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'[EE] Which coax'
2007\02\04@024744 by Paul Anderson

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I'm looking to make some patch cables for hooking together test
equipment.  I have some RG-58U, but I understand that isn't the choice
cable.  What is generally preferred?  For the most part, I'll probably
be dealing with 50 ohm impedance stuff.

--
Paul Anderson
VE3HOP
spam_OUTwackyvorlonTakeThisOuTspamgmail.com
http://www.oldschoolhacker.com
"May the electromotive force be with you."

2007\02\04@085238 by Mike Hawkshaw

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Paul,

It depends on the application...

I tend to use RG58 size coax for short connections which don't have to be
phase stable and loss isn't overly important. For applications which are
more demanding I use RG214 with N type connectors. This is the 10mm outside
diameter stuff and is double screened. It's about as good as you can get
with a braided screen.

If you need a 6mm o/s diameter cable which has a braided screen make sure
that it has a multi stranded inner (solid core inners snap fairly quickly in
test gear applications and are only any good for fixed installations) and
double screening to reduce radiation from or into the cable.

For the ultimate in screening and whilst retaining some flexability there is
the Andrews FSJ1-50A which has a solid corucated outer (but also a solid
inner). I'm not sure but an N type connector might be the smallest they do
for this cable.

Mike.

> {Original Message removed}

2007\02\04@151620 by David VanHorn

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>
> For the ultimate in screening and whilst retaining some flexability there
> is
> the Andrews FSJ1-50A which has a solid corucated outer (but also a solid
> inner). I'm not sure but an N type connector might be the smallest they do
> for this cable.


I was just about to suggest this.. :)

It's NOT very flexible, but you can't beat the shielding.

I use FSJ1-50 on several VHF and UHF repeaters for internal cabling.
Standard PL-259 connectors will fit, if you use the RG-59 reducer.
Prep the cable by peeling the covering so that the reducer covers the bare
area, and pre-tin the shield, then slip the shield into the reducer and add
some solder as needed, then screw into the body, solder the reducer to the
body, and solder the center pin, and call it a day.

Use silver-teflon connectors though, they handle the heat.

When I first saw this, I thought it was a kludge, but it turns out the
andrew PL-259 connector is practically the same thing.   I've also been able
to use N connectors designed to crimp on to LMR-400 this way, by adding a
piece of brass tubing as a filler.

Andrew does make N, PL-259, and BNC connectors for FSJ1-50, but they are
pricey.

RG-400 is nice for braided shield, and 9913F7 works well in the
half-inch-ish size, surprisingly flexible, though I don't trust that the
foil will hold up forever with constant bending.

RG-58 is ok for audio, but even the premium brands are pretty lossy at
higher frequencies.
That may or may not be an issue.

2007\02\04@161019 by Dave Lag

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David VanHorn wrote:

>
> When I first saw this, I thought it was a kludge, but it turns out the
> andrew PL-259 connector is practically the same thing.   I've also been able
> to use N connectors designed to crimp on to LMR-400 this way, by adding a
> piece of brass tubing as a filler.

Anybody know a stocking distributor for LMRXXX?
I've been quoted 2 weeks for Plenum LMR400 (LLPL)
big bucks too...

D

2007\02\04@174252 by David VanHorn

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> \
> Anybody know a stocking distributor for LMRXXX?
> I've been quoted 2 weeks for Plenum LMR400 (LLPL)
> big bucks too...


http://www.wlanparts.com/category/cables/

I've used these guys before for adaptors and dishes.

http://rfconnectors.rfdigital.com/

I use these guys for connectors.

2007\02\06@042155 by Mike Hawkshaw

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In my view.....

Stay well clear of the LMR400. We have experimentally tried it on some of
our UHF TV relay antennas as distribution tails. The cable is //very// not
flexable (though they say it is) and the connectors are not at all
waterproof - we had a system last for less than 1 year. We mostly use RG214
with N types and they last for years. We have also used the 1/2 inch
superflex from Andrews and that is also really good.

Mike.

