question about repeaters

[WRCZ387]

There are two repeaters in downtown Tampa

.575 antenna height is 500'

.700 is at 400'

I'm in North Clearwater which is about 25 miles away

.575 has covered up into Pasco County to the north, & into Polk County to the east, I don't know how far south that it's reached

I don't know how far .700 has reached

I can hit both repeaters from my location with an h-t, so they both cover more than 10 miles

[DarkHelmet]

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

[SkylinesSuck]

Where do people create these coverage maps? I'm super curious to play with whatever tool is used.

[n4gix]

Where do people create these coverage maps? I'm super curious to play with whatever tool is used.

 

Check out https://www.ve2dbe.com/rmonline_s.asp

 

Here is an example of the type of coverage map projection:

[SkylinesSuck]

Very cool! Thanks. I've been playing around with it for the past hour or so. I think it's a little optimistic and have turned the power down from 50w to 30w to make it better reflect my real world experience, but still very useful! Gives me an idea of how more power/gain/height might affect things.

[mbrun]

Very cool! Thanks. I've been playing around with it for the past hour or so. I think it's a little optimistic and have turned the power down from 50w to 30w to make it better reflect my real world experience, but still very useful! Gives me an idea of how more power/gain/height might affect things.

You have to make sure the receiver figures are correct as well. Those are the hard-ones to get correct.

 

Last summer I did extensive simplex testing around me, long before I found that program. Retroactively I modeled the coverage and when I got the receiver numbers adjusted the coverage pattern (good, marginal and no coverage) did end up being a good facsimile of all my results. The key learning item here was that spec sheet receive values and real-world effective receive values are different.

 

 

Michael

WRHS965

KE8PLM

[SkylinesSuck]

I have no idea how to even begin to mess with that. Any info to get me pointed in the right direction?

[mbrun]

I have no idea how to even begin to mess with that. Any info to get me pointed in the right direction?

Absent test equipment, it would be through experimentation, which is how I did it originally. In the end, I tweaked the receive threshold value in the software until its predicted coverage map reflected the same edge coverage limits I experienced in the field. This was done after I had already entered the transmit side information accurately. I knew I had found the right value when I all the nuances I experienced within the coverage area showed up clearly and accurately reflected my personal experiences. That told me I had gotten the receive value in the right ballpark.

 

While the radio manufactures do publish a sensitivity value, the only time that value means anything is in the lab. It is not usable for the real world range prediction. Once you hook up an antenna to the radio, the noise the radio sees from the area around it increase thus making the lab sensitivity value meaningless to use in the software. In the end, it is this effective sensitivity you would use as the receive threshold in the software (i.e. the value that you can reasonably reasonably expect to be required to open squelch on your radio in your area of concern and produce at least a minimally usable audio).

 

In my coverage maps I had to use an effective receive threshold of about -85dBm to get its edge coverage to align with my real-world experiences. Once I had found that number I was able to vary antenna elevation, gain and cable loss factors to see realistical coverage changes to expect from my transmit location. The key thing for me was learning just how much more elevation I would actually need to achieve a given objective.

 

Recently, I learned that could use my TinySA with its external antenna under some circumstances to get a ball park noise figure that could prove useful in establishing a baseline receive threshold for my radios if I were to go into another area. I also have acquired additional equipment too that affords me the ability to go into the field and conduct model-specific effective sensitivity measurements. Thanks to wisdom gained from interactions with Gman and RadioGuy.

 

Hope this helps.

 

 

Michael

WRHS965

KE8PLM

[n4gix]

Very cool! Thanks. I've been playing around with it for the past hour or so.

 

I highly suggest going to his HOME page and downloading the user guide and the companion book. They are very complete in covering all that may be done with the program.

[Sbsyncro]

As a repeater newbie reading as much as I can about the topic, I’m still curious about how one even “discovers” a repeater?

For example I’ve noticed while driving around my town with my radio (KG-1000G) in “scan” mode I will pick up intermittent signals on the radio’s pre-programmed “CH22-RPT” channel. Does this mean there is an unlisted repeater operating on the default frequencies? (e.g. 462.7250/467.7250)

Assuming that it is set up with tones, in order to “test” it (assuming I obtain permission), I would either need to scan for the rx/tx tones or obtain them from the owner, then program two radios and see if I can hit one radio from the other?

I’ve read a lot on the theory and concepts of repeaters (pretty straightforward) but not seen a nuts and bolts “repeaters for dummies” step by step on how to actually do it....


Sent from my iPhone using Tapatalk

[mbrun]

As a repeater newbie reading as much as I can about the topic, I’m still curious about how one even “discovers” a repeater?

For example I’ve noticed while driving around my town with my radio (KG-1000G) in “scan” mode I will pick up intermittent signals on the radio’s pre-programmed “CH22-RPT” channel. Does this mean there is an unlisted repeater operating on the default frequencies? (e.g. 462.7250/467.7250)

Assuming that it is set up with tones, in order to “test” it (assuming I obtain permission), I would either need to scan for the rx/tx tones or obtain them from the owner, then program two radios and see if I can hit one radio from the other?

