OpenGD77

kt4lh wrote: ↑

Thu Jan 30, 2020 11:55 pm

If you want to include a 50mW setting and get some feedback I imagine there are people that'd be willing to help. I can't measure mine, I have a junky meter that I'm not sure it's even accurate down below 5w honestly so I can't help out too much with calibration but can give you some feedback on 50mW hotspot usage.

VK3KYY wrote: ↑

Thu Jan 30, 2020 9:59 pm

I did some more tests and have slightly adjusted the parameters (scaling factors) for the 2,3 and 4W as well as the fixed offsets I use for the 250,500 and 750mW values.

One thing I have noticed is that the battery voltage makes a big difference to the output power.

My battery was at 100% and the battery screen displayed 8.3V.

I noticed if I transmitted on hight power, with the power meter connected, the power would start to drop after around 10 seconds, by a few hundred mW.

So I don't think we're ever going to be able to get completely accurate power outputs.


The other thing I tried was to completely turn off the PA, and I found that my Duplex Hotspot did not detect any signal from the radio, even though it was less than 1m away.

My other radios e.g. other GD-77's can detect the signal, but the hotspots are not very sensitive.

Currently power levels below 1W are calculated by subtracting a fixed value from the value required for 1W (from the calibration data)
However, I think that I should probably change this, and use a fraction of the value required for 1W.

But to get 250mW, the fraction would not be 1/4 (0.25) as the power curve is non linear.

I know people would like a 50mW setting, but I wonder whether the hotspots are sensitive enough even to receive a 50mW signal when you may be in another room and have multiple walls between the radio and the HS.

kt4lh wrote: ↑

Fri Jan 31, 2020 2:27 am

Interesting, my hotspot doesn't hear anything on 50mW, even close. 75mW seems fine. Even across the house. Like 50mW isn't doing anything at all.

Messed about a bit more, 50mW if the HT is literally touching the hotspot is heard, signal seems good, S9+30 but anything a inch or two away, nothing. 75mW is sketchy if it'll work. 100mW seems okay.

NA7Q wrote: ↑

Fri Jan 31, 2020 2:47 am

Hotspots are notoriously deaf.. To say the least. I was able to hit my repeater at 17 miles away with an RSSI of -103 at 50mW, and I'm not at all line of sight. And the signal increased accordingly as the power went up. So it's outputting power, but I wouldn't expect the hotspot to hear it well, or at all as you get much lower than 500mW.

kt4lh wrote: ↑

Fri Jan 31, 2020 2:53 am

250mW has worked since I moved to OpenGD77, I'm never more than like 30 feet from the hotspot generally, so it's not exactly DX but it's just a Pi-W-Z sitting on the desk with the junky antenna that came with the MMDVM, seems fine. For all I know, maybe 50mW is outputting zero on my radio, I have no way to tell.

Also don't have any sane way to tell if 100mW uses less power than 250mW, but always happy to test and report what I see. What do you guys use to measure such power levels?