> {Original Message removed}

2007\02\06@092403 by David VanHorn

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On 2/6/07, Mike Hawkshaw <.....mikeKILLspamspam@spam@spikey-mike.com> wrote:
>
> In my view.....
>
> Stay well clear of the LMR400. We have experimentally tried it on some of
> our UHF TV relay antennas as distribution tails. The cable is //very// not
> flexable (though they say it is) and the connectors are not at all
> waterproof - we had a system last for less than 1 year. We mostly use
> RG214
> with N types and they last for years. We have also used the 1/2 inch
> superflex from Andrews and that is also really good.


What... It's flexible.. It bends if you push it hard enough !  :)

The difference between that, and 9913F7 is amazing.

I wouldn't count on any connector being waterproof, I always flood with
silicone gel and tape anything that's going to be exposed.    At this point,
I have three runs of LMR-400 up the tower, transitioning to 9913F7 for the
rotor loop, and I have two runs of LDF4-50 ready to go up when the weather
gets better.

2007\02\06@131531 by Nate Duehr

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On 2/6/07, Mike Hawkshaw <mikespamKILLspamspikey-mike.com> wrote:
> In my view.....
>
> Stay well clear of the LMR400. We have experimentally tried it on some of
> our UHF TV relay antennas as distribution tails. The cable is //very// not
> flexable (though they say it is) and the connectors are not at all
> waterproof - we had a system last for less than 1 year. We mostly use RG214
> with N types and they last for years. We have also used the 1/2 inch
> superflex from Andrews and that is also really good.

Those connectors never claimed to be waterproof anywhere I've ever seen.

You need to learn how to apply Scotch 33 (or in some cases 88)
liberally and the right way.  :-)  SkotchKote can also be useful, if
you're really never going to tear back into it for a long long time.

(A friend has a pump in his water well that has a splice in the power
cable that was SkotchKote'd many years ago.  Pump is still running, no
breakers popping, and water still flowing, so ... I guess it worked to
keep the water out!)

Both LMR 400 and RG 214 are 50 ohm cables.  Why are you using 50 ohm
cables on UHF TV stuff?  Isn't your gear 75 ohm?  Maybe I missed what
you're doing with it... Just curious.

Good quality connectors on LMR 400 is a good cable, but NEVER
waterproof.  Who told you it was?  Never buy cheap connectors for LMR
(or anything else for that matter).

Nate

2007\02\06@134607 by David VanHorn

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>
>
> Good quality connectors on LMR 400 is a good cable, but NEVER
> waterproof.  Who told you it was?  Never buy cheap connectors for LMR
> (or anything else for that matter).


I hear that!   Silver/teflon is the only way to fly :)

I'm very tempted to use 75 ohm CATV hardline on my next repeater rebuild.
The mismatch loss is trivial, and it's loss is way better than the best 50
ohm lines that I can afford.

I went a long while before I came to the realization that in general, higher
impedance cables are lower loss, and lower impedance cables carry more
power, all other things being equal.

Then there's scope probe cables, another animal ENTIRELY.

2007\02\06@140637 by Mike Hawkshaw

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Hi, Nate,

I know they aren't waterproof from the experience of others; it wasn't me
who bought the system, but I've seen the results from one site. They
(whoever make the stuff) claim to make a waterproof cable varient though,
and I guess one would assume their connectors were too in that case.

N type connectors whether they claim to be or not are waterproof to a
certain extent.

We always apply a liberal layer of self amagamating tape followed by either
a layer of black pvc tape or a layer of denso. The idea of both
overcoverings is to keep UV light off the self amalg, but the denso keeps
90% of the weather off as well. If or rather when the tapes fail you rely on
the connectors being waterproof and they must be so for our application. We
expect our systems to last at least 5 years between visits to measure the
system and there will be joints which have remained undisturbed for 20+
years.

Our UHF TV stuff is braodcast transmit arrays (in the UK) generally of
between 1 and 8 log periodics or other types of antenna pannel which are
themselves 50 ohm and are connected together using 50 ohm cable and
splitters or 3db couplers. Transmit main feeders can range from 7/8" foam to
6 and 1/8" air spaced for the high power sites. We also do MF & VHF radio,
DAB etc.

Mike.

> {Original Message removed}

2007\02\06@142918 by Mike Hawkshaw

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> I went a long while before I came to the realization that in
> general, higher
> impedance cables are lower loss, and lower impedance cables carry more
> power, all other things being equal.

