Hardware

[G4KLB]

First 3 Prototypes ready for testing.

Plenty of work to do but a good start to the year.

First 3 test.jpg (950.51 KiB) Viewed 9391 times

[g0mjw]

Looking good. Nice to see its mainly surface mount, which I find so much easier to build than through hole once you know what you are doing and also the mounting holes so it can be easily put into a box.

If you have to re-spin the PCB might be worth getting that LO input SMA a but further away from the heatsink. Maybe on the board edge to facilitate mounting. Also a bit more copper around the Modamp tab might keep it a bit cooler.

Mike

[M0DTS]

Looks good, just what i wanted to do back when i started with DATV but never got round to it!

My only worry is how wide the signal is at low SR for use at 146MHz..?
It's normally 400KHz wide at 333Ks with shoulders some 50+dB down after that (due to the digital filtering with digithin or when using DATV Express), with an analogue filter the spectrum shape will be similar to digilite and only be 20 odd dB down at 800KHz bandwidth, then rolling off rapidly?

Would be interested to see the spectrum, but the other argument is, who else is actually using 146-147MHz.. nobody as far as i'm aware!
Wonder how much all the filter parts actually cost?

Rob

[MN-tech]

Hi Rob,
The 2 filter chips for SR125 to SR500 are LTC1569CS8-7 ($12.31 each). That's a 10th order filter.
From the datasheet;
The filter attenuation is 57dB at 1.5 • fCUTOFF, 60dB at 2 •
fCUTOFF, and in excess of 80dB at 6 • fCUTOFF.
The Digi-Key cost of all the LC filter parts is $6.84
John

[M0DTS]

Aha,
I missed the part of still using those filter chips, I'm a bit out of touch with the current home brew setups since getting the Express board!
Still much cheaper than custom uC/dac digital filter.

All is well!

Rob

[g0mjw]

Hi Rob,

The spectrum output from my second Digithin using filter chips is not as good as the first which is using the PIC. Neither are good as my DATV Express. This new design may be much better, I am looking forward to seeing how well it performs. Fortunately, now everyone can afford a spectrum analyser in the form of a TV dongle, transmitted spectrum can be readily monitored. If we ever get a higher power limit on 2m the cleanliness of the modulator may be an issue, though it may be masked by the spreading of the high power amplifier. We currently get around this by using 70W devices in class A at 3W output, but getting significantly more power is likely to be a challenge.

The LimeSDR can generate a clean modulation and may be able to support closed loop linearisation. I know you had some success with an open loop, but I think that closed loop would be beyond the processing capability of a PI and I am not sure if there is enough capacity in the FPGA to do it on board so likely to remain a niche activity for some time yet.

Mike

[DG8KD]

Hi,

I personally would prefer the good old wired components as they are much easier to solder than SMD.
I am not equipped with SMD soldering facilities and also my eyes/glasses aren´t so good ....

Does the shop will offer a fully assembled and tested board?

[keng8vdp]

Thanks for the photo, Looking great.
I am wondering how many people are holding their breath in anticipation.
The airwaves, forums, social media, is awash with people talking about it. All my friends are gearing up. This old dog is gearing up too.
Trying to understand all the terminology and technical stuff can be tricky , even that on the above posts leaves me baffled.
Having said that , that's what makes it interesting and any challenge is food to keep the brain active.

Now, get on with it please .... I can't wait much longer ( smiley )

Good luck ..Ken G8VDP

[Wolfie G8VAT]

Noooo..

Can you leave it at least a week? I'm skint until Payday.

Yes, I'm gearing up for it too.

[G4KLB]

Testing is proceeding better than anticipated, with only the levels we were expecting to fine tune to confirm correct.
The hardware side will soon have the green light to go into production and the parts list will be made available.
I expect Wolfie will have been paid by then