RG-400 source
 

Dear Group: I expect to craft a common-mode choke for 50 ohm coax that
works from 1.8 to at least 7 MHz using Type 31 (Fair-Rite) core material.
Use of any Fe material in coax at the lower HF frequencies is undesired - no
center conductors containing steel. Such coax should be able to tolerate
being bent with a small radius to facilitate multiple turns through the
core - no foam dielectric.

One such coax appears to be the expensive RG-400. Only need a few feet.

Question: What might be a source for short lengths of RG-400? I have tried
Newark, Mouser, and the like. . . .

Question: What other small diameter coax uses no steel and has a solid
dielectric?

Thanks. 73, Mac N8TT

J. C. Mc Laughlin
Michigan U.S.A.
Home:

RG-400 source
 

"J. C. Mc Laughlin" wrote in message
.. .
Dear Group: I expect to craft a common-mode choke for 50 ohm coax that
works from 1.8 to at least 7 MHz using Type 31 (Fair-Rite) core material.
Use of any Fe material in coax at the lower HF frequencies is undesired -
no center conductors containing steel. Such coax should be able to
tolerate being bent with a small radius to facilitate multiple turns
through the core - no foam dielectric.

One such coax appears to be the expensive RG-400. Only need a few feet.

Question: What might be a source for short lengths of RG-400? I have
tried Newark, Mouser, and the like. . . .

Question: What other small diameter coax uses no steel and has a solid
dielectric?

Thanks. 73, Mac N8TT


Look he
http://www.thewireman.com/coaxp.html

They list rg400 at about $ 2 per foot.

They may also have something you need for the choke.

RG-400 source
 

On Mon, 8 Oct 2012 23:34:11 -0400, "J. C. Mc Laughlin"
wrote:

One such coax appears to be the expensive RG-400. Only need a few feet.
Question: What might be a source for short lengths of RG-400? I have tried
Newark, Mouser, and the like. . . .

http://www.ebay.com/itm/230756316444
http://www.ebay.com/itm/160856544191
http://www.ebay.com/itm/380086386242

Question: What other small diameter coax uses no steel and has a solid
dielectric?

Are you looking for low triboelectric noise or low piezoelectric coax?

RG58A/U also known as "Cheapernet". The problem is that I've seen it
with both solid copper center conductor, and cheaper copper clad steel
center conductor. It also only comes in polyethylene foam dielectric.
If it's solid dielectric that you want, you're stuck with Teflon.

For RG58A/U in Teflon, there's Belden 88240:
http://www.belden.com/techdatas/english/88240.pdf
which also has a solid copper center conductor.

There's a potential problem with using RG400 or any Teflon dielectric
coax in a torroidal balun. It might cold flow. The center conductor
might shove its way through the Teflon dielectric and short to the
shield braid. I've only seen this in smaller diameter RG188 Teflon
coax, but it might happen with RG400. I don't really know if it will
be a problem, but methinks you should be aware of the possibility.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

RG-400 source
 

Dear Jeff: Many thanks! Comments below. . . as: **

"Jeff Liebermann" wrote in message
...

On Mon, 8 Oct 2012 23:34:11 -0400, "J. C. Mc Laughlin"
wrote:

One such coax appears to be the expensive RG-400. Only need a few feet.
Question: What might be a source for short lengths of RG-400? I have tried
Newark, Mouser, and the like. . . .

http://www.ebay.com/itm/230756316444
http://www.ebay.com/itm/160856544191
http://www.ebay.com/itm/380086386242
** I will look at these sources. Ebay, well, it is Ebay. . . Thanks.

Question: What other small diameter coax uses no steel and has a solid
dielectric?

Are you looking for low triboelectric noise or low piezoelectric coax?
** Fortunately, mechanical forces will be tightly suppressed and thus these
factors are not expected to be an issue. What are expected to be the two
most important factors are a need not to have non-linear effects (no Fe and
attention to avoiding braid issues - you are familiar with the extensive
testing of harmonic production in/with some coax) AND a desire to minimize
the probability of center-conductor migration (staying away from foam)
** A story from long ago: I saw center-conductor migration in RG8 type
(solid dielectric) in a piece of coax that was in a horizontal, outdoor
cable trough. This was a long time ago and it is possible that a
manufacturing defect was involved. Today, one would scan the long piece of
coax and discover such a latent defect if it existed.

RG58A/U also known as "Cheapernet". The problem is that I've seen it
with both solid copper center conductor, and cheaper copper clad steel
center conductor. It also only comes in polyethylene foam dielectric.
If it's solid dielectric that you want, you're stuck with Teflon.
** Thanks. I had just about reached the same conclusion.

For RG58A/U in Teflon, there's Belden 88240:
http://www.belden.com/techdatas/english/88240.pdf
which also has a solid copper center conductor.
** I had gone through Belden's info, but must have missed this entry.
Thanks.

