Today's Message Index:
----------------------
1. 11:38 AM - Re: Need Comm Troubleshooting Advice (Perry, Phil)
2. 07:04 PM - Re: Need Comm Troubleshooting Advice (Roger Roy)
3. 10:42 PM - Re: Need Comm Troubleshooting Advice (John Rippengal)
Message 1
INDEX | Back to Main INDEX |
NEXT | Skip to NEXT Message |
LIST | Reply to LIST Regarding this Message |
SENDER | Reply to SENDER Regarding this Message |
|
Subject: | Need Comm Troubleshooting Advice |
I agree with John.
The bird meters are great but they're just a company who built the
watt/swr meters. They've been around for years and are not manufactured
any more. and are more of a novelty for hard-core radio operators to
own.
There are certainly many modern meters out there that are less expensive
and more available. The $20 radio shack model is fine.
Here's some a few tips that you can squirrel away for the next time you
need to do some tuning.
First, make sure the antenna is properly grounded to the aircraft.
Several people will ground the antenna to a painted surface, this is a
bad idea! The paint/primer acts as an insulator and the antenna won't
be able to balance the ground plane (aircraft) with the transmitting
element (antenna). If you don't have a good ground, you will pull your
hair out trying to tune the antenna and it won't work very well anyway.
Checking grounding is always a great place to start.
Next, you'll need to tune your antenna to the appropriate length.
The frequency range determines the length of the antenna. The lower the
frequency; the longer the antenna. The higher the frequency; the
shorter the antenna. This is because low frequencies have longer wave
lengths and higher frequencies have shorter wave lengths. Since we're
dealing with frequencies in the VHF band (108Mhz - 137Mhz), we're
dealing with fairly short antenna lengths.
Keep in mind that an antenna is tuned EXACTLY for only one frequency.
As you deviate (up or down) from that frequency, the antenna becomes out
of tune. The further your deviation, the less in-tune the antenna will
be.
So you will want to tune for a frequency that is in the middle of your
transmit range. Since 108Mhz - 112Mhz are receive-only NAV frequencies,
we aren't too concerned in tuning for those frequencies. Since 112Mhz -
136Mhz is the range of communication frequencies that we transmit on,
you want to tune for those. So pick a frequency in the middle and make
that the frequency you tune for. In this case, 124Mhz is exactly in the
middle of 108Mhz and 136Mhz. If you tune for 124Mhz, the antenna will
be a perfect match at 124Mhz and only slightly off at the extreme edges
of your transmitting frequency range 112Mhz and 136Mhz.
Let's stop right here for a minute and talk about Standing Wave Ratios
or SWR.
When a transmitter is keyed, a signal is obviously transmitted down the
coax and ultimately destined for the antenna to broadcast. In a perfect
world (or a perfectly tuned antenna) all of the signal power from the
transmitter is radiated by the antenna. So if you have a transmitter
that is radiating 25watts of signal power, all 25 watts exit the antenna
and is radiated out in space for others to hear.
But what happens if the antenna isn't tuned perfectly? Actually the
signal will traverse the coax and reach the antenna. But since the
antenna isn't the appropriate length only a portion of the wave (signal)
will be radiated. The portion that isn't radiated is reflected back
down the coax and toward the transmitter. (YIKES!) Transmitters are
made to transmit 25 watt signals, not have them blasted back down the
coax like a fire hose.
The ratio of signal that is radiated by the transmitter vs the amount
reflected by the antenna is referred to as the Standing Wave Ratio
(SWR). In the perfect situation your standing wave ratio should be 1 to
1 (presented as 1:1). This means that all of your power is being
radiated and there is no reflective wave coming back to the transmitter.
So it's important to tune for the best SWR because: 1) You want as much
of your signal to leave the antenna and be radiated for the rest of the
world to receive and 2) Excessive reflected waves WILL RUIN your
transmitter.
So lets tune our antenna. Install it like the manufacture suggests and
put a SWR/Watt meter inline with the coax. (The closer to the
transmitter, the better)
If you have a low-power option on your radio, select it. The least
amount of power you can use, the better. This will keep the reflected
signals to a minimum, while the antenna still isn't correctly tuned.
Not to mention you'll be less likely to interrupt a frequency that's in
use.
Dial up 124Mhz and make sure the frequency isn't in use! If it is, just
change to another unused frequency nearby.
