[Lowfer] More info G137 SDR

[n8tl]

Some additional info on the Genesis G137 for 2200 meters is below.

Tom N8TL

3. G137 progress report- first on-air test!
    Posted by: "Nick" nick at clockmaker.com.au vk1aa
    Date: Wed Dec 8, 2010 4:44 pm ((PST))

Hi to all LF and LowFER 's

here is a quick progress report on the G137:

We are up to the RX phase and as expected, the G137 came to life late this 
morning.
(Tasa is doing engineering and schematics, Goran is working on GSDR and
I am the soldering slave and guinea pig)



The board is a modified G** PCB which looks so familiar to G40 owners!
Note the second divider chip glued on top of the osc. ic :-) and
massive L1 and L2 coils.

The initial on-air performance is very solid. My antenna is just a simple
active MiniWhip by PA0RDT. It is an amazing antenna, the size of a pen!
You can set it up on a wooden pole just a meter or two above the ground, on 
top of the roof or
on a tower. It is a true miracle and performs unbelievably well for its size 
from
VLF to HF.

Here is a screenshot of the G137 (29KHz- 221KHz RX coverage)
prior to the installation of two bandpass filters:
note the strong AM products (junk signals)



Here is the shot after installation of the filters:
note the nice, clean band without the slightest trace of any AM broadcast 
mix/junk
The hardware image rejection was perfect without even adjusting the trimmer 
pot




Since the RX was tested at 9am local time, there was no activity on 137KHz.
The first signal heard was of avio beacon BIK at 206KHz.

BIK is located in Bindook, 108 KM from my QTH and
according to the Aviation Authority, it runs a 15W output into a short 
vertical antenna.
Estimated ERP: 200mW at the best!
BIK was a solid copy. The carrier is a thick line right on 206
and upper/lower CW modulated offset is +/- 400 Hz.
Spot on the dial!



Another beauty of SDR: note how the lower sig is actually stronger than the 
upper one!
This is common with non-directional beacons but it is only
apparent when the signal is observed on a spectrum analyzer. Your analog RX 
is blind for such fine detail!

I've checked the BIK on my Perseus radio ($1300) and I could not hear any 
difference
in reception. Actually, the Winrad display was much clearer.
It is important to remember that the input filters of the G137 are not 
centered for 200KHz
which means at least 20dB attenuation on the top of the band!

Here is the snapshot of the same signal on GSDR:



(GSDR freq readout is not set yet)

So there you go. A small step for G137 - but hopefully a step in the right 
direction :-)

Next: to get the G137 TX up and running, then to get the second G137 RX 
assembled and
to play WSPR and JT65 on 137 KHz!

73 from LOW BAND de VK1AA (or AX2VKX on LF)