There's a potential problem with using RG400 or any Teflon dielectric
coax in a torroidal balun. It might cold flow. The center conductor
might shove its way through the Teflon dielectric and short to the
shield braid. I've only seen this in smaller diameter RG188 Teflon
coax, but it might happen with RG400. I don't really know if it will
be a problem, but methinks you should be aware of the possibility.
** As always with your contributions, this observation is right-on.
Fortunately, volume is not excessively restricted and thus a somewhat larger
radius will be used than the minimum, which should improve the probability.
** Thanks for the help. You are a great source of useful information. 73,
Mac N8TT
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558


J. C. Mc Laughlin
Michigan U.S.A.
Home:

RG-400 source
 

Dear Ralph: Thanks! The Wireman certainly looks like a source for
relatively short pieces of specialized coax. I have quite a bit of Type 31
on hand that I expect to use. Type 31 seems to be very useful for choking
in the lower HF region.

The Wireman must be on my list of suppliers, but too many entries is the
bane of the advent of the Internet grin.

Thanks again. 73, Mac N8TT

"Ralph Mowery" wrote in message
...


"J. C. Mc Laughlin" wrote in message
.. .
Dear Group: I expect to craft a common-mode choke for 50 ohm coax that
works from 1.8 to at least 7 MHz using Type 31 (Fair-Rite) core material.
Use of any Fe material in coax at the lower HF frequencies is undesired -
no center conductors containing steel. Such coax should be able to
tolerate being bent with a small radius to facilitate multiple turns
through the core - no foam dielectric.

One such coax appears to be the expensive RG-400. Only need a few feet.

Question: What might be a source for short lengths of RG-400? I have
tried Newark, Mouser, and the like. . . .

Question: What other small diameter coax uses no steel and has a solid
dielectric?

Thanks. 73, Mac N8TT


Look he
http://www.thewireman.com/coaxp.html

They list rg400 at about $ 2 per foot.

They may also have something you need for the choke.





J. C. Mc Laughlin
Michigan U.S.A.
Home:

RG-400 source
 

On Tue, 9 Oct 2012 10:32:35 -0400, "J. C. Mc Laughlin"
wrote:

** I will look at these sources. Ebay, well, it is Ebay. . . Thanks.

Good, fast, cheap. Pick any two.
eBay is fast and cheap at the expense of good. I buy quite a bit of
stuff on eBay and have had a good success rate. However, about once
or twice a year, I get a lemon. For cheap stuff like coax cable, it's
worth the risk.

What are expected to be the two
most important factors are a need not to have non-linear effects (no Fe and
attention to avoiding braid issues - you are familiar with the extensive
testing of harmonic production in/with some coax) AND a desire to minimize
the probability of center-conductor migration (staying away from foam)

PIM (passive intermod):
http://en.wikipedia.org/wiki/Intermodulation#Passive_Intermodulation_.28PIM.29
Also watch out for cadmium and nickel plated coaxial connectors.
Heliax and silver plated copper are the best so far. I recently spent
a weekend on a mountain top with a borrowed PIM tester.
http://www.kaelus.com/Kaelus/media/Site/QR%20Code%20Files/PIM-Testing-Guidelines_Brochure.pdf
http://boonton.com/products/pim-testers/pim21
We had the time to go through almost every coax cable in the building.
According to the tester, with the antennas connected, everything
needed to be replaced. With the dummy load, most everything looked
much better. I eventually determined that we were actually measuring
rectification from nearby antennas and the tower. Banging on the
antennas with a mallet and tightening tower screws fixed that. Most
of the IM came from stainless fasteners on zinc plated tower hardware
which was later replaced.

For an RF polluted radio site, PIM testing is a really good idea.
However, I just don't see it being very useful for ham radio unless
you're doing something that requires full duplex operation.

** A story from long ago: I saw center-conductor migration in RG8 type
(solid dielectric) in a piece of coax that was in a horizontal, outdoor
cable trough. This was a long time ago and it is possible that a
manufacturing defect was involved. Today, one would scan the long piece of
coax and discover such a latent defect if it existed.

I still use a home made TDR (time domain reflectometer) for testing
cables. Old habits and methods die slowly.

I usually have the opposite problem with coaxial cable. For example,
I would solder connectors onto a 100ft roll of RG8/u while it was
still rolled tight on the spool. Bad idea. When straightened, the
center conductor becomes slightly longer than the shield. The stiff
center conductor tries to push the center pins out from the
connectors. In one case, I found a mangled N connector pair where the
center pin had shoved its way into the mating receptacle.

