[time-nuts] 10 MHz Filters

John Ackermann N8UR jra at febo.com
Tue Dec 2 16:27:06 EST 2014


Thanks for the kind words, Dick. :-)

However, a couple of notes on the TADD-1 bandpass filter:

1.  I *don't* recommend installing it unless there is a good reason.  As 
others have noted, any tuned circuit is a thermometer and will degrade 
ADEV performance.  Other than the original test unit, I haven't built 
the filter into any of the several TADD-1s I've deployed in my lab.

2.  The component values for the example filter in the TADD-1 manual are 
wrong.  I haven't gotten around to fixing that, mainly because of point 1.

And since the topic of isolated grounds has come up: the TADD-1 uses 
transformer isolation on each input and output, and provides DC 
isolation by putting a 10nf cap between ground and the coax shield (with 
a very short path).  This seems to have worked pretty well for most users.

John
----

On 11/27/2014 11:41 AM, Richard Solomon wrote:
> If you want to see how to really do it right, check out this
> distribution Amp
> on the TAPR site.
>
> https://www.tapr.org/kits_tadd-1.html
>
> 73, Dick, W1KSZ
>
>
> On 11/26/2014 9:08 PM, Perry Sandeen via time-nuts wrote:
>> List,
>>
>>
>> I have seen on the net a 10 MHz filter using 10.7 IFtransformers but
>> have no idea how well they would work for isolation with thenew style
>> Lucent boxes.
>>
>>
>> Thoughts?
>>
>>
>> On Ebay venders are offering 10 MHz crystals for almostnothing if you
>> buy 30.  My question wouldthese be good for making some type of simple
>> ladder filter?
>>
>>
>> In his article *Modifying Lucent RFG-M-RB Rubidium FrequencyStandard*
>> the author used a 10MHz filter that was taken from an old
>> 10MbitEthernet LAN board. The part number he used was 20F001N and I
>> found them onEbay for low prices.
>>
>>
>> Now I don’t have any access to any old ethernet LAN boardsso I’d have
>> to build from scratch.
>>
>>
>> Does anyone of these methods have an advantage over theothers on the
>> new style Lucent boxes or in the making of a small
>> distributionamplifier with good isolation?
>>
>>
>> Regards,
>>
>>
>> Perrier
>>
>>
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>
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