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| Erecting the Comet CHA-250Bx Antenna |
Erecting My Comet CHA-250Bx HF Antenna
(by VE1CHI, Jim)
After purchasing a new rig this fall 2008 (Yaesu FT-897D HF/VHF/UHF All
Mode Transceiver), I found that my existing G5RV just didn't cut it. SWR was too
high so a reworking of this antenna or a new one was in order. I decided to test out
the club's Windom Antenna with the help of Rick, VE9RWS who was able to get it
to me through Brad, VE1ZX. This antenna was temporarily strung about 18' up at
the centre and both ends ran into the woods just a few feet off the ground. I was
able to check in to the Old Timers' Sunday morning net but my sig rpt was not the
best. When I looked at how many trees I would have to remove to accommodate
such a long wire antenna, my knees buckled. Besides, there were no convenient
attachment points for the centre or the ends. When living in a forest, a vertical
antenna is the only way to go.
I started doing a web search of the various verticals which would be low in wind
resistance and high in efficiency and spectral coverage. After considering about
half a dozen and making comparisons, I always came back to the Comet
CHA-250Bx which is a broadband radial-less and trapless HF antenna. Frequency
range is 3.5 MHz through to 57 MHz at 250 watts and a typical less than 1.5:1
SWR across this range. Without traps, how does it do it? The secret is in the base
tuning coil. I didn't take it apart as it is sealed.
Some time back, Brad, VE1ZX offered to help me erect my new Comet antenna
once I received it. We agreed on Thursday, October 23rd and Brad arrived in the
morning about 8:30 am. He had a 22' length of aluminum pipe on his truck as well
as all of the tools needed. Brad had a base plate made up to hold this pole in place
keeping it from kicking out. The antenna location was on a small upper story deck,
18' above the ground. We installed a stand-off board by attaching this to the
fascia board at the lower roof line. Brad had a clamp with two stainless bolts
which secured both to the existing fascia board. Holes were drilled into the
decking surface and the base plate was bolted in place. (See photos) Next, we
finished assembling the antenna which I had partially assembled and then
weather-proofed the joints as there are five sections in its nearly 24' length. The
support pole was leaning up against the deck, Brad worked from my ladder and I
worked from the deck. We got the antenna on the top of the aluminum mast and
tightened down. Once an RF choke was made and attached to the mast as well as
the RG-213U coax, Brad worked his way down the ladder installing cable ties to
fasten the coax to the mast.
The critical moment came when both of us were standing on the upper deck and
we slowly raised the mast with antenna on top in a vertical direction and finally up
over the railing. Clearing the deck railing was an exercise in concentration! Once
over, we lowered the mast end into the base plate tubing and breathed a sign of
relief.
Next, the fascia board bracket was tightened down and then a one inch hole
drilled into the soffit behind the fascia board. Brad fed nearly 200 feet of coax
up through this hole as Jim worked in the attic drawing it though. We thought we
would need two metre simplex to communicate and each had an HT on 146.55 MHz
simplex but we quickly found out we could easily hear each other through the
soffit venting. Just as well, as Jim was standing on the edges of joists in the attic!
When our house was built, I had a 2" plastic pipe run vertically through the wall
from attic to shack to carry coax. I was thinking ahead. I took the coax and fed it
down the pipe leading to the shack as I brought it up through the soffit hole. Brad
pulled it through into the shack and out the deck door and down to ground level.
Once we had this through and enough to reach the radio, the coax was cut and Brad
installed the second PL-259 connector.
Testing time so Brad got his MFJ Antenna Analyzer and screwed the coax to it.
I held my breath as I had already sunk a lot of $$$ into this antenna - it better
work.
After testing various frequencies on a number of different bands, we concluded
that not only did it work well, but it tested even better that the frequency
response SWR graph in the instructions! In many segments of certain bands, it
gave a flat 1:1 SWR. I breathed a sigh of relief for the second time!
Brad packed up his gear and left about 1:30 pm. I thanked Brad for all the
work, effort and expense he put into helping me with this project but words are
just not adequate. I need to find some way to adequately thank him for his service
above and beyond the call of duty. Our club is truly fortunate to have Brad as a
member. Thanks a heap, Brad!
After Brad left, I got into cleanup mode and worked until nearly 5 pm caulking
the fascia board, closing in the coax hole, putting away the tools and vacuuming the
floor and so on.
Since then, I have been learning the ins and outs of the FT-897D and did manage
to check in to the Old Timers' Net this past Sunday morning. I am pleased with the
new antenna as it fits my needs exactly and I don't have to start a forestry career
at this late stage in life either! :-)
Antenna Stats: 3.5 - 57 MHz TX / 2.0 - 90 MHz RX
250 Watts Max. SSB
50 Ohms
VSWR less than 1.5:1 typical
Length 23.8 feet max. (7.13 m)
Weight 7.11 lbs (3.2 Kg)
Wind Survival 67.5 mph (108 kph)
House is 250' above the Minas Basin, deck is 18' above ground, mast is 22' long
and antenna is about 24' long. Tip of antenna is 314' above the water!
(If anyone wishes to write a story about their antenna or radio related projects,
please do so and send it to me (*.doc please) along with some photos (jpeg) and
I will place it here on the website: ve1chi@rac.ca. Thanks.)
