Hello Dave:
I have used the BBR7731 cores for about 15 years, and have made hundreds of
transformers using these cores and NEVER had one returned to me.
I recently measured the insertion loss of these transformes, using 4 turns
trifilar. The results are:
single core: 0.5 dB on 1.8, 3.5 and 7 Mhz
stacks of 2 cores: 0.3 dB on the same frequencies.
The SWR of these transformers, when terminated with a 470 ohm resistor is
less than 1.05 /1 on the same frequencies.
If you can get these at the right price, you will be happy with them.
this does not mean that other (73 or 43 mix) won't work, but you will need
just as many if not more turns to get the same result.
73
John Devoldere,
ON4UN
To: <topband@contesting.com>
>Date: Thu, 03 Sep 1998 14:36:46 -0400
>From: "w8ji.tom" <w8ji.tom@MCIONE.com>
>Subject: Re: TopBand: Beverage transformer core question
>To: Raymond Dave-CSUS04 <csus04@lmpsil02.comm.mot.com>,
> Topband Reflector <topband@contesting.com>
>Reply-to: w8ji.tom@MCIONE.com
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>
>Hi Dave,
>
>> For the past few years, I have been using the BBR 7731 cores for
>SNIP
>> brand, part number, core material type, etc. Anyone have suggestions?
>
>The core Misek suggests (dc ui~10000) is actually not the correct core for
>160 anyway. Ui values should be picked at the lowest operating frequency,
>never at dc! The dc ui 10, 000 core has less permeability on 160 meters
>than the following core materials:
>
>77 ui 1800, 73 ui 800, 43 ui 900.
>
>All of these materials are suitable for broadband transformers. They have
>better RF performance and are more common. If you select a 73 or 43
>material, you can use about 40% less turns on the transformer (even fewer
>with the 77 core) for the same stack length. Fewer turns reduces unwanted
>coupling from primary to secondary, and they saturate at high signal
>levels. They also work much better at higher frequencies, making the
>Beverage very useful on 7 MHz and higher.
>
>Ameritron has a binocular core 412-5250 (73 mix) for $.60 each. A two turn
>primary is more than enough for 50 ohms at 160 meters, and the core
>saturates at about 30 watts. Alternately, a stack of FB73-601 beads can be
>substituted. I did use beads, but now switched to the free (eerrr $.60)
>412-5250 cores. I use #24 wire, and have yet to lose a core during
>lightning despite losing dozens of two watt resistors on my 11 Beverages.
>
>Alan Bond (770) 973-6251 (before 9 pm eastern time) e-mail mgs@avana.net
>has a large 43 material core (about 1" OD by 1" tall) that would make a
>killer transformer or feedline choke core.
>
>73 Tom
>
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