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jbeeghly(at)earthlink.net
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 Posted: Tue May 22, 2007 7:33 pm Post subject: High VSWR reading on my antenna lead |
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In the process of building up the avionics for our Wag Aero Super Sport I reached that point where I was ready to power up the used King KY 97A Comm. I had fabricated about a 10 - 12 foot long antenna lead using RG-400 and BNC connectors purchased from B&C (and assembled with a RCT-2 coax crimping tool also from B&C) to connect the comm to a used Cessna antenna (came from a 172.) I plugged in the headset, turned on the radio, and all seemed well. I listened (from inside the hanger) to airport traffic. I briefly keyed the mike and heard myself on the scanner across the hanger.
Then I turned off the radio and connected a DAIWA CN 720B SWR meter in the antenna circuit. this involved undoing the BNC connector from the back of the tray (The tray itself is fitted with a bulkhead type of female BNC connector so this was no problem.) The 720 B is a cross needle meter rated up to 150 MHz and with a 5 watt range at the lower end. It has two SO-239 connectors on the back, one marked antenna and one transmitter. I had gotten converters to use BNC connectors and had purchased a radio shack premade RG-58 cable, about 6 feet long, to patch the meter to the radio. The antenna lead connected to the Antenna connector on the 720 B.
My understanding (I bought this meter on E-bay and do not yet have a manual - one is ordered) is that reading VSWR is a matter of pushing transmit and finding the VSWR line corresponding to where the two needles intersect as they measure forward and reflected watts. If this is correct, my system has a VSWR of 9 or 10. Needless to say, I did not hold the transmit button down for long.
I know that I am looking for a VSWR as close to 1 as possible, so this is not acceptable. I don't quite know what to do next. I do not see a way to calibrate the meter. My understanding is that this kind of meter is not supposed to need calibration. I do not see what I could have done wrong in constructing the antenna lead to get this kind of VSWR.
I did try another experiment. I took my JVC handheld, and put the meter between it and the whip antenna. There was barely enough power to read VSWR, but it was still in the 9 or 10 range. I then measured VSWR using the JVC feeding the antenna lead and Cessna antenna. The reading for forward power was clearly improved, but the VSWR was still at the same high level. These results make me wonder if there isn't something wrong with the meter (or my measuring technique.)
Does anyone have any suggestions for what to consider next? As you can no doubt tell, I am new to this. Thanks.
Jim Beeghly
[quote][b]
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nuckollsr(at)cox.net
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| Posted: Tue May 22, 2007 8:44 pm Post subject: High VSWR reading on my antenna lead |
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At 10:33 PM 5/22/2007 -0500, you wrote:
| Quote: | In the process of building up the avionics for our Wag Aero Super Sport I
reached that point where I was ready to power up the used King KY 97A
Comm. I had fabricated about a 10 - 12 foot long antenna lead using
RG-400 and BNC connectors purchased from B&C (and assembled with a RCT-2
coax crimping tool also from B&C) to connect the comm to a used Cessna
antenna (came from a 172.) I plugged in the headset, turned on the radio,
and all seemed well. I listened (from inside the hanger) to airport
traffic. I briefly keyed the mike and heard myself on the scanner across
the hanger.
Then I turned off the radio and connected a DAIWA CN 720B SWR meter in the
antenna circuit. this involved undoing the BNC connector from the back of
the tray (The tray itself is fitted with a bulkhead type of female BNC
connector so this was no problem.) The 720 B is a cross needle meter rated
up to 150 MHz and with a 5 watt range at the lower end. It has two SO-239
connectors on the back, one marked antenna and one transmitter. I had
gotten converters to use BNC connectors and had purchased a radio shack
premade RG-58 cable, about 6 feet long, to patch the meter to the
radio. The antenna lead connected to the Antenna connector on the 720 B.
My understanding (I bought this meter on E-bay and do not yet have a
manual - one is ordered) is that reading VSWR is a matter of pushing
transmit and finding the VSWR line corresponding to where the two needles
intersect as they measure forward and reflected watts. If this is
correct, my system has a VSWR of 9 or 10. Needless to say, I did not hold
the transmit button down for long.
I know that I am looking for a VSWR as close to 1 as possible, so this is
not acceptable. I don't quite know what to do next. I do not see a way
to calibrate the meter. My understanding is that this kind of meter is
not supposed to need calibration. I do not see what I could have done
wrong in constructing the antenna lead to get this kind of VSWR.
I did try another experiment. I took my JVC handheld, and put the meter
between it and the whip antenna. There was barely enough power to read
VSWR, but it was still in the 9 or 10 range. I then measured VSWR using
the JVC feeding the antenna lead and Cessna antenna. The reading for
forward power was clearly improved, but the VSWR was still at the same
high level. These results make me wonder if there isn't something wrong
with the meter (or my measuring technique.)