(by VE1CHI, Jim)
After purchasing a new rig this fall 2008 (Yaesu FT-897D HF/VHF/UHF All
Mode Transceiver), I found that my existing G5RV just didn't cut it. SWR was too
high so a reworking of this antenna or a new one was in order. I decided to test out
the club's Windom Antenna with the help of Rick, VE9RWS who was able to get it
to me through Brad, VE1ZX. This antenna was temporarily strung about 18' up at
the centre and both ends ran into the woods just a few feet off the ground. I was
able to check in to the Old Timers' Sunday morning net but my sig rpt was not the
best. When I looked at how many trees I would have to remove to accommodate
such a long wire antenna, my knees buckled. Besides, there were no convenient
attachment points for the centre or the ends. When living in a forest, a vertical
antenna is the only way to go.
I started doing a web search of the various verticals which would be low in wind
resistance and high in efficiency and spectral coverage. After considering about
half a dozen and making comparisons, I always came back to the Comet
CHA-250Bx which is a broadband radial-less and trapless HF antenna. Frequency
range is 3.5 MHz through to 57 MHz at 250 watts and a typical less than 1.5:1
SWR across this range. Without traps, how does it do it? The secret is in the base
tuning coil. I didn't take it apart as it is sealed.
Some time back, Brad, VE1ZX offered to help me erect my new Comet antenna
once I received it. We agreed on Thursday, October 23rd and Brad arrived in the
morning about 8:30 am. He had a 22' length of aluminum pipe on his truck as well
as all of the tools needed. Brad had a base plate made up to hold this pole in place
keeping it from kicking out. The antenna location was on a small upper story deck,
18' above the ground. We installed a stand-off board by attaching this to the
fascia board at the lower roof line. Brad had a clamp with two stainless bolts
which secured both to the existing fascia board. Holes were drilled into the
decking surface and the base plate was bolted in place. (See photos) Next, we
finished assembling the antenna which I had partially assembled and then
weather-proofed the joints as there are five sections in its nearly 24' length. The
support pole was leaning up against the deck, Brad worked from my ladder and I
worked from the deck. We got the antenna on the top of the aluminum mast and
tightened down. Once an RF choke was made and attached to the mast as well as
the RG-213U coax, Brad worked his way down the ladder installing cable ties to
fasten the coax to the mast.
The critical moment came when both of us were standing on the upper deck and
we slowly raised the mast with antenna on top in a vertical direction and finally up
over the railing. Clearing the deck railing was an exercise in concentration! Once
over, we lowered the mast end into the base plate tubing and breathed a sign of
relief.
Next, the fascia board bracket was tightened down and then a one inch hole
drilled into the soffit behind the fascia board. Brad fed nearly 200 feet of coax
up through this hole as Jim worked in the attic drawing it though. We thought we
would need two metre simplex to communicate and each had an HT on 146.55 MHz
simplex but we quickly found out we could easily hear each other through the
soffit venting. Just as well, as Jim was standing on the edges of joists in the attic!
When our house was built, I had a 2" plastic pipe run vertically through the wall
from attic to shack to carry coax. I was thinking ahead. I took the coax and fed it
down the pipe leading to the shack as I brought it up through the soffit hole. Brad
pulled it through into the shack and out the deck door and down to ground level.
Once we had this through and enough to reach the radio, the coax was cut and Brad
installed the second PL-259 connector.
Testing time so Brad got his MFJ Antenna Analyzer and screwed the coax to it.
I held my breath as I had already sunk a lot of $$$ into this antenna - it better
work.
After testing various frequencies on a number of different bands, we concluded
that not only did it work well, but it tested even better that the frequency
response SWR graph in the instructions! In many segments of certain bands, it
gave a flat 1:1 SWR. I breathed a sigh of relief for the second time!
Brad packed up his gear and left about 1:30 pm. I thanked Brad for all the
work, effort and expense he put into helping me with this project but words are
just not adequate. I need to find some way to adequately thank him for his service
above and beyond the call of duty. Our club is truly fortunate to have Brad as a
member. Thanks a heap, Brad!
After Brad left, I got into cleanup mode and worked until nearly 5 pm caulking
the fascia board, closing in the coax hole, putting away the tools and vacuuming the
floor and so on.
Since then, I have been learning the ins and outs of the FT-897D and did manage
to check in to the Old Timers' Net this past Sunday morning. I am pleased with the
new antenna as it fits my needs exactly and I don't have to start a forestry career
at this late stage in life either! :-)
Antenna Stats: 3.5 - 57 MHz TX / 2.0 - 90 MHz RX
250 Watts Max. SSB
50 Ohms
VSWR less than 1.5:1 typical
Length 23.8 feet max. (7.13 m)
Weight 7.11 lbs (3.2 Kg)
Wind Survival 67.5 mph (108 kph)
House is 250' above the Minas Basin, deck is 18' above ground, mast is 22' long
and antenna is about 24' long. Tip of antenna is 314' above the water!
(If anyone wishes to write a story about their antenna or radio related projects,
please do so and send it to me (*.doc please) along with some photos (jpeg) and
I will place it here on the website: ve1chi@rac.ca. Thanks.)
The VE1WRC web server has a high speed line provided by http://www.cumberlandcounty.ns.ca.
