----- Original Message -----
From: <wng@daimlerchrysler.com>
> Of course, the theoretical loss from in to out (or out to in, if used as a
> combiner) is 3dB, but the additional losses just due to the F connectors
> (and the quality of their installation) probably approaches another 3dB as
> frequency approaches 1 GHz (Why do you think we use SMA, SMB, N, TNC, C
> and even more exotic connectors as frequency increases?)
Not neccessarily, Bill. F connectors are typically very low loss
provided that a good match is maintained. In fact in many cases
they will work well to beyond 2 GHz. The limiting factor is typically
the female connector. If the "clutch" that accepts the male pin is
very large and bulky it will present a lot of shunt C and make for
a very bad mismatch limiting performance to say 500 MHz. The
smaller clutches used in 1 GHz passives provide a very good
match and hence low insertion loss. If a round bifurcated female
pin is used the connectors will work to 2 GHz. In fact, satellite
TV IF components (splitters, taps, etc) that use F connectors
and work from 950 to 1450 MHz are produced by the tens of
thousands.
I've test more CATV splitters than I care to admit. The ones
my former employer used to sell were spec'd to have an
insertion loss of 4.2 dB at 1GHz and most of them met that
requirement (tested on an HP8753C vector network analyzer).
This did indeed include the losses of the F-connectors (the
calibration planes for the VNA were setup to be right at the
mating connector of the DUT). In fact, the additional insertion
loss of a pair of back-to-back F-connectors over and above
a pair of back-to-back 75 ohm N-connectors was very small
(0.2 dB at most). All of the 1 GHz parts I saw (we would often
get competitors products in for "evaluation") were done on
G-10 circuit boards. Alot of the 600 MHz product was
"fly jointed" as you describe, however. Fly jointed is done
for cost reasons (its cheaper than making a PC board), but
it is hard to get performance at 1 GHz because of lack of
layout consistency. BTW, on of the most important factors in
making the stuff work was getting a good ground connection
to the die cast housing for the RF return to each of the
connectors. If you mess that up, you'd be lucky to get
performance beyond 200 MHz :)
73 de Mike, W4EF
> Bill Gilmore, Electromagnetic Compatibility Engineer
> Core EMC, Electrical/Electronic Engineering
> Powertrain Component EMC / Rear Wheel Drive, SRT & HEV Platform EMC
>
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