Re: Modify BandPass Filter RX II
- Thanks for the reply. I already use a pre-selector type device that I made in front of the rx II. It has a basic impedance matching system, preselector (12 step L and tunable C), attenuator, then a pre-amp with drive control. Each part can be switched in and out of the circuit.
I live right near a 50kw RF thrower and several other "clear channel" monstrosities. They have all taken down solid receivers in one way or another. Also, there's a lot of business' and a firestation right on my block, not to mention the cabbies and cops that roll through all the time. Outside of that and the webbing of power-lines my neighbors (maybe like 20 within 40 foot)pretty much all have flat screens and whatnot. So I'm overly paranoid about attempting to filter out noise!
Anyhow, it's interesting using the device with the RX II. I'm finding that the impedance transformer takes on a much more important roll than it did with the superhets. It's making me consider making a full matching network for the receiver. I only use one antenna (about 25ft of flexweave horizontal with 9:1 unun at feedpoint) so there's definitely swings between the bands.
Anyhow, after the weekend I'll hopefully get the time to start tinkering with it a little more and see what I can figure out.
--- In firstname.lastname@example.org, "Alan" <alan4alan@...> wrote:
> ----- Original Message -----
> From: "homebrewer7"
> Subject: [softrock40] Modify BandPass Filter RX II
> > Have any of you experimented with modifying the BPF on the ensemble RX II?
> > The only real changes I'm looking to make would be to use larger cores (I
> > like the bigger ones from past projects) to get a higher Q in the filters.
> > These would have to be off-board which introduces some challenges though
> > into itself.
> If you are trying for greater out of band rejection why not just add more
> The best way might be to design a tight BPF for each band and place it in
> front of the Softrock.
> If you want to retain the same ABPF configuration then would an extra
> section or two be more effective than a slightly higher Q?
> A lower loss arrangement might be desirable for the highest range, depending
> on the soundcard.
> 73 Alan G4ZFQ