>From what I have gathered from your replies as well as my own reading
of the mil specs, the seemingly inconsistent results (everything from I
ran 14 KW into one, to they were a source of constant failure at 1500
watts) that users appear to have obtained with series N connectors, aren't
so contradictory after all. According to MIl-PRF-39012, a series N plug
is rated for 1500 volts RMS operating at sea level when tested from 5.7 to
7 MHz. In a matched 50 ohm system, this corresponds to 45 KW - pretty
impressive. Even if you use the more conservative working voltage rating
in MIL-PRF-39012 of 1000 volts RMS, you are still talking about 20 KW into
a matched 50 Ohms system.
Although this might seem like a lot of margin for the typical 1500 watt amateur
installation, the big numbers are a little misleading as the peak power rating
of
the connector will vary with the square of the voltage rating. Thus as VSWR
increases, power handling must be derated by the square of the VSWR (e.g. a
system with 2:1 VSWR must be derated by a factor of 4 in power). These ratings
also assume an ambient sea level environment. Throw in some moisture or
corrosion and a little center pin misalignment and the picture gets even worse.
Physical examination of the series N connector tends to bear these specs out.
A quick trip into our lab at work revealed that the minimum air gap spacing on
the series N although somewhat variable, was on the order of .05". This
corresponds
to a breakdown voltage of around 2500 volts RMS which is in pretty good
agreement
with the mil spec. Although these big numbers might seem pretty impressive,
the need to be put in perspective. Comparison with a BNC connector
reveals that although a series N male can mated to a BNC female, the
BNC actually has a larger air gap. This is because the series N plug has
an internal ridge which is used for matching. It is also an air dielectric
interface. The BNC is a combination air and plastic suggesting a higher
breakdown voltage. It also should be noted that the mil spec doesn't control
many of the series N connectors internal dimensions as several of the dimensions
are specified "dimension shall meet connector performance requirements". The
diameter of the matching section for example doesn't effect the mechanical
interface, it is sized for impedance matching characteristics (I noticed that
this
diameter tended to be larger on series N plug to BNC jack adapters, and smaller
on series N plugs for coax cable).
Even more revealing is a comparison of the series N with the venerable PL-259.
A typical UHF utilizes a solid dielectric with a conductor spacing
approximately
twice that of the series N air interface. This suggests that a UHF has at least
4 times the power handling capability of the series N in situations where the
connectors are voltage limited (e.g. HF).
In short, it would appear that although a properly installed and matched series
N
connector should be capable of handling 1500 W plus at HF, its internal features
are very small and sometimes delicate. The UHF connector despite its low cost,
would appear to be a better choice at HF where connector VSWR and insertion loss
are not significant.
Thanks to everyone who replied to my query. Please accept my apologies
if your reply does not appear in the summary, as I may have lost some of them
when upgrading my hard drive this past weekend
73 de Mike...............
All of the failures I have had with 7/8" connectors was the result
of the connection to the shield breaking down due to the effects of
weather and/or aging. I have NEVER (knock on wood) had a failure on
one of MY connections because after I put the barrel over the shield,
I flare out the copper making a flange that is trapped into compression
when the connector is tightened. I then triple tape the joint with
Scotch #88 tape, a layer of rubber electrical tape, and a top layer
of Scotch #88. I have seen no specs either, but my feeling is that a
properly installed "N" fitting for 7/8" cable is at least the rating
of the cable itself. GL! (((73))) Phil, K5PC
During some research activities I did a number of years ago, I discovered
MIL specs that suggested the max power for "N" connectors was approximately
800 watts at 150 MHz. If you look at that connector closely, you will
see that the internals are exactly the same dimensions as a BNC connector.
One conservative approach would be to limit power to that which you would
run through a BNC. Now having said all that, I have for years run about
1400 watts through BNC connectors used on my old EME array on 2 meters.
Never had a failure. Also I run full legal on most bands through N's, with
never a failuure in the 27 years or so that I have used them on outdoor
connections. If the coax you use with the connector is rated for the
power/frequency, your assembly techniques are above reproach, and you
always maintain a low VSWR in the system, you will never have a problem.
