[time-nuts] TBolt 10 MHz output ~1.7v rms / HP 8656B FG

Hui Zhang ba6it at 163.com
Tue Jul 21 08:14:33 EDT 2015

Hello Max:
    I use a SMA Coax attenuator to connect my GPSDO/Rb Stand with the EXT Ref port of other equipment, the GPSDO/Rb often provides +7 ~ +13dBm output level, I believe it's too high for a EXT ref source, so I often use a 10dB attenuator to put it there, actually I like use another 10 ~ 20dB attenuator  to series connect to input port, the advantage of these SMA attenuator is they are easy to connect in series, so can get  any flexible attenuation value. By using these SMA attenuator, I need a additional SMA-BNC convert jack. That's my way, hope it's useful to you.


Hui Zhang BA6IT   

At 2015-07-21 06:29:07, "M. George" <m.matthew.george at gmail.com> wrote:
>I picked up an HP 8656B from the usual place and have been cleaning it
>up... got around to testing the output which looks good on a cheap
>frequency counter etc...
>I'm wanting to use the 10 MHz output from my TBolt for the reference input
>on the HP 8656B and my Elecraft K3.  So I started digging around in the
>manuals I can find on the internet, including KO4BB's cool manual stash.
>I'm not finding the specs on the input for the reference on the 8656B.  I
>found an older reference for the 8646A that said to keep the input rms
>voltage between .2 and .4 volts, which scared me, because I had already
>hooked up the Tbolt direct.
>If this is correct, then .2 vrms - .4 vrms is around +2 dbm.
>The direct output on the TBolt to my scope is showing ~1.7 vrms which is
>close to +17 dbm.  Yikes, I had that hooked up to the 8656B for a while...
>I hope I didn't screw anything up.
>I have a K3 with the EXREF board hooked up direct to the TBolt and it's
>happy as a clam with the 1.7 vrms input.  Which is a tad bit high for the
>Elecraft docs which shows a nominal level of +4 dBm to +16 dBm.  I'm
>assuming the 1.7 vrms is falling in to the 'nominal' range.
>I'm not finding dire warnings about hooking the TBolt 10 MHz output direct
>to a K3EXREF or an HP FG...
>I don't have a frequency counter that takes an external reference (yet), so
>it's hard to know if the HP 8656B is using the external reference.  Again,
>I can't find much in the manuals to validate the external input, other than
>using a FC with the same reference input.
>Any input or tutoring would be helpful.  Are others just adding resistance
>in line with the TBolt output to drop voltage?  I tried a 50 ohm resistor
>and it dropped from 1.7 to just under 1v rms on the scope.
>Max NG7M
>M. George
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