MicroP25RX

[kb8q]

I trust Todd's abilities to sort out what will work for 700 & 800 MHz freqs being used at the same site. (This is common, and growing, with MPSCS. I presume the same goes for other large systems.)

As of the middle of this month 37 of the 208 Michigan sites now have both 700 & 800 MHz freqs. 4 of those are in Oakland Co where I live. As utilization of the statewide system continues to increase, the use of the 700 MHz freqs will probably continue to expand.

 

[dispatchgeek]

As of the middle of this month 37 of the 208 Michigan sites now have both 700 & 800 MHz freqs. 4 of those are in Oakland Co where I live. As utilization of the statewide system continues to increase, the use of the 700 MHz freqs will probably continue to expand.

It appears the combo 700/800 sites are a standard practice for not only new sites, but additional capacity on the MPSCS. It will grow in a big way as time marches on.

 

[maus92]

It's fairly common to see both 700 & 800 channels in a system and within sites. The District of Columbia P25 system has been this way for many years now, as has Harford County, MD which joined a regional 700 system and "donated" their existing 800 channels and some tower resources to expand the simulcast site that covers their county.

 

[btt]

Regarding the 700/800 systems, I hear you guys. In addition to the current single-band with high stop-band attenuation (>60dB) design, there will eventually be a slow-roll off filter covering the full 700/800 bands option or a more expensive (and larger) dual-switched filter with 60+ dB stop-band attenuation version available. I will have more details soon.

 

[btt]

I will have zoomed-in plots later, but this should give you an idea of the filter options I have now. Both filters are < 3dB insertion loss despite the one plot showing >4dB in this image.

 

[ScannerDude244]

Here's what mine looks like I dont have 800mhz. but I bet that filter will help some

 

[btt]

Here's what mine looks like I dont have 800mhz. but I bet that filter will help some

Yes, the 700 filter should eliminate that.

 

[btt]

Status update time. I received the analog boards. I had a lot of issues getting the first board up and running. I finally came to the conclusion it wasn't a design issue and that I should build a 2nd prototype. The 2nd board works! Unfortunately, I did make a few mistakes in the design and will not be able to use these boards for production. This may turn out to be a good thing. I will use this opportunity to design around the feedback regarding the need for a dual-band (700/800) filter solution. The largest problem with this small design is dissipation of the heat generated. The main voltage regulator (linear) can easily supply the currents, but only if the junction temperature is kept low enough : ) It wouldn't take much extra board size to resolve the thermal issue. A short 2 inch length of wire soldered to the thermal tab kept it running all night at room temperature. I'm favoring changing the design to include 2 front-end filters, with an automatic RF switch for selection based on tuned frequency, adding a header to allow directly plugging into the Wio-Terminal. I need to decide if I want to try and use the Wio-Terminal battery or have the new receiver supply power to the Wio Terminal. I welcome any thoughts feedback on this. Note that I'm not ditching the idea of the multi-receiver, single-band receiver idea yet. That will be a different product. I uploaded a short video demonstrating the prototype.

 

[FreqNout]

Super work! Header for the Wio is good news. Great work on the filters, too. Not a lot of options for cell blocking filters for the scanner crowd.

Re: The Wio battery chassis may not be an option as it is out of stock at most places with no ETA.

Edit: To be clear...The Wio Terminal device IS in stock at most venders. Digikey, Mouser, Adafruit, Amazon, etc. The battery chassis is not.

 

[cheif]

The audio sounds great. Could you put another board on the bottom for the filters make the case a little thicker and cut slots on the sides to dissipate the heat. Just a thought.

 

[btt]

The audio sounds great. Could you put another board on the bottom for the filters make the case a little thicker and cut slots on the sides to dissipate the heat. Just a thought.

Thanks. The filters (IF / front-end) are already on the analog board. The board in the video has the 850 MHz bandpass installed. A small increase to the pcb size / power planes (for heat dissipation) would be sufficient. Good thoughts. My original plan was to add two more pcbs for covers/rf-shields with silk-screening and buttons for a really small final product. The next rev will have more surface area, a metal-can rf shield, and will be sized to snap to the back of a Wio-Terminal display with the connecting header supplying power and a communications interface to the display (SPI master/slave).

 

[rr60]

Todd, audio sounds real nice. I am just starting down the Wio terminal path now, thanks to all for the PDF how to. I suspect header for that would be most welcome. Kudo’s.

 

[raidamation]

Great work Todd. I like the progress you are making. As for the Wio terminal battery I am okay with not using it. I only get 45 to 60 minutes time now with the current P25RX. If I need to I can use a USB battery. Keep us informed and place me towards the top of the order list.

