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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => Wireless and Communications => Topic started by: Denn Cimo on September 09, 2016, 07:48:51 PM
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Hi all, I was hoping I could get some wisdom from the RF experts on the forum.. My company, Sound Solutions of Ohio, LLC. just finished a new stadium sound install in Huron Ohio(44839) We installed a new Audio Technica 3000 series wireless bodypack system for the referee and integrated an older 3000 series Handheld System. Both systems are in C Band (542-565MHz) We installed a DA49 Wide Band Distro and remoted a pair of wide band paddle antennas to the outside front of the press box using RG8 cabling. The paddles are pointed at the end zones and are about 5 ft apart. We worked with AT to find TV/Intermod Free frequencies. Everything works beautifully, full bars of RF all over the field and no interfence. That is, until game time, when the microphones become unusable.
Main problem seems to be that there is an AM station WLEC 161.640 that does a remote broadcast from the press box. They are running a Marty SRPT 40A Transmitter to an antenna that is about 15 feet to the left of the pressbox and parallel to our antennas mounted on the front of the pressbox. As soon as he turns the Marty on, the RF bars on the AT receivers go up to 5 or 6 when their corresponding transmitters are not on. When the AT transmitters are turned on, so much noise is coming through that the wireless is unusable. I moved our antennas to the opposite side of the press box to get them as far away as possible from the AM antenna, (about 55 ft) but it did not help. The BCSN guys said the same antenna was interfering with their TV camera also.
Other known sources of RF during the game are as follows:
1:there is also occasionally an FM broadcast KM96 during the games, also using a Marty SRPT 40A
2: In addition, BCSN Erie is using a lectrosonics system to get their audio to their mobile broadcast vehicle. Running 540.500MHz) I am not sure if they are broadcasting a TV station from the vehicle or not. I have a call into them to get more info.
3: The home team coach comm system that is working in the 2.4GHz band.
So I am hoping that some experts will help me to weigh my options here. The only options I can see at this point are:
1) Try the Audio Technica AEW-DA550C Distro that only operates in C band with hopes that it will filter out the interference. I don’t have one of these in stock so I would have to sacrifice job profitability to try this.
2) Try a different band or different manufacturer of wireless systems. Again sacrificing job profitability, especially if it doesn’t solve the problem.
3) I purchased and received an RF Explorer and software today. I’m a newbie with the product but I figure I could go to the next game and do a scan to see what I’m really dealing with before ordering any additional gear, unfortunately this leaves the customer with no wireless mics for more games.
Please let me know if there is something that I am missing here or maybe someone has seen this sort of interference from an AM broadcast before and has a solution. Thanks in advance.
Denn Cimo
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The Marti (not Marty!) is a one box FM transmitter and mixer, used for remote linkups, and has, by wireless microphone standards, a lot of RF output, depending on the exact model, perhaps 50W, and if your wireless mic antennas are near, then your receivers may well be desensed. There is a matching receiver somewhere else, and then the signal goes in to the station audio chain, eventually appearing at their AM transmission facility, almost certainly by another UHF FM STL link (STL - Studio to transmitter).
You mention 161.640, is that the Marti is on 161.640MHz? If so, its a long way away from C band stuff, so I'm firstly surprised that the filters already in the wireless mic receivers are not removing that already.
Our remote Marti is on 159.something, and we have no problems at all with radio mics on 500-odd MHz, but... by wireless mic I just mean a receiver with its bugs ears, not paddles and amps and stuff.
So the other thing that occurs to me is perhaps you have too much reception gain on the wireless mic system, which is pushing that out of band signal all over your receivers.
The "standard" solution is filters after your antennas. Employ an RF expert.
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The Marti (not Marty!) is a one box FM transmitter and mixer, used for remote linkups, and has, by wireless microphone standards, a lot of RF output, depending on the exact model, perhaps 50W, and if your wireless mic antennas are near, then your receivers may well be desensed. There is a matching receiver somewhere else, and then the signal goes in to the station audio chain, eventually appearing at their AM transmission facility, almost certainly by another UHF FM STL link (STL - Studio to transmitter).
You mention 161.640, is that the Marti is on 161.640MHz? If so, its a long way away from C band stuff, so I'm firstly surprised that the filters already in the wireless mic receivers are not removing that already.
