Re: Strefans LF: LF/MF modification of TS850 for LF

[Stefan Schäfer <Stefan.Schaefer@iup.uni-heidelberg.de>]

Hi Laurence,

Am 02.10.2012 23:20, schrieb Laurence KL7UK:

http://kl7uk.com/850.png
 
Stefan - heres the part of the circuit concerned - its the coupling after the 3rd mixer - so its at TX base band frequency, so I can see perhaps why this C219 could be increased to reduce LF losses, but not a lot me thinks as the reactance to "Earth" is pretty low at 137 - the aim is to improve LF without mucking up the HF side so you can only go so far.

Maybe you can make a series resonance for LF by adding a L in series. This L must have a C in parallel or a low self resonance frequency. My first guess...
At least a to high C across C219 will make a almost short cut for HF to ground...

 
Still very poor LF and MF - nearly no signals from Siberia/Mongolia on LF - still at least the snow has stayed away. Loran was around 15dB down from "average" last nite. Getting very dark in the mornings and a Huge Male Moose ran into a car on the road into work this morning - both car/driver and Moose didnt make it.

R. Tell me when the band opens. BTW i'm 3...5 dB stronger since the last success in december so we may play a lot more this year.


Just played arround with a NE612 for the first time in my life ;-) Quite useful IC! It became a 475 kHz transmit mixer (460 kHz LO) and is used in combination with my mechanical filter which i use for MF RX as well. Then applying white noise from the SpecLab SG i can see the resonance curve again, now confirming > 50 dB att. in 2 kHz outside the passband!

73, Stefan/DK7FC