Does anyone have any suggestions for what to consider next? As you can no
doubt tell, I am new to this. Thanks.
|
First, go to Radio Shack and get the stuff to build one of these:
http://www.aeroelectric.com/Pictures/Tools/DummyLoad.jpg
Use it to replace the antenna connection on the output of
the SWR meter and see if it shows 1:1 SWR. If not, the meter
is bad. If so, the antenna (or more probably) the coax connectors
at one end or the other . . . but your duplicated experiment
on two different antennas suggests that meter is bad.
Bob . . .
----------------------------------------
( "Physics is like sex: sure, it may )
( give some practical results, but )
( that's not why we do it." )
( )
( Richard P. Feynman )
----------------------------------------
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bobf(at)feldtman.com
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| Posted: Wed May 23, 2007 3:47 am Post subject: High VSWR reading on my antenna lead |
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borrow a known good meter from a ham in the area. make sure you set the forward power to exactly full deflection, then read the reflected power. you may have the gain set way too high. If it is 9 to one the radio would have detected this on it's own and decreased the power. I suspect the meter is bad or you don't have it adjusted right. get a ham to help you. Don't spend more money - get a ham to help you
bobf
W5RF and glastar owner
ps - don't do it in the hangar - too much metal. roll it outside away from the hanger more than 30 feet or so
On 5/22/07, James Beeghly <jbeeghly(at)earthlink.net (jbeeghly(at)earthlink.net)> wrote:[quote] In the process of building up the avionics for our Wag Aero Super Sport I reached that point where I was ready to power up the used King KY 97A Comm. I had fabricated about a 10 - 12 foot long antenna lead using RG-400 and BNC connectors purchased from B&C (and assembled with a RCT-2 coax crimping tool also from B&C) to connect the comm to a used Cessna antenna (came from a 172.) I plugged in the headset, turned on the radio, and all seemed well. I listened (from inside the hanger) to airport traffic. I briefly keyed the mike and heard myself on the scanner across the hanger.
Then I turned off the radio and connected a DAIWA CN 720B SWR meter in the antenna circuit. this involved undoing the BNC connector from the back of the tray (The tray itself is fitted with a bulkhead type of female BNC connector so this was no problem.) The 720 B is a cross needle meter rated up to 150 MHz and with a 5 watt range at the lower end. It has two SO-239 connectors on the back, one marked antenna and one transmitter. I had gotten converters to use BNC connectors and had purchased a radio shack premade RG-58 cable, about 6 feet long, to patch the meter to the radio. The antenna lead connected to the Antenna connector on the 720 B.
My understanding (I bought this meter on E-bay and do not yet have a manual - one is ordered) is that reading VSWR is a matter of pushing transmit and finding the VSWR line corresponding to where the two needles intersect as they measure forward and reflected watts. If this is correct, my system has a VSWR of 9 or 10. Needless to say, I did not hold the transmit button down for long.
I know that I am looking for a VSWR as close to 1 as possible, so this is not acceptable. I don't quite know what to do next. I do not see a way to calibrate the meter. My understanding is that this kind of meter is not supposed to need calibration. I do not see what I could have done wrong in constructing the antenna lead to get this kind of VSWR.
I did try another experiment. I took my JVC handheld, and put the meter between it and the whip antenna. There was barely enough power to read VSWR, but it was still in the 9 or 10 range. I then measured VSWR using the JVC feeding the antenna lead and Cessna antenna. The reading for forward power was clearly improved, but the VSWR was still at the same high level. These results make me wonder if there isn't something wrong with the meter (or my measuring technique.)
Does anyone have any suggestions for what to consider next? As you can no doubt tell, I am new to this. Thanks.
Jim Beeghly
[quote][b] http://www.matronics.com/Navigator?AeroElectric-List http://forums.matronics.com [quote][b]
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khorton01(at)rogers.com
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| Posted: Wed May 23, 2007 4:57 am Post subject: High VSWR reading on my antenna lead |
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Will a VSWR meter designed for the ham radio band produce valid results with aviation Com frequencies?
Kevin Horton
On Wed, 23 May 2007 06:45:39 -0500
"Robert Feldtman" <bobf(at)feldtman.com> wrote:
| Quote: | borrow a known good meter from a ham in the area. make sure you set the
forward power to exactly full deflection, then read the reflected power. you
may have the gain set way too high. If it is 9 to one the radio would have
detected this on it's own and decreased the power. I suspect the meter is
bad or you don't have it adjusted right. get a ham to help you. Don't spend
more money - get a ham to help you
bobf
W5RF and glastar owner
ps - don't do it in the hangar - too much metal. roll it outside away from
the hanger more than 30 feet or so
On 5/22/07, James Beeghly <jbeeghly(at)earthlink.net> wrote:
>
> In the process of building up the avionics for our Wag Aero Super Sport I
> reached that point where I was ready to power up the used King KY 97A Comm.