Our remote Marti is on 159.something, and we have no problems at all with radio mics on 500-odd MHz, but... by wireless mic I just mean a receiver with its bugs ears, not paddles and amps and stuff.
So the other thing that occurs to me is perhaps you have too much reception gain on the wireless mic system, which is pushing that out of band signal all over your receivers.
The "standard" solution is filters after your antennas. Employ an RF expert.
Sounds to me like you have an intermod hit on frequency with the Marti unit. A spectrum analyzer would confirm this.
If so filtration on the receivers is useless in this case.
If the intermod is mixing in the marti a cavity and circulator on it's output would clear this up. If there is a community repeater or some other land mobile asset participating in the mix then the remediation could become more complex.
Is the interference constant when the Marti is radiating?
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As soon as he turns the Marty on, the RF bars on the AT receivers go up to 5 or 6 when their corresponding transmitters are not on.
The Marti could be raising the noise floor a considerable amount. If that's the case filters on your receiver inputs won't help because if that's the case it would be a signal to noise issue. You're headed in the right direction running a scan of the environment with/without the Marti. Are you able to get some face time with the the unit before the next game? Is the ac ground pin still there? Is the Lectrosonics at 540.500mhz having any issues when the Marti is on?
If the Marti is creating that much noise it would need to be serviced as it is causing harmful interference to yourself and probably every DTV in the vicinity.
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Sounds to me like you have an intermod hit on frequency with the Marti unit. A spectrum analyzer would confirm this.
If so filtration on the receivers is useless in this case.
If the intermod is mixing in the marti a cavity and circulator on it's output would clear this up. If there is a community repeater or some other land mobile asset participating in the mix then the remediation could become more complex.
Is the interference constant when the Marti is radiating?
Thanks so much for the reply! The effect of the Marti is as follows. The RF meter goes up immediately when the Marti is turned on, but it is not constant. It will clear for a few minutes, then go to anywhere from 5-8 bars, then flash up and down, then clear again for a few minutes. When the AT transmitter was turned on during the 1st game it would just get drop outs and crackling noise. The 2nd game it was completely unusable and the receiver was putting out AF noise the entire time it's transmitter was on.
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The Marti could be raising the noise floor a considerable amount. If that's the case filters on your receiver inputs won't help because if that's the case it would be a signal to noise issue. You're headed in the right direction running a scan of the environment with/without the Marti. Are you able to get some face time with the the unit before the next game? Is the ac ground pin still there? Is the Lectrosonics at 540.500mhz having any issues when the Marti is on?
If the Marti is creating that much noise it would need to be serviced as it is causing harmful interference to yourself and probably every DTV in the vicinity.
Thanks so much for your reply!
I also suspect a bad noise floor issue with that Marti. When I was asking him questions, the AM commentator told me that the station owned a rack full of AT wireless systems that are unusable when they used that Marti unit. He seemed to be saying it was a problem with the Audio Technica systems. I can get there early and take a scan. He gets there about an hour and 15 minutes before the game starts. I might have about 15 minutes to scan with just the Marti on before everyone else turns their transmitters on. The cable guys say there is no interference on their Lectrosonics at 540.500, however they have quarter wave rubber duckies and are farther away from the AM antenna. Thanks again
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I looked up the Marti SRPT-40A and it looks like it is a 40watt output unit that operates from 430 MHz to 480 MHz. You mention that the antenna for this is on the press box. I have to assume that they are broadcasting on the Marti transmitter back to their studio or transmitter. Did you know or were you told that these stations broadcast the games? If you were did you in any way coordinate or at least talk to these people? It is very likely with a transmitter that strong and that close is going to just over saturate the front end of your receivers. The only solution would probably be to convince these people to send it down a landline or as I understand it being done lately is over a cell phone signal. This is assuming that you haven’t added unnecessary gain in your antenna system making it more susceptible to this problem.
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I looked up the Marti SRPT-40A and it looks like it is a 40watt output unit that operates from 430 MHz to 480 MHz.
Frequency depends on the exact model, there are several available, the entire range of units covers from 135 MHz to 965, specs here (http://bdcast.com/information-center/product-information/srpt-40a---specifications).
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Have you tried a using the AT receivers frequency scan mode to see if it can find an open frequency, you may need to try scanning in several of the frequency groups.
