[amsat-bb] Diplexer use for 70Cm/10M...2M/10M.

["Ernest A. Erickson" <eaerme@xxxxxxxxxxxx>]

Members:
I just finished a short test of a CATV diplexer from Viewsonics.
Model # VSREDP-40, this item has two output/input port(bi-directional)
and a single common port. I fed a 2 watt 446 Mhz signal into the HIGH
port and metered the output on both HIGH and LOW ports. I noticed a 3+dB
signal loss in the diplexer through the HIGH port(due to impedance
mismatch) and also noticed that the LOW port had NO signal output. I
thought of this test due to a gent posting about a "dual-band" VHF/UHF
to 10M antenna, and feeding problems associated with same. I remembered
i had a diplexer connected to the test ports of my Wavetek "stealth"
analyzer, so i disconnected it, placed it on the bench and ran this
simple test to see IF it was possible to get a "decent" signal into and
out of the diplexer without inducing desense/intermod to my el-cheapo
scanner...IT WORKED! I do not have any HF gear here, so i was forced to
use the scanner<sigh>. Since the diplexer is a bi-directional device,
you can (theoretically) feed two antennas from a common TX or a single
antenna with two TXs, as long as the PO is kept low enough to prevent
heating damage to the diplexer. The diplexer handled the 2 watt UHF
signal with ease, and i know it was designed to handle a 20dBm level
"all day". CATV gear is, in my view, cheaply designed because the
equipment is fed a high level signal at all times so the need for
quality connectors was/is not necessary to ensure a good signal over X
lengths of cable. Who else would even consider a pin connector for
signals that extend to 1 Ghz.? I decide to attempt this because CATV
gear has been pressed into service in many areas of ham radio, and this
area is no different, just a different application which demands a
differing mindset. Why not use line amps or even distribution amps to
feed an "auxiliary" receiver? The amps are easy to reconfigure to meet
the feed impedance needed by most 50 ohm radios, if not as a part of a
whole comm. system as well? Think about this please; Antenna output to a
distribution/line amp leading to a splitter, then to a tap in each room,
and still another amp feeding more taps/splitters for the rooms you want
to have a receiver located..."CABLE SAT" anybody? It would make for an
interesting receive project i am sure. This same scenario could be used
on TX also, with the appropriate switches/relays and sequencers should
you get "motivated" to attempt such an undertaking. Just move the
equipment to whatever room you want, connect, and talk! (antenna
rotation and location is up to you). Remember; it is the amateur's
responsibility to "tinker" as much as he/she can! *To tinker, is to
learn*. Recently, i was given an old, beat up G.E Phoenix UHF mobile, it
was past repair, but the amp stages were still good, so i got out the
dremel tool and cut out the amp circuit and placed it in a box mounted
to a large heat sink and now i have a nice 25 watt PA with a 250mW drive
requirement..free! All i have to do now, is bias it for AB service to
use on my 439.250 ATV exciter and i have a great mobile ATV station!
I just wanted to bring up yet another way to make use of surplus gear
that hams have been so great at using for their needs. 
HAVE FUN!
73!
Ernest, KA9UCE, A.E.C
eaerme@newnorth.net
http://www.geocities.com/aec9823
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