Frontend design 6m-4m-2m-70cm

[PE5PVB]

I'm thinking about designing a frontend for these VHF bands in use for the Minitiouner. It also should have a spectrum view in a display and an option to manually finetune the received channel. Second, filter it with a narrow SAW filter to 315MHz.

Attached a raw sketch of my plans. I do have a lot of experience designing for 70cm and up, but not with the VHF bands. Maybe you guys can give me some tips for filtering and frontends on 6m, 4m and 2m.

[PE5PVB]

Schematics

[G4EWJ]

Just a thought for future-proofing. Whichever NIM is used after the supply of FTS4334s is exhausted may not work below the standard satellite band edge of 950MHz.

An output above 950MHz might be useful. Also a 740MHz LNB input, with psu option.

Brian

[G3VZV]

Wondering if there is any possibility of including the provision for a 29 MHz input?
thanks
Graham G3VZV

[G3VZV]

Wondering if there is any possibility of including the provision for a 29 MHz input?
thanks
Graham G3VZV

[g0mjw]

This is a good idea but looking a little complex, I would make it modular as far as possible. So you have a block for each band, maybe a common 1 GHz LO would put everything within range of a standard NIM.

Ideally we need to find a way to receive RB DATV without relying on upconverting and a NIM not designed for the lower symbol rates, then we would not need anything other than a standard SDR, preamps and filtering. What we lack is the modem. There are software solutions out there but not as good as the NIMs, The NIMs chipsets are now so highly integrated with the tuners we can't use them directly. I am not sure why the software solutions are not as good, maybe it is the processing power required.

Mike

[PE5PVB]

About 10 meters. Are countries outside Europe allowed to transmit DATV on 10 meters? For example, in USA it is not allowed.
Second, I think DVB-T will work better at 10 meters.

I use 315MHz because a lot of narrowband SAW filters are available and it's far enough away from our bands.Another option could be 915MHz.

Just coded the bandscanner, I now can see my DVB carrier on a small 128x128 pixel OLED display.

[g0mjw]

I am not sure the US can or can't but they are only one out of hundreds of DXCCs so it is not especially important if they are excluded. There is nothing to stop them receiving impatiently waiting for more common sense regulations.

I agree DVB-T will work better, but perhaps we should also be looking at DRM which is designed for HF. The older standard allows up to 60kb/s so we would be looking at DRM+ I think, or maybe something in between.

The reason I was suggesting 1 GHz is because the standard tuners tend to cover 950-1750 and sometimes higher. Perhaps 23cm IF would make sense. You can get SAW filters, but they cost quite a bit more if not on a common frequency.

Congratulations on coding the OLED. Do you think you could display it on the Minitiouner OLED or the Minitiouner Pro TFT LCD?

Mike

[SkyVision]

Hi Sjef

Looks good, I like it

Mouser are reporting the LO transformer is end of life
Also the UPC2750 is discontinued
I noticed that it's a 75ohm transformer, does that provide a better match or more level than a 50ohm one?
I think you are on the right track and people can "forkanbodge" it to their own spec if they want

I'm sure if the ADF4351 was attached that would be handy
External reference as an option seems very popular too these days
LO purity and correct level is helpful
Do you need any contributions to get this moving

Cheers Roger VK5YYY

[PE5PVB]

Hi Roger,

About the transformer. I used this transformer in other projects with the ADF4351. It's easily available on Aliexpress and not that expensive. If you have a better idea, please let me know.

About the UPC2708, I choose this one just because I have over 100 in stock. I know it's obsolete, but also easily available at Aliexpress. My experience with this one is that it has less pulling on the ADF4351 than other MMIC's I've tested in the past. Also it has the exact signallevel to drive the mixer.

I don't want to use the external ADF4351 boards, because the RF is very dirty. I used this circuit on other project to get a very clean carrier. I know not everyone is able to solder these chips, but it's a good stimulance to learn it

I use a 25MHz TCXO and added a trimmer to calibrate the frequency.

Yesterday I took the change to draw the PCB. It will be a 74x55mm PCB. I'm now working on the controller PCB. I'm testing several displays to select the right one for the spectrum display. First tests with an I2C OLED are good, but the display was rather slow (building a full screen took about 1.5S). This week I'll try SPI LCD's on higher datarate, but I also need to take into account that these SPI lines can cause RFI.

DATV_Frontend.jpg (116.77 KiB) Viewed 4250 times

The RFM69 is mounted at the bottom of the PCB.