[Lowfer] dds for dreamers band?

[John Andrews]

Jim,

Two issues that come to mind:

1. Stability. If the DDS is clocked by the typical on-the-board crystal 
clock oscillator, it will not be stable or accurate enough for the slow 
speed, phase stable modes typically used for weak signal work at VLF. 
Those clock modules are subject to temperature, power supply and crystal 
aging variations. On the other hand, if you can provide an external 
clock signal that is GPS-locked, then you would be all set.

2. Exact Frequency. The typical 32-bit DDS frequencies will have 
round-off errors down in the milli-Hertz range, because they are fed 
integer numbers rather than floating-point numbers. All you need to do 
is to refer to the chip manufacturer's docs, and do the calculation for 
what the output frequency would be from that close (but not exact) integer.

Also, and others who know more about the topic can correct me, the lower 
limit for regulation in the U.S. is now 8.3 kHz. There may also be some 
restrictions for meteorological research work. Regulations in Europe, 
where most of this activity has taken place, may vary or the users may 
be working from special permits. Just a thought.

John, W1TAG

On 3/21/2020 8:18 AM, James Fisher wrote:
> I have a chinese dds vfo in my junkbox. It is capable of putting a signal
> out on the dreamers band at 9kc. Is a dds vfo stable enough for use on this
> band considering the slow data rates needed to make contact?
> 
> Best Regards
> 
> Jim
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