On the hand the receivers may be so saturated with RF from the Marti that they may never be able to find a clear channel.
Try using the 1/4 wave antennas that come with the receivers on the DA49's inputs for a test, also try it with just the 1/4 wave antennas connected directly to the receivers.
Here's a few really long shot ideas, but strange things can happen in a strong RF field.
Is the stadium sound system connected in any way to the radio broadcast system?
Is pin 1 tied to any of the shells on the XLR connectors?
How are you connection the receivers to the sound system, XLR or 1/4 inch?
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Have you tried a using the AT receivers frequency scan mode to see if it can find an open frequency, you may need to try scanning in several of the frequency groups.
On the hand the receivers may be so saturated with RF from the Marti that they may never be able to find a clear channel.
Try using the 1/4 wave antennas that come with the receivers on the DA49's inputs for a test, also try it with just the 1/4 wave antennas connected directly to the receivers.
Here's a few really long shot ideas, but strange things can happen in a strong RF field.
Is the stadium sound system connected in any way to the radio broadcast system?
Is pin 1 tied to any of the shells on the XLR connectors?
How are you connection the receivers to the sound system, XLR or 1/4 inch?
Thanks so much for the input. At the first game when i arrived on site the Marti was already turned on. As soon as i observed the RF interference on the meters, i tried to do a scan, i tried a scan in all 9 groups and the receivers could not find a single clear frequency. So i think you are correct the receivers are too saturated with RF.
I did not try the quarter wave antennas, mainly because the receivers are in a metal wall swing rack and i also did not have the quarter waves with me anymore.
I can try that next game. I did try bypassing the distro and going antennas straight into the receiver but that made no difference.
The only sound system connection to the radio broadcast system that i can think of would be through the 120VAC circuit. The first game the guy plugged the Marti into the same 120VAC outlet as the sound system. The second game i asked him to plug into a different outlet but it was unfortunately was still on the same circuit.
The thought crossed my mind that it might be a chassis to chassis sort of thing happening. However, when i unplug the antennas the interference goes away, so im pretty sure its getting to the receiver through the antenna.
All of the connections are balanced,(using the XLR's on the receiver) Pin 1 is not tied to ground.
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I looked up the Marti SRPT-40A and it looks like it is a 40watt output unit that operates from 430 MHz to 480 MHz. You mention that the antenna for this is on the press box. I have to assume that they are broadcasting on the Marti transmitter back to their studio or transmitter. Did you know or were you told that these stations broadcast the games? If you were did you in any way coordinate or at least talk to these people? It is very likely with a transmitter that strong and that close is going to just over saturate the front end of your receivers. The only solution would probably be to convince these people to send it down a landline or as I understand it being done lately is over a cell phone signal. This is assuming that you haven’t added unnecessary gain in your antenna system making it more susceptible to this problem.
Thanks for the input Kevin. I had no idea about the specific broadcast. Since the inception of the company in 2010, i have installed similar systems in roughly a dozen high schools stadiums and a college stadium all with wireless mics, several of them had radio broadcasts also. This is the first time i have ever had a problem. I have definitely learned a lesson about digging into what is being broadcast in advance. In this case, noone from the school seems to know anything about the broadcasts.
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Thanks so much for the input. At the first game when i arrived on site the Marti was already turned on. As soon as i observed the RF interference on the meters, i tried to do a scan, i tried a scan in all 9 groups and the receivers could not find a single clear frequency. So i think you are correct the receivers are too saturated with RF.
I did not try the quarter wave antennas, mainly because the receivers are in a metal wall swing rack and i also did not have the quarter waves with me anymore.
I can try that next game. I did try bypassing the distro and going antennas straight into the receiver but that made no difference.
The only sound system connection to the radio broadcast system that i can think of would be through the 120VAC circuit. The first game the guy plugged the Marti into the same 120VAC outlet as the sound system. The second game i asked him to plug into a different outlet but it was unfortunately was still on the same circuit.
The thought crossed my mind that it might be a chassis to chassis sort of thing happening. However, when i unplug the antennas the interference goes away, so im pretty sure its getting to the receiver through the antenna.
All of the connections are balanced,(using the XLR's on the receiver) Pin 1 is not tied to ground.
