EMRFD Message Archive 7343

Message Date From Subject
7343 2012-03-18 04:05:28 Ashhar Farhan feed through capacitor sources
can anyone help me with a source for feed-through capacitors? i need
them to be used for HF and VHF, low power work.

- farhan
7344 2012-03-18 05:53:15 Tim Re: feed through capacitor sources
In decades past these were a staple at hamfests but I haven't seen them in a long long time... a couple times I've asked previous sellers and the guy told me he was out.

I've had excellent luck buying feedthroughs
7345 2012-03-18 06:20:34 john lawson Re: feed through capacitor sources
You can try www.msg4u.com.....Max-Gain Systems....they sell to Hams in small quantities and I have purchased from them some 5000 pf feed thru caps that are pulls from military equipment. They also sell hard to find glass piston caps that can be used in the 110 MHz IF filter that is in Wes's SA..........In both instances I have found them to be high quality parts. If you click on the link below, then scroll down you will find both of those parts as well as others.

http://www.mgs4u.com/RF-Microwave/doorknob-capacitors.htm%c2%a0


Hope this can be of help to you. John K5IRK


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7346 2012-03-18 07:05:46 Fernando Krouwel Re: feed through capacitor sources
I also purchased FT caps from him (Gintaras, LY2KW, the man with the
bycicle and the giant log-periodic antenna in the QSL photo) and the
material is first quality (I think maybe russian military surplus).
Here in Brazil I had some difficult about getting nuts with the
threading in that standard, but I could get some.

73' s
Fernando - PY2FZU

7347 2012-03-18 08:36:57 Tim Re: feed through capacitor sources
I think you're talking about something similar to the red insulator body threaded feedthroughs he sells. I found the nut too but usually I am soldering these to boxes made out of PCB so I don't even need the nut.

Yeah, that HF log periodic he carries around on his bike is impressive :-) (BIG SMILEY for those who haven't seen his QSL card! I literally had to look at it for a couple minutes to figure out if I could believe what I was seeing!)

Tim N3QE

7348 2012-03-18 08:51:57 Thomas S. Knutsen Re: feed through capacitor sources
I have also good experience with those, and the threads are regular M5
(metric).

2012/3/18 Fernando Krouwel <flky661@terra.com.br>

> **
>
>
> I also purchased FT caps from him (Gintaras, LY2KW, the man with the
> bycicle and the giant log-periodic antenna in the QSL photo) and the
> material is first quality (I think maybe russian military surplus).
> Here in Brazil I had some difficult about getting nuts with the
> threading in that standard, but I could get some.
>
> 73' s
> Fernando - PY2FZU
>
>
>
7349 2012-03-18 08:53:19 Ashhar Farhan Re: feed through capacitor sources
Thanks all,
Is there a way to improvise a feedthrough cap? I have tried using four
smd caps arranged in a cross shape, soldered on the inner surface with
the supply line passing through the center.
It has worked, but the leakage was audible in the lab receiver. Not as
effective as the only feedthrough I have from a junked tv tuner.
- farhan

On 3/18/12, Fernando Krouwel <flky661@terra.com.br> wrote:
> I also purchased FT caps from him (Gintaras, LY2KW, the man with the
> bycicle and the giant log-periodic antenna in the QSL photo) and the
> material is first quality (I think maybe russian military surplus).
> Here in Brazil I had some difficult about getting nuts with the
> threading in that standard, but I could get some.
>
> 73' s
> Fernando - PY2FZU
>
>
7350 2012-03-18 09:04:49 Thomas S. Knutsen Re: feed through capacitor sources
If space is not an issue, have you considered making small PCB boxes with
inductors and capacitors formed like an lowpass filter, inside the box.
I have good experience using that in an receiver IF that had some BC feed
through via the DC supply cable.

73 de Thomas LA3PNA.

