only in one particular spot. That
is because there is aluminum foil backed insulation in the walls. It has
to face a window and I have to make sure the screen isn't pushed over
that window at night or it won't receive.

How did you get the wires through the pipe joints? How many turns could
you squeeze in?

The only antenna like that I ever made was round. When I bent the copper
pipe I pushed sand into it first so it would not flatten out too much.
Then I found out the sand was too moist and didn't want to come out so I
had to let it sit to dry for a week or so. That was before shop vacs
became ubiquitous.

Regards, Joerg
 
J

Jim Thompson

Jan 1, 1970
0
Hello Michael,


Wow, you must yield a heck of a SNR out of that after they beefed up the
transmitter. I can barely receive it here in the office (California).
The clock only works on one wall and only in one particular spot. That
is because there is aluminum foil backed insulation in the walls. It has
to face a window and I have to make sure the screen isn't pushed over
that window at night or it won't receive.

How did you get the wires through the pipe joints? How many turns could
you squeeze in?

The only antenna like that I ever made was round. When I bent the copper
pipe I pushed sand into it first so it would not flatten out too much.
Then I found out the sand was too moist and didn't want to come out so I
had to let it sit to dry for a week or so. That was before shop vacs
became ubiquitous.

Regards, Joerg

I've made two types of copper-pipe-shielded loop antennas...

(1) Bend pipe into a circle joining ends with a fiber joint and
junction box (to prevent shorted turn). Saw slot around perimeter.
Wind wire through slot. Squeeze slot closed with pliers (and solder
if you like :)

(2) Bend as above. Use multi-pair telephone wire. Thread through
once, then solder ends together in sequence.

BTW, WWVB reception in Arizona is pretty bad, probably due to lack of
any rational water table ;-)

...Jim Thompson
 
B

Bernhard Kuemel

Jan 1, 1970
0
Hi!

Here are the pics:
http://bksys.at/bernhard/img/laseruhr/-gallery.html
Are there any capacitors across the diodes in the power supply? If
not, it will generate a lot of RF garbage.

There are caps across the rectifier diodes. There are none across
the voltage regulating diodes. And as you can see from the pics
there is a energy saver lamp nearby.

Now that I moved the trafo away from the clock it receives the time
signal. The signal level at the ceiling is not that bad after all, I
even get 5s on the 0-5 scale. I also adjusted the antenna.
Previously I directed the ferrite rod perpendicular to the radio
waves as if it was the antenna. But then I realized that the coil is
a loop antenna which has to be perpendicular to the waves and the
ferrite rod must point at the sender.

The clock also seemed to lock up and would not step at all which it
does when it detects the signals at each second. I got it back to
work by reflecting the waves with a metal platter at the clock.
Maybe I caused the lock up when I shorted the clocks power
connectors too short or with chatter.

Bernhard
 
J

Joerg

Jan 1, 1970
0
Hello Jim,
I've made two types of copper-pipe-shielded loop antennas...

(1) Bend pipe into a circle joining ends with a fiber joint and
junction box (to prevent shorted turn). Saw slot around perimeter.
Wind wire through slot. Squeeze slot closed with pliers (and solder
if you like :)

Cool. But I didn't have problems getting wire pulled through the
circular pipe, using some electrician's lube. Or maybe it was soap,
don't remember.

(2) Bend as above. Use multi-pair telephone wire. Thread through
once, then solder ends together in sequence.

That stuff is usually pre-twisted and you won't get as many turns. May
be ok if you don't have to cram in too much.

BTW, WWVB reception in Arizona is pretty bad, probably due to lack of
any rational water table ;-)

Yes, I remember you mentioning that. The SNR in Northern California is
nothing to write home about either. The dry lands of Nevada and huge
mountains around the Tahoe basin might be the reason for us.

What surprises me is that they don't make 'atomic clocks' that run on
one of the shortwave WWV frequencies. Most come in strong, anywhere in
the world where I tried. Also during the day here in California which is
nice because I sometimes need that for calibration. The missus
appreciates that I don't have to do that after dinner.

Me thinks the code used on shortwave WWV isn't too conducive to
auto-setting but I am not sure.

Regards, Joerg
 
J

Joerg

Jan 1, 1970
0
Hello Bernhard,
There are caps across the rectifier diodes. There are none across
the voltage regulating diodes. And as you can see from the pics
there is a energy saver lamp nearby.

Zeners should be fine. They can generate some noise but it shouldn't
spread much.

Now that I moved the trafo away from the clock it receives the time
signal. The signal level at the ceiling is not that bad after all, I
even get 5s on the 0-5 scale. I also adjusted the antenna.


Turn the energy saver bulb on and off when the signal isn't too strong.
A high field strength doesn't always indicated that the received stuff
is clean. I can drive the field strength indicator on some receivers
around here to 3 and 4 just by turning on the angle grinder.

