EMRFD Message Archive 8607

Message Date From Subject
8607 2013-05-01 21:43:18 Bob L Question about Capacitors in Phase Circuits
In the phasing DC receiver circuits in EMRFD there is heavy use of "poly" capacitors. There is no discussion as to why these have been chosen.

Is it because they are available in tight tolerance 1% and 5% units?

Are there other factors that make "polys" a choice for phasing circuits?

Some discussions suggest I and Q phase components can have some variance compared to the circuit diagram. But the corresponding components between the I and Q phases should be closely matched. If this is so it is not necessary to buy expensive 1% tolerance components. Rather, pairs of components can be selected by measurement.

Vendors treat "poly" as a subset of "film" capacitors. Vendors separate these out as combinations of polyester, polyproprolene, polystyrene, paper and other plastics. Are there reasons to select one of these types from others?
8615 2013-05-02 07:11:18 Stacy Williams Re: Question about Capacitors in Phase Circuits
Hello Bob

Looking at all the poly-n names of the capacitors, it strike me that
actually polystyrene would be the most stable. This stability is accounted
for by the extremely stable benzene ring structure which, was inherited
from the Styrene monomer. Then, it would be polypropylene, polyester,
other plastics and finally paper. As the paper is made from cellular, a
sugar, but, I believe the paper capacitors are soaked in oil or a wax.

Regards & 73
Stacy
m0wsa

Spooky action at a distance.......
On May 2, 2013 5:43 AM, "Bob L" <bobledoux@proaxis.com> wrote:
>
>

>
> In the phasing DC receiver circuits in EMRFD there is heavy use of "poly"
capacitors. There is no discussion as to why these have been chosen.
>
> Is it because they are available in tight tolerance 1% and 5% units?
>
> Are there other factors that make "polys" a choice for phasing circuits?
>
> Some discussions suggest I and Q phase components can have some variance
compared to the circuit diagram. But the corresponding components between
the I and Q phases should be closely matched. If this is so it is not
necessary to buy expensive 1% tolerance components. Rather, pairs of
components can be selected by measurement.
>
> Vendors treat "poly" as a subset of "film" capacitors. Vendors separate
these out as combinations of polyester, polyproprolene, polystyrene, paper
and other plastics. Are there reasons to select one of these types from
others?
>
>


[Non-text portions of this message have been removed]
8617 2013-05-02 08:09:10 Andy Re: Question about Capacitors in Phase Circuits
> As the paper is made from cellular, a
> sugar, but, I believe the paper capacitors are soaked in oil or a wax.

Yeah ... I was kind of surprised to see old paper capacitors
classified as "poly".
But what do I know.

Andy
8618 2013-05-02 08:15:25 ha5rxz Re: Question about Capacitors in Phase Circuits
The accuracy of the capacitor value is important but so it its structure. Ceramic capacitors for example are very bad when used in some stages because they are microphonic.

Peter HA5RXZ

8619 2013-05-02 19:09:54 Dana Myers Re: Question about Capacitors in Phase Circuits
8620 2013-05-02 19:10:01 Bob L Re: Question about Capacitors in Phase Circuits
I received a personal email that provided this link. He suggested polypropolene were the best choice.

http://en.wikipedia.org/wiki/Film_capacitor#Characteristics_of_film_materials_for_film_capacitors
8622 2013-05-02 22:30:17 John Kolb Re: Question about Capacitors in Phase Circuits
65 years ago, digging in the trash behind a local radio (TV? what's that?)
repair shop, I found these neat cardboard tubes with a blob of wax and
wires coming out each end. Pulling out my trusty pocketknife (every
6 yer old boy had one back then), the cardboard tubes could be opened
and 2 long strips of metal foil and 2 strips of an oily feeling translucent
paper could be unrolled.

John
KK6IL

At 06:43 AM 5/2/2013, you wrote:
Hello Bob

Looking at all the poly-n names of the capacitors, it strike me that
actually polystyrene would be the most stable. This stability is accounted
for by the extremely stable benzene ring structure which, was inherited
from the Styrene monomer. Then, it would be polypropylene, polyester,
other plastics and finally paper. As the paper is made from cellular, a
sugar, but, I believe the paper capacitors are soaked in oil or a wax.

Regards & 73
Stacy
m0wsa