[Lowfer] First Impressions: AMRAD Converter and Lowpass Filter

[Ben Hall]

Hi Douglas and list,

On 2/2/2015 7:05 PM, Douglas D. Williams wrote:
> Glad it's working well for you Ben. Todd advised me to be sure to use a
> good quality jumper between the LPF and the converter. I use LMR-195 for
> most of my receive jumpers.

Last night, I was using a roughly 16" piece of RG-174 with BNC's using 
SMA to BNC adapters, as my filter uses thru-hole BNC connectors attached 
directly to the PCB.

That will get replaced with a 5" (at most) piece of RG-174 with 
high-quality (Huber-Suhner, I believe) right-angle SMA connectors as 
that is what I have available.  Actually, now that I think about it, I 
may have some LMR-195 and a pair of right-angle SMA's.  I need to check. 
  May use that instead of the RG-174.

So...continuing last night's discussion where I was wondering how the 
low-pass filter was working...  I left the house extra-early and took 
the lowpass filter into work.  Last night I was joking about the 40 GHz 
network analyzer not going down low enough in frequency...turned out to 
be no joke!  The 40 GHz unit only went down to 10 MHz.  Sheesh.  So I 
used a much older, but still serviceable 6 GHz unit that went down to 
300 kHz.  ;)

After some tweaking of the slugs in the Coilcraft coils...I'm pretty 
happy:  (I'd post the photo, but my ugly face is reflected in the screen 
of the analyzer and I don't want to scare anyone, heh heh heh.)

The -3dB point is about 570 kHz.

With the slugs tuned to get rid of my two "problem children" on 730 and 
770 kHz:

At 730 kHz, -59.8 dB.  :)
At 770 kHz, -60.3 dB.  :)

At 850 kHz, response is only -38.2 dB, but with Elsie predicting -46 dB, 
so I'm not unhappy.

At 1000 kHz, we're back down to -60 dB, and by 1200 KHz we're back to 
-70 dB territory.

So there was no problem with the filter and I do need to do some more 
detective work to understand what's going on with the Spanish-language 
(and other) stations that appear at 530 kHz.

Thanks much and 73,
ben, kd5byb