Fw: Fw: Re: [softrock40] Re: Bandpass filter smilter
- On the other hand, I tried SR-40 V4.0 and Rocky with a BPF for 80m, then switched to "direct" (no BPF ahead of T1) and could see no notable difference at various points of the 80m band with the "no BPF" frontend .....you would think 7-8Mhz would be all over the place.With a little pin "swizzling" you can connect the Mini-Ckts T1-1T transformer for T1. It's spec says 1dB insertion loss from 0.8Mhz to 80 Mhz and a 3dB insertion loss from 0.08Mhz to 200Mhz. ........that's a pretty good range for a cheap RF transformer.73 Kees K5BCQ----- Forwarded Message -----From: windy10605@...Date: Mon, 30 Jan 2006 13:42:11 -0600Subject: Fw: Re: [softrock40] Re: Bandpass filter smilterOK, good point Art. They --do-- respond to harmonics and I can see how this would be a really serious problem for using it as an LF receiver design.73 Kees K5BCQky1k@...>Date: Wed, 01 Feb 2006 14:15:03 -0500Subject: Re: [softrock40] Re: Bandpass filter smilterMessage-ID: <22.214.171.124.0.20060201140602.059a6eb0@...>
softrock type detectors! Although it's not a serious problem, you
have to be aware of it and limit front end filters response to
The ratio between the lowest frequency passed by the front end filter
and the highest frequency passed cannot be more than two to one-for
exactly the reason you describe.
It responds to harmonics.
Several have thought of using the softrock for VLF and ULF receivers,
say from 2 KHz to 80 KHz. And, of course they run into the same problem.
2 KHz to 4 KHz is ok, 4 KHz to 8 KHz is ok.......but don't try 2 KHz
to 8 KHz without separate filters for eash 'band'.
GL to all.
At 11:46 AM 2/1/2006, you wrote:
>Kees,replaced the input transformer
> When I first received my SR40 I
>with a wide band transformer made byRELCOM. I was using a DDS board
>to supply the Xtal input with the idea ofjust using bandpass or
>lowpass filters ahead of rx. to cover a largefrequency. It seened to
>work ok at hf frequencies but when i tried it aLF 200-450khx I
>received a lot of broadcast stations that i didn't havewith my
>superhet SD40 as sugested by wa6ufq. Further testing revealedthe
>following problems.multiples of the receive fqequency
>Strong spurious response at odd
>3x,5x 7x as a example when tuned to300khz receiver would respond
>to 900,1500,2100khz ect. now you can seewhy i was hearing strong
>broadcast stations at LW.input transformer I used i rated to 50khz, maybe my receiver has
>aproblem but phase and balance look good.
>I also checked another SR40 at10mhz it also could hear 30mhz.
>automatic phase and balance changes
>Another problem the shows up is
>when changing bands such as goingfrom 40 to 20 mtrs. Not a concern
>if this data can be stored for eachband.
>Can you please verify the above on your