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MG

M. George

Mon, Jul 20, 2015 10:29 PM

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.

Thanks

Max NG7M

--
M. George

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. Thanks Max NG7M -- M. George

HZ

Hui Zhang

Tue, Jul 21, 2015 12:14 PM

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.

Regards.

Hui Zhang BA6IT

At 2015-07-21 06:29:07, "M. George" m.matthew.george@gmail.com wrote: