[time-nuts] GPDSO Distribution amp that does not radiate ?

[Eric Scace]

   As others have mentioned, leaks can occur from the distribution amp via any connected cable (including data power cables) or from the case itself. Ditto for the TBolt. These lines should be “cold” at RF by making them high-Z paths.

   Proper ferrite treatment raises RF impedance in its design range and can can help kill RF signals leaking out via a cable. RF bypass capacitors inside the box (penetration point through the Faraday cage that a good chassis enclosure should represent) can also help.

   Similarly, the SDR itself may be picking up RF via paths other than the RF-input connector; e.g., power supply lines, control/data lines, audio lines, headphone jack.

— Eric

> On 2019 Jul 13, at 20:13 , Bob kb8tq <kb8tq at n1k.org> wrote:
> 
> Hi
> 
> Running and shielding a 10 MHz standard signal is never easy. Ground loops
> here or there are highly likely to exist and create all sorts of issues. In some 
> setups, -10 to -20 dbm is not an uncommon result ( = fix the termination on 
> your Spectracom system …). Getting below -90 is actually doing pretty well.
> 
> Bob
> 
>> On Jul 13, 2019, at 12:53 PM, Jerry O. Stern <jsternmd at att.net> wrote:
>> 
>> I have been using a Tbolt and TAPR TADD-1 for a few years, mainly as an
>> external reference source for my workbench equipment.  Just got a SDR radio
>> kit (Ubitx) and trying to calibrate the local oscillators found this
>> annoying substantial 10MHz signal heterodyning with the LO's (45MHz and
>> 12MHz).   Taking a look on my SA with just a broad band telescopic antenna
>> in the SA input, I see a 10MHZ at about -55 dBm and no other signals > -120
>> dBm.  The Tbolt is about 4-5' away from the workbench BUT I disconnected
>> everything and it is only connected to the TADD-1 distribution amplifier
>> The TADD has no distribution coaxes attached, it is in the TAPR metal
>> cabinet which I always thought was well shielded and every port has been
>> terminated with 50 Ohm  dummy load plugs.  When I take the TADD-1 out of the
>> equation and just run the Tbolt into a 50 ohm termination plug, the 10MHz
>> signal on my SA drops down to  > -90 dBM.     I duplicated this with a
>> Lucent RFTGm-Xo/Rb pair and the TADD-1 with similar results.    Has anyone
>> else seen this with their distribution amp?
>> 
>> 
>> 
>> Jerry 
>> 
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