Previously I directed the ferrite rod perpendicular to the radio
waves as if it was the antenna. But then I realized that the coil is
a loop antenna which has to be perpendicular to the waves and the
ferrite rod must point at the sender.

Oops.

When you bought your Christmas tree did you go out an look for one that
fits exactly? It looks like its tip is a couple of centimeters under the
ceiling.

Regards, Joerg
 
M

Michael A. Terrell

Jan 1, 1970
0
Joerg said:
Hello Michael,


Wow, you must yield a heck of a SNR out of that after they beefed up the
transmitter. I can barely receive it here in the office (California).
The clock only works on one wall and only in one particular spot. That
is because there is aluminum foil backed insulation in the walls. It has
to face a window and I have to make sure the screen isn't pushed over
that window at night or it won't receive.

How did you get the wires through the pipe joints? How many turns could
you squeeze in?


I used 22 AWG stranded hookup wire. I laid the wire on the ground
outside to let it relax in the hot Florida sun, then I put 100 8-32 hex
nuts on the end of the wire and squirted some old silicone "Solenoid
Lube" ('50s military surplus in lead tubes) into the pipe. I dropped the
wire with the nuts into the pipe and gently shook the pipe so the nuts
would go through the 90° corners. When the wire had made it through the
loop back to the starting point I tied the far end of the wire securely
to the outside of the copper pipe and pulled all of the wire through,
till it was tight. Then, like it says on the shampoo bottle, you repeat
the process till you run out of wire. I don't remember the number of
turns, but I am trying to get it dug out of storage and put it back up.
I am going to rebuild it, this time with a sweatable copper insulated
union made for a hot water heater and run the wires through the bottom
of the diecast electrical box. the fittings will thread together, and
provide more strength than the PVC coupling I used in the original
design.

The only antenna like that I ever made was round. When I bent the copper
pipe I pushed sand into it first so it would not flatten out too much.
Then I found out the sand was too moist and didn't want to come out so I
had to let it sit to dry for a week or so. That was before shop vacs
became ubiquitous.


I would have poured water through it to wash the sand out of the
pipe. :)

BTW, I used a shop vac to pull wire through a large conduit in 1970
when I ran electricity to my dad's garage in an underground conduit. It
was 1 1/2" so I tied a wad of paper towels to a thin rope and stuffed
them into one end, then taped the hose to the other end and turned it
on. You could hear the motor struggling at first, then it started to
move. Finally it popped into the canister of the shop vac a minute or so
later. I did this because the only fish tape available was a 50 foot,
and the run was about 80 feet and ran under the driveway and I didn't
want a pull box under the drive.

Another time I was installing the sound system in a new church. They
had waited till a week before their first service for us to install the
equipment. We quickly discovered that the general contractor had used
blown insulation, and had managed to fill a 200 foot run of one inch
conduit with blown insulation. (I think that they did it on purpose.) I
spied some of the tapered rubber plugs from the pre charged Freon lines
and that they were mostly hollow. I cut a hole in the tip and put it
over the nozzle of our large portable air compressor. I started pumping
compressed air into the pipe. It whined and changed pitch for almost
five minutes, then it started snowing the fine particles of insulation
in the church, and missing the tarps we had put under the pull boxes.
We swept up a couple 5 gallon buckets, then let the church vacuum up the
rest while we finished the job.

Its fun to find quick solutions to problems on the job.
Regards, Joerg


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
B

Bernhard Kuemel

Jan 1, 1970
0
Joerg said:
Hello Bernhard,


Zeners should be fine.

Hehe, it's not zeners. I use the 1.6 V forward drop of a red LED for
the clock and a pair of other (forward) diodes for the 3V laser (30
mA). I first wanted to use zeners but instead of walking to the shop
I scrounged some parts from old PCBs.

The clock draws 3 mA when it quickly turns the hands to find their
position and about 0 mA :) in normal mode between the 1 s ticks.
Turn the energy saver bulb on and off when the signal isn't too strong.
A high field strength doesn't always indicated that the received stuff
is clean. I can drive the field strength indicator on some receivers
around here to 3 and 4 just by turning on the angle grinder.

When I move my signal meter clock near the bulb the signal level
drops to 0.
When you bought your Christmas tree did you go out an look for one that
fits exactly? It looks like its tip is a couple of centimeters under the
ceiling.

As we had large trees when I was a kid I still like them big. But it
would be too hard to find exact matches. I sometimes buy one that's
a bit too high and cut out a piece from below the tip and put the
tip back on so it matches by a cm or so. Always amazes people :)).
This one my father brought and it sits on a stool which happened to
match it nicely. We typically buy a 3+ m tree (our rooms are 3.6 m)
on the 24th (that's the celebration day in Austria) as they are
cheaper then.

Bernhard
 
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