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DarkHelmet

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  1. A duplexer isn't going to reject something that far off frequency generally. It's a moot point here as we're not using a duplexer in this system. In this case it's not the output causing issues on 457, but rather the users on their radios at the port causing interference to the 467.575 input. A 5 watt radio a mile away is enough to cause severe interference to a mobile user 5 miles away. Well that capability is a concern, but I don't anyone using a purpose built GMRS radio. I've not seen one IRL, and the majority of the lower end radios are the baofeng uv5r and others which can do any split. Some times they even will occupy multiple frequencies at the same time As it's just another input frequency in use, there's the likelihood of how many simultaneous GMRS conversations are going in the same area at the same time. In Tampa, it's really not that many. A duplexer isn't a bandpass filter, and there's not much we can do about on frequency interference. Changing the frequency would involve ordering new interconnect cables and retuning the cavity/isolator for this channel. I'd also have to do a new IMD study for the stack (8 different channels here). I think this is the easiest path. On the plus side, it might encourage people to get better radios that can program odd splits.
  2. The frequencies I listed are the permitted maritime frequencies, they are paired 10 MHz split. I listed them as they may be high out, low in and you may find the users on their 457 MHz pairs too. When you have a strong signal on the input (multiple ships in this case) PL only keeps it from keying up the repeater. It will still affect the users transmitting through the repeater as the repeater receiver will capture on the stronger signal. Digital modes will suffer just as analog too. .
  3. Recently I've come to have at least two other co-channel users on our input frequency of 467.5750. These are not FRS users, but rather maritime users of ship based repeaters while parked at the Port of Tampa. This is just under a mile from our site in downtown Tampa at 500' up and clobbers anyone coming in on it. As I can't readily change the output frequency to anything other than 462.5750, I setup the receiver to scan between 467.5750 and 467.7250. This way the receiver will treat the 725 input as a priority (it's still not scanning when 575 is busy of course, it's only one receiver). This way if we're seeing interference or noise, we can just go to the alternate input in the radio and avoid the interference until the ship leaves port. 457.525 MHz, 457.550 MHz, 457.575 MHz, 467.525 MHz, 467.550 MHz and 467.575 MHz are permitted frequencies per US287 footnote in https://transition.fcc.gov/oet/spectrum/table/fcctable.pdf so it looks like they are 100% legal :-) Has anyone else experienced this sort of interference before, and/or is anyone running an odd split or alternate input frequency repeater?
  4. The 39 dBu coverage area of the Tampa 575 repeater is below. This is at 6' off the ground and roughly would translate to a 90 dBm signal in a 1/2 wave antenna. If you're on a base station or mobile, expect a greater coverage than this. http://flscg.org/wp-content/uploads/2021/03/Tampa-575-GMRS-Repeater.jpg
  5. Yes, I recall the conversation we had. This time of year can experience troposphere ducting, and K factor changes which are more pronounced. Under normal conditions radio waves are refracted in atmosphere and will experience about a 15% greater radio horizon than the direct path. This is due to refraction in the atmosphere, and gives radio it's greater reach. Under certain conditions the stratosphere can segment and form ducts of different densities which will act like a wave-guide. This can cause low-loss propagation over hundreds of miles. Florida is ideal for this due to the weather patterns off both coasts, and can cause north-south ducts over hundreds of miles in the evening and early mornings. These ducts can enhance propagation at UHF and above. I've had interference on a 18 GHz radio system north of Orlando caused by a system south of Miami, and even light (same electromagnetic radiation) can be propagated over these ducts, case in point the superior mirage of ships "floating" over the water. It will come in, start fast and have great signal strengths, then fade quick and it's over. However in Florida, these can last for hours or even days. South Florida had their LTE in 700 MHz taken out due to a Dominican TV station for several days last year. This is no one's fault, as there's thousands of miles between the DR and south Florida.
  6. Bill, been years, hope you're doing well. N4GIX is still active, it should be showing canceled if you did a vanity callsign.
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