 

[W0RS]

Status update time. I received the analog boards. I had a lot of issues getting the first board up and running. I finally came to the conclusion it wasn't a design issue and that I should build a 2nd prototype. The 2nd board works! Unfortunately, I did make a few mistakes in the design and will not be able to use these boards for production. This may turn out to be a good thing. I will use this opportunity to design around the feedback regarding the need for a dual-band (700/800) filter solution. The largest problem with this small design is dissipation of the heat generated. The main voltage regulator (linear) can easily supply the currents, but only if the junction temperature is kept low enough : ) It wouldn't take much extra board size to resolve the thermal issue. A short 2 inch length of wire soldered to the thermal tab kept it running all night at room temperature. I'm favoring changing the design to include 2 front-end filters, with an automatic RF switch for selection based on tuned frequency, adding a header to allow directly plugging into the Wio-Terminal. I need to decide if I want to try and use the Wio-Terminal battery or have the new receiver supply power to the Wio Terminal. I welcome any thoughts feedback on this. Note that I'm not ditching the idea of the multi-receiver, single-band receiver idea yet. That will be a different product. I uploaded a short video demonstrating the prototype (see the video description for more details).

edit- I forgot to mention that the firmware is coming along very nicely for the new processor. The demodulation and decoding is very solid. A bunch more work has been done to get the audio perfected. It sounds really good now! I will work on getting these developments into the other models very soon.

I believe for me anyway, that having the new receiver supply power to the wio terminal would be very beneficial. I currently have both the wio terminal and wio battery supply, but I now have a P25RX-II that I don't believe the wio battery is enough....Great work your doing!

Status update time. I received the analog boards. I had a lot of issues getting the first board up and running. I finally came to the conclusion it wasn't a design issue and that I should build a 2nd prototype. The 2nd board works! Unfortunately, I did make a few mistakes in the design and will not be able to use these boards for production. This may turn out to be a good thing. I will use this opportunity to design around the feedback regarding the need for a dual-band (700/800) filter solution. The largest problem with this small design is dissipation of the heat generated. The main voltage regulator (linear) can easily supply the currents, but only if the junction temperature is kept low enough : ) It wouldn't take much extra board size to resolve the thermal issue. A short 2 inch length of wire soldered to the thermal tab kept it running all night at room temperature. I'm favoring changing the design to include 2 front-end filters, with an automatic RF switch for selection based on tuned frequency, adding a header to allow directly plugging into the Wio-Terminal. I need to decide if I want to try and use the Wio-Terminal battery or have the new receiver supply power to the Wio Terminal. I welcome any thoughts feedback on this. Note that I'm not ditching the idea of the multi-receiver, single-band receiver idea yet. That will be a different product. I uploaded a short video demonstrating the prototype (see the video description for more details).

edit- I forgot to mention that the firmware is coming along very nicely for the new processor. The demodulation and decoding is very solid. A bunch more work has been done to get the audio perfected. It sounds really good now! I will work on getting these developments into the other models very soon.

 

[btt]

I finished the routing of the analog board for the MicroP25RX rev-2 today. It ended up being 2.7 x 1.4 inches. This design is going to cover the 700/800 bands. It will be low cost. It will allow for a 2nd pcb to act as a cover / RF shield. There may end up being multiple options for this cover pcb. The first option will be an adaptor board that will extend up the backside of a Wio Terminal and will have a 40-pin (2x20) connector that will allow snapping the Wio Terminal onto the board. The connector will allow the MicroP25RX to communicate with and provide power to the Wio Terminal. This pcb will also allow attaching a couple of interlocking pieces that will form a base/stand with some selectable angles. The SD card, audio jack, and SMA connector will be easily accessible in the area between the Wio terminal and the base where the MicroP25RX receiver will set. I'll try to put a visual together if the description isn't clear. Next step is to get the bill-of-materials together and get the 2nd round of boards ordered.

 

[btt]

Bad news guys. Mouser and Digikey (my two main vendors) have changed their policy in order to save the earth or whatever. They talk about rare resources and prioritizing customers with important projects, etc. I normally design around part availability. This was true before the parts shortages, but especially now. So, even though they have tens of thousands of certain parts available and in stock, they will only sell me small quantities. Mouser said it was because they recently classified me as a reseller and Digikey would not give me a reason. I let them both know that I brought them millions of dollars in sales over my career, but that doesn't seem to make any difference. I may try and see if I can find others with more pull to order for me, but this makes it very difficult to design if you don't know what parts they are going to pull this crap on. I'll think about how to proceed this evening and update you when I have a plan.

 

[btt]

I found another vendor and have a request for quote in. We'll see how that goes. Here is a short video showing a model rotation to give you an idea of how the MicroP25RX rev2 (analog + digital boards) and Wio Terminal adapter stack up.

 

[freqseeker]

I think that looks good. I'm sure it will, but in case the Wio becomes scarce the MicroP25RX will work without it correct? I know raspberry pi's are hard to get and double the price now.
It's crazy that the vendors are limiting quantities like that. You have my luck, just can't catch a break.

 

[btt]

I think that looks good. I'm sure it will, but in case the Wio becomes scarce the MicroP25RX will work without it correct? I know raspberry pi's are hard to get and double the price now.
It's crazy that the vendors are limiting quantities like that. You have my luck, just can't catch a break.

Thanks. Yes, the display is not needed for it to receive and output audio. Yes, I've been doing business with Mouser and Digikey since the 80's. I've said many times over the years that Digikey was my favorite company to deal with. I guess all good things come to an end. It feels like the end.

 

[cmjonesinc]

If you wanted to email me those parts I'd be happy to buy my limited quantity worth and send them your way at cost. I'm certain others feel the same way.