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Author Topic: Help with QST HBR-11 1600 kHz IF xformer, please?  (Read 504 times)
KC9KEP
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« on: March 28, 2009, 07:02:08 PM »

Hello all,

I am building the QST HBR-11 double conversion superhet receiver as featured in QST magazine.

I’m building my way “backwards”, from audio output, BFO, detectors, 100 kHz I.F. strip, mixer, second oscillator, and am now at the point the I need to link to the first detector and 1610 kHz section.

I could use some suggestions on building my “T1” 1610 kHz I.F. transformer.

The article uses two separately wound tuned coils that are linked via a twisted pair.

I’m winding my own coils on adjustable slug cores, using Litz wire.

I calculate that 68 pF and 144 mH will get me close to the target of 1.61 MHz for the first stage of I.F.

The original construction article (Mar 63 QST) indicates that the two I.F. coils are mounted in different locations within the receiver and “linked” to each other via a twisted pair of wires.

My assumption is that each separate-adjustable-slug coil must also include a second winding that couples to the tank coil and makes it possible to link the two separate-adjustable-slug coils.

So, what would be the nature of this link-winding?  Would it be of just a few turns of wire, being just enough in order to induce the tank’s energy and link via the twisted pair to the other coil?

Can coupling winding just be solid 22 gauge wire?

Thanks all!

--Big Nick AKA KC9KEP
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KA5N
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« Reply #1 on: March 28, 2009, 07:32:03 PM »

The IF cans are commerically built.  The "link coupling" is just a couple of turns of wire wound next to the existing coils.  Twisted pair is used to prevent unwanting coupling to other circuits.
If you are building the IF transformers yourself, I wonder what kind of results you will get.  Often IF transformers were jumble wound rather than being solenoid wound.  
You really need to have been born earlier (or started sooner) when such parts were easy to obtain, often at your nearby radio/tv electronics supplier.
Good luck
Allen
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W8JI
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« Reply #2 on: March 28, 2009, 08:12:54 PM »

Nick,

When I built my first superhet I used a similar conversion scheme. I used IF cans from a BC-454 R26 for my first IF (1415 kHz) and followed that single stage with an 85 kHz IF using IF cans from a BC-453 command set receiver.

If I were building the HBR16 or a loose copy I would not worry about Litz wire or a cross lay winding. It just is not that important. I'd probably use local oscillator coils from an AM BC receiver for the 1650 kHz IF.

Be aware when the HBR-16 was popular the upper end of the BCB was near 1600 kHz, so 1650 was a dead guard band between navigation and telemetry and the AM band.

You might run into a problem with blow-through from AM stations now unless you are very careful with wiring and traps.

You have a number of options. Small iron toroids with a link to minature 50 ohm coax, or using an IF above 160 meters and below 80 meters. You don't have to use such a high ratio of L to C, you could use more C and less L without ill effect.

There are a number of solutions.

73 Tom
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KC9KEP
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« Reply #3 on: March 29, 2009, 05:28:38 AM »

OK, gentlemen, thank you for the replies!

Actually, I guess it's a 1610kHz coil, hopefully far enough away from the high-end of the AM radio band.

For that matter, I suppose I could move the frequency if need be.

Last night, I found the orignal Ted Crosby design from 1957, his HBR-11.

He simply wound 90 turns around a 1" poly tube for the tank and used 5 turns for the coupling section in order to make these coils.

I have heard that this isn't very critical, but these homebrews are such gigantic projects that I'd like to make it as functional out-of-the-gate as possible, so I like to ask around first :-)

I already wound the coils last night, which is fairly simple with my home-brew coil winder.

The best thing about using Litz wire (for me) is that it winds so nicely!  The single strand cotton covered doesn't like to stay-put on the coil form :-(

And the best thing about building these receivers is the learning experience and the friends that one makes along the way!

But thanks again, I hope be receiving DX soon :-)

73!

--KC9KEP
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