Now it's time to check the SWR. Key the transmitter and check your
reading on the meter. (You'll need to follow the directions that came
with your meter on how to set it up. I can't go through the setup
procedure for your meter, but I promise. It's not complicated!)
Measure your SWR. If you see 1:1, you're lucky! More than likely, you
won't. You might see something like 1.7:1 or 2:1 or worse.
So how do you figure out if you have to lengthen or shorten your
antenna? It's pretty simple, trial and error.
Most antennas have a set screw that you can loose and adjust then
antenna length. First try lengthening the antenna by 1/4 inch and
re-checking your SWR. Did it improve or did it get worse? If it got
worse, try the other direction and shorten the antenna by 1/4 inch. If
it got better, try lengthening it a hair more.
It's a good idea to keep track of each adjustment on a piece of paper,
so you can get an idea of how each change is affecting your SWR. This
will help you zero in on that perfect length. As you get closer and
closer to 1:1, you're adjustments need to be refined with smaller
increments.
Don't be surprised is you can't get exactly 1:1. The transmitted waves
can be reflected back toward the antenna by metal (such as your
empennage). So when you tune your antenna, get it away from metal
buildings or other structures and tune for the best available SWR at
124Mhz. You want the signal to be as unaffected as possible.
If you can get it down to 1.1:1 or 1.2:1, you're doing great! I
wouldn't be happy with anything over 1.5:1. 1.5 is my personal minimum
and it's easy to obtain.
Once you think you've tuned your antenna for 124 Mhz, you need to check
the extreme edges of your transmit range.
Dial down to 112 Mhz. Once again, make sure you won't be interrupting
anyone. Check your SWR.
It will be higher than it was at 124 Mhz, because at 112Mhz the antenna
is slightly out of tune. But if your inside 1.5:1, you're good. I'd be
okay with 1.7:1 on the extreme edges.
Next dial up 136Mhz and give it a shot. Once again, make sure no one is
using the frequency. I'm okay with 1.7ish:1 up there too.
Antenna problems really aren't that complex or difficult to tune. A
little practice and you'll have it in no time.
A couple of other things.
1) Make sure you use the correct coax. Usually 50 Ohm and don't buy the
cheap stuff!! Radio shack and other retailers have cheap coax. I am a
fan of Belden RG58-A/U coax. It has relatively low loss at the cable
lengths required for an airplane, the center conductor is braided
(important for high vibration installations), it has a very good braided
external conductor (Most cheap cables will skimp here), and it has a
solid inner-core insulator. Nearly any Amateur Radio (Ham) store will
carry Belden Cable. If you can't find it, I know aesham.com carries it.
The coax is the only thing between your transmitter and your antenna,
make sure you use good cable! It's worth a couple of extra dollars.
2) If you suspect a cable issue or short in the cable, disconnect the
cable from both the transmitter and the antenna. Use a continuity meter
and check to make sure you have continuity through the center conductor.
Same thing for the external braided conductor, check it.
If you've got continuity all the way through, you've eliminated the
possibility of a broken wire.
Next check and see if you have continuity from the center conductor to
the external conductor. If you do, there's a problem. Either your
cable has a short or you've got a connector that isn't soldered on
properly. Check the connectors first be re-soldering them. If that
doesn't fix it, you need a new cable.
Finally, if you're still having problems, check your connectors. Make
sure the solder joints are good. Your continuity can be fine, but if
you've got a cold solder joint, that can cause problems.
Please don't use the cheap retail connectors, they're junk. Get good
quality connectors. If you can find silver connectors, they are the
best and are the easiest for solder to stick to. I use the ones made by
Amphenol. If you're gonna get the good coax, make sure you get the good
connectors too! Most places that sell Belden also sells Amphenol
connectors. I know aesham.com has them too, but it's been several years
since I've had to place and order with them. I'm sure they still carry
both brands.
Anyway, that's all I can think of. Hopefully you'll tuck this stuff
away somewhere and use it one day. Otherwise,the delete button looks
like a red "X" at the top of the screen. :)
Take care,
Phil
________________________________
From: John Rippengal [mailto:j.rippengal@cytanet.com.cy]
Sent: Tuesday, July 03, 2007 2:00 PM
Subject: Re: Avionics-List: Need Comm Troubleshooting Advice
Glad it seems to be ok now Roger. An aircraft standing around for quite
a time while a new avionics pack is being fitted is a good clue to there
being a flat battery. However the other advice given to you to check
with a VSWR meter is a good one. The Bird Thru' Line meter is a sort of
Rolls Royce professional type and you really don't need that for a good
check on your antenna/coax/connector setup. Try Radio Shack or similar
for a cheap VSWR meter that covers the 2 metre amateur band. Should only
cost about $20 or less and every home installer of avionics should have
one. It will give you confidence in the antenna installation together
with the feeders and connectors.
