capacitors
 

I wish to put capacitors across some standard audio feeds (between some
weird satellite receivers and some weird modulators) in order to block
anything much above AF. Could anyone suggest a value and type that would be
suitable (and the RS number if I might be so cheeky?). Various old caps from
the junk box all seem to work to a greater or lesser extent, but they don't
have values marked on them.

As to why I'm doing this, well it's a long story. I'll tell it all in a few
days. It wouldn't make sense at the moment because I don't have all the
facts myself.

But I'd like to put the caps in place pretty quickly.

Bill

capacitors
 

"Bill Wright" wrote in message
...
I wish to put capacitors across some standard audio feeds (between some
weird satellite receivers and some weird modulators) in order to block
anything much above AF. Could anyone suggest a value and type that would be
suitable (and the RS number if I might be so cheeky?). Various old caps
from the junk box all seem to work to a greater or lesser extent, but they
don't have values marked on them.

As to why I'm doing this, well it's a long story. I'll tell it all in a
few days. It wouldn't make sense at the moment because I don't have all
the facts myself.

But I'd like to put the caps in place pretty quickly.

Bill


You want a low pass filter - look at
http://en.wikipedia.org/wiki/Low-pass_filter

Didn't you do this stuff at college?

Try
http://www.maplin.co.uk/module.aspx?...2&doy=20m2#faq
says it is 40-32HZ, but I am pretty sure it means 40Hz-32kHz.
or
http://uk.rs-online.com/web/search/s...ct&R=545544 9

capacitors
 

"Bill Wright" wrote in message
...
I wish to put capacitors across some standard audio feeds (between some
weird satellite receivers and some weird modulators) in order to block
anything much above AF. Could anyone suggest a value and type that would be
suitable (and the RS number if I might be so cheeky?). Various old caps
from the junk box all seem to work to a greater or lesser extent, but they
don't have values marked on them.

As to why I'm doing this, well it's a long story. I'll tell it all in a
few days. It wouldn't make sense at the moment because I don't have all
the facts myself.

But I'd like to put the caps in place pretty quickly.

Bill

How about ferrite rings.....
http://www.maplin.co.uk/Search.aspx?...source=15&SD=Y

Fred

capacitors
 

In article ,
Bill Wright wrote:
I wish to put capacitors across some standard audio feeds (between some
weird satellite receivers and some weird modulators) in order to block
anything much above AF. Could anyone suggest a value and type that would
be suitable (and the RS number if I might be so cheeky?). Various old
caps from the junk box all seem to work to a greater or lesser extent,
but they don't have values marked on them.

As to why I'm doing this, well it's a long story. I'll tell it all in a
few days. It wouldn't make sense at the moment because I don't have all
the facts myself.

But I'd like to put the caps in place pretty quickly.

I'd use transformers if you're trying to sort a safety/ground loop issue.
This range has something to suit most apps.

http://www.rapidonline.com/productin...moduleno=62120

--
*When companies ship Styrofoam, what do they pack it in? *

Dave Plowman London SW
To e-mail, change noise into sound.

capacitors
 

"Bill Wright" wrote in message
...
I wish to put capacitors across some standard audio feeds (between some
weird satellite receivers and some weird modulators) in order to block
anything much above AF. Could anyone suggest a value and type that
would be suitable (and the RS number if I might be so cheeky?). Various
old caps from the junk box all seem to work to a greater or lesser
extent, but they don't have values marked on them.

As to why I'm doing this, well it's a long story. I'll tell it all in
a few days. It wouldn't make sense at the moment because I don't have
all the facts myself.

But I'd like to put the caps in place pretty quickly.

Bill



If you have RF coupling down the audio leads and need to get rid, try
1nF ceramic to start with, and then go to 10nF or 22nF.

At the impedences of audio (usually about 1K source and anything 10-150K
load, those sort of values will have little effect in the audio but will
kill RF.

As an aerial man however I would have thought you would have seen th
possibility of it being conducted along the braid - even if it is
supposedly earthed - so as someone else suggested try a ferrite ring or
even one of the clamp-over block variety. Bardwells or Maplins are you
best source.


--
Woody

harrogate three at ntlworld dot com

capacitors
 

Bill Wright wrote:
I wish to put capacitors across some standard audio feeds (between some
weird satellite receivers and some weird modulators) in order to block
anything much above AF. Could anyone suggest a value and type that would be
suitable (and the RS number if I might be so cheeky?). Various old caps from
the junk box all seem to work to a greater or lesser extent, but they don't
have values marked on them.

As to why I'm doing this, well it's a long story. I'll tell it all in a few
days. It wouldn't make sense at the moment because I don't have all the
facts myself.

But I'd like to put the caps in place pretty quickly.

