---------------------------------------------------------- Avionics-List Digest Archive --- Total Messages Posted Wed 07/11/07: 4 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 06:27 AM - Re: Need Comm Troubleshooting Advice (Hopperdhh@aol.com) 2. 06:52 AM - Re: Need Comm Troubleshooting Advice (Perry, Phil) 3. 08:03 AM - Re: Need Comm Troubleshooting Advice (Noel Loveys) 4. 11:39 AM - Re: Need Comm Troubleshooting Advice (Noel Loveys) ________________________________ Message 1 _____________________________________ Time: 06:27:37 AM PST US From: Hopperdhh@aol.com Subject: Re: Avionics-List: Need Comm Troubleshooting Advice A very good instrument for checking antenna SWR is the MFJ-259B. Many hams have this instrument. It has a signal generator, frequency counter, and SWR bridge in one compact battery operated unit. Dan Hopper K9WEK RV-7A ************************************** See what's free at http://www.aol.com. ________________________________ Message 2 _____________________________________ Time: 06:52:36 AM PST US Subject: RE: Avionics-List: Need Comm Troubleshooting Advice From: "Perry, Phil" You're correct, John. 118 is the bottom and my mistake. No clue where I got 112 from! Thanks for pointing that out. Phil ________________________________ From: John Rippengal [mailto:j.rippengal@cytanet.com.cy] Sent: Wednesday, July 11, 2007 12:38 AM Subject: Re: Avionics-List: 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 o nics.com/Navigator?Avionics-List href="http://forums.matronics.com">http://forums.matronics.com href="http://www.matronics.com/Navigator?Avionics-List">http://www.matr o nics.com/Navigator?Avionics-List href="http://forums.matronics.com">http://forums.matronics.com ________________________________ Message 3 _____________________________________ Time: 08:03:20 AM PST US From: "Noel Loveys" Subject: RE: Avionics-List: Need Comm Troubleshooting Advice Well written Phil. Two additions for the totally uninitiated. 1 The grounding Phil was talking about is not the centre radiator of the antenna but the ground from the coaxial braid. Even a small bit of corrosion under that connection can drive your SWR into the stratosphere. 2 Under an antenna mounted on a cloth plane ( on one of the frame tubes ) it is a good idea to install a nice foil ground plane. I like to see a circle of foil where the radius is equal to the height of the radiator ( centre radiating post ) I don't have a Bird but if any one is going to junk one...... They are a lot lighter than lugging around a Cushman ;-) Noel -----Original Message----- From: owner-avionics-list-server@matronics.com [mailto:owner-avionics-list-server@matronics.com] On Behalf Of Perry, Phil Sent: Tuesday, July 10, 2007 4:04 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 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 ________________________________ Message 4 _____________________________________ Time: 11:39:20 AM PST US From: "Noel Loveys" Subject: RE: Avionics-List: Need Comm Troubleshooting Advice you also check the VSWR for corrosion at the ground plane. All things being equal a new antenna should be almost flat across the band. Generally aircraft coming in with TX problems are well corroded at the antenna and radio ends of the Coax. Depending on the condition of the coax ( its wet and salt here) the connectors are cleaned and the coax may be replaced. The VSWR meter will tell all. BTW I never tune for the centre of the band ( older wire antennas ) I always tune for .39 the band (.61 top down). = 125.5mHz. Some antennas are used for the full VHF band (e.g. small nav/com) there fore the antenna should cover the whole band, nav and com, 108 to 137 MHz. for that I tune for 119.5mHz. centre. Here in Canada the amateurs are allowed to run a full Kw on all bands, Exception is some 160Meters in maritime locations, One learns very fast that line of site 5W is more than enough power for aircraft..... in many instances 1W is more than enough. Still waiting for somebody to donate a nice Bird to the cause. :-) Noel -----Original Message----- From: owner-avionics-list-server@matronics.com [mailto:owner-avionics-list-server@matronics.com] On Behalf Of John Rippengal Sent: Wednesday, July 11, 2007 3:08 AM Subject: Re: Avionics-List: 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 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. 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