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.

Joe W3GW


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.

Bob, K1AO
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

42IF123

 

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,

chuck, k7qo
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?

73, Steve.
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.


10367 2014-10-11 13:29:09 Ephemeral Re: Testing Xtal Ladder Filter Impedance
I have learnt lots by playing around with the "Filter Design" program by AADE. It is free
so I presume there is no problem plugging it here. It makes it quick and easy to compare
different designs and observe the effects of varying parameter values. I have used it to
design several filters for my current project - it does LC filters too. Be sure to save your
filter before first running the analysis tools as it will crash if you tell it to divide by zero.
 
 
Adrian, England

Sent: Saturday, October 11, 2014 10:04 AM
...
 

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...

...

|
10368 2014-10-11 13:41:26 radioaustralia123 Re: [emrfd] Testing Xtal Ladder Filter Impedance
Hi Steve,


Attached is a Smith Chart with TP 3 showing what the Filter impedance is for the filter in the Youtube video. Smith Chart was produced using “Smith” software that is free on the Internet.


Regards,


Roderick Wall, vk3yc.






10369 2014-10-11 20:16:54 Steve VK2SJA Re: Testing Xtal Ladder Filter Impedance
Hi Rod,

Thanks very much for the information! I have not yet looked at the video
but will do so soon. As this approach sounds a lot more exacting/straight
forward than what I did today.

I have however managed to muddle my way through matching the filter
impedance today and have successfully got passband ripple down to about
0.2dB!! Assuming I can believe what the VNA is telling me and that I'm
driving it correctly of course!

I don't often do a victory dance around the shack but I did when than scan
came in!

73, Steve


> 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.
>
>
> https://www.youtube.com/watch?v=C8wUUngmxew
>
>
> A Google search should find RFsim99.
>
>
> Then use the matching circuit component values to determine the filter
> impedance.
>
>
> Regards,
>
>
> Roderick Wall, vk3yc.
>
>
>
>
>
>
>
>
>
10370 2014-10-11 20:33:19 Todd F. Carney / ... Re: Testing Xtal Ladder Filter Impedance
10371 2014-10-11 22:32:39 Steve VK2SJA Re: Testing Xtal Ladder Filter Impedance
Hi Todd,

I've got a MiniVNA-Pro. I'm aware of its limitations but still select this
one to buy because the price was right --and-- more importantly there was
good software available in the form of vna/J for my preferred OS (Linux).

73, Steve.


> ​
>
10372 2014-10-12 05:34:29 radioaustralia123 Re: [emrfd] Testing Xtal Ladder Filter Impedance
Hi Steve,

Good, it looks like you have it under control. 0.2dB is better than 2dB ripple.

Roderick Wall, vk3yc.

10373 2014-10-15 11:18:44 Ramiro Aceves Re: Testing Xtal Ladder Filter Impedance
Hello

I did several experiments with home made Cohn filters months ago, using a cheap 100 crystal batch from Ebay. I used VNWA3 vector analyzer. I measured S parameters forward and reversed at 50 ohms system impedance
.
Then I used the "matching" tool to find the input and ouput impedances that origin the lowest ripple.

Do not know if it is correct or not. The measurements  follow the simulations pretty well.

You have all the information at my ugly WEB page:

http://ea4nz.ure.es/rtrx/rtrx.html

Regards

Ramiro, EA4NZ.

10374 2014-10-15 19:02:01 Todd F. Carney / ... Re: Testing Xtal Ladder Filter Impedance
10375 2014-10-16 00:36:39 Kirk Kleinschmidt Re: Testing Xtal Ladder Filter Impedance
Ramiro,

Thanks for letting us know about your efforts!

You are blazing a trail for me, as I have just purchased a 100-QTY bag of 9-MHz XTALS, also on eBay, and am getting ready to experiment with characterizing them.

I have a miniVNA on hand (50 dB dynamic range), but Santa is threatening to bring me a Rigol spectrum analyzer this year, as I have BEEN VERY GOOD :)

I know Wes and the Gang will be pleased because you're actually experimenting :)  They seem to really like that  :)

Please keep us posted on the rest of your retirement rig.

Once I have access to a spectrum analyzer, one experiment I'd like to do is to see whether I can make an IF filter with adjustable impedance-matching elements (R or C) and to tweak them in real-time to effect the best impedance match/power transfer between the mixer output and the IF output.

I haven't thought this through completely, but it seemed to me that, if I actually connected the entire IF strip (mixer, post amp, filter, IF amp) and measured the output of the IF amp on the spectrum analyzer, the actual performance of the entire subsystem could be measured and characterized, and if the filter matching sections were adjustable, I should be able to adjust them as I "watch" the IF output, looking for whatever setting provide a "best match."