Bill


Bill
I suggest you use Y2 and X2 rated polypropylene suppression capacitors
available from RS/CPC/Farnell etc. Start at 1nF and work up from there.
If you have surges, spikes or (heaven forbid) mains floating about they
are rated to withstand such conditions. Ceramic caps, mylar and some
polyester caps can fail short circuit at the slightest hint of a voltage
spike.
Dave


--
Blow my nose to email me

capacitors
 

In article , Woody
writes

If you have RF coupling down the audio leads and need to get rid, try
1nF ceramic to start with, and then go to 10nF or 22nF.

At the impedences of audio (usually about 1K source and anything 10-150K
load, those sort of values will have little effect in the audio but will
kill RF.

Agreed and as the catalogue is handy RS 464-7300 or 464-7366 at 10p each
fits the bill ?, 1nF 100V and COG dielectric is good to RF, keep the
leads short (less than 5mm). Tacked at destination probably most
effective.

As an aerial man however I would have thought you would have seen th
possibility of it being conducted along the braid - even if it is
supposedly earthed - so as someone else suggested try a ferrite ring or
even one of the clamp-over block variety. Bardwells or Maplins are you
best source.

--
fred
Plusnet - I hope you like vanilla

capacitors
 

"Bill Wright" wrote in message
...
I wish to put capacitors across some standard audio feeds (between some
weird satellite receivers and some weird modulators) in order to block
anything much above AF. Could anyone suggest a value and type that would be
suitable (and the RS number if I might be so cheeky?). Various old caps
from the junk box all seem to work to a greater or lesser extent, but they
don't have values marked on them.

As to why I'm doing this, well it's a long story. I'll tell it all in a
few days. It wouldn't make sense at the moment because I don't have all
the facts myself.

But I'd like to put the caps in place pretty quickly.

Bill


In order to design the filter network we need more information, in
any case the filter will ideally be more than a C on its own, but
may be a simple R/C combination will do the trick.We need to
know the frequency range of the RF component and where is it coming
from. Also the impedence of the receiver output and modulator
input. I am guessing that maybe you have some unwanted processer
"hash" from the receivers. This may be because of poor design of
the A/D converters but equally may be caused by a ground-loop
in the interconnect. Try bonding the cases of the receiver and
modulator with a stout piece of wire then ensuring the braid
of the screened lead connecting the two units together is only
connected at the receiver end.
Is the audio level correct of are you swamping the modulator,
requiring the gain control on the modulator to be turned right down?

--
Graham

%Profound_observation%

capacitors
 

"R. Mark Clayton" wrote in message
...

Didn't you do this stuff at college?

It would be surprising since I trained as a schoolteacher with a bias
towards the arts. I have no electronics background whatsover. It's a cause
of much regret, but there it is. We can't all be ****ing clever like you. I
do wish you wouldn't be so patronising.


Try
http://www.maplin.co.uk/module.aspx?...2&doy=20m2#faq
says it is 40-32HZ, but I am pretty sure it means 40Hz-32kHz.
Could be worth a try, but since a single cap across the feed seems to work
perfectly (with no discernable HF audio loss) I think that will be a simpler
solution.

or
http://uk.rs-online.com/web/search/s...ct&R=545544 9

Good grief, I'm not messing about like that.

So, anyone suggest a cap value?

Bill

capacitors
 

"Bob Latham" wrote in message
...
In article ,
Bill Wright wrote:
I wish to put capacitors across some standard audio feeds (between some
weird satellite receivers and some weird modulators) in order to block
anything much above AF. Could anyone suggest a value and type that would
be suitable (and the RS number if I might be so cheeky?). Various old
caps from the junk box all seem to work to a greater or lesser extent,
but they don't have values marked on them.

Blimey, I may be able to help Bill, there's a turn up.

Placing a capacitor across the output of the satellite receiver will
progressively short out the signal with rising frequency which I would
have thought was a bit dodgy for a man of your calibre.
Well, the caps I've tried cure the fault and have no discernable effect on
the HF audio. I think the problem is something well above AF which is
upsetting the modulators. The plan is to find out just what the frequency of
the interfering signal is, but at present all I know by inference is that it
is well above AF.

I've just had a hard look at the caps I tried, thro a magnifier. One marked
47n works perfectly. One marked 4n7 worked, but not quite perfectly. I'm
assuming these mean 47 and 4.7nanoFarad respectively. My present hypothesis
is that there's something RF coming from the receivers (maybe some hash from
the psu?) and the modulators have a fault whereby this bothers them.


I would suggest you need a series resistor first then the cap to earth and
this would be even more predictable if there was a high input impedance
buffer amp between the capacitor and the modulator.

Maybe a 10K or 20K series resistor before the connecting coax would do the
job using the coax as the capacitor. You will have some level loss though.

It all depends how low you want the cut off frequency. If you want little
impact on the audio and a sharp cut off low down, a simple 1st order
filter may not be sufficient.

Thanks for that.

Bill