[CVRC] DCART meeting 21Nov05
Glenn Thomas
glennt at charter.net
Fri Nov 18 17:07:30 EST 2005
Hi all!
The monthly DCART meeting will be 6:30PM next Monday, November 21,
2005, at the usual place at Minden Airport. Dale, KV7S, will be
leading this meeting as I will be unfortunately detained elsewhere.
The topic will be HF radio as it relates to emergency communications.
The exercise will be a drill that simulates typical HF SSB conditions.
There will be no DCART meeting in December. Merry Christmas!
The January meeting will repeat the traffic handling exercise we did
for SET. No, I don't have the accuracy measurement yet, but I
certainly will by January. I'll also have a new set of test messages
with even more scintillating content! Details later.
73 de Glenn Thomas WB6W
DCART Coordinator
DCART November meeting outline
1) HF upside (Why use HF?)
a) Repeaters not required (NVIS)
i) Usable when repeaters are not available
(1) RF hole, in a canyon
(2) Repeaters not operable due to disaster
ii) Additional channels when repeaters saturated
b) Long range comms available
i) Local/regional coverage via NVIS can
"leap tall mountains in a single bound!"
ii) Regional/national/worldwide coverage available
2) HF downside (Why isn't?it used more?)
a) Many ops are tech/tech+, no HF available
b) Channel availability is medium to low
i) Typically 50% to 90%, vs. 99+% for VHF/UHF
ii) Affected by time of day
iii) Affected by solar weather (sunspots, geomagnetic state etc.)
iv) Skip zone may exclude part of region
v) Availability questionable around sunrise/sunset
due to day/night propagation transition
c) One-way skip DOES exist
i) fairly common
ii) Occurs when one station has a higher noise/interference
level than the other
d) Antenna size may be large(er than VHF/UHF)
i) Several tens of feet for HF vs. tens of inches for VHF
ii) Real estate for HF antenna may not be available at EMCOMM site
(shelter, fire camp etc.)
e) Adjacent channel interference is common
f) ElectroMagnetic Interference (EMI) issues
i) Some agency systems (dispatch?) very susceptible
3) Different bands have different characteristics
a) Low HF (30m and down)
i) 160m
(1) Excellent ground wave coverage
(2) Usable night time only (to several hundred miles NVIS)
(3) full sized antenna is ~240 feet
(4) mobile antennas very narrow bandwidth (several kHz)
very low efficiency (~0.01%)
(5) not a great choice for EMCOMM
ii) 80/75m
(1) Fair ground wave coverage
(2) Usable night time only (to several hundred miles NVIS)
(3) Skip zone small (miles) to none
(4) full sized antenna is ~120 feet
(5) mobile antennas narrow bandwidth (several tens of kHz)
low efficiency (~0.1%)
(6) primary choice for regional EMCOMM at night
iii) 60m
(1) Fair ground wave coverage
(2) Usable night and day (to several hundred miles NVIS)
(3) Skip zone moderate (~hundred miles at night) to none (day)
(4) full sized antenna is ~90 feet
(5) mobile antennas narrow bandwidth
(several tens of kHz)/low efficiency (~0.3%)
(6) channelization (5 channels) and low power (50w ERP)
limits usability
(7) good choice for 24hr inter-regional EMCOMM coordination
(8) Radios for this band not yet common
iv) 40m
(1) Poor ground wave coverage
(2) Usable night and day
(a) Nighttime coverage is long with a significant
(several hundred mile) skip zone.
NVIS usually not available at night.
(b) Daytime coverage is moderate (<500 miles. NVIS
usually available)
(3) full sized antenna is ~70 feet
(4) mobile antennas modest bandwidth (~60 kHz)/low efficiency (~1.0%)
(5) primary choice for regional daytime EMCOMM
v) 30m
(1) Digital modes only (no 'phone)
(2) Poor ground wave coverage
(3) Usable night and day
(a) Nighttime coverage is long with a significant
(several hundred mile) skip zone.
NVIS usually not available at night.
(b) Daytime coverage is moderate
(<1000 miles. Significant skip zone, NVIS
sometimes available)
(4) full sized antenna is ~50 feet
(5) mobile antennas good bandwidth (whole band)/modest
efficiency (~10%)
(6) regional digital for EMCOMM
b) Hi HF (20 and up)
i) 20m
(1) Very poor ground wave coverage
(2) Usable night and day
(a) Coverage is long (DX QRM not uncommon)
(b) Significant (several hundred to thousand mile) skip zone.
(c) NVIS not available.
(d) Band sometimes unavailable at night
(3) full sized antenna is ~35 feet
(4) mobile antennas good bandwidth (~250 kHz)/good efficiency (~50%)
(5) primary choice for national/regional EMCOMM
ii) 17m, 15m, 12m, 10m
(1) Very poor ground wave coverage
(2) Usable daytime
(a) Coverage is long (DX QRM not uncommon)
(b) Significant (several hundred to thousand mile) skip zone.
(c) NVIS not available.
(d) Bands often unavailable at night
(3) full sized antenna is ~35 feet
(4) mobile antennas good bandwidth (whole band)
excellent efficiency (70% to 100%)
(5) backup for national/regional EMCOMM
(6) High antennas provide VHF-like coverage for local comms.
Some 10m FM repeaters available.
4) Portable antennas
a) Antenna efficiency
i) proportional to square of length (in wavelengths) up to 1/4 wave
ii) short antennas affected by antenna/environment losses
(1) CAREFUL! - improvements to a short antenna may make the
SWR worse at the same time they make the antenna more efficient!
5) Exercise to pass traffic point of exercise is to simulate the
co-channel and/or adjacent channel interference that is common on HF.
More than one person will be talking at the same time!
a) in the room, via voice (no radios)
b) two nets simultaneously
i) members of each net do not acknowledge members of the other net
ii) each net member should send and receive one message
iii) net discipline to be maintained
c) Use messages from SET
i) 3 or 4 per net
ii) don't worry about timing
-30-
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