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 Post subject: rf chokes
PostPosted: Mar Thu 11, 2021 3:27 pm 
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Joined: Feb Thu 19, 2015 1:49 pm
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Has anyone used the little rf chokes that resemble carbon resistors. They are much cheaper smaller and more available than say the pi wound which seem hard to find nowadays. Just curious I have some ordered and am anxious to try them !


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 Post subject: Re: rf chokes
PostPosted: Mar Thu 11, 2021 5:10 pm 
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Sure! They are a convenient size and work okay for a lot of things but not always the best. It all depends on what you want to accomplish. For some uses DC resistance is important, like to reduce noise in/out of a cpu power connection. For other uses DC resistance is not important. Self-resonance is a big deal for rf work, not so much for audio. Q factor is usually important but not always and when it is important, you may want more or less. For a resonant circuit you may want a very high Q whereas for an rf bypass you may want a broader-acting Q. Different manufacturing materials and methods have different losses too.

So, what are you using them for?

edit: I find that for resonant circuits, like part of antenna matching of a part-15 transmitter, the little inductors are not the best by far.

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 Post subject: Re: rf chokes
PostPosted: Mar Thu 11, 2021 5:17 pm 
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Using for a one tube 12au7 sw. regen


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 Post subject: Re: rf chokes
PostPosted: Mar Thu 11, 2021 6:33 pm 
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Location: Santa Rosa, CA
In your regen, will you use the choke in the tuning L/C combo or as a choke in the detector circuit?

I find that chokes with a low SRF (self resonant frequency) don't work well in the detector. When we had ham swaps, I would buy all the Miller, Millen, etc. pi-wound that I could find. I think Hammond still sells the pi-wound chokes?

https://www.mouser.com/datasheet/2/54/5 ... 777302.pdf

Notice, a 270 uH inductor, as might be used for tuning, has an SRF of 2.1 MHz, so should be OK in the normal AM BC band. An 1800 uH, that might be used as a choke, has an SRF of 720 KHz, so you might encounter some degraded performance at the high end of the band. Also note, these inductors are tested at 1 KHz, which may not be a good prediction of how they will work at RF.

https://www.everythingrf.com/community/ ... -frequency

Rich


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 Post subject: Re: rf chokes
PostPosted: Mar Thu 11, 2021 8:43 pm 
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The MSS1038T series inductors from Coilcraft have better specs and are shielded. For example, the max value 1mH part has an SRF of 3MHz. They are surface mount, not convenient to solder as leaded counterparts.

Image

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 Post subject: Re: rf chokes
PostPosted: Mar Sun 14, 2021 9:21 pm 
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They work fine at low power, like in a regen or the low power stage of a transmitter. I will often use one in the cathode circuit of a one-tube transmitter, but will use a traditional pi-wound RFC in the plate circuit where the RF voltage is much higher.


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 Post subject: Re: rf chokes
PostPosted: Mar Sun 14, 2021 9:36 pm 
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I used two 1.5 mH chokes to replace two open primary coils in the interstage transformers of a TRF, and they work just fine.

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 Post subject: Re: rf chokes
PostPosted: Mar Mon 15, 2021 8:10 pm 
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Some here posted a thread about his making of 455khz IF transformers with those mini-chokes.


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 Post subject: Re: rf chokes
PostPosted: Mar Mon 15, 2021 10:01 pm 
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Location: Santa Rosa, CA
https://antiqueradios.com/forums/viewto ... 6&t=196404

Rich


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 Post subject: Re: rf chokes
PostPosted: Mar Tue 16, 2021 9:15 pm 
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Are these drum cores any good for RF?
They are used in RF blocking inductors.

These inductors are 20 cents a piece. I want to remove the winding and use my own bifilar or trifilar winding for use in my HF transceiver. You could try them too but I guess they are too lossy at RF and maybe unusable. The drum cores cost 10 cents each if purchased separately.


