Upper freq limit

[John Harper]

Hello all - Can someone tell me what sets the upper limit of the HL2 to 38 MHz? Is this a limitation of the radio's hardware (and is it an absolute limit) or firmware? I have an experimental license to transmit WSPR on 40.6 MHz and would like to not have to use a 28/40 transverter if I can help it.

Tnx/73,

John AE5X/WL2XZQ

[ron.ni...@gmail.com]

The AD9866 data sheet specifies a maximum ADC sample rate of 80 MHz and a maximum transmit frequency of 36 MHz.  So 40.6 MHz would be above twice the chips maximum Nyquist sampling frequency.  

The standard HL2 gateware uses a sample rate of 76.8 MHz, slightly lower than the spec'd max.  There's also an anti-alias low-pass filter on the HL2's transmit path (with a cutoff somewhere just above 30 MHz?)

For computer controlled modulation of WSPR beacons at 40 MHz (up to 200 MHz), I might try using a (buffered and bandpass filtered) Raspberry Pi GPIO pin and the WsprryPi software driver (on GitHub).  I've used that with success on the 20M band.

73,

Ron

n6ywu

[Steve Haynal]

Hi John,

As Ron said, the maximum according to the spec is a sampling rate of 80 MHz, so 40 MHz real theoretical bandwidth. In practice, we use 76.8 MHz because it is a nice multiple of 384kHz * 8, the highest bandwidth after DSP. supported by openhpsdr protocol 1 software. Furthermore, it is not best to use up to 76.8/2=38.4 MHz as you will start to see some aliasing and effects from the anti-aliasing filter. We used to run at ~73 MHz sampling rate and the AD9866 ran cooler. I think it will run very hot if you try to overclock it.

How much activity is there on 40.6MHz WSPR?

73,

Steve

kf7o

[Reid Campbell]

Hi John,

The following two links on under sampling might be of interest to you. There are problems at 50 MHz but 40 MHz might work.

http://g4jnt.com/FDM-DUO_at_VHF.pdf
https://github.com/ji1udd/Hermes-Lite/tree/6M

Cheers

Reid
Gi8TME/Mi0BOT  

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[John Harper]

Thanks for all the replies. Tracking says I'll receive my HL2 today - can't wait. I'll continue with my original plans for the 8m band and use the HL2 for other projects.

Steve, there isn't too much activity yet. Only 2 of us in the US have experimental licenses (others are applying); Ireland, South Africa and Slovenia hams have 8m without requiring special authorization. My license is good for 2 years...hopefully by then there will be more activity. The other US station's WSPR signal was recently copied in Ireland.

73,

John AE5X

https://ae5x.blogspot.com/