Good luck, Larry - W7IUV
Well, after a lot of blather from people saying, "Well I've done this
or I've seen this." you still don't have an answer for your question of
ratings. I sell connectors as part of my living and have real numbers
available for you, not ham type speculation and experimentation! For
standard 50 Ohm N-connectors: VSWR: ~1.04:1 (up to 1.2:1 at 11 GHz) IM
Products: -90 dBm (-133 dBc @ 20 Watts) Insertion loss (straight connector):
< 0.15 dB max at 10 GHz RF Leakage: -90 dB min from 2 to 3 GHz Insulation
Resistance: 5000 MOhms min Contact resistance: 1 mOhm (center), 0.2 mOhm
(outer) Sea level Working voltage in VRMS (for RG213): 1400 Volts (for
RG58): 850 Volts Dielectric Withstanding Voltage: 2500 V (RG213), 1500 V
(RG58) RF Testing Voltage: 1500 VRMS (5 MHz SineWave) The maximum power
that is specified through the connectors is 8 KW (I=13 A) up to 10 MHz.
At 20 MHz, the maximum power is rated at 4.75 KW and at 30 MHz it is just
over 4 KW. At 100 MHz, the rated power is just over 2 KW, at 400 MHz the
rated power is 1 KW, and at 500 MHz, the rated power is 900 Watts. The
connector derates to about 180 Watts at 10 GHz. Beyond 10 GHz the connector
starts to go into other modes than the TEM mode. The connector is also
rated at 100% power up to 25 degrees C. At 50 C, it drops to 80%. It
falls linearly to 0% at 155 C. There, that should help! The others are
correct when they talk about the need to have good center pin contacts
with the N connector. The center pin is very small and as such needs to
be mated well and it needs to be neither too short nor too long. Remember
that the business part of an N and a BNC are the same! I hope this helps
everyone on the list. 73, Jon KE9NA -------------------------------------
Jon Ogden KE9NA
Good information, Jon. Thanks. Is the spec you quoted a recent commercial
spec or an (old) MIL spec? Also, do you have altitude derating info? What
is the spec for a BNC? Thanks & 73, Larry - W7IUV
Some of the specs I gave were MIL. The voltage specs were CECC specs.
at 70,000 feet the N connector has the following voltage specs: Working
Voltage for RG-213: 400 Volts. Working Voltage for RG-58: 250 Volts
Dielectric Withstanding Voltage for RG-213: 600 Volts Dielectric
Withstanding Voltage for RG-58: 350 Volts Those are the only altitude
related specs. OK, for BNC: VSWR 1.30:1 max (straight) up to 11 GHz
Insertion Loss (straight): 0.2 dB max at 3 GHz RF Leakage: -55 dB min
from 2-3 GHz Insulation Resistance: 5000 MOhm min. Contact Resistance:
Center: 1.5 mOhm, Outer 0.2 mOhm RMS Voltage: 500 VRMS max, at 21,000 meters:
125 VRMS max Withstanding Voltage: 1500 VRMS, at 21 KM: 375 VRMS RF High
Potential with standing Voltage (5 MHz): Sea level: 1000 V RMS That's all
I have on BNCs. The MIL spec is: MIL-C-39012 C. 73, Jon KE9NA
AG6K wrote:
I have put 14kw pep (1200v-peak) through a N fitting at 7MHz. .
However, if a Type N center pin looses spring tension there can be grief.
A better connector is the Type-C.. It's like a BNC for RG-213.
A Type-C fitting has way more contact area than a Type-N.
>With a 1:1 VSWR into 50 ohms, 1500 Watts corresponds to 5.5 amps rms and
>270 volts rms respectively. Given the airgap size in the series N
>connector, I would expect the breakdown voltage to much higher
>than this (one old Mil spec I found for a type N adapter suggested ....
I measured it at c. 4kV.
Amen, Rich :-) When they're perfect, N connectors are fine for US legal
power up to at least 432MHz - but as Rich says, the weak point of N
connectors is the inner connection which isn't much bigger than a BNC.
Unfortunately there are too many ways for that connection to go wrong.
Creep of the inner conductor in the cable can either pull the connection
apart (so it arcs) or splay the female contacts out (so either it splits
now, or it arcs later when you re-use the connector). The MIL-style N
connector is even worse because there's no positive axial location for
the inner pin. With big cable the inner pin can easily be forced off-
center, again causing damage to the female part. The tendency to arc
seems to be frequency-dependent. Many people use Ns with several kW up
to 144MHz, but I've had a lot of trouble at 432. Unfortunately even
7/8in heliax connectors are not immune... and that's expensive.
>A better connector is the Type-C.. It's like a BNC for RG-213.
>A Type-C fitting has way more contact area than a Type-N.
C connectors are indeed very good, but are not very common (I was lucky
to have a local supply for several years, from scrap nucleonic testgear).
