MiniP25RX / Wio Terminal

[btt]

After receiving input for the MicroP25RX idea and building the first prototype of that design, I have been working on the next revision. Based on the feedback, I decided to start working on a dual-band receiver (700/800) with 60 dB stop band rejection of out-of-band signals (including cell tower downlinks). The feedback also seemed to indicate that it was important that Bluetooth remained and that the design could be interfaced with the Wio Terminal display. I will provide a block-diagram of the system soon, but first I would like some feedback on the mechanical aspect of the design so that I can get the next round of PCBs on the way. Please take a look at the image and let me know what you guys think. This PCB will plug directly into the back of the Wio Terminal (blue outline). At the lower side of the PCB, there are slots cut that will allow a couple of interlocking PCBS with slots cut at multiple angles (to accommodate viewing angle preferences). I want to get this right this time. This is why I'm sharing before I complete the layout and order more PCBs. The attached image is looking at the "backside" relative to looking at the Wio Terminal display attached to the other side of this board. Obviously this design will be more expensive than the MicroP25RX idea. I will do my best to keep the cost low, but this is definitely going to be more expensive.

 

[FreqNout]

@btt Looks like size will be about 4.5 inches x 4 inches?

I do like the multiple angled stand idea.

On the lower left would there be any desire to have an amp/speaker to make it a complete stand alone unit (if not using bluetooth). Just tossing out the idea.

Nice work!

 

[btt]

@btt Looks like size will be about 4.5 inches x 4 inches?

I do like the multiple angled stand idea.

On the lower left would there be any desire to have an amp/speaker to make it a complete stand alone unit (if not using bluetooth). Just tossing out the idea.

Nice work!

Thanks. Yes, 4.2 x 3.5 inches (not including the length of the SMA connector). I thought about adding an amp / speaker, but that area will be needed by some of the other components and possibly another shield. I experimented with some small speakers in the past and they were definitely less than what I hoped for. The speakers in cell phones that sound good are somewhat special from what I can gather. Anyone have more information on a cheap cell-phone type speaker?

 

[FreqNout]

I experimented with some small speakers in the past and they were definitely less than what I hoped for.

You are right. Small speakers can be a problem. Best to go with Bluetooth for good audio choices as many already have good bt speakers.

 

[btt]

I think my quick drawing in the first post is causing some confusion. I should have drawn the Wio outline with hidden lines to indicate it was on the backside of the board. The Wio Terminal is connected to the MiniP25RX board by the 2x20 pin header. Here is an updated drawing. If there isn't more feedback, I will start working on the PCB layout / routing tomorrow morning.

 

[brndnstffrd]

My thoughts on this are that my goal is to put the entire assembly inside of some type of enclosure, whether 3d printed or something to protect the PCB and to keep everything enclosed nicely. This would then be installed on some type of mount or bracket in my vehicle so centering the display left to right inside the housing would be preferred. I realize that the board could have the same offset that the picture shows and the enclose could just be made bigger so the display is centered, however that would leave extra space to one side, although if the extra space could be used for a battery......

One option to make centering for an enclosure easier would be instead of pushing the unit to the far side of the board, could the offset be vertical, instead of horizontal? Basically rotating the board 90 degrees?

 

[FreqNout]

@btt I have a few questions on the Mini vs. Micro designs.

The 'more expensive' part may be confusing some people. The dual bands/filters etc and the Bluetooth additions most likely driving up the costs.

In theory, would two single band Micros linked together be much more expensive than the Mini design?

Could this Mini be designed with the Bluetooth module as an add-on option that would lower the cost of not needed?

People could buy an off the shelf Bluetooth Transmitter for $30 if that were a less expensive way to go.

I really like the Micro design. But both are great designs!

 

[maus92]

My thoughts on this are that my goal is to put the entire assembly inside of some type of enclosure, whether 3d printed or something to protect the PCB and to keep everything enclosed nicely. This would then be installed on some type of mount or bracket in my vehicle so centering the display left to right inside the housing would be preferred. I realize that the board could have the same offset that the picture shows and the enclose could just be made bigger so the display is centered, however that would leave extra space to one side, although if the extra space could be used for a battery......

