[Boatanchors] HF Receiving Balun

[Carl]

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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