4498	2010-04-02 14:16:30	Dave	Interesting filter construction
Message	Date	From	Subject
Hi All, Opened up a 50 year old 75 ohm low pass filter that was recently given to me. I was going to write down the LC values so I could figure out the 3 db points and possibly modify it for 50 ohms. However, when I opened it I found it had a construction technique I haven't seen before. It looks useful for easily building transmitting filters and LC networks. I think this may be of interest to the group so I posted some pictures in my emrfd album at http://groups.yahoo.com/group/emrfd/photos/album/1350936423/pic/list. Let me know if there is interest in the actual component values. When I get some time I plan to unsolder the coils and measure them and the capacitors to generate a schematic. Cheers, Dave
4499	2010-04-02 14:19:02	Anthony Gabriel S...	Re: Interesting filter construction
Hi Dave I can't have access to the link. Could you upload the photos on group's album? _________________________________________________________________ Connect to the next generation of MSN Messenger http://imagine-msn.com/messenger/launch80/default.aspx?locale=en-us&source=wlmailtagline [Non-text portions of this message have been removed]
4500	2010-04-02 14:22:26	Dave	Re: Interesting filter construction
Fixed link. (Stupid period) Dave wrote: > > > Hi All, > > Opened up a 50 year old 75 ohm low pass filter that was recently given > to me. I was going to write down the LC values so I could figure out > the 3 db points and possibly modify it for 50 ohms. However, when I > opened it I found it had a construction technique I haven't seen before. > It looks useful for easily building transmitting filters and LC > networks. I think this may be of interest to the group so I posted some > pictures in my emrfd album at > http://groups.yahoo.com/group/emrfd/photos/album/1350936423/pic/list > <http://groups.yahoo.com/group/emrfd/photos/album/1350936423/pic/list.> > > Let me know if there is interest in the actual component values. When I > get some time I plan to unsolder the coils and measure them and the > capacitors to generate a schematic. > > Cheers, > > Dave > > [Non-text portions of this message have been removed]
4501	2010-04-02 14:25:00	Dave	Re: Interesting filter construction
Please let me know if you can see the pictures with the fixed link. TNX Dave Anthony Gabriel Sotillet Marquez wrote: > > > > > Hi Dave > > I can't have access to the link. Could you upload the photos on > group's album? > > __________________________________________________________ > Connect to the next generation of MSN Messenger > http://imagine-msn.com/messenger/launch80/default.aspx?locale=en-us&source=wlmailtagline > <http://imagine-msn.com/messenger/launch80/default.aspx?locale=en-us&source=wlmailtagline> > > [Non-text portions of this message have been removed] > > [Non-text portions of this message have been removed]
4502	2010-04-03 05:43:35	Alan Melia	Re: Interesting filter construction
Hi Dave I think you are refering to the use of PCB material as the shunt capacitors. This has been written up before. What I am not impressed with (and I may be missing something ?) is that the coils can all "see" one-another. Surely this will lead to very poor out-of-band attenuation figures. Either the coil axes should be at right-angles or there should be screens between the sections. Not difficult with pcb stock material. Alan G3NYK ----- Original Message -----
4503	2010-04-03 06:59:16	Dave	Re: Interesting filter construction
Hi Alan, Not PCB capacitors. The round disks are copper washers. They are insulated from the chassis by one thin piece of plastic for each side. This is repeated on the other side so the capacitance is doubled. There is a threaded rod that runs thru the washers and the chassis connecting the two sides together and providing a place to connect the inductors to the capacitors. Brass washers would be fine also and maybe even steel washers. I noticed the same thing you did about the coils being lined up. Toroids would solve that problem. Or just turning the coils at right angles to each other like in my more conventional Ameco LPF. Regards, Dave Alan Melia wrote: > > > Hi Dave I think you are refering to the use of PCB material as the shunt > capacitors. This has been written up before. What I am not impressed with > (and I may be missing something ?) is that the coils can all "see" > one-another. Surely this will lead to very poor out-of-band attenuation > figures. Either the coil axes should be at right-angles or there should be > screens between the sections. Not difficult with pcb stock material. > > Alan G3NYK > > ----- Original Message ----- >
4504	2010-04-03 07:48:23	Brooke Clarke	Re: Interesting filter construction
Hi Dave: Indeed interesting. It appears that the design includes coupling between the coils in addition to the capacitance of the feedthroughs. -- Have Fun, Brooke Clarke, N6GCE http://www.PRC68.com
4505	2010-04-03 17:09:42	R Wall	Re: Interesting filter construction
Hi Dave, Yes please, it would be interesting to make some Tx LPFs for the PicaStar. And when you have the L,C values to simulate it in Elsie. Do you know what it was used for? Regards, Roderick Wall, vk3yc. ----- Original Message -----
4512	2010-04-05 11:58:22	Tim	Re: Interesting filter construction
Cool. Is this a Johnson/Nye-Viking, or maybe Eico, filter? I remember those using this kind of construction. The copper plated steel looks remarkably good for something that's 50 years old but often it did hold up. My two cents, is that plastic disks are not necessarily the best or highest Q dielectrics, but that they can be "good enough" with enough engineering. The art of making PCB material good enough for stripline, for example, has been exploited a lot by microwave engineers. If the plastic disk is tefl