This ins't completely true. It is possible to solve the equation for the
impedance of a circular coax cable for lowest loss, highest power rating or
highest voltage rating. The lowest loss is 77ohm which is presumably why it
is still used for domestic TV downleads etc, the highest power is 30 ohms
and the higest voltage is about 60ohms. 50 ohms is a compromise from the
last 2. We have a lot of 4 channel high power UHF TV systems where there
isn't much voltage headroom for the feeders.

It's best to use the same impedance throughout the entire system, though. If
you start to mix impedences you can get strange frequency dependent effects
and a filter you setup into a 50 ohm load will look very different into some
strange impednece transformed by the wrong impedance cable.

Mike.

> {Original Message removed}

2007\02\06@145309 by David VanHorn

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> This ins't completely true. It is possible to solve the equation for the
> impedance of a circular coax cable for lowest loss, highest power rating
> or
> highest voltage rating. The lowest loss is 77ohm which is presumably why
> it
> is still used for domestic TV downleads etc, the highest power is 30 ohms
> and the higest voltage is about 60ohms. 50 ohms is a compromise from the
> last 2. We have a lot of 4 channel high power UHF TV systems where there
> isn't much voltage headroom for the feeders.


True, I wasn't going to get that complicated :)
Then you get into ladder line, and open wire line.

Belden used to make a shielded twin-lead that had almost the loss figure for
dry unshielded twin-lead, but it dissapeared. :(   I guess cable TV did it
in.

It's best to use the same impedance throughout the entire system, though. If
> you start to mix impedences you can get strange frequency dependent
> effects
> and a filter you setup into a 50 ohm load will look very different into
> some
> strange impednece transformed by the wrong impedance cable.


In general, we don't put much of anything between the duplexer and the
antenna, and we tune the duplexer on-site, since we need to eke every last
bit of performance out of it to work on the 2M band with only 0.6MHz split,
so it's not much of a worry.  I know a number of people running systems like
this.

I pre-tune on the bench with 50 ohm loads, but reality on site is usually
different, even when everything is supposedly "50 ohm".

2007\02\06@154854 by Nate Duehr

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On 2/6/07, Mike Hawkshaw <.....mikeKILLspamspam.....spikey-mike.com> wrote:
> Hi, Nate,
>
> I know they aren't waterproof from the experience of others; it wasn't me
> who bought the system, but I've seen the results from one site. They
> (whoever make the stuff) claim to make a waterproof cable varient though,
> and I guess one would assume their connectors were too in that case.

Nah, never seen anything that would ever support that assumption.

> N type connectors whether they claim to be or not are waterproof to a
> certain extent.

Never seen anything that would support that claim either, but have
seen water intrusion into hard-line make a mess of things!

We found water in a 1/2" foam dielectric hard-line on a VHF radio
system last year that had been up for only a few years.  The borrowed
Aniritsu Sitemaster analyzer was helpful in figuring out what was
going on.

(We took the antenna down and inspected it too, luckily that tower is
on top of a mountain and is only about 35' tall... makes that job
easier.  We've got taller towers to work on, but that one's a piece of
cake.  One guy, and some tackle to lower it down, lay it down, look it
over... re-weatherproof where needed -- if needed -- and haul it back
up.  Photos @ <web.mac.com/wy0x/iWeb/Site/Cheyenne%20Mountain%20Summer%202006.html>
).

> We always apply a liberal layer of self amagamating tape followed by either
> a layer of black pvc tape or a layer of denso. The idea of both
> overcoverings is to keep UV light off the self amalg, but the denso keeps
> 90% of the weather off as well. If or rather when the tapes fail you rely on
> the connectors being waterproof and they must be so for our application. We
> expect our systems to last at least 5 years between visits to measure the
> system and there will be joints which have remained undisturbed for 20+
> years.

There's no way that was applied correctly if it leaked into the cable
in less than 5 years.  (Our screwup included.  Someone installed the
end on the hard-line correctly, but didn't weatherproof it properly on
the tower.  Oh well...)

You have to wrap so that the ridges of the tape are not collecting
water top-down, but shedding it; overlapping.  You also have to wrap
quite a ways out onto the cable itself after cleaning it thoroughly.

Everyone has "their" technique.  I haven't had one of mine leak yet,
so I go with it...