John
From: Roger Roy <mailto:Savannah174@msn.com>
Hi John,
How's the avionics guru? I did as you suggested and put my
battery charger on the battery and all seem to workload and clear. I was
unable to had another person TX with the portable I will check this out
tomorrow, again thank you, Cheers
RJ
From: John Rippengal <mailto:j.rippengal@cytanet.com.cy>
Roger,
What are the battery volts when you switch the equipment
on?? The fault is common to both comms so suspect something common like
the battery. You should check the equipment with the battery on charge
and a battery voltage of about 14v WITH the equipment switched on.
John
Message 2
INDEX | Back to Main INDEX |
PREVIOUS | Skip to PREVIOUS Message |
NEXT | Skip to NEXT Message |
LIST | Reply to LIST Regarding this Message |
SENDER | Reply to SENDER Regarding this Message |
|
Subject: | Re: Need Comm Troubleshooting Advice |
Hi Phil,
Thanks for the step by step use of the SWR meter. I would like to check
my VHF antenna and the RG-400 cable installed in my aircraft but was
wondering how I would accomplish this task, I at least have a guide,
Cheers
Regards,
RJ Roy
----- Original Message -----
From: Perry, Phil<mailto:Phil.Perry@netapp.com>
To: avionics-list@matronics.com<mailto:avionics-list@matronics.com>
Sent: Tuesday, July 10, 2007 2:34 PM
Subject: RE: Avionics-List: Need Comm Troubleshooting Advice
I agree with John.
The bird meters are great but they're just a company who built the
watt/swr meters. They've been around for years and are not manufactured
any more. and are more of a novelty for hard-core radio operators to
own.
There are certainly many modern meters out there that are less
expensive and more available. The $20 radio shack model is fine.
Here's some a few tips that you can squirrel away for the next time
you need to do some tuning.
First, make sure the antenna is properly grounded to the aircraft.
Several people will ground the antenna to a painted surface, this is a
bad idea! The paint/primer acts as an insulator and the antenna won't
be able to balance the ground plane (aircraft) with the transmitting
element (antenna). If you don't have a good ground, you will pull your
hair out trying to tune the antenna and it won't work very well anyway.
Checking grounding is always a great place to start.
Next, you'll need to tune your antenna to the appropriate length.
The frequency range determines the length of the antenna. The lower
the frequency; the longer the antenna. The higher the frequency; the
shorter the antenna. This is because low frequencies have longer wave
lengths and higher frequencies have shorter wave lengths. Since we're
dealing with frequencies in the VHF band (108Mhz - 137Mhz), we're
dealing with fairly short antenna lengths.
Keep in mind that an antenna is tuned EXACTLY for only one frequency.
As you deviate (up or down) from that frequency, the antenna becomes out
of tune. The further your deviation, the less in-tune the antenna will
be.
So you will want to tune for a frequency that is in the middle of your
transmit range. Since 108Mhz - 112Mhz are receive-only NAV frequencies,
we aren't too concerned in tuning for those frequencies. Since 112Mhz -
136Mhz is the range of communication frequencies that we transmit on,
you want to tune for those. So pick a frequency in the middle and make
that the frequency you tune for. In this case, 124Mhz is exactly in the
middle of 108Mhz and 136Mhz. If you tune for 124Mhz, the antenna will
be a perfect match at 124Mhz and only slightly off at the extreme edges
of your transmitting frequency range 112Mhz and 136Mhz.
Let's stop right here for a minute and talk about Standing Wave Ratios
or SWR.
When a transmitter is keyed, a signal is obviously transmitted down
the coax and ultimately destined for the antenna to broadcast. In a
perfect world (or a perfectly tuned antenna) all of the signal power
from the transmitter is radiated by the antenna. So if you have a
transmitter that is radiating 25watts of signal power, all 25 watts exit
the antenna and is radiated out in space for others to hear.