One option to make centering for an enclosure easier would be instead of pushing the unit to the far side of the board, could the offset be vertical, instead of horizontal? Basically rotating the board 90 degrees?

I'm not so sure a Wio screen display will be readable inside a vehicle during the day. It would need some serious nits.

 

[btt]

@btt I have a few questions on the Mini vs. Micro designs.

The 'more expensive' part may be confusing some people. The dual bands/filters etc and the Bluetooth additions most likely driving up the costs.

In theory, would two single band Micros linked together be much more expensive than the Mini design?

Could this Mini be designed with the Bluetooth module as an add-on option that would lower the cost of not needed?

People could buy an off the shelf Bluetooth Transmitter for $30 if that were a less expensive way to go.

I really like the Micro design. But both are great designs!

It all starts adding up. Because of the dual filter path, the signal has to pass through two switches causing more insertion loss. Because of this, I decided to add an amplifier and pre-selection filter before the switches / filters. PCBs are priced by area (L x W). With all the added current, there are multiple voltage regulators. It really needs to be USB type-C for the extra current, so that was added. There is an RF shield + cover. There are also some extra filters and amps. This is going to be a really nice receiver, but it will cost more. I'm willing to drop this for now and go back to making the smallest / cheapest possible if that is what will generate more interest in sales.

 

[btt]

My thoughts on this are that my goal is to put the entire assembly inside of some type of enclosure, whether 3d printed or something to protect the PCB and to keep everything enclosed nicely. This would then be installed on some type of mount or bracket in my vehicle so centering the display left to right inside the housing would be preferred. I realize that the board could have the same offset that the picture shows and the enclose could just be made bigger so the display is centered, however that would leave extra space to one side, although if the extra space could be used for a battery......

One option to make centering for an enclosure easier would be instead of pushing the unit to the far side of the board, could the offset be vertical, instead of horizontal? Basically rotating the board 90 degrees?

If you could do a quick hand drawing or something to show what you are thinking with the new placements for connectors, etc, I will consider it.

 

[goldmyne99]

I really like the Micro design. But both are great designs!

I agree both designs ARE great. Nice job @btt !!

.... This is going to be a really nice receiver, but it will cost more. I'm willing to drop this for now and go back to making the smallest / cheapest possible if that is what will generate more interest in sales.

That is the bottom line. @btt needs YOUR feedback!

Regarding Bluetooth: I was thinking the Wio Terminal Bluetooth would be an option for the new design. Unfortunately, there has been no Bluetooth A2DP (audio) code developed for the Wio. Using the Wio Bluetooth is a deadend right now.

: BTW, I have been running the MicroP25RX (smaller design) for days now without issue after adding a small heat sink. I can definitely get that design to work without issues.

EDIT: I am a big fan of the MicroP25RX design.

 

[btt]

That is the bottom line. @btt needs YOUR feedback!

Yes, it really does come down to that. I want to do what will generate the most interest to start with so that we can keep this going. I am currently out of stock for the P25RX-II due parts shortage, so I need to do something that I can execute somewhat quickly. I could remove the highly selective filter from the front-end of the MicroP25RX and replace it with a slow roll-off 700/800 filter. That would keep the design small, inexpensive and allow 700/800 MHz operation.

 

[FreqNout]

I could remove the highly selective filter from the front-end of the MicroP25RX and replace it with a slow roll-off 700/800 filter. That would keep the design small, inexpensive and allow 700/800 MHz operation.

You got my vote!

How would the dual band slow roll off filter compare to the P25RX and the RXII filters?

Edit: Any chance an off board or inline 700 MHz cell band filter could be designed to be added to later?

 

[btt]

You got my vote!

How would the dual band slow roll off filter compare to the P25RX and the RXII filters?

Edit: Any chance an off board or inline 700 MHz cell band filter could be designed to be added to later?