There's also an SC which is like an N, but with a C-size centre pin, the size
it oughta be. Watch out for 7/16 DIN connectors, which are coming into
cellular base station applications world-wide. They originated in Germany
and are already appearing as surplus here in Europe, in all sizes from
7/8in heliax down to RG-213. These are serious connectors (7mm inner,
16mm outer = 50 ohms) which go together with a satisfying clunk. They
are constant impedance, self-centering, have lots of contact area and
are good for any amateur power up to several GHz. 73 from Ian G3SEK
N8SM wrote:
Mike,
Saw your post on Amps, then saw the same question asked on the
rec.radio.amateur.antenna news group. Here's some of the replies (I
filtered a lot of off topic BS....)
>Is the type N connector rated for maximum amateur
>legal power? The center pin while gold plated looks
>to be a tad small.
>
>Imax = sqrt( Pwr x Zo x SWR ) / Zo and if we let
>Pwr = 1500w, Zo = 50ohms, and SWR = 3:1
>
>then Imax = 9.5amp RMS. I have never seen a current
>rating for the type N connector. I asked this question
>a while back and never saw a reply.
>
>Thanks & 73,
>Larry Benko, W0QE
--------------------------------------
N connectors are a source of constant failures at 1500 watt power
levels unless SWR is always reasonably low. They are not only subject
to current failures, they also have less air gap and tend to arc
easier than good UHF type connectors.
While they marginally handle 1500 watts or more, good quality UHF
connectors are much more reliable.
The "N's" main advantage occurs at VHF and above, where they add less
of an impedance bump than the 1/2 inch long 30-40 ohm bump area of a
SO-239. (The male UHF PL-259 is about perfect).
50 ohm N connectors are dimensionally almost identcal to BNC
connectors. If you remove the locking bayonnet section from a male BNC
it will plug right into a N female 50 ohm connector.
I avoid N connectors unless the circuit is on VHF and is impedance
critical. They are such maintainence pains at high power, when I get
used 7/8 inch 50 ohm hardline with N connectors, I machine the N's and
modify them to UHF type and use teflon inserts.
Then I don't have to worry about a momentary "wrong band" selection
popping a connector. I hate having the weakest link in the system
outside and up in the air!
73 Tom W8JI
--------------------------------------
I have seen N-connectors used in 5KW+ amps, with no trouble.
--------------------------------------
That seems to be the general experience. A good N connection will handle
1500W on 432MHz forever, but if there's any problem it will burn up very
unpleasantly - welding the center pins together, arcing from center to
shield, or both.
It certainly seems to be frequency-dependent - the higher the frequency,
the greater the stresses on connectors and cables, and the greater the
risk of a runaway situation ending in destruction.
In a different newsgroup, someone recently said that a lot of problems
in the cellular industry were due to the (mis)use of "screwless" N
connectors in push-to-mate situations at the rear of plug-in racks -
something they were never designed to do, because neither the inner nor
the outer is self-centering.
The trend in cellular seems to be toward 7/16 DIN connectors, which are
bigger, stronger, self-centering and also have better intermodulation
performance in critical cellular applications. As 7/16 hardware trickles
through to the surplus market, hams are changing over too.
--------------------------------------
check:
http://www.amphenolcnp.com/RFpartsearch3.cfm?partid=19&cfid=27160&cftoken=17
--------------------------------------
I haven't been following this thread so I hope I'm answering a question that
was asked.
The Andrew catalog #36 specs an N connector at
2 KV DC Test Voltage
0.6 KW Average Power
10 KW Peak Power
a footnote says that average power is based on a frequency of 900 MHz. Remember
that voltage ratings are for peak, not RMS,
values.
--------------------------------------
73 OT,
Last century I came upon a system where type N connectors were
constantly failing. They were used on the output connectors on RCA
Y-1086 and Y-1070 cavities, which use 7651 tetrodes at 200 MHz. The
highest power was about 5 kW peak, and 12% duty factor. This is about
600 watts average power. Being the drivers for another stage, they
were subjected to VSWR during tuning of the grid input tuner for that
state - and no isolator was present. The original cavities were rated
for the peak but not the average (only 6% DF), and someone TURNED
THEM UP. The input to the next stage also had N. We removed the N
and replaced with Shuner 7/16 DIN connectors and mating cables. We
replaced the Jones micromatch Directional couplers (having N
connectors) with Weralatone couplers having the 7/16 DIN connnector.
We got rid of the 7651 and went MOSFET for the 5500 watt stage
(MRF151Gs). End of problem. Never had another connector failure since
1995 changeover.
john
K5PRO
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