2012/3/18 Ashhar Farhan <farhanbox@gmail.com>

> **
>
>
> Thanks all,
> Is there a way to improvise a feedthrough cap? I have tried using four
> smd caps arranged in a cross shape, soldered on the inner surface with
> the supply line passing through the center.
> It has worked, but the leakage was audible in the lab receiver. Not as
> effective as the only feedthrough I have from a junked tv tuner.
> - farhan
>
>
> On 3/18/12, Fernando Krouwel <flky661@terra.com.br> wrote:
> > I also purchased FT caps from him (Gintaras, LY2KW, the man with the
> > bycicle and the giant log-periodic antenna in the QSL photo) and the
> > material is first quality (I think maybe russian military surplus).
> > Here in Brazil I had some difficult about getting nuts with the
> > threading in that standard, but I could get some.
> >
> > 73' s
> > Fernando - PY2FZU
> >
> >
7351 2012-03-18 09:42:57 Roelof Bakker Re: feed through capacitor sources
Hello Farhan,

I have used screened cable, with the shield spread out and soldered around
the hole.
On the inside of the box, I used a 10 nF ceramic capacitor, a RFC of
around 30 uH, wound on a small ferrite bead and again a 10 nF capacitor as
a pi-filter.

73,
Roelof, pa0rdt
7352 2012-03-18 09:45:55 Phil Sittner Re: feed through capacitor sources
Farhan-

Check out "Dans small parts" website. He generally has them along with a variety of other RF parts and at good prices.

Phil
kd6rm
----- Original Message -----
7353 2012-03-18 09:47:07 William Carver Re: feed through capacitor sources
>
> Is there a way to improvise a feedthrough cap? I have tried using four
> smd caps arranged in a cross shape, soldered on the inner surface with
> the supply line passing through the center.
> It has worked, but the leakage was audible in the lab receiver. Not as
> effective as the only feedthrough I have from a junked tv tuner.
> - farhan

I make a "pi" filter with a ferrite bead as a series impedance.

I use two PCB with pad and wire hole and mounting holes on each. That
could be etched if you're so inclined, or just drilled using a Vector
"pad cutter" tool.

I make an identical 1/16" thick aluminum plate with the same mounting
holes and a hole the outside diameter of a ferrite bead where the wire
hole is on the PCB.

Drill holes in chassis for mounting hole and OD of the bead, and
assemble a sandwich with the PCB copper facing outward, on on inside,
other on the outside, with capacitors on each side of the bead.

Lot of work? In fact what I do put multiple "feedthroughs" as one
assembly: I stagger two rows of beads spaced 0.1" apart (for tighter
packing of beads), enough to handle all the anticipated wires (plus a
couple of spares) so it becomes a "feedthrough assembly".

One can use a -61 bead and 470 pF feedthough caps and RF-filter SPI
logic signals (put a series resistor in series with the driving logic so
it doesn't go bonkers with the capacitive load), or -43 beads and
0.1/0.01 uF capacitors, or even multiple capacitors, on supply lines.

If that's not enough filtering, one can put another bead on the wires
leaving the feedthrough assembly. Both inside and outside if necessary.
For HF/VHF signals that should provide a lot of filtering.

When you have just ONE wire its a lot of work. I've cannibalized old hp
gear and have a handful of big .001 uF feedthrough capacitors. That's
not enough capacitance to shunt RF to ground at HF, so I put a 1/4"
solder lug under the feedthrough bushing on the inside and augment
the .001 uF with a larger value capacitor to augment it. And ALWAYS a
ferrite bead at least on the inside wire to form an L network if I'm
trying to keep a signal from getting out. Occasionally a bead on the
outside, too.

W7AAZ
7354 2012-03-18 09:47:48 Ashhar Farhan Re: feed through capacitor sources
yes, i just saw the site again and discovered it way down. a friend is
returning to india from usa in a few weeks. i will get them posted to him.
the site is a wonder :)

i will try the box approach and see where it takes me. i wish i had the
proper instrumentation to check this out.

- farhan

7355 2012-03-18 10:02:57 William Carver Re: feed through capacitor sources
I can also vouch for the quality of parts and honesty of Max-Gain
Systems. .005 uF would be better than .001 uF for HF filtering, but
still believe a series impedance is very important: a ferrite bead
slipped over wire inside if cosmetics demand nothing show on the
outside, but better with one bead slipped over the wire going in,
another on the outside wire to form a T network.

http://www.mgs4u.com/RF-Microwave/doorknob-capacitors.htm

W7AAZ
7356 2012-03-18 14:24:22 Cliff McCreery Re: feed through capacitor sources
Tim wrote:
>. . .
>Yeah, that HF log periodic he carries around on his bike is
>impressive :-) (BIG SMILEY for those who haven't seen his QSL card!
>I literally had to look at it for a couple minutes to figure out if
>I could believe what I was seeing!)
>
>Tim N3QE
. . .
In a note from Gintaras LY2KW:
"the picture was taken in Qatar by the Al Jazeera Broadcast log
periodic yagi, I thought it could look funny as if it is attached to
a bicycle. The security came after I shoot it, but they let me go."
7357 2012-03-19 01:55:51 Robert Bennett Re: feed through capacitor sources
I am sure I originally saw this particularly neat idea on this site, but I
cannot find the reference.