But what happens if the antenna isn't tuned perfectly? Actually the
signal will traverse the coax and reach the antenna. But since the
antenna isn't the appropriate length only a portion of the wave (signal)
will be radiated. The portion that isn't radiated is reflected back
down the coax and toward the transmitter. (YIKES!) Transmitters are
made to transmit 25 watt signals, not have them blasted back down the
coax like a fire hose.
The ratio of signal that is radiated by the transmitter vs the amount
reflected by the antenna is referred to as the Standing Wave Ratio
(SWR). In the perfect situation your standing wave ratio should be 1 to
1 (presented as 1:1). This means that all of your power is being
radiated and there is no reflective wave coming back to the transmitter.
So it's important to tune for the best SWR because: 1) You want as
much of your signal to leave the antenna and be radiated for the rest of
the world to receive and 2) Excessive reflected waves WILL RUIN your
transmitter.
So lets tune our antenna. Install it like the manufacture suggests
and put a SWR/Watt meter inline with the coax. (The closer to the
transmitter, the better)
If you have a low-power option on your radio, select it. The least
amount of power you can use, the better. This will keep the reflected
signals to a minimum, while the antenna still isn't correctly tuned.
Not to mention you'll be less likely to interrupt a frequency that's in
use.
Dial up 124Mhz and make sure the frequency isn't in use! If it is,
just change to another unused frequency nearby.
Now it's time to check the SWR. Key the transmitter and check your
reading on the meter. (You'll need to follow the directions that came
with your meter on how to set it up. I can't go through the setup
procedure for your meter, but I promise. It's not complicated!)
Measure your SWR. If you see 1:1, you're lucky! More than likely,
you won't. You might see something like 1.7:1 or 2:1 or worse.
So how do you figure out if you have to lengthen or shorten your
antenna? It's pretty simple, trial and error.
Most antennas have a set screw that you can loose and adjust then
antenna length. First try lengthening the antenna by 1/4 inch and
re-checking your SWR. Did it improve or did it get worse? If it got
worse, try the other direction and shorten the antenna by 1/4 inch. If
it got better, try lengthening it a hair more.
It's a good idea to keep track of each adjustment on a piece of paper,
so you can get an idea of how each change is affecting your SWR. This
will help you zero in on that perfect length. As you get closer and
closer to 1:1, you're adjustments need to be refined with smaller
increments.
Don't be surprised is you can't get exactly 1:1. The transmitted
waves can be reflected back toward the antenna by metal (such as your
empennage). So when you tune your antenna, get it away from metal
buildings or other structures and tune for the best available SWR at
124Mhz. You want the signal to be as unaffected as possible.
If you can get it down to 1.1:1 or 1.2:1, you're doing great! I
wouldn't be happy with anything over 1.5:1. 1.5 is my personal minimum
and it's easy to obtain.
Once you think you've tuned your antenna for 124 Mhz, you need to
check the extreme edges of your transmit range.
Dial down to 112 Mhz. Once again, make sure you won't be interrupting
anyone. Check your SWR.
It will be higher than it was at 124 Mhz, because at 112Mhz the
antenna is slightly out of tune. But if your inside 1.5:1, you're good.
I'd be okay with 1.7:1 on the extreme edges.
Next dial up 136Mhz and give it a shot. Once again, make sure no one
is using the frequency. I'm okay with 1.7ish:1 up there too.
Antenna problems really aren't that complex or difficult to tune. A
little practice and you'll have it in no time.
A couple of other things.
1) Make sure you use the correct coax. Usually 50 Ohm and don't buy
the cheap stuff!! Radio shack and other retailers have cheap coax. I
am a fan of Belden RG58-A/U coax. It has relatively low loss at the
cable lengths required for an airplane, the center conductor is braided
(important for high vibration installations), it has a very good braided
external conductor (Most cheap cables will skimp here), and it has a
solid inner-core insulator. Nearly any Amateur Radio (Ham) store will
carry Belden Cable. If you can't find it, I know aesham.com carries it.
The coax is the only thing between your transmitter and your antenna,
make sure you use good cable! It's worth a couple of extra dollars.
2) If you suspect a cable issue or short in the cable, disconnect the
cable from both the transmitter and the antenna. Use a continuity meter
and check to make sure you have continuity through the center conductor.
Same thing for the external braided conductor, check it.
If you've got continuity all the way through, you've eliminated the
possibility of a broken wire.
