Category: Ham Radio
Created: Monday, 05 October 2020 13:38
Last Updated: Monday, 05 October 2020 13:45
Written by Rick Swenton
Software Defined Radios offer an excellent view of the characteristics of transmitted signals.
Good operating etiquette requires that your signal occupies the smallest bandwidth for the mode of transmission. A Software Defined Radio is the perfect way to evaluate your signal.
Here's a view of a very wide SSB signal on 3868 kHz. You can see he is taking up almost 8 kHz. His signal should be under 3.7 kHz wide. My receiver bandwidth is set to 3.3 kHz. That is noted by the vertical yellow bars. He is occupying double the space he should. This is considered rude as it prevents other stations from using the band on either side of him.
Here is an example of a very nice SSB signal on 3868 kHz. His bandwidth looks like it is around 3 kHz. In the waterfall you can see the wide SSB signal below the good one. To the right there is an AM signal on 3885. Notice that the bad SSB signal is almost as wide as the AM signal. AM by its nature takes up a wider bandwidth. The audio is carried in both the upper and lower sidebands so it is twice as wide as SSB. SSB audio is carried in only one of the sidebands so it should be half as wide as an AM signal.
If your transmitter is operating properly there are steps you can take to be more polite and reduce your bandwidth. One is to reduce your mic audio gain. Don't use heavy compression. If you use speech processing make sure it's adjusted properly. Use equalization to reduce high frequency audio. Most importantly, ask a knowledgeable person on the air to evaluate your signal. Don't ask your best friend. He will always tell you that you sound great.
Category: Ham Radio
Created: Monday, 09 September 2019 18:53
Last Updated: Tuesday, 29 June 2021 15:55
Written by Rick Swenton
Radioddity markets a relatively inexpensive dual band DMR handheld radio called the GD-77. It is manufactured by TYT and is their model MD-760 but is not widely available. Radioddity markets this radio under their own name and provides a fully functional firmware and CPS. They also deliver reasonably timely updates to both the firmware and CPS, Radioddity provides excellent customer support.
Roger Clark, VK3KYY from Melbourne, Australia is a prominent figure in the ham radio DMR world. Roger modified the Radioddity CPS and released a "Community Edition" that provides compatibility among all the various versions of codeplugs and added features. Roger, Kai Ludwig DG4KLU, Colin Durbridge G4EML, Daniel Caujolle-Bert F1RMB and others are developing an open source firmware for the GD-77, DM-1801 and RD5R called OpenGD77.
For simplicity, when I mention GD-77, it means Radioddity GD-77 / GD-77S, Baofeng DM-1801 and RD-5R radios.
The firmware is designed for Amateur Radio use, especially on DMR, and has a number of features for Amateur Radio use which are not normally available on commercial DMR radios. These include direct numerical entry of DMR TalkGroup numbers and use of the Rx Group list to control the TG’s selectable for each DMR “channel”
I am fortunate to have been one of the original alpha testers for this firmware.
This new firmware begins to transform the GD-77 to operate the way hams would like to use it. For example, in the past we had to set up a channel for every talk group you want to use. Now you can set up one channel and just scroll through the talk groups. Another feature, shown in the photo above, is to use the GD-77 as a hotspot replacing your MMDVM or DVMega modem board. Just take a Raspberry Pi with Pi-Star and remove the modem board. Connect your GD-77 with the OpenGD77 firmware to the Raspberry Pi USB port with the GD-77 programming cable. Select OpenGD77 as your Radio/Modem type in Pi-Star and off you go. The GD-77 automatically detects Pi-Star and changes from handheld mode to hotspot mode.
In the past I was posting Roger's updates here on my web site. The improvements have been fast and furious. It was becoming difficult to keep this page updated. I thought I would just refer you directly to Roger's blog so you could get the most current information. For example, the June release now has a spectrum scan display on the screen.
The latest firmware now supports Hotspot Mode. Connect the GD-77 to the Raspberry Pi with the programming cable. Power up the GD-77 while holding the side black button. Then power up your Raspberry Pi running Pi-Star. The GD-77 must be powered up in Hotspot Mode before Pi-Star is booted.
If you want to test Hotspot Mode using Pi-Star you can leave your MMDVM HAT or DVMEGA HAT plugged into the Paspberry Pi. Just connect the GD-77 radio through its programming cable to the RPi and select OpenGD77 DMR Hotspot (USB) as the Radio/Modem Type on the Pi-Star configuration screen.
Here's Roger's Blog Page where you can learn all about the exciting developments. A conflict with the Open Source licensing has required a change in how the firmware and programs will be distributed. Consult the OpenGD77 Forum for more information.
Also take a look at Jason Reilly's page Modifications, hints, tips and technical information for the Radioddity GD-77
Running OpenGD77 as a Hotspot on BlueDV for Android
Riku Bister, OH1E, has a great Youtube video that explains how to get the OpenGD77 running as a hotspot on BlueDV for Android.
Please keep in mind that functionality between Open GD77 and BlueDV is not guaranteed. The developers for each project do not possess the hardware for each other's project for testing.