I put up a Hy-Gain AV640 a few years back for a backup and as the HF
antenna for my shop. The antenna was on top of a 32 foot aluminum
tower at the West end of the shop. The match on all the bands was
near perfect, or at least it was slightly better than I'd expected
with 1.1:1 at resonance. Bandwidth on each band was more than adequate
and much wider than any trap, multi band vertical id used in the he
past.

I had mainly been listening to W1AW code practice on 40 but did make a
few contacts on 40 and 6-meters.

I recently replaced the old Henry 2K4 with a Tokyo Hy-Power HL-1.5KFX
solid state amp which happens to cover 6-meters as well. With the
little Yaesu FT-897D it also gives auto band switching and will
remember which of two antennas connected to the amp you were using for
each band.

At-any-rate a couple weeks back 6-meters opened up and a spent a few
hours making contacts from the East, West, and Gulf coasts. (no DX
sigh) When I went to operate on 40 the amp was kicking out due to
high SWR and started doing the same on six. Both 40 and 15 were
resonant about 1 MHz below the bottom end of the bands. Minimum SWR
at resonance had gone from 1.1:1 to between 1.6 and 2:1.

We (several other hams and myself) let the Tower/antenna down. It had
one broken insulator which would not have caused the problem, but I
built a new one out of Lexan which is a lot more sturdy than the old
*stuff*. THEN I got to the matching network. That thing was packed
solid with Wasp nests and crispy crittered Wasps along with a pile of
dead Wasps and Wasp *goo* on the coax chassis connector in the bottom
of the box. That goo made it through the chassis connector and badly
corroded about 3' of 9913 which is being replaced with LMR-600. NOTE
the original drain holes are just a tad too large and just right for
Wasp entry for their new home. So if you use one of these antennas,
plugging the drain holes and drilling a series of smaller ones might
be in order. OTOH Hy-Gain does state you should take the antenna down
and clean out the matching network every year or so. (Wasps can build
a *big* nest in a few days)

Apparently there is some truth to the RF exposure hazard, or there was
for the wasps in close proximity to high power on 6-meters. None of
them complained when I cleaned the nests out. BTW I had to completely
remove the tuning unit from the box to be able to get the nests and
*glue* they make off the torroids.

Having the antenna down, I took the opportunity to give it an
overhaul. I cleaned all the connections which looked pretty bad (lots
of white powder), used a tiny bit of nolox (similar to Pentrox) on
each coil and jumper connection after cleaning, which was then sealed
with liquid electrical tape. The jumper from the tuning unit to the
counterpoise had to be replaced. After 5 years the fiberglass is
showing some deterioration due to UV exposure. Be careful about
coating these coils while trying to protect the fiberglass. The coils
are right under the top hats and clear Krylon or liquid electrical
tape may add a bit of capacitance in parallel to the coils and with
them being right under the capacitive hats a little capacity can go a
long way resulting in the resonant frequency going down substantially
for that specific band.

I put the antenna back up on a 14foot pole anchored to the NW guy
anchor for my big tower. On checking, the SWR for 40, 20, and 6-meters
is just where it's supposed to be as is the resonant frequency and the
SWR at resonance is showing 1.0:1. However two bands, 15 and 10 are
showing 1.6:1 and 1.9:1 at resonance. (resonance is back where it
belongs) All solder joints in the matching network have been
resoldered and checked. Wires and cores were also checked for
insulation and burn marks. Tech support told me not to worry about
running 750 watts output PEP even though the ratings show 300 watts
for 6-meters as long as there were no signs of overheating or arcing.
The network should handle that with ease.

So the problem, or question is, why the change in minimum SWR on 15
and 10 meters? What may I have missed? The analyzer is no help for
this.

I gotta get that antenna system on the big tower repaired and the
rotator reinstalled for the DX season. Then maybe I can set up an
interconnect so I can use those antennas from the shop as well while
keeping the AV640 as a backup. I rebuilt the PST-61 (seals failed and
water took out the main bearings) and it's ready to go back in.
Unfortunately nature gave me a bit of a set back last April and I had
to learn to walk again. However I'm about ready to tackle the tower
work real soon. I've been working at 30 to 40 feet, but that doesn't
take near the energy of climbing to 100', working for a couple
hours, and still have the energy/strength to climb back down.