Looking at the spectrum on a spectrum analyzer or or scanner like a TTi or RF explorer will let you see if the Marti is operating as it should, or if it's splashing all over the RF spectrum. If it is broadcasting a clean RF signal knowing how strong that signal is at you receivers and antennas will help you determine if overloading your RF inputs is the problem. If the Marti is defective tell them to get it fixed, if it's not, you may need to find a way to filter your system, or get your antennas farther from the Marti and closer to your transmitters, or get the Marti antenna in the null of your antennas, or get mics that have better input filtering, like Lectrosonics with tracking filters.
Mac
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Looking at the spectrum on a spectrum analyzer or or scanner like a TTi or RF explorer will let you see if the Marti is operating as it should, or if it's splashing all over the RF spectrum. If it is broadcasting a clean RF signal knowing how strong that signal is at you receivers and antennas will help you determine if overloading your RF inputs is the problem. If the Marti is defective tell them to get it fixed, if it's not, you may need to find a way to filter your system, or get your antennas farther from the Marti and closer to your transmitters, or get the Marti antenna in the null of your antennas, or get mics that have better input filtering, like Lectrosonics with tracking filters.
Mac
This kind of interference mitigation is really in my wheelhouse.
I have to reiterate that a properly placed filter on the output of the Marti, even if it is not malfunctioning is much easier than trying to reduce the interference at the RX input. Anything installed on the input is going to have some attenuation of the fundamental or unwanted gain.
A three or four cavity bandpass filter, on the output of the Marti will have sufficient Q for the task and be very compact. A circulator should also be added to keep any RF from getting back into the output amp of the Marti and mixing.
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This kind of interference mitigation is really in my wheelhouse.
I have to reiterate that a properly placed filter on the output of the Marti, even if it is not malfunctioning is much easier than trying to reduce the interference at the RX input. Anything installed on the input is going to have some attenuation of the fundamental or unwanted gain.
A three or four cavity bandpass filter, on the output of the Marti will have sufficient Q for the task and be very compact. A circulator should also be added to keep any RF from getting back into the output amp of the Marti and mixing.
Thanks again to all for these great responses! In light of all of your suggestions i think my best strategy here will be:
1) Scan with spectrum analyzer as Mac and many others suggested. I know that i need to find out what FM frequency the Marti is actually broadcasting and whether the output is clean or not and what its input level is at the AT receiver/antennas.
2) Ask the AM guys if they would be willing to put the bandpass filter on the output of their Marti when they broadcast from that stadium.
3) Back up solution: Try filters on the receiver input if the AM guys are not willing to try the bandpass filter. Not as good of a solution and may attenuate the desired RF signal.
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There are many more people on here that know a lot more about wireless and Marti units then I do but I will put my slant on this here. I am sure I am also repeating some of what has already been said but maybe in a slightly different way. Part of the time I was writing this I was on the phone with a fellow I work with who knows a lot more about Radio then me.
It looked like the Marti model you said it is has thumbwheel setting on the front to tune the transmitter to. So I would start by looking at that. Then you will know where to start scanning for issues. I would start at least a little bit below that frequency (if your RF Explorer goes that low) if not even more. Ideally if you can do it with one thing on at a time, in this case just the Marti you should be able to see what it is doing in relationship to what else is on air. You say that – “Main problem seems to be that there is an AM station WLEC 161.640.” This is WLEC 1450 (it’s frequency is 1450) in Sandusky, Ohio. And the 161.640 looks like it is the frequency of the Marti transmitter back to the station itself.
Which RF-Explorer model did you get? If it is capable of going as low as the Marti transmitter I would gather that you would see if the output looks right. But if you can only scan in your wireless mic range then you should see if there is a lot of garbage there. Hopefully the radio people will be cooperative enough that they will meet you at the stadium at a time when you aren’t about to have a game so you can work together to see if you can figure out what the problem is.
Others have mentioned you could have problems if you have more gain in your antenna system (then is needed to make up for cable lengths) for your wireless. It causes the front end of the receivers to take in too much and can desensitize the receiver. I don’t know if your paddles use power or not and if there is any gain setting on them. I use Shure antennas that need power from the antenna distro and have gain switches on them. You said you bypassed the distro and it made no difference but did the antennas themselves have the gain setting like I mentioned. You could try putting the quarter wave antennas on the cable in place of the paddles and see what happens. Also check with the antennas completely disconnected and see if this interference is still getting into the receiver. If the receiver is being saturated without any antennas then maybe it is getting into it some other way then over the air. But I just reread the thread and I see that with the antennas disconnected there is nothing being picked up so forget that.
