EMRFD Message Archive 10358
Message Date From Subject 10358 2014-10-09 12:05:23 jliving2001 Old Toko 10.7Mhz IF transformers I want to use an old Toko 10.7 Mhz IF transformer as a variable inductor. I suspect I can use the primary winding if I can remove the Capacitor that is in parallel with the primary winding. Is there an easy way to do this? I want to use it for the VXO inductor in the pass band tuning board of an old Corsair I I am rebuilding.
10359 2014-10-09 12:44:33 bobtbobbo Re: Old Toko 10.7Mhz IF transformers The way I have always done it is to take a small screwdriver and merely break away the cap that is in the slot in the base of the transformer.
10360 2014-10-09 14:11:34 Mike Re: Old Toko 10.7Mhz IF transformers I believe the original "Neophyte" receiver design that appeared in QST many years ago used Toko 10.7 mhz inductors; the tuned circuit at the antenna input (and maybe the LO also) used a 10.7 mhz inductor with the parallel (180 pf?) capacitor removed. The instructions in the original article, IIRC, called for the builder to use a pair of diagonal cutters to remove the capacitor from the bottom of the inductor "can", cutting the capacitor in the middle to begin the process. It was implied in the original article that it wan not necessary to take the enclosure apart to do this.
Can you see the inductor that shunts the winding when you look at the bottom of the transformer? In other words, is it accessible without taking the enclosure apart?
10361 2014-10-09 19:05:46 bob_ledoux Re: Old Toko 10.7Mhz IF transformers By the way, W8DIZ still sells 10.7 Mhz can adjustable transformers
10362 2014-10-10 12:48:56 arfghans Re: Old Toko 10.7Mhz IF transformers I'm glad there's a group like this that supports folks like us who tinker with electronic things in this manner. Sometimes I feel like a refugee...73,Gary NA6O 10363 2014-10-10 13:07:20 chuck adams Re: Old Toko 10.7Mhz IF transformers If I may, I'd like to offer one more tidbit as a warning.
The internal cap of IF transformers consists of a
glass cylinder with two metal end caps in the bottom
of the device and open to modification.
I use a small bladed straight screwdriver to break the
glass cylinder. Do this over a trash bin and away from
your face as the glass is dangerous if you are not careful.
And this is the important part. I did an experiment. DO NOT
REMOVE the end cap pieces. They harm nothing. But, if you use
your chain nose pliars and pull on the end caps and remove
them you are very likely to damage the IF transformer.
The coils in the IF transformer are wound around an internal
form and then soldered to the pins that come out of the bottom.
The wire is in one piece and it continues from the pin and out
to the capacitor. Pulling on the end pieces can break the
wire between the coil and the pin in the process. The
wire is #40 or smaller and very fragile.
I always check the continuity of the IF transformer before
installing. No use in soldering into a PCB and then having
to come back and uninstall, which is a non-pleasant job.
Call me OCD, but I'm willing to bet that there are a large
number of kits that asked you to remove the cap and the xfmr
was damaged in the process by thinking that the end
pieces of the capacitor needed to come out too.
Go back and check non-working receivers and transmitters
with 'modified' IF transformers to see if the coil is open.
FYI and hope this helps,
10365 2014-10-11 10:01:40 Steve VK2SJA Testing Xtal Ladder Filter Impedance Hello All,
Greetings from Nowra NSW, Australia.
First post to the group. Newbie in need of mentor/Elmer.
I'm playing with QER min-loss Cohn filter(s). First time building Xtal
ladder filters. I have questions...
What is the typical passband ripple for a 2.7kHz SSB filter both
commercial and home brew? Or to ask the question another way. What level
of passband ripple is Good, Passable and Bad?
My filter is at 20Mhz IF (Minima). I have about 2dB ripple at the moment.
Next question. What is the correct procedure to experimentally confirm the
filters input and output impedance. Two resistive pads on input and
output. Parallel 50 ohm resistor to ground at both input and output.
Series variable resistor between input and output and crystal filter both
ends. Adjust variable resistors for best passband ripple. Then measure
resistance? Should I expect resistance values to be same at both ends?
Looking at filter shape with either MiniVNA Pro or DSA-815 SA. Both 50ohm
devices of course.
Have I got this procedure right?
10366 2014-10-11 13:18:11 radioaustralia123 Re: [emrfd] Testing Xtal Ladder Filter Impedance Hi Steve,You may find this video interesting. Use you VNA to produce a Touchstone s-parameter file for your filter. Then use RFsim99 to design the matching circuits as shown in this video.A Google search should find RFsim99.Then use the matching circuit component values to determine the filter impedance.Regards,Roderick Wall, vk3yc.