BTW I had been working on top of the guy anchor post Thursday
afternoon for about a half an hour when I noticed a couple of bees
flying around. They weren't bothering me, but when I looked down into
that 5" pipe I saw a very large Wasp nest with Wasps crawling all over
it. At that point I hosed it down with Wasp and Hornet killer. I
decided I had pushed my luck far enough.

Roger (K8RI)

On Thursday, September 6, 2007 at 3:46:50 AM UTC-4, Roger (K8RI) wrote:
I put up a Hy-Gain AV640 a few years back for a backup and as the HF
antenna for my shop. The antenna was on top of a 32 foot aluminum
tower at the West end of the shop. The match on all the bands was
near perfect, or at least it was slightly better than I'd expected
with 1.1:1 at resonance. Bandwidth on each band was more than adequate
and much wider than any trap, multi band vertical id used in the he
past.

I had mainly been listening to W1AW code practice on 40 but did make a
few contacts on 40 and 6-meters.

I recently replaced the old Henry 2K4 with a Tokyo Hy-Power HL-1.5KFX
solid state amp which happens to cover 6-meters as well. With the
little Yaesu FT-897D it also gives auto band switching and will
remember which of two antennas connected to the amp you were using for
each band.

At-any-rate a couple weeks back 6-meters opened up and a spent a few
hours making contacts from the East, West, and Gulf coasts. (no DX
sigh) When I went to operate on 40 the amp was kicking out due to
high SWR and started doing the same on six. Both 40 and 15 were
resonant about 1 MHz below the bottom end of the bands. Minimum SWR
at resonance had gone from 1.1:1 to between 1.6 and 2:1.

We (several other hams and myself) let the Tower/antenna down. It had
one broken insulator which would not have caused the problem, but I
built a new one out of Lexan which is a lot more sturdy than the old
*stuff*. THEN I got to the matching network. That thing was packed
solid with Wasp nests and crispy crittered Wasps along with a pile of
dead Wasps and Wasp *goo* on the coax chassis connector in the bottom
of the box. That goo made it through the chassis connector and badly
corroded about 3' of 9913 which is being replaced with LMR-600. NOTE
the original drain holes are just a tad too large and just right for
Wasp entry for their new home. So if you use one of these antennas,
plugging the drain holes and drilling a series of smaller ones might
be in order. OTOH Hy-Gain does state you should take the antenna down
and clean out the matching network every year or so. (Wasps can build
a *big* nest in a few days)

Apparently there is some truth to the RF exposure hazard, or there was
for the wasps in close proximity to high power on 6-meters. None of
them complained when I cleaned the nests out. BTW I had to completely
remove the tuning unit from the box to be able to get the nests and
*glue* they make off the torroids.

Having the antenna down, I took the opportunity to give it an
overhaul. I cleaned all the connections which looked pretty bad (lots
of white powder), used a tiny bit of nolox (similar to Pentrox) on
each coil and jumper connection after cleaning, which was then sealed
with liquid electrical tape. The jumper from the tuning unit to the
counterpoise had to be replaced. After 5 years the fiberglass is
showing some deterioration due to UV exposure. Be careful about
coating these coils while trying to protect the fiberglass. The coils
are right under the top hats and clear Krylon or liquid electrical
tape may add a bit of capacitance in parallel to the coils and with
them being right under the capacitive hats a little capacity can go a
long way resulting in the resonant frequency going down substantially
for that specific band.

I put the antenna back up on a 14foot pole anchored to the NW guy
anchor for my big tower. On checking, the SWR for 40, 20, and 6-meters
is just where it's supposed to be as is the resonant frequency and the
SWR at resonance is showing 1.0:1. However two bands, 15 and 10 are
showing 1.6:1 and 1.9:1 at resonance. (resonance is back where it
belongs) All solder joints in the matching network have been
resoldered and checked. Wires and cores were also checked for
insulation and burn marks. Tech support told me not to worry about
running 750 watts output PEP even though the ratings show 300 watts
for 6-meters as long as there were no signs of overheating or arcing.
The network should handle that with ease.