Next check and see if you have continuity from the center conductor to
the external conductor. If you do, there's a problem. Either your
cable has a short or you've got a connector that isn't soldered on
properly. Check the connectors first be re-soldering them. If that
doesn't fix it, you need a new cable.
Finally, if you're still having problems, check your connectors. Make
sure the solder joints are good. Your continuity can be fine, but if
you've got a cold solder joint, that can cause problems.
Please don't use the cheap retail connectors, they're junk. Get good
quality connectors. If you can find silver connectors, they are the
best and are the easiest for solder to stick to. I use the ones made by
Amphenol. If you're gonna get the good coax, make sure you get the good
connectors too! Most places that sell Belden also sells Amphenol
connectors. I know aesham.com has them too, but it's been several years
since I've had to place and order with them. I'm sure they still carry
both brands.
Anyway, that's all I can think of. Hopefully you'll tuck this stuff
away somewhere and use it one day. Otherwise,the delete button looks
like a red "X" at the top of the screen. :)
Take care,
Phil
-------------------------------------------------------------------------
-----
From: John Rippengal [mailto:j.rippengal@cytanet.com.cy]
Sent: Tuesday, July 03, 2007 2:00 PM
To: avionics-list@matronics.com
Subject: Re: Avionics-List: Need Comm Troubleshooting Advice
Glad it seems to be ok now Roger. An aircraft standing around for
quite a time while a new avionics pack is being fitted is a good clue to
there being a flat battery. However the other advice given to you to
check with a VSWR meter is a good one. The Bird Thru' Line meter is a
sort of Rolls Royce professional type and you really don't need that for
a good check on your antenna/coax/connector setup. Try Radio Shack or
similar for a cheap VSWR meter that covers the 2 metre amateur band.
Should only cost about $20 or less and every home installer of avionics
should have one. It will give you confidence in the antenna installation
together with the feeders and connectors.
John
From: Roger Roy<mailto:Savannah174@msn.com>
Hi John,
How's the avionics guru? I did as you suggested and put my battery
charger on the battery and all seem to workload and clear. I was unable
to had another person TX with the portable I will check this out
tomorrow, again thank you, Cheers
RJ
From: John Rippengal<mailto:j.rippengal@cytanet.com.cy>
Roger,
What are the battery volts when you switch the equipment on?? The
fault is common to both comms so suspect something common like the
battery. You should check the equipment with the battery on charge and a
battery voltage of about 14v WITH the equipment switched on.
John
href="http://www.matronics.com/Navigator?Avionics-List">http://www.matr
onics.com/Navigator?Avionics-List
href="http://forums.matronics.com">http://forums.matronics.com
http://www.matronics.com/Navigator?Avionics-List<http://www.matronics.com
/Navigator?Avionics-List>
Message 3
INDEX | Back to Main INDEX |
PREVIOUS | Skip to PREVIOUS Message |
NEXT | Skip to NEXT Message |
LIST | Reply to LIST Regarding this Message |
SENDER | Reply to SENDER Regarding this Message |
|
Subject: | Re: Need Comm Troubleshooting Advice |
Yes but Phil the low edge of the band is 118Mhz NOT 112 Mhz so the
centre frequrency is 127 not 124. Second I would most certainly not
bother tuning a broadband antenna. Assuming it is a professionally made
antenna or something like Jim Weir's tape antenna then there is no point
whatever in tuning it. Just check that the VSWR stays between 2:1 max
over the range - it should be closer to 1:1.5 over most of the band -
but the main idea is to check that there is no fault in the coax or
connectors in which case you would see figures way over the 2:1.
John
From: Perry, Phil
I agree with John.
The bird meters are great but they're just a company who built the
watt/swr meters. They've been around for years and are not manufactured
any more. and are more of a novelty for hard-core radio operators to
own.
There are certainly many modern meters out there that are less
expensive and more available. The $20 radio shack model is fine.
Here's some a few tips that you can squirrel away for the next time
you need to do some tuning.
First, make sure the antenna is properly grounded to the aircraft.
Several people will ground the antenna to a painted surface, this is a
bad idea! The paint/primer acts as an insulator and the antenna won't
be able to balance the ground plane (aircraft) with the transmitting
element (antenna). If you don't have a good ground, you will pull your
hair out trying to tune the antenna and it won't work very well anyway.
