Re: Help: how to design air-core transformer?
From: Jim (jmgong74_at_tom.com)
Date: 11/23/04
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Date: 23 Nov 2004 09:53:58 -0800
legg <legg@nospam.magma.ca> wrote in message news:<n076q0l32ektjtrb9fq93mkvkk2ish00oc@4ax.com>...
> On 22 Nov 2004 15:08:36 -0800, jmgong74@tom.com (Jim) wrote:
>
> >I hope to design an air-core transformer which may operate at 100-500 MHz.
> >However I found the loss is too high.
> >Can anybody give me some advices to design air-core transformer?
> >Thanks a million!
>
> What is your loss like WITH a core? Maybe the core is not your
> problem. What application/environment?
>
> Google 'air-core transformer', 'air cored transformer', 'coreless
> transformer', 'contact-free transmission', 'contactless transmission',
> 'transcutaneous energy' etc.
>
> RL
I observed two unwanted phenomenon:
1. direct capacitive coupling between primary/secondary coils. It
interferes with the mutual inductance, and makes the transmissivity of
the transformer change significantly with frequency.
2. Insertion loss is higher than 10dB.
I googled air core transformer before i posted my question. It is
weird that the concept is mentioned in many places, but I can never
find a real one which works in VHF/UFH band except transmission-line
type.
My purpose is for impediance matching, from 50 ohm cable to a 0.5 ohm
load.
To my understanding, air-core transmission-line transformers have
fixed conversion ratio, e.g. 1:1, 4:1 or 1:4, is it right? What i need
is a ratio of 10:1.
I saw some companies provide RF transformer with ferrite coil inside.
The insertion loss is only 1-2dB, however, for UHF band, the maximum
ratio is 4:1 or 6:1 only.
Thank you all again! And hope to hear from you again.
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