I am assuming that the AM station is using the Marti to send the signal back to their station or transmitter. So you know how far away that is? Do you know what type of antenna they are using? Is there a land line in the press box that they could use instead of the Marti? I understand that the output power of the Marti is adjustable. Do they need it at full power to reach the receiver? Maybe if they could do it with less power it might help reduce your problems.
You mention that there is an FM station that is using a Marti transmitter also. The same exact questions apply to them as to the AM station people.
And just to clarify in case you don’t know. The Marti units are a transmitter that is used to get the signal to their station or transmitter. Usually the receive end (antenna and receiver) is on their broadcast antenna site because it gets it up in the air. They receive this signal and rebroadcast it over there station transmitter. We were doing an event years ago that had a radio station broadcasting the event and we had a tape player for some singers music and it was crystal controlled. The Marti was messing with the playback speed. Luckily there was enough cable to the Marti’s antenna that as soon as it happened we realized what the problem was and someone moved the antenna as far away from us as they could and it fixed the problem. Their studio was across the street but the receiver was on their transmitter tower about a mile away.
I understand that these Marti transmitters aren’t used as much as they used to be. There are cellular solutions that give them 2way communications like the Tieline systems. http://www.tieline.com/ our local HS uses the Tieline Report-IT and Bridge-IT system when they do remote games so they can broadcast them on their radio station. And also versions that use the internet for the link.
Please let us know what you eventually find is the cause and solution.
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Thanks again to all for these great responses! In light of all of your suggestions i think my best strategy here will be:
1) Scan with spectrum analyzer as Mac and many others suggested. I know that i need to find out what FM frequency the Marti is actually broadcasting and whether the output is clean or not and what its input level is at the AT receiver/antennas.
Clarification, FM (Frequency Modulation) is the type of modulation where the center frequency is deviated to correspond with the input signal.
FM can be used in any frequency range.
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Clarification, FM (Frequency Modulation) is the type of modulation where the center frequency is deviated to correspond with the input signal.
FM can be used in any frequency range.
Duh, yes, duly noted. Hey Scott, I sent you a PM
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It looked like the Marti model you said it is has thumbwheel setting on the front to tune the transmitter to. So I would start by looking at that. Then you will know where to start scanning for issues. I would start at least a little bit below that frequency (if your RF Explorer goes that low) if not even more. Ideally if you can do it with one thing on at a time, in this case just the Marti you should be able to see what it is doing in relationship to what else is on air. You say that – “Main problem seems to be that there is an AM station WLEC 161.640.” This is WLEC 1450 (it’s frequency is 1450) in Sandusky, Ohio. And the 161.640 looks like it is the frequency of the Marti transmitter back to the station itself.
Which RF-Explorer model did you get? If it is capable of going as low as the Marti transmitter I would gather that you would see if the output looks right. But if you can only scan in your wireless mic range then you should see if there is a lot of garbage there. Hopefully the radio people will be cooperative enough that they will meet you at the stadium at a time when you aren’t about to have a game so you can work together to see if you can figure out what the problem is.
Others have mentioned you could have problems if you have more gain in your antenna system (then is needed to make up for cable lengths) for your wireless. It causes the front end of the receivers to take in too much and can desensitize the receiver. I don’t know if your paddles use power or not and if there is any gain setting on them. I use Shure antennas that need power from the antenna distro and have gain switches on them. You said you bypassed the distro and it made no difference but did the antennas themselves have the gain setting like I mentioned. You could try putting the quarter wave antennas on the cable in place of the paddles and see what happens. Also check with the antennas completely disconnected and see if this interference is still getting into the receiver. If the receiver is being saturated without any antennas then maybe it is getting into it some other way then over the air. But I just reread the thread and I see that with the antennas disconnected there is nothing being picked up so forget that.
I am assuming that the AM station is using the Marti to send the signal back to their station or transmitter. So you know how far away that is? Do you know what type of antenna they are using? Is there a land line in the press box that they could use instead of the Marti? I understand that the output power of the Marti is adjustable. Do they need it at full power to reach the receiver? Maybe if they could do it with less power it might help reduce your problems.