Checking grounding is always a great place to start.
Next, you'll need to tune your antenna to the appropriate length.
The frequency range determines the length of the antenna. The lower
the frequency; the longer the antenna. The higher the frequency; the
shorter the antenna. This is because low frequencies have longer wave
lengths and higher frequencies have shorter wave lengths. Since we're
dealing with frequencies in the VHF band (108Mhz - 137Mhz), we're
dealing with fairly short antenna lengths.
Keep in mind that an antenna is tuned EXACTLY for only one frequency.
As you deviate (up or down) from that frequency, the antenna becomes out
of tune. The further your deviation, the less in-tune the antenna will
be.
So you will want to tune for a frequency that is in the middle of your
transmit range. Since 108Mhz - 112Mhz are receive-only NAV frequencies,
we aren't too concerned in tuning for those frequencies. Since 112Mhz -
136Mhz is the range of communication frequencies that we transmit on,
you want to tune for those. So pick a frequency in the middle and make
that the frequency you tune for. In this case, 124Mhz is exactly in the
middle of 108Mhz and 136Mhz. If you tune for 124Mhz, the antenna will
be a perfect match at 124Mhz and only slightly off at the extreme edges
of your transmitting frequency range 112Mhz and 136Mhz.
Let's stop right here for a minute and talk about Standing Wave Ratios
or SWR.
When a transmitter is keyed, a signal is obviously transmitted down
the coax and ultimately destined for the antenna to broadcast. In a
perfect world (or a perfectly tuned antenna) all of the signal power
from the transmitter is radiated by the antenna. So if you have a
transmitter that is radiating 25watts of signal power, all 25 watts exit
the antenna and is radiated out in space for others to hear.
But what happens if the antenna isn't tuned perfectly? Actually the
signal will traverse the coax and reach the antenna. But since the
antenna isn't the appropriate length only a portion of the wave (signal)
will be radiated. The portion that isn't radiated is reflected back
down the coax and toward the transmitter. (YIKES!) Transmitters are
made to transmit 25 watt signals, not have them blasted back down the
coax like a fire hose.
The ratio of signal that is radiated by the transmitter vs the amount
reflected by the antenna is referred to as the Standing Wave Ratio
(SWR). In the perfect situation your standing wave ratio should be 1 to
1 (presented as 1:1). This means that all of your power is being
radiated and there is no reflective wave coming back to the transmitter.
So it's important to tune for the best SWR because: 1) You want as
much of your signal to leave the antenna and be radiated for the rest of
the world to receive and 2) Excessive reflected waves WILL RUIN your
transmitter.
So lets tune our antenna. Install it like the manufacture suggests
and put a SWR/Watt meter inline with the coax. (The closer to the
transmitter, the better)
If you have a low-power option on your radio, select it. The least
amount of power you can use, the better. This will keep the reflected
signals to a minimum, while the antenna still isn't correctly tuned.
Not to mention you'll be less likely to interrupt a frequency that's in
use.
Dial up 124Mhz and make sure the frequency isn't in use! If it is,
just change to another unused frequency nearby.
Now it's time to check the SWR. Key the transmitter and check your
reading on the meter. (You'll need to follow the directions that came
with your meter on how to set it up. I can't go through the setup
procedure for your meter, but I promise. It's not complicated!)
Measure your SWR. If you see 1:1, you're lucky! More than likely,
you won't. You might see something like 1.7:1 or 2:1 or worse.
So how do you figure out if you have to lengthen or shorten your
antenna? It's pretty simple, trial and error.
Most antennas have a set screw that you can loose and adjust then
antenna length. First try lengthening the antenna by 1/4 inch and
re-checking your SWR. Did it improve or did it get worse? If it got
worse, try the other direction and shorten the antenna by 1/4 inch. If
it got better, try lengthening it a hair more.
It's a good idea to keep track of each adjustment on a piece of paper,
so you can get an idea of how each change is affecting your SWR. This
will help you zero in on that perfect length. As you get closer and
closer to 1:1, you're adjustments need to be refined with smaller
increments.
Don't be surprised is you can't get exactly 1:1. The transmitted
waves can be reflected back toward the antenna by metal (such as your
empennage). So when you tune your antenna, get it away from metal
buildings or other structures and tune for the best available SWR at
124Mhz. You want the signal to be as unaffected as possible.
