[Elecraft] Connectors

Wed Apr 25 19:09:45 EDT 2012

(Changing to a more descriptive Subject line)

1.  One nice thing about female BNC connectors is that they are
compatible with male type-N connectors.  Try it - they plug right in.
Of course, there is no locking mechanism, so it wouldn't be good for
something like a mobile installation, but otherwise it works fine and
saves an adapter.

2.  One advantage that BNC and N have over UHF is that the ground
connection doesn't depend on the shell being properly tightened.

3.  I've had excellent reliability from UHF plugs as long as I pre-tin
the coax braid and solder it through the holes.  That's true both with
RG-8 type cable as well as the smaller RF-58 with the adapter.

4.  Regarding RF loss in UHF connectors, it isn't as bad as many people
think.  I did an Internet search and found the Usenet posting I made on
the subject about 20 (!) years ago:

From: ... (Alan Bloom)
Date: Fri, 18 Sep 1992 23:03:13 GMT
Subject: The Truth about UHF Connectors
Organization: Hewlett-Packard, Santa Rosa, CA
Newsgroups: rec.radio.amateur.misc

Ya gotta feel sorry for UHF connectors. Recent strings on this notes
group lambasted them as worthless at VHF and above, and barely tolerable
at HF. One poster called them "5 dB attenuators", and many agreed that
there must be some sort of conspiracy among ham equipment manufacturers
to inflict such garbage connectors on the amateur community.

Today I finally remembered to bring some UHF adapters from home so I
could do some relative measurements of UHF versus type-N.  As expected,
the type-N showed lower insertion loss at high frequencies, but the UHF
connectors were hardly "5 dB attenuators."

For the test I connected an HP8753 RF network analyzer through two short
BNC cables into the following arrangement:
   _______    ____________    ___________    ____________    _______
  |       |  | BNC female |  | N female- |  | N male to  |  |       |
__| 10 dB |__| to N male  |__| N female  |__| BNC female |__| 10 dB |__
  | Atten.|  | adapter    |  | adapter   |  | adapter    |  | Atten.|
  |_______|  |____________|  |___________|  |____________|  |_______|

Then I repeated the measurement with the N adapters replaced with UHF.
I normalized the measurements by replacing the 3 adapters with a BNC
double-female. (That is, this was assumed to have 0 dB loss.)

Since two N or UHF adapters were used, I assume the loss per connector
is half the total. The vertical scale was .1 dB/division, so I estimated
the insertion loss to the nearest .01 dB or so:

            --------- Type N --------   ---------- UHF ----------
FREQ (MHz)  TOTAL  LOSS PER CONNECTOR   TOTAL  LOSS PER CONNECTOR
1.8         0 dB   0 dB                 0 dB   0 dB
30          0      0                    0      0
100         0      0                    0      0
150         0      0                    0.02   0.01
200         0      0                    0.03   0.015
450         0      0                    0.18   0.09
600         0      0                    0.26   0.13
900         0      0                    0.66   0.33
1000        0.05   0.025                0.8    0.4
1300        0.1    0.05                 0.86   0.43
1600        0.05   0.025                0.5    0.25
2000        0.05   0.025                0.02   0.01

Insertion loss increases until about 1300 MHz, and then starts to
decrease until it is almost zero for the UHF connector at 2 GHz!  At
that frequency, the connectors are about 1/4 wave long (1 inch,
assuming .66 velocity factor), so I assume that the two adapters are
providing a conjugate match to each other. This confirms my assumption
that the insertion loss is due to reflections (impedance mismatch), not
absorption (true power loss).

Bottom line: UHF connectors work fine through the VHF range, and are not
too bad even on the 420 MHz band if you can stand about .1 dB mismatch
loss per connector.

By the way, I did not do the full 2-port calibration on the HP8753, so
there was a couple hundredth's dB ripple in the plots. I averaged this
out by eye to come up with the numbers in the above chart.

AL N1AL

P.S. Sorry, I guess I violated the Usenet rule against posting objective
data... :=)

On Wed, 2012-04-25 at 09:50 -0800, Edward R. Cole wrote:
> I assume all you have read this thread so not going to repeat all 
> prior e-mail in my post.
> 
> First off only place you will find PL259/SO239 "UHF" connectors is on 
> ham, CB and some marine radio equipment made today.  Commercial 
> radios long have gone to other connectors with N-connectors being 
> favored for VHF+ site located systems.  Mobiles and HT's have a 
> variety of connectors from BNC, TNC, mini-UHF, RCA-phono (gawd 
> awful), sma and a whole host of tiny specialty connectors used on 
> wireless stuff, smart phones, etc.
> 
> In my professional life I moved most cabling to either N or BNC vs 
> UHF.  This was for reliability.  BNC were normally used on RG-58 
> cable jumpers and lower power stuff where measurements were frequent 
> requiring cable removal.
> 
> The use of pliers to tighten connectors had gotten too many folks in 
> trouble due to "super mechanic" mentality that if tight is good 
> tighter is better.  Sorry these are not water or gas lines.  If you 
> use a plier to tighten only rotate 1/8 turn beyond finger-tight.  I 
> can see wanting to do this on antenna connections or mobile 
> installations where vibration is possible.  Use of heat-shrink over 
> the connector will result in longer reliability (also because it is 
> now wx tight).
> 
> BTW I have measured improvement of half a dB at VHF+ by proper 
> tightening of N connectors.  At HF this is probably not even noticed 
> but on receivers at UHF it will make a difference.  Sma connectors 
> are particularly susceptible to inadequate tightening but again 
> should only be tightened with a sma wrench with 1/8 turn or by proper 
> torque wrench according to the mfr's specs.  Sma do not like repeated 
> removal and installation so be careful with that.  I find the threads 
> in N connectors wear if removed too much and work much better the 
> first or few times.
> 
> Impedance match on low noise preamps is critical so many hams are 
> moving to use of either N or sma connectors over BNC.  I have not 
> seen a UHF on a preamp since the 1960's.
> 
> Finally, my highest connector failure is with UHF on RG-58 size 
> cable.  I really dislike the critters for that.  Crimp-style 
> connectors also seem to have a higher failure if they are cables that 
> are repeatedly removed (esp BNC).
> 
> So that is my two-cents on the topic.
> 
> 
> 
> 73, Ed - KL7UW, WD2XSH/45
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