So the problem, or question is, why the change in minimum SWR on 15
and 10 meters? What may I have missed? The analyzer is no help for
this.

I gotta get that antenna system on the big tower repaired and the
rotator reinstalled for the DX season. Then maybe I can set up an
interconnect so I can use those antennas from the shop as well while
keeping the AV640 as a backup. I rebuilt the PST-61 (seals failed and
water took out the main bearings) and it's ready to go back in.
Unfortunately nature gave me a bit of a set back last April and I had
to learn to walk again. However I'm about ready to tackle the tower
work real soon. I've been working at 30 to 40 feet, but that doesn't
take near the energy of climbing to 100', working for a couple
hours, and still have the energy/strength to climb back down.

BTW I had been working on top of the guy anchor post Thursday
afternoon for about a half an hour when I noticed a couple of bees
flying around. They weren't bothering me, but when I looked down into
that 5" pipe I saw a very large Wasp nest with Wasps crawling all over
it. At that point I hosed it down with Wasp and Hornet killer. I
decided I had pushed my luck far enough.

Roger (K8RI)

Hi Roger,
I just started having very high swr on my av-640
it was jumping around in high winds. So down comes
the antenna when the winds stop. Go figure, I just
received my flex radio...

To your answer about 10m and 15m the 5ft sections of
rod in my antenna are joined together by 4 inch sections of threaded rod
when screwed together there was a gap of 1 to 2 inches between the
sections. I seems either the threaded holes inside the ends of the 5ft
sections were too short or the 4 inch threaded rods were too long. Either way,
this made the overall length too long. Which changed the swr sweet spot
which for me is the center of the voice band. So none of the av-640
settings worked for me without an antenna tuner.

I have a table I created to measure the dimensions of each so I could
compare to the stock dimensions. What was your dimensional measurement for
the top part of the antenna to get swr lowest at 7.250 (40m). I had a real
hard time to tune this as when you crank down the antenna parallel with the ground you can't get it right regardless of what you do.
I do have an MFJ259-C antenna analyzer. I will probably have to
take apart the black box and go thru it......

Art

On Sunday, January 5, 2020 at 5:28:53 PM UTC-5, wrote:
On Thursday, September 6, 2007 at 3:46:50 AM UTC-4, Roger (K8RI) wrote:
I put up a Hy-Gain AV640 a few years back for a backup and as the HF
antenna for my shop. The antenna was on top of a 32 foot aluminum
tower at the West end of the shop. The match on all the bands was
near perfect, or at least it was slightly better than I'd expected
with 1.1:1 at resonance. Bandwidth on each band was more than adequate
and much wider than any trap, multi band vertical id used in the he
past.

I had mainly been listening to W1AW code practice on 40 but did make a
few contacts on 40 and 6-meters.

I recently replaced the old Henry 2K4 with a Tokyo Hy-Power HL-1.5KFX
solid state amp which happens to cover 6-meters as well. With the
little Yaesu FT-897D it also gives auto band switching and will
remember which of two antennas connected to the amp you were using for
each band.

At-any-rate a couple weeks back 6-meters opened up and a spent a few
hours making contacts from the East, West, and Gulf coasts. (no DX
sigh) When I went to operate on 40 the amp was kicking out due to
high SWR and started doing the same on six. Both 40 and 15 were
resonant about 1 MHz below the bottom end of the bands. Minimum SWR
at resonance had gone from 1.1:1 to between 1.6 and 2:1.

