Fw: Re: Fw: Re: [HBR] Small 100Khz IF transformers

Tue, 7 May 2002 19:27:31 -0500

Bob,

Probably more than you asked for........ I added a few comments 
which I know is "old hat" to you but might be interesting for the 
rest of the group ....and maybe get some additional discussion 
going.

The DC resistance of the 262Khz 15-H IF coils is 41 ohms and 
they are wound with 1 strand of #40. The resistance of the 100Khz 
#1710 coil is 53 ohms and the winding is made up of bifilar #40 
or #41....hard to tell. Each wire has a resistance of 105 ohms.
The inductance of the #1710 is, of course, higher ...it goes from 
3.3-9.3mH and resonance with the integrated 333pf capacitor is 
at 6.4mH. The 15-H range is about 2.0-6.0mh and is set at 5.0mH
which dictates 520pf. The #1710 coil is larger in diameter (due to 
the two wires and more wire) and the RF resistance should be 
less due to the increased surface area of bifilar wire, but there is 
more of it which increases the RF resistance. RF resistance 
below 2-3Mhz plays a substantial factor in coil Q....that's why all
those old broadcast radios used plenty of Litz wire in the frontend. 
Then they got enough stations all over the place and the need fell
off ....I guess that's why.

The one thing that still causes some question is those Q numbers 
are the "unloaded Q" measurements of the coil on a Q meter. The 
"loaded Q", between the two, may well change that. I don't like the 
fact of adding 520pf total for resonance vs 333pf total on the 
#1710. One better indication of overall performance of the whole 
transformer and "Q" would be to see how much of a peak relative 
to the noise floor you can get on the Spectrum Analyzer. I have 
always looked at "Q" as supplying a higher voltage peak vs a 
sharper peak ....they don't necessarily go hand in hand. In other 
words, everyone is talking about -6dB BW and you might have a 
-6dB BW of 4Khz on one and 3Khz on the other, yet the peak of 
the 4Khz might be 60dB above the noise floor and the 3Khz might 
be 40dB above the noise floor. That's where those BC-453 IFs 
really excell. 

Maybe that should just be looked at as insertion loss and add 
another IF stage ?? I don't think so. If the gain of a stage is 
typically around 150, that's about +40dB. ....but with amplifiers 
they do just that ...amplify and everything goes up, signal, noise 
floor, etc ....and they add "stuff".   

73s  Kees K5BCQ

--------- Forwarded message ----------
From: "Bob Duckworth, WB4MNF" <[email protected]>
To: [email protected]
Date: Tue, 07 May 2002 19:50:59 -0400
Subject: Re: Fw: Re: [HBR] Small 100Khz IF transformers
Message-ID: <[email protected]>
References: <[email protected]>

Kees-

Did you measure the DC resistance
and is it enough to account for most of the
difference in Q?

-bob

Sandy and Kees Talen wrote:

> I just tried puting the two coils in the 262Khz JW Miller 15-H
> in series and you get approx 10mH ....that's expected. This 
> and a 250pf capacitor provides resonance at 100Khz. Only 
> thing is that with the windings, when connected so they are 
> in the same direction, or connected so they are bucking, 
> results in a "Q" of 62-64 ......less than the previous measurements. 
> I would guess it has something to do with the coil spacing ? 
> or the physical design of K-TRAN transformers ? 
> 
> All Q measurements are made without any internal/external 
> capacitors except for what's in the Q meter and stray 
> capacitance to the shield, etc.
> 
> 73s  Kees K5BCQ  
> 
> --------- Forwarded message ----------
> From: [email protected]
> To: [email protected]
> Date: Sun, 5 May 2002 10:06:59 EDT
> Subject: Re: [HBR] Small 100Khz IF transformers
> Message-ID: <[email protected]>
> 
> In a message dated 5/5/02 7:24:14 AM Eastern Daylight Time, [email protected]

> writes:
> 
> 
>>Have you given any thought to using two of these 262 coils?
>> Place the windings in series on each and wind yourself a link
>> coil on each, between the windings. Use this link coil as your
>> coupling between the two tuned circuits. If you experiment a
>> bit, you can likely stick a cap across the link to vary bandwidth.
>>
> 
> Better yet, try this:
> 
> Connect the two coils in series-aiding but leave one end of the winding
> free 
> (may require destruction of the internal capacitors). Use "bottom
> coupling" 
> like in the DC-500 receiver to obtain adjustable bandwidth. The DC-500 
> claimed bandwidths suitable for AM, SSB and CW from 50 kc. IFs made
from
> TV 
> width coils, whose Q is probably not as good as the Miller IFs. 
>   
> 
>> I've not built this, just a thought. I get them sometimes
>> when it's still early in the AM and I've just had my morning coffee
>>
> :-)
> 
> Great thought, tho!! Only real problem is getting enough of the 262's.
> 
> With 2 IF stages and a single transformer feeding the detector, 5 cans
> would 
> be needed - 6 if you use one for the BFO. With 3 IF stages the number
> jumps 
> to 7 and 8, respectively.
> 
> 73 de Jim, N2EY  
> ************************************
> Visit the HBR Receiver Web Site with over 100 pictures of receivers and

> construction notes...... via http://www.qsl.net/k5bcq/ 
> 
> Retrieve reflector archived data via
> http://mailman.qth.net/mailman/listinfo/hbr
> 
> 
> ************************************
> Visit the HBR Receiver Web Site with over 100 pictures of receivers and

> construction notes...... via http://www.qsl.net/k5bcq/ 
> 
> Retrieve reflector archived data via
http://mailman.qth.net/mailman/listinfo/hbr
> 
> 
> 
> 

************************************
Visit the HBR Receiver Web Site with over 100 pictures of receivers and 
construction notes...... via http://www.qsl.net/k5bcq/ 

Retrieve reflector archived data via
http://mailman.qth.net/mailman/listinfo/hbr