> I had fabricated about a 10 - 12 foot long antenna lead using RG-400 and
> BNC connectors purchased from B&C (and assembled with a RCT-2 coax crimping
> tool also from B&C) to connect the comm to a used Cessna antenna (came from
> a 172.) I plugged in the headset, turned on the radio, and all seemed well.
> I listened (from inside the hanger) to airport traffic. I briefly keyed
> the mike and heard myself on the scanner across the hanger.
>
> Then I turned off the radio and connected a DAIWA CN 720B SWR meter in the
> antenna circuit. this involved undoing the BNC connector from the back of
> the tray (The tray itself is fitted with a bulkhead type of female BNC
> connector so this was no problem.) The 720 B is a cross needle meter rated
> up to 150 MHz and with a 5 watt range at the lower end. It has two SO-239
> connectors on the back, one marked antenna and one transmitter. I had
> gotten converters to use BNC connectors and had purchased a radio shack
> premade RG-58 cable, about 6 feet long, to patch the meter to the radio.
> The antenna lead connected to the Antenna connector on the 720 B.
>
> My understanding (I bought this meter on E-bay and do not yet have a
> manual - one is ordered) is that reading VSWR is a matter of pushing
> transmit and finding the VSWR line corresponding to where the two needles
> intersect as they measure forward and reflected watts. If this is correct,
> my system has a VSWR of 9 or 10. Needless to say, I did not hold the
> transmit button down for long.
>
> I know that I am looking for a VSWR as close to 1 as possible, so this is
> not acceptable. I don't quite know what to do next. I do not see a way to
> calibrate the meter. My understanding is that this kind of meter is not
> supposed to need calibration. I do not see what I could have done wrong in
> constructing the antenna lead to get this kind of VSWR.
>
> I did try another experiment. I took my JVC handheld, and put the meter
> between it and the whip antenna. There was barely enough power to read
> VSWR, but it was still in the 9 or 10 range. I then measured VSWR using the
> JVC feeding the antenna lead and Cessna antenna. The reading for forward
> power was clearly improved, but the VSWR was still at the same high level.
> These results make me wonder if there isn't something wrong with the meter
> (or my measuring technique.)
>
> Does anyone have any suggestions for what to consider next? As you can no
> doubt tell, I am new to this. Thanks.
>
> Jim Beeghly
>
> *
>
>
> *
>
>
|
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aadamson(at)highrf.com
Guest
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| Posted: Wed May 23, 2007 5:16 am Post subject: High VSWR reading on my antenna lead |
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Kevin, the Ham Radio *band*, is a very large frequency spectrum  ....
However, something designed for VHF and in Ham Speak, 2 meters, will work
just fine.
As a side note. Most SWR meters are DC-Daylite and should work just fine.
There are units like a "bird wattmeter" that have specific "slugs" for
specific power settings and frequencies, but if you have an SWR meter that
simply measures forward and reverse power, you should be fine.
Alan
--
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luckymacy(at)comcast.net
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| Posted: Wed May 23, 2007 5:18 am Post subject: High VSWR reading on my antenna lead |
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Worked for us. Exact numbers are going to be incorrect but the relative deflection is still valid. ie, it will still read toward the "bad" end if there's a lot of reflection and read more towards the "good" end of the scale after you fix a problem but won't tell you just how good your SWR really is if you are anal about your exact number...
[quote]-------------- Original message --------------
From: Kevin Horton <khorton01(at)rogers.com>
| Quote: | --> AeroElectric-List message posted by: Kevin Horton
Will a VSWR meter designed for the ham radio band produce valid results with
aviation Com frequencies?
Kevin Horton
On Wed, 23 May 2007 06:45:39 -0500
"Robert Feldtman" wrote:
> borrow a known good meter from a ham in the area. make sure you set the
> forward power to exactly full deflection, then read the reflected power. you
> may have the gain set way too high. If it is 9 to one the radio would have
> detected this on it's own and decreased the power. I suspect the meter is
> bad or you don't have it adjusted right. get a ham to help you. Don 't spe nd
> more money - get a ham to help you
>
> bobf
> W5RF and glastar owner
>
> ps - don't do it in the hangar - too much metal. roll it outside away from
> the hanger more than 30 feet or so
>
> On 5/22/07, James Beeghly wrote:
> >
> > In the process of building up the avionics for our Wag Aero Super Sport I
> > reached that point where I was ready to power up the used King KY 97A Comm.