I’ve read a lot on the theory and concepts of repeaters (pretty straightforward) but not seen a nuts and bolts “repeaters for dummies” step by step on how to actually do it....


Sent from my iPhone using Tapatalk

Good Day.

There is nothing you can do to definitely discover a repeater just by scanning. A repeater transmits on the same frequencies that both GMRS and FRS radios use for simplex operation. So you will hear the exact same signal on RPT-22 as you do on simplex 22, since the only difference between the two is which frequency is used when you press the PTT button on your radio.

You will have truly discovered one if you find that you can open it up by transmitting on its corresponding input frequency (using the tone/code it requires to open it up) and you hear either the squelch tail (hang time) of the repeater when you let off the PTT button, or you hear yourself being received on a second radio in real time that is tuned to the same frequency the repeater is transmitting on.

If you hear morse code on the channel +/- 15 minutes from when a conversation occurred on the frequency, you may have heard a repeater. If you hear a pre-recorded announcement giving a call sign +/- 15 minutes from when a conversation occurred on the frequency, you may have heard a repeater. If you hear the exact same ‘booop’ or ‘beep’ at the end of every transmission on a frequency, regardless of who was talking last you have likely found a repeater.

Repeaters are private property and there is no requirement that they be listed anywhere. Chances are there are far more repeaters out there that we don’t know about then there are ones we do know about. Since repeaters are private property, you need the permission of the repeater owner to use their equipment.

Hope this helps a little.


Michael
WRHS965
KE8PLM

[Sbsyncro]

3 hours ago, mbrun said:

Good Day.

There is nothing you can do to definitely discover a repeater just by scanning. A repeater transmits on the same frequencies that both GMRS and FRS radios use for simplex operation. So you will hear the exact same signal on RPT-22 as you do on simplex 22, since the only difference between the two is which frequency is used when you press the PTT button on your radio.

You will have truly discovered one if you find that you can open it up by transmitting on its corresponding input frequency (using the tone/code it requires to open it up) and you hear either the squelch tail (hang time) of the repeater when you let off the PTT button, or you hear yourself being received on a second radio in real time that is tuned to the same frequency the repeater is transmitting on.

If you hear morse code on the channel +/- 15 minutes from when a conversation occurred on the frequency, you may have heard a repeater. If you hear a pre-recorded announcement giving a call sign +/- 15 minutes from when a conversation occurred on the frequency, you may have heard a repeater. If you hear the exact same ‘booop’ or ‘beep’ at the end of every transmission on a frequency, regardless of who was talking last you have likely found a repeater.

Repeaters are private property and there is no requirement that they be listed anywhere. Chances are there are far more repeaters out there that we don’t know about then there are ones we do know about. Since repeaters are private property, you need the permission of the repeater owner to use their equipment.
 

Thanks Michael.   I forgot to mention in my previous post that the thing that tipped me off to the nearby CH-22 RPT possibly being a repeater was the periodic morse code.   I figure the only time I'm going to be anywhere near a public repeater, I won't know far enough in advance to gain permission and setup details, so unfortunately the likelihood of me ever being able to use one are fairly low... 

[H8SPVMT]

14 hours ago, Sbsyncro said:

Thanks Michael.   I forgot to mention in my previous post that the thing that tipped me off to the nearby CH-22 RPT possibly being a repeater was the periodic morse code.   I figure the only time I'm going to be anywhere near a public repeater, I won't know far enough in advance to gain permission and setup details, so unfortunately the likelihood of me ever being able to use one are fairly low... 

Sbsyncro you have made a very knowledgeable observation in dealing with travel, and repeaters.

But first off remember the repeaters aren’t “public” but, private property even though they identify themselves ever so often.

Travel planning is a necessity in the probable use of a repeater outside your area of normal travel. 

Say, you decide to prepare for getting a signal report while on the road, in the area just to ensure your unit is really working as designed.  Contact the owner beforehand and get (and record) the necessary information and permission to program the radio before the trip.

As you get closer to the repeater setup you’ll likely want to PTT and ask for a signal report and listen for the squelch report to ensure you are actually hitting the repeater.

My new radio experience has taught me to:

-Safety First & pull over to a safe place and stop,

-Ensure the radio is set to the correct channel,

-Ensure I have the correct CTCSS or DCS tone selected,

-Think about what you’re going to say then,

-Transmit and evaluate the results even though I think I am close enough to be heard.

You may or may not reach the repeater. Listen for hearing static after letting go of the PTT button.  If you hear the static, you’ll know you have not opened the repeater with your transmission.  If the release of the PTT produces a clear silence for several seconds (squelch trail), know you have been received and should wait for a response.

I have learned that somedays I can hear a repeater a long way off (30 - 45 miles) but I can't quite hit it depending on my angle of approach or area of reception I am in.  Too, somedays the repeater my be down for any number of issues and just available for use at the time you arrive ot use it.

Safe Travels!