Solder through the enclosure wall a short length of hobby brass tubing of
appropriate length and diameter to accommodate down the inside a small low
value resistor, or rf choke, with a ferrite bead slipped over each end, the
assembly being held in place by a 0.1 capacitor soldered to the tubing at
each end.

73 Robert
7358 2012-03-19 12:19:22 Gary, WB9JPS Re: feed through capacitor sources
My favorite feedthru supplier: <http://www.emifiltercompany.com/>

Click on Bargains, then click on a link at the top of the page like 4-40 filters. Most part are $1. Sometimes they have a limited supply, since they are over-stock parts and such. Also have accessories like mounting hardware. Small orders OK. I haven't tried getting quotes are regular catalog parts, not sure how expensive those are.

TIP: When you enter a quantity to buy sometimes the ordering system says they don't have stock. What they mean is they don't have that many. Try again with a smaller quantity and eventually you get it to work!

73,
Gary, WB9JPS
7359 2012-03-19 12:53:11 Donald Re: feed through capacitor sources
I also bought some feed through capacitors from Gintaras LY2KW. He seems like a fine gentleman.

Nebraska Surplus also sells feed through capacitors.

http://www.surplussales.com/Feedthrus/FTholeMntindex.html

Fellas, what exactly do you look for when you buy feed throughs for 1 - 30MHz? What value(s) of C?

I don't work with much VHF/UHF.

Don
7360 2012-03-19 13:09:38 William Carver Re: feed through capacitor sources
I grab onto .005 uF to 0.1 uF when I see them at swapmeets, supplemented
with ferrite beads to create series impedance. They work well to feed
power or audio into an HF enclosure. If you are feeding digital signals,
say to operate a DDS or PLL chip, then I use .001 uF feedthroughs and
lower-u -61 ferrite beads so the digital signals aren't damaged too
much.

You'd have to have a very specialized application, or have a lot of
loose money, to justify the prices of feedthroughs from Surplus Sales of
Nebraska!



On Mon, 2012-03-19 at 19:53 +0000, Donald wrote:
>
>
> I also bought some feed through capacitors from Gintaras LY2KW. He
> seems like a fine gentleman.
>
> Nebraska Surplus also sells feed through capacitors.
>
> http://www.surplussales.com/Feedthrus/FTholeMntindex.html
>
> Fellas, what exactly do you look for when you buy feed throughs for 1
> - 30MHz? What value(s) of C?
>
> I don't work with much VHF/UHF.
>
> Don
>
>
>
>
>
7361 2012-03-19 13:17:42 William Carver Re: feed through capacitor sources
Wow, Gary. That is a GREAT link. They have overruns that look great. But
check what you're ordering, some of them have ZERO capacitance, that's
just a mechanical solution to getting one wire through a bulkhead!

On Mon, 2012-03-19 at 19:19 +0000, Gary, WB9JPS wrote:
>
> My favorite feedthru supplier: <http://www.emifiltercompany.com/>
>
> Click on Bargains, then click on a link at the top of the page like
> 4-40 filters. Most part are $1. Sometimes they have a limited supply,
> since they are over-stock parts and such. Also have accessories like
> mounting hardware. Small orders OK. I haven't tried getting quotes are
> regular catalog parts, not sure how expensive those are.
>
> TIP: When you enter a quantity to buy sometimes the ordering system
> says they don't have stock. What they mean is they don't have that
> many. Try again with a smaller quantity and eventually you get it to
> work!
>
> 73,
> Gary, WB9JPS
>
>
>
>
>
7362 2012-03-19 21:13:58 john lawson Re: feed through capacitor sources
Hi Robert, I believe you are referring to Rick Campbell's post 5623 dated 12/31/2010 on the feed thru cap technique you are describing. It also includes some additional information about feed thru caps that is very helpful....John K5IRK


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