> > I had fabricated about a 10 - 12 foot long antenna lead using RG-400 and
> > BNC connectors purchased from B&C (and assembled with a RCT-2 coax crimping
> > tool also from B&C) to connect the comm to a used Cessna antenna (came from
> > a 172.) I plugged in the headset, turned on the radio, and all seemed well.
> > I listened (from ins ide th e hanger) to airport traffic. I briefly keyed
> > the mike and heard myself on the scanner across the hanger.
> >
> > Then I turned off the radio and connected a DAIWA CN 720B SWR meter in the
> > antenna circuit. this involved undoing the BNC connector from the back of
> > the tray (The tray itself is fitted with a bulkhead type of female BNC
> > connector so this was no problem.) The 720 B is a cross needle meter rated
> > up to 150 MHz and with a 5 watt range at the lower end. It has two SO-239
> > connectors on the back, one marked antenna and one transmitter. I had
> > gotten converters to use BNC connectors and had purchased a radio shack
> > premade RG-58 cable, about 6 feet long, to patch the meter to the radio.
> > The antenna lead connected to the Antenna connector on the 720 B.
> >
&g t; > ; > My understanding (I bought this meter on E-bay and do not yet have a
|
[quote] > > manual - one is ordered) is that reading VSWR is a matter of pushing
> > transmit and finding the VSWR line corresponding to where the two needles
> > intersect as they measure forward and reflected watts. If this is correct,
> > my system has a VSWR of 9 or 10. Needless to say, I did not hold the
> > transmit button down for long.
> >
> > I know that I am looking for a VSWR as close to 1 as possible, so this is
> > not acceptable. I don't quite know what to do next. I do not see a way to
> > calibrate the meter. My understanding is that this kind of meter is not
> > supposed to need calibration. I do not see what I could have done wrong in
> > constructing the antenna lead to get this kind of VSWR.
> >
> > ; I di ====== [quote][b]
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nuckollsr(at)cox.net
Guest
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| Posted: Wed May 23, 2007 6:10 am Post subject: High VSWR reading on my antenna lead |
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At 08:55 AM 5/23/2007 -0400, you wrote:
| Quote: |
Will a VSWR meter designed for the ham radio band produce valid results
with aviation Com frequencies?
Kevin Horton
|
Some do, some don't. I recall a lot of wasted $time$ many moons
ago when building a new colinear array for use on our repeater
installation at the 1200 foot platform of KTVH in Hutchinson
KS. See:
http://www.aeroelectric.com/Pictures/Misc/KTVH.gif
Glen Brasch and I worked for several days bending aluminum drilling
brackets, bolting elements and cutting coax for the feedline transformers.
Each step of the way was checked with a reflectometer style SWR
meter . . .
http://www.aeroelectric.com/Pictures/Tools/SWR/SWR_Sometimes_4.jpg
http://en.wikipedia.org/wiki/SWR_meter
. . . and we thought we were doing really good work as each step
of the process produced an excellent SWR reading. Imagine our
dismay when the assembled array tested with anther meter
( A Bird Model 43)
http://www.aeroelectric.com/Pictures/Tools/Bird_43.jpg
called it less than the best we should expect. Bottom line
is that there are easy mistakes to be made in the design
and assembly of many test instruments with those crafted
for use at high RF frequencies being strong candidates
for obtuse behavior. Just 'cause the label says so don't
make it so.
I dumped my $low$ reflectometer in the trash and bought
a Bird. If it's important to know what the numbers are,
its a safe bet to go with the repeatable experiments like
Tektronix, HP, Bird, Fluke, etc. This doesn't mean you
can't find good value in other brands . . . but if there
is doubt and the expenditure of $time$ is a critical part
of your efforts, the repeatable experiments are often the
most economical choices in spite of their higher prices
off-the-shelf.
Here's a montage of examples for repeatable experiments
-AND- experiments to be tested for repeatability in
the world of RF instrumentation . . .
http://www.aeroelectric.com/Pictures/Tools/SWR/
Bob . . .
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matronics(at)rtist.nl
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| Posted: Wed May 23, 2007 6:45 am Post subject: High VSWR reading on my antenna lead |
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That depends on the frequency range it's designed for. If it's for 0-30MHz
(most el-cheapo VSWR's and CB stuff) then there's a big chance that it won't
work. If you get one designed for 2m (144-148MHz) then you should have no
problems gettng an accurate VSWR reading. Power readings will most likely be
unreliable though, except if you use something professional like the Bird
model that Bob mentioned.
Rob
---
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