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DD Mode at the Medtronic Twin Cities Marathon 2013
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Erik Westgard
开云体育This year we were back to having six RP-1D /RP-2D systems online on area rooftops.? We are having a lot of antenna issues- the Comet GP-95s wobble and the base set screw falls out and they spin and the hardline either fails or falls off.? ?A fix seems to be to add a hose clamp over the set screw.? Four sites are now using Linksys WRT-54GL routers and OLSR software as back ends, and are not on any gateways or the Internet.? We are using DHCP and small subnets, so any ID-1 that comes in gets an IP address in a unique subnet and then it is easy to route between ID-1 attached networks.? ?This provides any to any and one to many for repeater attached ID-1s.? One of the strengths of the DD mode gear besides high power is the ability to support multiple concurrent data sessions.? We get routine 12+ mile (omni-omni) paths from our low lying data trailer site and remote trucks to our repeaters with minimal packet loss and 100ms rtd using either base antennas or mobile whips on ground plane mounts.? ?Two of (our) DD modules are on the USRoot gateway and we need to experiment with that.? We again ran two ID-1s as uplink radios side by side to two repeaters from our server trailer to support three ID-1s at the remote sites.? Note our remote stations had a lot of trouble with antennas/coax- the quite rare Comet 1.2 SWR bridges would have been useful and avoid NMO mounts.? ?50% of our voice traffic from 140 hams is digital, and that will increase in 2014.? ? ? Erik, NY9D? ? |
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George Jones
开云体育Antennas are another issue.? For several tears
now we have tried to operate a full-stack system on various Japanese antennas
with poor results.
All of the currently available antennas just does
not stand up to tower top mounting. They eventually break the internal solder
joints or the hardware comes apart. The other big issue we face here in Florida
is lightening. None of the Japanese antennas are DC grounded. Most use coupling
capacitors that blocks any connection to ground not to mention they will not
handle any power due to the caps being undersized for repeater
service.?Remember that the TX power going to the antenna is cumulative when
all of the TX modules in the stack come up together.
The mechanical problems causes noise that manifest
in desense on the receivers.
?
On a commercial tower you are lucky if you get a
years service out of Japanese antenna before needing to change it out. This
results in the cost of another tower climb plus the new antenna cost.? The
ideal situation would be to use separate antennas for each band. That is just
not possible in our case due to the extra wind loading and additional hard line
required.? If you are lucky enough to talk your way onto a good commercial
tower, more than likely the owner is just allowing you one space and feed line.
This necessitates installing one of the TRI-BAND models.
?
We have presented this problem to all of the
current antenna manufactures and none of them seem to be interested in
manufacturing an antenna that will work for us. Most of the Japanese
manufactures say that it is a very narrow market and they can not make
enough? in sales to make it profitable.
?
Out of all the antennas we have gone through we
have found that the Comet GP-95 works the best with some modifications.?
All of the internal capacitors are replaced using short lengths of RG-142 coax
as the cap. The feed is modified to make the antenna DC grounded.? All of
the solder joints and mechanical screws are silver soldered into place. Since
the GP-95 is a one piece radome you do not need to add additional WX protection
at the center joint as needed with the GP-98. You still need flooded heat shrink
at the base to cover the fiberglass to metal joint. One other importaint point
is to support the antenna at the top as well as the bottom to keep it steady in
the wind. This is especially important at 23cm. Antenna movement results in
radiation pattern shift thus causing the signal to fluctiate at the receiving
station.
?
Any comments?
?
George - W4AQR
?
?
????
From: Erik Westgard
Sent: Wednesday, November 06, 2013 6:13 AM
To: D-STAR_23cm@...
Subject: [D-STAR_23cm] DD Mode at the Medtronic Twin Cities Marathon
2013 This year we were back to having six RP-1D /RP-2D systems online on area rooftops.? We are having a lot of antenna issues- the Comet GP-95s wobble and the base set screw falls out and they spin and the hardline either fails or falls off.? ?A fix seems to be to add a hose clamp over the set screw.? Four sites are now using Linksys WRT-54GL routers and OLSR software as back ends, and are not on any gateways or the Internet.? We are using DHCP and small subnets, so any ID-1 that comes in gets an IP address in a unique subnet and then it is easy to route between ID-1 attached networks.? ?This provides any to any and one to many for repeater attached ID-1s.? One of the strengths of the DD mode gear besides high power is the ability to support multiple concurrent data sessions.? We get routine 12+ mile (omni-omni) paths from our low lying data trailer site and remote trucks to our repeaters with minimal packet loss and 100ms rtd using either base antennas or mobile whips on ground plane mounts.? ?Two of (our) DD modules are on the USRoot gateway and we need to experiment with that.? We again ran two ID-1s as uplink radios side by side to two repeaters from our server trailer to support three ID-1s at the remote sites.? Note our remote stations had a lot of trouble with antennas/coax- the quite rare Comet 1.2 SWR bridges would have been useful and avoid NMO mounts.? ?50% of our voice traffic from 140 hams is digital, and that will increase in 2014.? ? ? Erik, NY9D? ? |
开云体育So what's a matter with NMO mounts? About all I've seen is that and UHF mounts for mobile usage.?Sly n5gqb |