The SkotchKote helps a lot, and I like it better than I like the
mastic material.  Mastic's a icky mess when/if you have to take it
apart on the tower to change the antenna, and I've worked with enough
"icky pick" and telco cables filled with the stuff in my life that
even one more would be too many... but I'm sure I'll get the
"opportunity" again someday.  (GRIN)

But... dragging a can of SkotchKote up a tower is a PITA.

> Our UHF TV stuff is braodcast transmit arrays (in the UK) generally of
> between 1 and 8 log periodics or other types of antenna pannel which are
> themselves 50 ohm and are connected together using 50 ohm cable and
> splitters or 3db couplers. Transmit main feeders can range from 7/8" foam to
> 6 and 1/8" air spaced for the high power sites. We also do MF & VHF radio,
> DAB etc.

Ahh - broadcast.  That's what I missed.  Thought you were working on a
closed CATV system.  I'm surprised they're using LMR400 on that at
all... good old Andrews hard-line and/or double-shielded teflon cables
for flexible jumpers are the way I like to go.

(But... of course, I'll be breaking this "personal rule" soon, and
installing a bunch of 1/4"  superflex at a site that has some
questionable jumper cables... had a box full of the connectors and
since they're expensive I hunted around for a short roll of superflex
and found a local seller on ePay that had 140' of the stuff.  That'll
be more superflex than I'll need in a lifetime for jumpers, probably!
Well, I'm sure I'll find uses for it... but it's a lot more of a pain
to work with than something like RG400, bend radius limits being the
big PITA.  The RF numbers on small superflex suck anyway... but it'll
be better than what's up there!)

Numerous people have reported problems with LMR 400 in duplex
applications (receive and transmit on the same antenna)... due to it
being a foil under braid construction made of dissimilar metals.
Thousands of little RF diode-points where they touch makes for lovely
passive intermod and noise problems, especially if the cable is moved
at all in service.  Tie-wraps and tape are your friend if you're using
LMR...)

Nate

2007\02\06@161044 by Mike Hawkshaw

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> -----Original Message-----
> From: EraseMEpiclist-bouncesspam_OUTspamTakeThisOuTmit.edu [piclist-bouncesspamspam_OUTmit.edu]On Behalf
> Of David VanHorn
> Sent: 06 February 2007 19:52
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] Which coax
>
>
.....
> Then you get into ladder line, and open wire line.
I've worked on a big HF site which had open wire feeders. Spacing was about
30cms or maybe a bit bigger impedance was 300 ohms. The curtain arrays
typically had 16 dipoles with reflectors; all this was connected together
with open wire feeder and then matched to 300 ohm and taken back to the
switching matrix where any transmitter could be switched into any array.
Transmitter power (there were 12 transmitters if I remember correctly) was
300kW (there are sites with 500kW tx's). Each service output erp would have
been about 20MW.

This was really big gear, and when there was an arc over, bits of antenna
fell out of the sky!!

Mike.

2007\02\06@162717 by David VanHorn

picon face
>
>
> Well, I'm sure I'll find uses for it... but it's a lot more of a pain
> to work with than something like RG400, bend radius limits being the
> big PITA.  The RF numbers on small superflex suck anyway... but it'll
> be better than what's up there!)


I'm using this on all the jumper cables in our repeaters.
It dosen't make sense to use coax with "99%" shield effectiveness when
you're trying to get 90dB supression.

I made a little "hockey puck" from plywood, a bit larger than the minimum
bend radius, and that's how I do my bends, just form around the puck.  I'm
sort of surprised andrew dosen't make them, at least for the smaller stuff.

The loss isn't wonderful, but I think the longest cable I have with it is 4'
inside the repeater.
I did make up a 50' for my wifi dish, but I may replace that with better
stuff if it turns out to be needed.


> Numerous people have reported problems with LMR 400 in duplex
> applications (receive and transmit on the same antenna)... due to it
> being a foil under braid construction made of dissimilar metals.


I talked to Times about this, and got a grudging admission of the problem,
though they professed not to know WHY it was a problem.


Thousands of little RF diode-points where they touch makes for lovely
> passive intermod and noise problems, especially if the cable is moved
> at all in service.  Tie-wraps and tape are your friend if you're using
> LMR...)


Could be..

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