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 Post subject: Re: rf chokes
PostPosted: Mar Tue 16, 2021 9:32 pm 
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Rich, W3HWJ wrote:
https://antiqueradios.com/forums/viewtopic.php?f=6&t=196404

Rich


Thanks for that link, Rich. I remembered seeing it here but would never have found it

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 Post subject: Re: rf chokes
PostPosted: Mar Wed 17, 2021 9:54 am 
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Location: Springwater, NY
Dare4444 wrote:
Are these drum cores any good for RF?


I've used them several times in low power transmitters and oscillators up to 14MHz and had good results. I recall one power oscillator that did not like them in the grid circuit and that oscillator worked fine with a hand-wound choke or the pi-wound equivalent. They are worth trying.


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 Post subject: Re: rf chokes
PostPosted: Mar Wed 17, 2021 3:37 pm 
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NW2K wrote:
Dare4444 wrote:
Are these drum cores any good for RF?


I've used them several times in low power transmitters and oscillators up to 14MHz and had good results. I recall one power oscillator that did not like them in the grid circuit and that oscillator worked fine with a hand-wound choke or the pi-wound equivalent. They are worth trying.


Wow! Cool. I was expecting a feedback like that.
No. 43 material ferrite cores are hard to get in asian countries and I'm designing a low cost SSB transceiver for college students. Wish to use these in front end mixer and product detector.


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 Post subject: Re: rf chokes
PostPosted: Mar Wed 17, 2021 3:43 pm 
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forumuser wrote:
Some here posted a thread about his making of 455khz IF transformers with those mini-chokes.

That might have been Peter (PBpix)

One man's choke is another man's low-Q coil......To learn more, get a good impedance bridge.....

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 Post subject: Re: rf chokes
PostPosted: Mar Wed 17, 2021 6:21 pm 
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Joined: Jan Sun 26, 2020 3:39 pm
Posts: 44
Location: Hudson, MA 01749
I use these and similar for my 6888 AM transmitter:
Digikey AIUR-08-101K-ND
I find them to be rugged and reliable.

Mike


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 Post subject: Re: rf chokes
PostPosted: Mar Wed 17, 2021 8:30 pm 
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Joined: Mar Thu 01, 2018 1:30 am
Posts: 514
ab1aw wrote:
I use these and similar for my 6888 AM transmitter:
Digikey AIUR-08-101K-ND
I find them to be rugged and reliable.

Mike


Wow. Cool. Finally I've confirmation that others have successfully used them. Here's a switching mixer. I tested it today and adding a trimmer cap nulled LO - RF port carrier leakage. Core is BN 43-2402. I'll replace with a drum core once they arrive in mail.


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 Post subject: Re: rf chokes
PostPosted: Mar Thu 18, 2021 12:55 am 
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Joined: Jan Sun 26, 2020 3:39 pm
Posts: 44
Location: Hudson, MA 01749
Dare4444 wrote:
ab1aw wrote:
I use these and similar for my 6888 AM transmitter:
Digikey AIUR-08-101K-ND
I find them to be rugged and reliable.

Mike


Wow. Cool. Finally I've confirmation that others have successfully used them. Here's a switching mixer. I tested it today and adding a trimmer cap nulled LO - RF port carrier leakage. Core is BN 43-2402. I'll replace with a drum core once they arrive in mail.


Yes, I also use them in my home made switching power supplies to power my tube circuits.


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 Post subject: Re: rf chokes
PostPosted: Mar Thu 18, 2021 1:01 am 
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jimbob wrote:
Has anyone used the little rf chokes that resemble carbon resistors. They are much cheaper smaller and more available than say the pi wound which seem hard to find nowadays. Just curious I have some ordered and am anxious to try them !

Yes I used them for inductance value in a home-made IF filter:
viewtopic.php?t=86553
https://www.antiqueradios.com/forums/vi ... 6&t=196404
Image

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 Post subject: Re: rf chokes
PostPosted: Mar Thu 18, 2021 4:47 am 
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Joined: Mar Thu 01, 2018 1:30 am
Posts: 514
Quote:
Yes I used them for inductance value in a home-made IF filter:
viewtopic.php?t=86553
https://www.antiqueradios.com/forums/vi ... 6&t=196404
Image


Wow. I saved the image for future reference.


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