Knucker beta testing feedback

Discussion about the Knucker DVB-T Tuner DVB-T Receive Software. See also https://wiki.batc.org.uk/Knucker
f4fdw
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Re: Knucker beta testing feedback

Post by f4fdw » Thu Jan 21, 2021 8:00 pm

Today, test with lp17 on PC win10 and knucker on Jetson nano, thanks to Charles for the linux ARM version, it works well with a bandwidth of 150khz in 16qam and 64qam, all that remains to be amplified because the pluto does not gives no more than -23dbm !!!!!

73 Laurent F4FDW

G4GUO
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Joined: Tue Feb 16, 2010 12:51 pm

Re: Knucker beta testing feedback

Post by G4GUO » Fri Jan 22, 2021 10:10 am

Being the lazy person I am, I now have a second 'Knucker' rather than assembling a board I simply swapped over the NIM on a Minitiouner 1.0,
cut the 5V track to pin 5 on the board, grounded pin 5 and 6, cut the track supplying pin3 with 3v3 (probably not necessary to do).
put a 150K resistor in parallel with R5 (to set the supply voltage to 1.2V) and changed the name in flash memory of the FTDI chip to
CombiTuner-Express.

The inspiration was from Brian G4EWJ who posted a picture of a Minitiouner 1.0 being used as a Knucker.

A bit of upcycling!

- Charles

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G1LPS Terry
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Re: Knucker beta testing feedback

Post by G1LPS Terry » Fri Jan 22, 2021 10:20 am

Test today
Express TX at 150khz and above.
RX on knucker Portsdown4
All working. Also tested BBC1 broadcast DVB-T at 8000khz and that works well on the Portsdown 7" display.

Had a contact with M0DTS a few days ago on DVB-T 16Qam 500 and 1000khz

BR
Terry G1LPS

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G1LPS Terry
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Re: Knucker beta testing feedback

Post by G1LPS Terry » Tue Jan 26, 2021 8:59 am

Summary of brief testing.

Last night ran some tests with M0DTS on 437.5Mhz
Pluto TX c920 and Portsdown4 RX no preamp and 1mhz wide filter 9element Tonna
The 26KM link was on the edge at 50mw and 1000khz
Lowest we could decode was 150khz. which was reliable (140khz 125khz wouldn't go)
Once the bandwidth was below 500khz the SNR dropped and the power levels had to be increased to maintain the link.
Loss of signal to re-displaying a signal is around 10 seconds at the lower khz bandwidths.

Terry

G3GJA
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Re: Knucker beta testing feedback

Post by G3GJA » Tue Jan 26, 2021 3:52 pm

Noticed an anomaly with the keyboard frequency entry.

I've only found it around 513.800MHz so far and it may be insignificant on an 8MHz wide channel but it may be more of an issue on the narrower bandwidths used for DATV if the same problem occurs in an amateur band.

Enter 513.82MHz and the green highlighted frequency shows 513.82
Enter 513.810MHz and it shows 513.809
Edit the key again and it has retained 513.809
Enter 513.800MHz and it shows 513.799
Enter 513.790MHz and it shows 513.789
Enter 513.780MHz and it shows 513.78

Clive G3GJA

G8GKQ
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Re: Knucker beta testing feedback

Post by G8GKQ » Tue Jan 26, 2021 4:50 pm

Thanks Clive

It won't surprise you to hear that this is a "float to integer to float" rounding error involved in the conversion between MHz and kHz and back. I've put a small bias in there now to try to make sure that it always falls the right way. It'll be in the next update.

Thanks for reporting this.

Dave

g8vpg
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Re: Knucker beta testing feedback

Post by g8vpg » Fri Jan 29, 2021 5:02 pm

My Knucker is now finished and boxed up and working well. UPS took ten days to get my Digikey parcel from Donnington airport! I am using the latest version of Express software with the DATV Express hardware. Across the bench, this is working well, although I could not get 125kHz bandwidth to lock on Portsdown 4. Two other local stations are also building the Knucker and so I hope to do off air tests soon. I am unfamiliar with DVB-T and hence it would be useful if someone could write a basic primer about the various settings and perhaps initial values for best quality, dx etc.
73 Shaun.

g8gtz
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Re: Knucker beta testing feedback

Post by g8gtz » Fri Jan 29, 2021 5:59 pm

Hi Shaun,

Well done for getting the build complete - surprised about Digikey, normally very fast.

We have noted that the system does not currently perform reliably below 250KHz so suggest you focus testing above that bandwidth.

Re DVB-T parameters, the first point to note is that we directly refer to the bandwidth and not symbol rate, which in DVB-S has an impact on bandwidth. And of course, the narrower the bandwidth, the better s/n ratio so it should go further....

There are 2 other parameters:

FEC performs the same function as FEC in DVB-S but changing it in DVB-T only affects the error correction and payload bits (hence picture quality) and not bandwidth as it does in DVB-S.

Guard interval is specifically related to multipath protection and nothing else and does again affect the payload bit rate - hence when we did tests on QO100 we set this to 1/32 as there is no multipath on the satellite link.

Charles may have some input on what parameters to set for what path but I suspect we don't really know what to expect, particularly on the lower VHF and HF bands - we suspect for 70cms mobile we will need heavy guard interval protection but of course we can't try that until the lockdown is relaxed :-)

Hope this helps

Noel

G4GUO
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Re: Knucker beta testing feedback

Post by G4GUO » Fri Jan 29, 2021 6:52 pm

Hi all,

I have no recomendations, personally I prefer to use wider bandwidths, lower order constellations and heavier FEC rather high order constellations
and very narrow bandwidths.

In a mobile environment multipath from buildings is around 5us I believe, short and sharp, again wide bandwidths allow for Doppler spreading as
the carriers are futher apart and the extra FEC allows for the deep spectral nulls.

- Charles

g8vpg
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Joined: Fri Oct 11, 2013 9:35 am

Re: Knucker beta testing feedback

Post by g8vpg » Sat Jan 30, 2021 3:38 pm

Just completed the first two way DVB-T contacts across Bristol between G4BVK & G8VPG. It is working well on 437MHz, 250-1000kHz bandwidth, up to 64QAM. I have also got Knucker working with the Ryde. I did notice that audio is about 20sec. behind the video. Thanks to everyone who have worked so hard to get this working.
73 Shaun.

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