[Boatanchors] HF Receiving Balun

Carl km1h at jeremy.mv.com
Sun Mar 15 17:02:48 EDT 2009 

> Actually, the 9:1 un-un has become one of my favorites.  This
> transforms 50-ohm coax to 450 ohms.  Now, 450 is a good approximation
> of a random-wire antenna, being the geometric mean of a 50-ohm'ish
> quarter-wave wire and a 3000-ohm'ish half-wave.


Yup


( SQRT (50 x 3000) =
> 387 )  This is the value assumed for short-wave in the design of the
> golden-era all-wave broadcast and communications receivers, and 400
> ohms  is value used in the RMA "dummy antenna" (see the SM-35/URM 25
> Antenna Simulator)


Yup again and also have a 25D with the full kit. Carried one for a few
years in the Navy.


 This is also the basis of the "Magnet Long-Wire
> Balun," which ain't a balun at all.


Dont recognize that



>
> I chose mix-43 ferrite, the recommended material for MF/HF broadband
> transformers, but something like mix-73 or 77 is probably a reasonable
> facsimile.


You have 73 on your web page.


The appropriate magnetic material makes a big difference in
> these things.


More yups. And with 73 you get a bit better bandwidth at not enough loss
to bother with. Its when you try and run power that things warm up.

Ive been working with ferrites since the 60's back when I was designing
cup core IF filters.

Carl
KM1H



>
> Al
>
>
> Carl wrote:
>> I strongly agree with Al. The TV baluns start to fall off rapidly
>> below 10-12 mHz and most are pretty useless below 5 mHz according to
>> VNA tests that I have run on a large number of different versions.
>>
>> Some receivers are especially fussy about antenna impedances as they
>> do not have antenna trimmers or are purpose designed. Others such as
>> the Hammarlunds are more forgiving.
>>
>> My own baluns are 9:1 as MDS tests show a slight improvement but its
>> probably more for talking points than actual use. A balanced to
>> balanced tuneable LP style (pi net) passive preselector before the
>> balun also helps with some antenna configurations and also improves
>> image rejections on the old single IF radios.
>>
>> Binocular cores are great but a small parallel stack of regular
>> ferrites beads or toroids epoxied together works just as well if
>> those are more readily available.
>>
>> Broadband receiver baluns should use a ferrite mix that would be used
>> at a lower frequency in a tuned circuit application. In this case a
>> 73 mix for a balun core or a stack of beads, and 77 mix if using
>> regular toroids. This results in less capacitance between turns and a
>> broader plus flatter frequency response.
>>
>> In high power transmitter use different rules apply and powdered iron
>> is preferred in voltage baluns and tuned circuits.
>>
>> Carl
>> KM1H
>>
>> PS: I just noted that Al specifies 73 mix in the article.




>> ----- Original Message ----- 
>> From: "Al Klase" <al at ar88.net>
>> To: "Byron Tatum" <bjtatum1 at att.net>
>> Cc: <Boatanchors at mailman.qth.net>
>> Sent: Sunday, March 15, 2009 10:14 AM
>> Subject: Re: [Boatanchors] HF Receiving Balun
>>
>>
>>
>>> Hi Byron,
>>>
>>> Go to this page on my site and follow the "BALUNS" link:
>>> http://www.skywaves.ar88.net/ANTENNA/antsys.htm
>>>
>>> Core material is very important.  E.g., TV baluns roll off below 
>>> 5-10
>>> MHz.  If you round up some of the BN-43-202 "binocular" cores, my
>>> designs are good from about 100Khz - 60MHz.  In any event the 
>>> winding
>>> topology info should be what you need to know.
>>>
>>> Hope this helps,
>>> Al
>>>
>>> Byron Tatum wrote:
>>>
>>>> Hello-
>>>>     I recall an article by Mr. Glenn Zook about using a TV-type
>>>> receiving balun with older shortwave receivers (such as HQ-129X) 
>>>> that
>>>> have around 300 ohms input impedance. The balun would noticably
>>>> improve reception.
>>>>     I have just finished restoring and re-capping a HQ-129X. I am
>>>> thinking of aligning it using signal generator fed through the 
>>>> balun.
>>>>     I would like to build my own as I have a lot of torroid and 
>>>> balun
>>>> cores for QRP use.
>>>>     Does anyone know of a good construction article showing how to
>>>> build such a receiving balun?
>>>>                                                     Thanks,
>>>>                                                             Byron
>>>> WA5THJ
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>>>>
>>> -- 
>>> Al Klase - N3FRQ
>>> Jersey City, NJ
>>> http://www.skywaves.ar88.net/
>>>
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>>
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>
> -- 
> Al Klase - N3FRQ
> Jersey City, NJ
> http://www.skywaves.ar88.net/
>
>
> ______________________________________________________________
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