If you can get it down to 1.1:1 or 1.2:1, you're doing great! I
wouldn't be happy with anything over 1.5:1. 1.5 is my personal minimum
and it's easy to obtain.
Once you think you've tuned your antenna for 124 Mhz, you need to
check the extreme edges of your transmit range.
Dial down to 112 Mhz. Once again, make sure you won't be interrupting
anyone. Check your SWR.
It will be higher than it was at 124 Mhz, because at 112Mhz the
antenna is slightly out of tune. But if your inside 1.5:1, you're good.
I'd be okay with 1.7:1 on the extreme edges.
Next dial up 136Mhz and give it a shot. Once again, make sure no one
is using the frequency. I'm okay with 1.7ish:1 up there too.
Antenna problems really aren't that complex or difficult to tune. A
little practice and you'll have it in no time.
A couple of other things.
1) Make sure you use the correct coax. Usually 50 Ohm and don't buy
the cheap stuff!! Radio shack and other retailers have cheap coax. I
am a fan of Belden RG58-A/U coax. It has relatively low loss at the
cable lengths required for an airplane, the center conductor is braided
(important for high vibration installations), it has a very good braided
external conductor (Most cheap cables will skimp here), and it has a
solid inner-core insulator. Nearly any Amateur Radio (Ham) store will
carry Belden Cable. If you can't find it, I know aesham.com carries it.
The coax is the only thing between your transmitter and your antenna,
make sure you use good cable! It's worth a couple of extra dollars.
2) If you suspect a cable issue or short in the cable, disconnect the
cable from both the transmitter and the antenna. Use a continuity meter
and check to make sure you have continuity through the center conductor.
Same thing for the external braided conductor, check it.
If you've got continuity all the way through, you've eliminated the
possibility of a broken wire.
Next check and see if you have continuity from the center conductor to
the external conductor. If you do, there's a problem. Either your
cable has a short or you've got a connector that isn't soldered on
properly. Check the connectors first be re-soldering them. If that
doesn't fix it, you need a new cable.
Finally, if you're still having problems, check your connectors. Make
sure the solder joints are good. Your continuity can be fine, but if
you've got a cold solder joint, that can cause problems.
Please don't use the cheap retail connectors, they're junk. Get good
quality connectors. If you can find silver connectors, they are the
best and are the easiest for solder to stick to. I use the ones made by
Amphenol. If you're gonna get the good coax, make sure you get the good
connectors too! Most places that sell Belden also sells Amphenol
connectors. I know aesham.com has them too, but it's been several years
since I've had to place and order with them. I'm sure they still carry
both brands.
Anyway, that's all I can think of. Hopefully you'll tuck this stuff
away somewhere and use it one day. Otherwise,the delete button looks
like a red "X" at the top of the screen. :)
Take care,
Phil
-------------------------------------------------------------------------
-----
From: John Rippengal [mailto:j.rippengal@cytanet.com.cy]
Sent: Tuesday, July 03, 2007 2:00 PM
To: avionics-list@matronics.com
Subject: Re: Avionics-List: Need Comm Troubleshooting Advice
Glad it seems to be ok now Roger. An aircraft standing around for
quite a time while a new avionics pack is being fitted is a good clue to
there being a flat battery. However the other advice given to you to
check with a VSWR meter is a good one. The Bird Thru' Line meter is a
sort of Rolls Royce professional type and you really don't need that for
a good check on your antenna/coax/connector setup. Try Radio Shack or
similar for a cheap VSWR meter that covers the 2 metre amateur band.
Should only cost about $20 or less and every home installer of avionics
should have one. It will give you confidence in the antenna installation
together with the feeders and connectors.
John
From: Roger Roy
Hi John,
How's the avionics guru? I did as you suggested and put my battery
charger on the battery and all seem to workload and clear. I was unable
to had another person TX with the portable I will check this out
tomorrow, again thank you, Cheers
RJ
From: John Rippengal
Roger,
What are the battery volts when you switch the equipment on?? The
fault is common to both comms so suspect something common like the
battery. You should check the equipment with the battery on charge and a
battery voltage of about 14v WITH the equipment switched on.
John
href="http://www.matronics.com/Navigator?Avionics-List">http://www.matr
onics.com/Navigator?Avionics-List
href="http://forums.matronics.com">http://forums.matronics.com
Other Matronics Email List Services
These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.
-- Please support this service by making your Contribution today! --
|