You mention that there is an FM station that is using a Marti transmitter also. The same exact questions apply to them as to the AM station people.
And just to clarify in case you don’t know. The Marti units are a transmitter that is used to get the signal to their station or transmitter. Usually the receive end (antenna and receiver) is on their broadcast antenna site because it gets it up in the air. They receive this signal and rebroadcast it over there station transmitter. We were doing an event years ago that had a radio station broadcasting the event and we had a tape player for some singers music and it was crystal controlled. The Marti was messing with the playback speed. Luckily there was enough cable to the Marti’s antenna that as soon as it happened we realized what the problem was and someone moved the antenna as far away from us as they could and it fixed the problem. Their studio was across the street but the receiver was on their transmitter tower about a mile away.
Please let us know what you eventually find is the cause and solution.
I got the 3G combo RF explorer. So it will go down to 15MHz I believe. I spent about 8 hours over the weekend trying to get it to work with my laptop and had no luck, the laptop will just not recognize the device. (but that's a whole other problem.)
The paddles have no power on them or amplification. About the quarter wave antennas, I thought that quarter waves need a ground plane to work. I do think I have a pair of C band half waves rubber duckies, I will take those with me to the game Friday night.
The AM station in Sandusky, I believe is about 10 miles from Huron as the crow flies. I will have to ask the AM guy if he has experimented with different power settings. He does remote broadcasts from several HS stadiums so if I had to guess, he probably just operates the thing at full power.
That is good info about using a land line for the broadcast, I will investigate that possibility. Thanks for the links!
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We installed a DA49 Wide Band Distro and remoted a pair of wide band paddle antennas to the outside front of the press box using RG8 cabling. The paddles are pointed at the end zones and are about 5 ft apart.
They are running a Marty SRPT 40A Transmitter to an antenna that is about 15 feet to the left of the pressbox and parallel to our antennas mounted on the front of the pressbox.
1. Are your antennas amplified? if so try passive.
2. Move your RX antennas further away. Ideally locate the RX at field level with the antennas but even a <200' low loss (LMR400) antenna cable to the field would be better.
As a test try the RX on the field with just the whips and see if the Martty affects the RX level meters at all.
3. Definitely ask them what the freq if their marti is. A simple hi pass or low pass might help if they are at least 100 mHz away
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STL (studio-transmitter links) like the Marti are licensed operations with strict power limits, frequency assignment, and transmitter location. They should be used with tuned, highly directional antennas (usually Yagi type) pointing directly at the receiver site. If the operator is using an omni antenna and blasting full power to reach the receiver, this must be corrected or your problems will continue.
Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.
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STL (studio-transmitter links) like the Marti are licensed operations with strict power limits, frequency assignment, and transmitter location. They should be used with tuned, highly directional antennas (usually Yagi type) pointing directly at the receiver site. If the operator is using an omni antenna and blasting full power to reach the receiver, this must be corrected or your problems will continue.
What you say is true for a STL, but this isn't a STL link, its an OB link. OB links are usually licenced over an area, because the remote box could be anywhere. Ours is licensed to transmit anywhere in our state, which is a far larger area than a Marti could ever cover!
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STL (studio-transmitter links) like the Marti are licensed operations with strict power limits, frequency assignment, and transmitter location. They should be used with tuned, highly directional antennas (usually Yagi type) pointing directly at the receiver site. If the operator is using an omni antenna and blasting full power to reach the receiver, this must be corrected or your problems will continue.
Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.
Thanks so much for the input.. They are definitely using a yagi and are likely pointing in the direction of the receiver site. I just found the public record of their FCC license for that frequency (161.640.) The station class is:Mobile (probably similar to what David said their license was for) They are licensed for 30Watts of output power.
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Thanks so much for the input.. They are definitely using a yagi and are likely pointing in the direction of the receiver site. I just found the public record of their FCC license for that frequency (161.640.) The station class is:Mobile (probably similar to what David said their license was for) They are licensed for 30Watts of output power.
30W of output power? I would think that would be ERP.
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30W of output power? I would think that would be ERP.
I'm with Scott on this. If their licensed power is specified in ERP, it means that the amp should be outputting just under 2W (33 dBm) to a 14dBd Yagi for compliance.