This could potentially eliminate unknown effects from other parts of the circuit / IF subsystem that might go unnoticed if only the XTAL filter is measured.

Of course, I could be way off base here...but I hope not :)

73,

--Kirk, NT0Z

My book, "Stealth Amateur Radio," is now available from
www.stealthamateur.com and on the Amazon Kindle (soon)


10376 2014-10-16 11:02:18 Harold Smith Re: Testing Xtal Ladder Filter Impedance
The Rigol SA is a verynice instrument for the money.  Be sure and spend the extra $200 for the tracking generator version, if you're into setting up filters.  The TG-SA makes it a snap, almost trivial.

de KE6TI, Harold

10382 2014-10-24 14:12:04 Ramiro Aceves Re: Testing Xtal Ladder Filter Impedance
Thank you very much!

73, Ramiro, EA4NZ.

2014-10-16 4:01 GMT+02:00 'Todd F. Carney / K7TFC' k7tfc@arrl.net [emrfd] <emrfd@yahoogroups.com>:
 

10383 2014-10-25 09:14:44 Ramiro Aceves Re: Testing Xtal Ladder Filter Impedance

Thanks so much. I encourage you to experiment with the batch of crystals. With the aid of the VNA things are easy. The Vnwa3 is one of the best things I have bought for the money during my life.

The retirement transceiver is stopped at this moment, I must continue it soon. Now I am now doing some experiments at microwave frequencies. I was lucky and I bought a Marconi 6200 10MHz-24GHz test set and an Advantest 26 GHz spectrum analyzer at good price. A new world of  measurements has appeared in front of me.

Keep us tuned about your experiments. I would like to write more often in my web about my experiments but I realize that writing takes more time than experimentation itself :-)

73, Ramiro.EA4NZ

El 16/10/2014 09:36, "Kirk Kleinschmidt sohosources@yahoo.com [emrfd]" <emrfd@yahoogroups.com> escribió:
 

Ramiro,

Thanks for letting us know about your efforts!

You are blazing a trail for me, as I have just purchased a 100-QTY bag of 9-MHz XTALS, also on eBay, and am getting ready to experiment with characterizing them.

I have a miniVNA on hand (50 dB dynamic range), but Santa is threatening to bring me a Rigol spectrum analyzer this year, as I have BEEN VERY GOOD :)

I know Wes and the Gang will be pleased because you're actually experimenting :)  They seem to really like that  :)

Please keep us posted on the rest of your retirement rig.

Once I have access to a spectrum analyzer, one experiment I'd like to do is to see whether I can make an IF filter with adjustable impedance-matching elements (R or C) and to tweak them in real-time to effect the best impedance match/power transfer between the mixer output and the IF output.

I haven't thought this through completely, but it seemed to me that, if I actually connected the entire IF strip (mixer, post amp, filter, IF amp) and measured the output of the IF amp on the spectrum analyzer, the actual performance of the entire subsystem could be measured and characterized, and if the filter matching sections were adjustable, I should be able to adjust them as I "watch" the IF output, looking for whatever setting provide a "best match."

This could potentially eliminate unknown effects from other parts of the circuit / IF subsystem that might go unnoticed if only the XTAL filter is measured.

Of course, I could be way off base here...but I hope not :)

73,

--Kirk, NT0Z

My book, "Stealth Amateur Radio," is now available from
www.stealthamateur.com and on the Amazon Kindle (soon)


10384 2014-10-26 10:18:52 Steve VK2SJA Re: Testing Xtal Ladder Filter Impedance
Hi Rod/All,

Rod, I finally got around to watching that video while playing with the
software. Very useful/powerful stuff. Thanks.

I was able to import my vna/J .s2p file without any difficulty and was
looking at my filter sweep in no time. All to easy in fact.

But when I went I told RFSim99 to generate a "Auto Match" -> "Simultaneous
conjugate", I got the following error message:-

"Simultaneous conjugate match not possible at that frequency because
S-Parameters produce a negative square root in the solution."

I found that if I told it to match Port 1 only it gave me values (only for
port 1 of course) that were *very* close the the values it had arrived at
by a much longer and arduous route.

Anyway just wondering if there is something that I could have done to work
around the error? And if you may happen to know why my filter caused a
negative square root?

73, Steve.


> Hi Steve,
>
>
> Good, it looks like you have it under control. 0.2dB is better than 2dB
> ripple.
>
>
> Roderick Wall, vk3yc.
>
>
>
>
>
>
>