Yes Bill, I'm a little concerned about this as well. Can you recommend a better alternative?
David --- In [email protected], Bill Dumke <[EMAIL PROTECTED]> wrote: > > RG-174 will add about 32 pF/foot of capacitance to your circuit, unless > it is well matched, (50 Ohms in and out) > > Bill WA9PWR > > > drmail377 wrote: > > Hi Pete, > > > > I thought about switching the BPF's and adding a rotary hex encoded > > switch instead of the DIP switch to change the Si570 frequency. Below > > is a link where you can download a .pdf that shows a BPF switch > > schematic, a data sheet for a plausible rotary BPF switch, and a price > > quotation for the switch. I would connect the switch to the BPF's with > > RG-174 (or similar) coax. Yes you do need to switch both the input and > > the output of each filter. The balanced nature of the input > > transformer's secondary requires you to switch both secondary > > windings, the center-tap can be common. > > > > www.datafilehost.com/download-6b52d2cd.html > > > > The link to the YU1LM BPF mentioned by Javier is not really a switched > > BPF, it is a variable pre-selector that uses switches to select > > various combinations of reactive elements for covering different parts > > of the full HF spectrum. This is an interesting design, especially for > > general-coverage. I've simulated the YU1LM design and sourced the > > components. But the large air-variable cap is an issue, and finding > > polyvaricons with such large values isn't possible. In addition, I > > would consider wideband 4:1 transformers at the input and output of > > the YU1LM design to improve Q, although the design as-is results in > > selectivity similar to the Softrock fixed frequency input filters. > > > > Alas, there is a problem with using the YU1LM pre-selector with > > Softrock. The Softrock input transformer introduces a reactive element > > that screws up the response of the YU1LM pre-selector. An isolating > > amplifier would help, but that seems like heresey in a design like the > > softrock. In the end, the input transformer makes it very difficult to > > use the Softrock as a general coverage receiver without using fixed > > switchable BPF's like the one available at www.wb6dhw.com. > > > > In the end, I would like to see if someone can design a way to > > broadband the Softrock input for general-coverage. Yes without input > > filtering it is possible to recieve harmonically related interference > > if it exists at sufficient level, and even receive signals at the > > wrong frequency (but this can be checked by listening at double and/or > > triple the receive frequency). But having a "no filter" board to > > swtich in along with the ham-band BPF boards would at least allow some > > form of general-coverage and the ability to listen to short-wave > > broadcasts, certainly worthy of a position on the BPF switch! I've > > looked at this too - but again, without a pre-amplifier, the input > > transformer's inductance rears it's ugly head when directly connected > > to an antenna impedance. > > > > 73's, David > > > > --- In [email protected], "Javier Albinarrate" <javier@> > > wrote: > > > >> Hi Pete, > >> > >> I think you have to switch both, input and output, since if the > >> other inputs are not switched off, they will be seen as a paralel > >> > > impedance, > > > >> thus, altering the behaviour. Although, I wonder how much would that > >> > > really > > > >> affect. > >> Here you have an interesting design from YU1LM, mainly > >> > > places the > > > >> switches in different way. > >> http://yu1lm.qrpradio.com/bp%20yu1lm.htm > >> > >> Regards! > >> > >> ----- Original Message ----- > >> From: "Pete Smith" <n4zr@> > >> Sent: Tuesday, May 13, 2008 4:46 PM > >> Subject: Bandswitching BPF modules - softrock Lite+xtall 8.3 > >> > >> > >> > >>> Is there any particular good/best way to switch the bandpass filter > >>> modules? I am working out a design for a bandswitched SoftRock > >>> > > Lite+Xtall > > > >>> and the 5-pole BPF modules are a bit of a challenge. Do I need to > >>> > > switch > > > >>> all 5 leads, or would it suffice to switch the three on the output > >>> > > side, > > > >>> while paralleling the antenna input and return ports of all 4 > >>> > > modules. > > > >>> 73, Pete N4ZR > >>> > > > > > > > > ------------------------------------ > > > > Yahoo! Groups Links > > > > > > > > > > > > > > > > >