See https://apps.fcc.gov/kdb/GetAttachment.html?id=fzlsGm%2Fe68Ymx58IAmzNbw%3D%3D&desc=412172%20D01%20Determining%20ERP%20and%20EIRP%20v01r01&tracking_number=47469
Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.
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30W of output power? I would think that would be ERP.
License shows 30.000 output power. The maximum ERP column on the license is blank (no entry). This license was originally granted in 1964. My guess is that back then a maximum ERP field was not required by the FCC. From what I understand, unless the license is modified, the information on the license is not required to be updated.
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Please let us know what you eventually find is the cause and solution.
Wanted to provide an update to everyone who took the time to respond to my post. I did get some data with my RF explorer. I am attaching a couple of screenshots that I feel are the most relevant. Two Scans from 100MHz to 700MHz. Both are after the game on Friday night and from the perspective of our wide band paddle antenna. The first is after everyone else except for the AM station had turned their equipment off. The AM crew was interviewing a coach and were the only ones left in the press box. I waited until they turned their Marti off and took another reading. So the difference between the two traces is definitely the influence of the 160.640 transmitter. I am not sure what acceptable tolerances for transmitter spurs are. This looks pretty bad to me, but I'm just a newbie. Was hoping that some of you could take a look at these traces and give me an opinion. I also have some traces with higher freq resolutions in various bands if that would help.
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Wanted to provide an update to everyone who took the time to respond to my post. I did get some data with my RF explorer. I am attaching a couple of screenshots that I feel are the most relevant. Two Scans from 100MHz to 700MHz. Both are after the game on Friday night and from the perspective of our wide band paddle antenna. The first is after everyone else except for the AM station had turned their equipment off. The AM crew was interviewing a coach and were the only ones left in the press box. I waited until they turned their Marti off and took another reading. So the difference between the two traces is definitely the influence of the 160.640 transmitter. I am not sure what acceptable tolerances for transmitter spurs are. This looks pretty bad to me, but I'm just a newbie. Was hoping that some of you could take a look at these traces and give me an opinion. I also have some traces with higher freq resolutions in various bands if that would help.
Nice detective work!
It's very difficult to say, from those measurements, whether the spurs shown are actually being transmitted by the Marti or are rather occurring inside the measuring instrument. Unfortunately, the overload compression warning with the Marti operating is an indication that the latter is likely, and reveals the trouble with using inexpensive instruments for this kind of measurement; they just don't have enough dynamic range to remain linear when measuring strong signals among weaker ones.
On the bright side, this may be an indication of what's also happening inside your mic receiver's front end.
I recommend that you try inserting a high pass filter on your antenna coax and repeat the experiment. It very well may solve your problem.
Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.
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Nice detective work!
It's very difficult to say, from those measurements, whether the spurs shown are actually being transmitted by the Marti or are rather occurring inside the measuring instrument. Unfortunately, the overload compression warning with the Marti operating is an indication that the latter is likely, and reveals the trouble with using inexpensive instruments for this kind of measurement; they just don't have enough dynamic range to remain linear when measuring strong signals among weaker ones.
On the bright side, this may be an indication of what's also happening inside your mic receiver's front end.
I recommend that you try inserting a high pass filter on your antenna coax and repeat the experiment. It very well may solve your problem.
Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.
I have never had to do that YET, I have been lucky. Where does one find an RF high pass filter to do what needs to be done and exactly what would the device be (Range?) that would block the problem frequencies? It sounds like something I should have in my bag of tricks.
Sent from my computer after composing it in MS Word. But still, please excuse my inevitable spelling and grammatical errors. :D
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Filters!
http://www.minicircuits.com/products/Filters.shtml
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Filters!
http://www.minicircuits.com/products/Filters.shtml
Yessir. 500 MHz is a good general purpose HPF for UHF systems.
http://www.minicircuits.com/MCLStore/ModelInfoDisplay?14743077420300.8613180731067597
Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.
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Yessir. 500 MHz is a good general purpose HPF for UHF systems.
http://www.minicircuits.com/MCLStore/ModelInfoDisplay?14743077420300.8613180731067597
At $37 in small quantities that seems like a pretty good investment.
Mac
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At $37 in small quantities that seems like a pretty good investment.
Mac
I thought so as well until the $86 USD shipping charge to Toronto!!!!! :o