Fw: [softrock40] Re: Bandpass filter smilter
- Interesting. I've not tried any LF reception and would believe there to be problems due to the broadcast stations. As I mentioned earlier, since the BPF is really wide, the focus might be better placed on what you don't want to hear vs what you do want to hear. The only things I can see to filter out or trap are the BC stations and FM stations to keep then from interfering with or at least desensing the SDR reception. You can make one heck of a fine fixed 100dB HF BP filter to use on all HF bands .....but that does not take into account LF reception if that's what you want. I tried the SR-40 V4.0, using only the T1 toroid for isolation and matching and the results are quite impressive. It works "as is" but further improves if you add a variable capacitance to match the antenna (antenna tuner) and the fixed T1 does have it's limitations at higher frequencies.73 Kees K5BCQ----- Forwarded Message -----From: "joe price" <joeprice@...>Date: Wed, 01 Feb 2006 16:46:53 -0000Subject: [softrock40] Re: Bandpass filter smilterMessage-ID: <email@example.com>
When I first received my SR40 I replaced the input transformer
with a wide band transformer made by RELCOM. I was using a DDS board
to supply the Xtal input with the idea of just using bandpass or
lowpass filters ahead of rx. to cover a large frequency. It seened to
work ok at hf frequencies but when i tried it a LF 200-450khx I
received a lot of broadcast stations that i didn't have with my
superhet SD40 as sugested by wa6ufq. Further testing revealed the
Strong spurious response at odd multiples of the receive fqequency
3x,5x 7x as a example when tuned to 300khz receiver would respond
to 900,1500,2100khz ect. now you can see why i was hearing strong
broadcast stations at LW.
The input transformer I used i rated to 50khz, maybe my receiver has
a problem but phase and balance look good.
I also checked another SR40 at 10mhz it also could hear 30mhz.
Another problem the shows up is automatic phase and balance changes
when changing bands such as going from 40 to 20 mtrs. Not a concern
if this data can be stored for each band.
Can you please verify the above on your receiver?
Thanks Joe wa9cgz