The P25RX and P25RX-II are wide-band, slow roll-off. The filters block WiFi and Bluetooth well.

Yes, they could be added externally. I already have pcbs for supporting the new filters inline (male / female SMA), external to the receiver. This is how I characterized them with the analyzer. They are impressive, but are probably not needed in the majority of circumstances.

The less expensive design has my vote too. It seems this larger board may not be what everyone is looking for. Cheaper and smaller it is! I should be able to have another MicroP25RX board for 700/800 MHz bands ready to go within the next couple of days. I will update then.

 

[freqseeker]

The original P25RX's work great at my location on a external antenna, I have never experienced interference with my setup. The filtering works better than any scanner I own.

I want what is best for Bluetail Technologies to continue. My vision as a consumer is to eventually be able to go to the website and choose from multiple receivers, filters and accessories. I'm good with the cheaper route, but would like to see what the top of the line would look like. Modular is still a great idea so you can add to it as budget allows.

It's easy for me to say but accessories could be the money maker here. External filters, antenna multicouplers, proven antennas etc. It would take time for development, but I think it would pay off in the long run.

 

[btt]

I should probably make it clear that we are talking about the front-end filters here and not the IF filter. The IF filter is a narrow channel filter and greater than 90+ dB of stop band attenuation. This goes for the P25RX-II and this new design. That will not change.

 

[n0esc]

Late to the party here but throwing my vote for smaller/cheaper as being the good place to start. My vision is to replace cheap RTL dongles and a woefully underpowered W10 laptop to get something with better receive to feed to BCalls. Nice to have the Wio Terminal for quick visual diagnostics, but if this lives on a shelf and can manage to just run pretty much unattended that would be awesome in my idea case. Might be way out in left field here, but hopefully I am at least playing the same ball game.

 

[FreqNout]

I want what is best for Bluetail Technologies to continue. My vision as a consumer is to eventually be able to go to the website and choose from multiple receivers, filters and accessories.

I agree 100% @freqseeker

Yes, they could be added externally. I already have pcbs for supporting the new filters inline (male / female SMA), external to the receiver.

The inline 700 MHz cell band filter product has great potential for other radios, too. My sds gets hammered by LTE.

The less expensive design has my vote too. It seems this larger board may not be what everyone is looking for. Cheaper and smaller it is! I should be able to have another MicroP25RX board for 700/800 MHz bands ready to go within the next couple of days. I will update then.

There is a real need for a low cost P25 radio. Keep up the great work!

 

[maus92]

High performance and connectivity for future applications is my goal; cost is secondary.

 

[btt]

The inline 700 MHz cell band filter product has great potential for other radios, too. My sds gets hammered by LTE.

Although I thought it was bullet proof in the beginning, the original P25RX model has some issues with cell towers getting through the IF filter. It has a very good filter, but there are certain frequencies that can get through. The P25RX-II has a very good IF filter that stops everything outside the channel. It is very good. I'm not aware of cell phone towers being an issue for anyone. I went through many different approaches, filters, revisions, models, hardware to get that kind of performance. (for both P25RX models). As some of you probably know, once you get aliasing distortion, spurious, multiples of Fs, and other undesired signals entering the A/D converter, there is nothing you can do to fix it in the digital domain. The IF filter is very important. The front-end filters won't help with those issues, but it will definitely get rid of the issues with the AGC getting hammered / saturation of the front-end. I do plan on making some external filter products available. As freqseeker mentioned, I probably should start concentrating on those types of accessories to try and reach a wider base. I thank you guys for the support and feedback. I will continue to get the MicroP25RX ready to sell. I will also continue to produce the P25RX-II as soon as I can get parts again. It is a whole other story, but I am starting to wonder if things are ever going to recover. One of my main vendors is treating me like dirt now that they went to an AI based system. Their new "classification system" decided I am a reseller and that it can't sell me certain parts even if they have tens of thousands in stock. If you need to contact someone for help, IT is the help! Crazy times we live in. Hopefully things will turn around after the November cleanup.