Very good chaps - yes the trick is to stay away from
some resonaces and get others! If it were soley for LF MF Id go in hard
and change that out put circuit but dont want to cripple the HF side as I can
still use it as a true transverter too - as L89 is accessible from the
top of the board I can play pretty easily and try a few things. Changing the
drive routing and termination Z will also have an effect which Ill
investigate
Ill do some more checking, but what is evident is that as the RX
is dang hot at LF/MF its going to be a pretty good addition to the
portfolio. Im presently building a 2X drive source from the 10MHz ref
which will replace the internal ref osc in the 850 and lock it down
- I got the "kit" off Ebay but Im a little shaky with the soldering iron
nowadays so Ill see how I do with this SM stuff.
Over the pole -
well Im someways in a much better position s/n wise this year though
we have new noisy neighbors but using Cardoid or Mults/Beverage I think we are
going to do fine.
Ive never got a signal to Eu from here (I cant recall ever being
heard further than the poor East coast USA route), but I reckon that its
going to do pretty well into VK and ZL and Eu on good N Polar days (rarer
this year no doubt) but some ( alot) of the USA will be in a null
http://kl7uk.com/lobes.png -
the appx -6dB pattern is estimated but is derived from
real time survey coverage from the WD2XDW loop in Oklahoma taken at
7 mile radii back a few years ago - very rough and ready version as
I drove with GPS here
http://kl7uk.com/XDWpolar.png
With all these nearby mountains the signal get bounced around in
any case so will see what empircally turns sup. (sic) Havnet heard
the 510kHz Fairbanks NDB yet this autumn...
Laurence KL1X
Wasilla AK
Date: Tue, 2 Oct 2012 23:50:40 +0200
From:
[email protected]To:
[email protected]Subject: Re: Strefans LF: LF/MF modification
of TS850 for LF
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
