Testing Your Radio - Expected RSSI Values

Matt Johnson

Well-Known Member
5PLS
I wanted to post this slide from this months workshop.

1627754502112.png
 

Matt Johnson

Well-Known Member
5PLS
Is there any difference between a LS vs LS+ In your testing?

The test was done by the communications team. Both units use the same LMR400 radio so in theory there should be no difference. With a LS with 1 watt of power being transmitted a RSSI of -43 dBm was observed with the internal antenna. With a LS+ a RSSI of -44dBM with the internal antenna was observed, so no significant difference.
 

Matthew D. Sibole

Well-Known Member
5PLS
I knew there was a difference early on in the LS+ with the radio needing the external antenna. That was also compounded by a radio issue with the T3 when it first came out. I was not sure of all of those issues have been resolved.
 

Kelly Bellis

ME PLS 2099
5PLS
Although Matt J. attributed the test results to the Javad team in Armenia, he doesn't go into detail as to how they conducted their test(s). Is there a separate paper or other publication by the team doing the tests in Armenia describing in-depth which radio-to-antenna cables, ground plane discs, TX antenna(s), etc. were used in each of the radio tests. For example, were all tests completed using the same cable (14-578117-06) and a 2.4 dBd gain antenna (99-587309-01) without ground plane disc with the base of the broadcast antenna at a height of 2 meters and the LS HI at 1.5 meters? The photos included in July's radio workshop look like they were using a 5dBd gain UHF antenna with a ground plane disc at about 4 meters above the ground used for their 1-watt viewshed test, but likely not the same arrangement for received signal strength indicator table above. Without knowing the testing conditions, the stated expectations may possibly vary.
 

Jim Campi

Active Member
I wanted to post this slide from this months workshop.

View attachment 11672
Hi Matt,

I was using my LS and T1+ via UHF yesterday. The initial 90 mins of a topo it was taking 90 to 120 seconds to collect a point. The base was above me, in clear sight and the site was mostly open. The latter part of my survey it was taking 10-20 seconds to collect a point.

I did note that GPS and GLONAS interference was high on multiple bands throughout the survey.

I checked the RSSI numbers on the LS (when at the same elevation) at 100 ft. I was getting -85 dBm for both the internal and external antenna.

Typically my LS simply will not see a UHF signal when I am more than a few feet from the base and will be directed to change to the external antenna. I was very surprised to see that when conducting the test, the numbers did not change by more than 1 dB/m.

Please note that I leave the external antenna permanently installed. It's in place when instructing me to switch to external. When I tested the internal antenna I disconnected via the software only.

I didn't realize when testing that the modulation should have been changed. It was set at d8psk.

I suspect that the radio may not be working correctly and impacting the collection time.

If those numbers are correct, that's a difference of 54 db/m. If every 3 db doubles the power, does that mean my unit is seeing a signal 2^17/m lower than what is expected?
 

Matt Johnson

Well-Known Member
5PLS
I was using my LS and T1+ via UHF yesterday. The initial 90 mins of a topo it was taking 90 to 120 seconds to collect a point. The base was above me, in clear sight and the site was mostly open. The latter part of my survey it was taking 10-20 seconds to collect a point.
I suspect that the radio may not be working correctly and impacting the collection time.

What was the link quality when you were having problems? If LQ is less than 100% then the communication loss is causing problems.


I didn't realize when testing that the modulation should have been changed. It was set at d8psk.
The modulation should not affect the signal strength.


If those numbers are correct, that's a difference of 54 db/m. If every 3 db doubles the power, does that mean my unit is seeing a signal 2^17/m lower than what is expected?
It is 2^18 times lower than expected.


Have you tried your external base radio to determine rather the issue is with the LS or internal base radio?
 

Jim Campi

Active Member
What was the link quality when you were having problems? If LQ is less than 100% then the communication loss is causing problems.
Link quality is rarely 100%.
The modulation should not affect the signal strength.



It is 2^18 times lower than expected.
Got it, thank you.
Have you tried your external base radio to determine rather the issue is with the LS or internal base radio?
I was having the same problem with the external radio and T2.
 

Matt Johnson

Well-Known Member
5PLS
I can look at the radio sometime when you have it setup and running if you want. It sounds like the LS needs a RMA for the radio.
 

Jim Campi

Active Member
What was the link quality when you were having problems? If LQ is less than 100% then the communication loss is causing problems.


Now that I am thinking back on the survey, when I started the base and attempted to survey, I immediately received a message to connect the external antenna. I was 10 ft from the base and the UHF icon was red indicating a poor signal. For the next 90 mins or so, the collection of points was 90 to 120 secs. I am in the middle of the survey, trying to understand the problem and the system suddenly is now collecting points in a reasonable time period. At the end of the survey I tested the signal strength. If I would have done this at the beginning of the survey there would not have been a measurement at 100 ft with the internal antenna.

I can tell you that about the 2 years ago the nut that holds the uhf antenna male connector in place would continually loosen, allowing the connector to spin. At the time I was thinking that the wiring might be tightening up with every rotation. Perhaps this resulted in bad connection. Of course this does not explain the internal antenna not working.
 

Jim Campi

Active Member
I can look at the radio sometime when you have it setup and running if you want. It sounds like the LS needs a RMA for the radio.
I am working on a deadline this eve. I will send you a message if I finish early or perhaps you are available this weekend?
 

Matt Johnson

Well-Known Member
5PLS
I can tell you that about the 2 years ago the nut that holds the uhf antenna male connector in place would continually loosen, allowing the connector to spin. At the time I was thinking that the wiring might be tightening up with every rotation. Perhaps this resulted in bad connection. Of course this does not explain the internal antenna not working.
The wire for the antenna could have broke or become disconnected. There is a switch that switches that antenna between the internal and external feed. If neither work then then the wire is probably broken before the switch.
 

DickHeavner

New Member
So last evening I tested my HPT35BT radio using Matt's instruction and work sheet. It was getting late so I skipped the 4 watt setting and did 1 watt, 10 watts, and 35 watts.
BER was the same for all, 0E-0. RSSI on 1 watt was -47 dBm with external antenna and -54 dBm on internal. 10 watts had -50 dBm external, and -48 dBm internal. 35 watt setting shows -50 dBm for both internal and external. Signal strength showed around 85%. At 100' this seems to be a problem. With the onboard radio on my T-3 the signal strength was 100%, as expected.
I guess the HPT35BT is bad. The bad thing is, this radio hasn't worked right since brand new. After complaining about the range I was getting with it, Michael Glutting had me send it back to be checked. The only thing they found was when the radio got too hot, it quit working. So they sold me a fan for the radio. Still didn't get any range to speak of. If I could get 2000' with the radio on my T1-M, I could maybe get 3000'-3500' with the HPT35BT set to 35 watts.
 
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