[time-nuts] new WWVB BPSK dev board

[jimlux]

On 12/4/18 1:48 PM, Attila Kinali wrote:
> On Tue, 4 Dec 2018 13:12:48 -0800
> jimlux <jimlux at earthlink.net> wrote:
> 
>> I maintain that it's the lack of a cheap RF front end that is the sticky
>> point.
> 
> Doing a 2-3 stage transistor based amplifier should give the signal
> enough gain to be sampled with the ADC of a uC. I have such a design
> sitting around, that I did a couple of years back for DCF77, but never
> got around to actually built it (see attachment).
> 
> It is meant to be run from 4V, so that one can use an unstable/noisy
> 5V source with an 4V LDO and should give ~70dB of total gain. I used
> BC547 in the simulation, but any NPN with decent h_fe and f_t should
> do (eg 2N2222, 2N3904,...). The 2N5484 is a bit harder to replace,
> as I selected it for its low V_th and narrow specified V_th range.
> 
> All that is needed for this to work is a tuned antenna, ie a ferrite
> rod with a capcitor on it that is approximately tuned to 60/77.5kHz.
> 
> 			Attila Kinali
> 
> 

17 passive components and 4 active components. plus the loopstick and 
tuning cap. I think you'd need pretty substantial volumes to get the 
"assembled and delivered" price below $20.

I usually use the rule of thumb that the BOM cost has to be 1/5th to 
1/10th the retail price.  So $2.
You might get there.. the MMBF5484 is 12 cents in qty 100. I assume you 
can find a NPN for less than 10 cents - The LDO might be the most 
expensive part.