I've seen what I suspected was center conductor migration on long
horizontal coax runs, but have never done a post mortem on the coax.
By the time it gets to the point where it's shorted, other problems
(i.e. losses) usually inspire a pre-emptive replacement. These days,
I just happen to have a roll of RG6/u with a messenger wire attached,
which eliminates all the stresses.

Good luck, whatever you're building.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

RG-400 source
 

On 10/9/2012 11:10 AM, Jeff Liebermann wrote:

I still use a home made TDR (time domain reflectometer) for testing
cables. Old habits and methods die slowly.

Do you have any construction information available for your TDR?

I usually have the opposite problem with coaxial cable. For example,
I would solder connectors onto a 100ft roll of RG8/u while it was
still rolled tight on the spool. Bad idea. When straightened, the
center conductor becomes slightly longer than the shield. The stiff
center conductor tries to push the center pins out from the
connectors. In one case, I found a mangled N connector pair where the
center pin had shoved its way into the mating receptacle.

Ooooo, thanks for the heads-up. Great comment!

John

RG-400 source
 

I still use a home made TDR (time domain reflectometer) for testing
cables. Old habits and methods die slowly.

Do you have any construction information available for your TDR?

You can do this with a function generator (fast-edge square-wave
pulses are what you want), possibly a resistive pad, a T connector,
and a fast oscilloscope. I used this approach to test out and
identify some poorly-labeled ham radio antenna cables at my city's EOC
a couple of years ago.

Connect a BNC "T" junction to the oscilloscope's vertical input. To
one side of the "T", connect a coax to a function/pulse generator that
has a 50-ohm output (or use a low-Z generator and a 50-ohm series
resistor pad). To the other side of the "T", connect the coax you
want to test. Set the o'scope vertical sensitivity so that it covers
3-4 times the step voltage of the generator, and set the horizontal
sweep rate to cover 2-3x the length of the coax you want to probe
(figure 1 nanosecond per foot as a starting value, and triple it).
Set the function/pulse generator for pulses that are at least twice
the sweep length, and (if it's a pulse generator) a reasonable
repetition rate (1 kHz or so). Set the scope for DC coupling, and set
it to trigger on the rising edge of the pulse.

If the far end of the coax is open, and the coax is in good shape,
what you should see during the sweep is an initial abrupt rise (to the
generator's nominal output voltage), a flat trace for 2x the cable's
end-to-end propagation time, and then an abrupt rise to twice the
generator's nominal outut voltage.

If you terminate the coax in its characteristic impedance, the second
rise won't occur (or you'll see just a tiny discontinuity at that
point, if the termination resistor isn't an exact match). If you
short the far end of the coax, the second rise will be replaced by an
abrupt dive down back to zero.

Any wiggles or bumps in the first part of the trace (between the
initial rise, and the reflection) will be the result of impedance
discontinuities in the cable... damage, bends, connectors, conductor
migration, etc. Measure the time delay between start-of-trace and
wiggle, apply the cable's propagation-speed factor, and you can tell
how far down the cable the discontinuity lies.

If you have a scope with dual sweep speeds and a sweep delay, you can
"zoom in" on interesting sections of the trace and look at them in
more detail.

If you don't want to lug a big pulse generator around with you, you
can build a small one which connects right onto the front of your
o'scope. A 555 driving a fast Schmitt-trigger inverter, a PIC with a
fast discrete output-driver circuit... there are probably about a
zillion circuits which would give a fast 50-ohm pulse that would work.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

RG-400 source
 

On Tue, 09 Oct 2012 12:06:43 -0500, John S
wrote:

On 10/9/2012 11:10 AM, Jeff Liebermann wrote:

I still use a home made TDR (time domain reflectometer) for testing
cables. Old habits and methods die slowly.

Do you have any construction information available for your TDR?

I actually have serveral. All you need is a pulse generator and a
decent oscilloscope. Pulse width and frequency will depend on the
length of coax cable you're trying to test.

These designs work well:
http://www.epanorama.net/circuits/tdr.html
http://www.fccps.cz/download/adv/frr/Reflectoprobe/reflectoprobe.html

This one is similar, but in my never humble opinion, not as good as
the previous one.
http://www.mouthmusic.com/TEMP/aa6dd/Time_Domain_Reflectometer.jpg

Mo
http://www.ecnmag.com/articles/2009/07/low-cost-high-resolution-time-measurement-application
http://www.youtube.com/watch?v=jOUhg07N2-U
http://www.youtube.com/watch?v=Il_eju4D_TM
etc.

Also look on eBay for a Tekronix 1502, 1503c or similar TDR.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

RG-400 source
 

On 10/9/2012 2:16 PM, Jeff Liebermann wrote:

Also look on eBay for a Tekronix 1502, 1503c or similar TDR.


I have a 1502. I want something which will give me info within tenth of
an inch on a PCB.

Thanks.

John