-
Posts
9 -
Joined
-
Last visited
Content Type
Profiles
Forums
Events
Gallery
Classifieds
Posts posted by DarkHelmet
-
-
No, The website this "network" is running is broken. You should never allow invalid certs.
-
You may have no choice but to shift frequencies, THOUGH, a good duplexer should
be blocking out anything from 457 on the receive side of the repeater, in fact it
should be blocking anything below 467.0000.
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.
The big concern with using offset frequencies is that in the end
you end up blocking 2 repeater pairs. This may not be a big deal if there are no
other repeaters in the area, however if you do have other repeaters, it can cause more
interference issues. Another thing to point out is that a lot of pre-programmed 95E radios will
not allow you to do an offset like this, meaning there will be radios which would not be able to
reach your repeater.
In my opinion, you may be best checking/upgrading your duplexer to block lower frequencies,
and perhaps moving the repeater away from the harbor if needed.
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.
-
There appears to be an accidental typo in the GMRS frequencies listed. All GMRS frequencies begin with 462 and 467, none are 457.
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.
Is the off-shore traffic sufficiently frequent that even with different PL codes,
communications cannot reasonably occur through the repeater? If the interference is frequent
and disruptive enough I would consider shifting frequencies.
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.
.
-
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?
-
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
-
yes I was able to confirm the repeater, it is listed on this site. the person I talked to owned the repeater and was very nice and said feel free to use his repeater anytime.
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.
-
Bill, been years, hope you're doing well.
N4GIX is still active, it should be showing canceled if you did a vanity callsign.
Odd repeater splits or inputs?
in General Discussion
Posted
Not only do you necrobump the thread, but you do it by spewing this horseshit.
A BpBr filter is nothing but a notch cavity with a anti-resonance reactance across it to improve close in pass. This will give a "band pass" with notches high and low from it in most designs. As you get further away from the pass frequency, past the notches, you'll see the pass band loss decrease. At 10-20 MHz away the band pass the match will be poor and the notch will be almost non-existent; 6 dB at best.
This repeater doesn't have a duplexer on it, it's fed from a window filter on receive and transmit goes into a combiner which is a number of true bandpass filters all feeding the same antenna.
Here's what the transmitter sees https://gallery.keekles.org/d/31221-1/chan+04+to+antenna.gif
You can see the RX filters here http://gallery.keekles.org/d/31182-1/dual+filters.gif
And with the RF pre-amp, this is an old (circa 1990) bipolar pre-amp with poor input match (-10 dB). This shows how important input match is. http://gallery.keekles.org/d/31185-1/Filters+with+pre-amp.gif
The TX and RX antenna have over 45 dB of isolation between them. This was measured as part of the system commissioning.
This issue is one of _ON_FREQUENCY_ interference. There is nothing that can be filtered. https://flscg.org/2021/05/tampa-gmrs-interference/