T&T: VHF and antenna

[Ed Bruette]

Clyde,

I just went back to my outgoing msg and it worked for me
(http://www.qsl.net/vk3jeg/pl259tst.html).  Here is the title info if you
want to Google or otherwise search for it.  

The UHF type connector under network analysis
A closer look at the non-constant 
Impedance PL-259 and SO-239. 
By Chris J Arthur VK3JEG 

On the chance that the article is unreachable here are the "Conclusions."

"Conclusion Before wrapping things up I must admit that the UHF type barrel
connector employed here was of fairly poor quality, as one would find in
most hobby type outlets. I suspect that it contributed significantly to the
poor results gained but we should also keep in mind that good quality
connectors of the UHF type are not easily found. In real world terms the 0.2
dB Insertion loss at 144 MHz would be a transmission loss of more than 1
Watt from a 25 Watt input at 144 MHz. The real bad news is at 432 MHz where
we see a loss in the order of 1.0 dB, this equates to a transmission loss of
around 6 Watts with 25 Watts input. This phenomenon is of course due to the
Impedance "bump", the power is not actually lost but reflected in the
transmission lines. 

Most of use have used a VSWR meter, a useful device for looking at reflected
waves, a lot of these units also give a relative power reading. Perhaps at
sometime or another you may have noticed some particularly strange
indications while using your meter at VHF/UHF frequencies. The problem with
this type of instrument is that it is both frequency and impedance
sensitive. We can normally recalibrate for the frequency of operation but
impedance is fixed at 50 Ohms, therefore any mismatches on the line both
before or after the meter will cause error in the indicated parameters. As
we can see from our test results of the UHF type connector the Impedance is
non-constant and at VHF and UHF frequencies offers a varying mismatch to 50
Ohms. This in turn will cause error in both VSWR and Power readings
particularly at UHF frequencies. A more detailed description of interpreting
Antenna and line measurements directed particularly at the Amateur was
written by R Bertrand VK2DQ in the mid 1980's, it can be found in the
Amateur Radio Action, Antenna Book 3. 

I would like to finish with these few points. The first being that the so
named UHF connector from the past is not really suitable for use above 300
MHz at all. Perhaps the exception to this would be when a cheap and rugged
system is required where loss and good signal to noise ratio is of little
concern. Unfortunately it appears that both Amateur and CB Radio UHF type
equipment fall into this category as many manufactures still supply SO-239
UHF receptors as standard equipment. The second point is that from our
results we can see that utilisation of the UHF connector at 146 MHz for FM
type transceivers is not such a problem. A cheap rugged connector is
probably an advantage as many FM units are used for mobile applications.
However, for 144 MHz SSB type work where low loss and good signal to noise
ratio is very desirable, again I would not recommend the use of UHF type
connectors. The UHF connector still has a place in many applications where a
robust economical RF connector is required but for serious applications its
use should be limited to below 100 Mhz. As we have shown the N type is far
superior in performance, it should also be noted the BNC type connector is
similar in performance to that of the N type but has the disadvantage of
being less rugged. In the end, one should always check with the manufactures
specifications." 

Ed, N7NVP
PT-38  "Makin' Do"
Poulsbo, WA
 

-----Original Message-----
On Behalf Of clyde fernortner

ed...went to the site, but found nada abt connectors! lotsa ways to get to
their various web pages tho...c
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