We (several other hams and myself) let the Tower/antenna down. It had
one broken insulator which would not have caused the problem, but I
built a new one out of Lexan which is a lot more sturdy than the old
*stuff*. THEN I got to the matching network. That thing was packed
solid with Wasp nests and crispy crittered Wasps along with a pile of
dead Wasps and Wasp *goo* on the coax chassis connector in the bottom
of the box. That goo made it through the chassis connector and badly
corroded about 3' of 9913 which is being replaced with LMR-600. NOTE
the original drain holes are just a tad too large and just right for
Wasp entry for their new home. So if you use one of these antennas,
plugging the drain holes and drilling a series of smaller ones might
be in order. OTOH Hy-Gain does state you should take the antenna down
and clean out the matching network every year or so. (Wasps can build
a *big* nest in a few days)

Apparently there is some truth to the RF exposure hazard, or there was
for the wasps in close proximity to high power on 6-meters. None of
them complained when I cleaned the nests out. BTW I had to completely
remove the tuning unit from the box to be able to get the nests and
*glue* they make off the torroids.

Having the antenna down, I took the opportunity to give it an
overhaul. I cleaned all the connections which looked pretty bad (lots
of white powder), used a tiny bit of nolox (similar to Pentrox) on
each coil and jumper connection after cleaning, which was then sealed
with liquid electrical tape. The jumper from the tuning unit to the
counterpoise had to be replaced. After 5 years the fiberglass is
showing some deterioration due to UV exposure. Be careful about
coating these coils while trying to protect the fiberglass. The coils
are right under the top hats and clear Krylon or liquid electrical
tape may add a bit of capacitance in parallel to the coils and with
them being right under the capacitive hats a little capacity can go a
long way resulting in the resonant frequency going down substantially
for that specific band.

I put the antenna back up on a 14foot pole anchored to the NW guy
anchor for my big tower. On checking, the SWR for 40, 20, and 6-meters
is just where it's supposed to be as is the resonant frequency and the
SWR at resonance is showing 1.0:1. However two bands, 15 and 10 are
showing 1.6:1 and 1.9:1 at resonance. (resonance is back where it
belongs) All solder joints in the matching network have been
resoldered and checked. Wires and cores were also checked for
insulation and burn marks. Tech support told me not to worry about
running 750 watts output PEP even though the ratings show 300 watts
for 6-meters as long as there were no signs of overheating or arcing.
The network should handle that with ease.

So the problem, or question is, why the change in minimum SWR on 15
and 10 meters? What may I have missed? The analyzer is no help for
this.

I gotta get that antenna system on the big tower repaired and the
rotator reinstalled for the DX season. Then maybe I can set up an
interconnect so I can use those antennas from the shop as well while
keeping the AV640 as a backup. I rebuilt the PST-61 (seals failed and
water took out the main bearings) and it's ready to go back in.
Unfortunately nature gave me a bit of a set back last April and I had
to learn to walk again. However I'm about ready to tackle the tower
work real soon. I've been working at 30 to 40 feet, but that doesn't
take near the energy of climbing to 100', working for a couple
hours, and still have the energy/strength to climb back down.

BTW I had been working on top of the guy anchor post Thursday
afternoon for about a half an hour when I noticed a couple of bees
flying around. They weren't bothering me, but when I looked down into
that 5" pipe I saw a very large Wasp nest with Wasps crawling all over
it. At that point I hosed it down with Wasp and Hornet killer. I
decided I had pushed my luck far enough.

Roger (K8RI)

Hi Roger,
I just started having very high swr on my av-640
it was jumping around in high winds. So down comes
the antenna when the winds stop. Go figure, I just
received my flex radio...

To your answer about 10m and 15m the 5ft sections of
rod in my antenna are joined together by 4 inch sections of threaded rod
when screwed together there was a gap of 1 to 2 inches between the
sections. I seems either the threaded holes inside the ends of the 5ft
sections were too short or the 4 inch threaded rods were too long. Either way,
this made the overall length too long. Which changed the swr sweet spot
which for me is the center of the voice band. So none of the av-640
settings worked for me without an antenna tuner.

I have a table I created to measure the dimensions of each so I could
compare to the stock dimensions. What was your dimensional measurement for
the top part of the antenna to get swr lowest at 7.250 (40m). I had a real
hard time to tune this as when you crank down the antenna parallel with the ground you can't get it right regardless of what you do.
I do have an MFJ259-C antenna analyzer. I will probably have to
take apart the black box and go thru it......

Art
KB1YAP Cape Cod