[Test-Equipment] Helper Instruments SM-1000

[John Kolb]

Very Interesting.

With an Icom R-7000 receiver, I pick up a moderate strength beeping 
signal at
879.600, about 1 PPS. What sort of modulation is used? AM so there's a
constant carrier?

Would it be reasonable to take a 10 MHz time base, divide down to 100 kHz,
make a skinny pulse rich in harmonics and adjust the time base so the 
8796 th
harmonic is zero beat with the signal?

John

Eric Lemmon wrote:

>Jim,
>
>I owned an SM-1000 service monitor for a while, and I found a listing
>for it in an old TESSCO catalog.  The published specification is +/- 0.5
>PPM after a 24-hour warmup.  It should be left plugged in, even if not
>turned on, in order to keep the oven running.
>
>It will work fine without a battery, but make certain the battery wires
>are taped and stowed.  You did replace all of the metallic tape used to
>make the seams RF-tight after you buttoned up the unit, didn't you?  A
>lot of RF can leak out otherwise, corrupting measurements at very low RF
>levels.
>
>One way to calibrate the master oscillator to a very high accuracy is to
>tune in a GPS-disciplined control channel on one of your local 800 MHz
>cellular telephone sites.  There are 21 control channels on each of two
>blocks of assignments, Block A and Block B.  The Block A control
>channels are at 30 kHz intervals beginning at 879.390 MHz and ending at
>879.990 MHz.  The Block B control channels are at 30 kHz intervals
>beginning at 880.020 MHz and ending at 880.620 MHz.  Each cell site will
>have one control channel operating continuously, and the modulation
>sounds like a musical buzz.  There is no voice on a control channel, so
>there is no issue of eavesdropping.  One of the cellular blocks is
>assigned to the local wireline carrier, and the other is assigned to a
>non-wireline carrier.
>
>Put a short antenna on the receive input jack of your service monitor,
>and search for the strongest control signal.  If each of the control
>channels within a block show a similar frequency error, they are very
>likely synchronized to GPS and the error is in your service monitor. 
>The SM-1000 has a small hole in the rear panel for adjusting the master
>oscillator.
>
>The accuracy of the GPS-synchronized control channels is about 1 Hz, or
>about 0.001 PPM.  You can't get that accuracy by tuning in WWV at the
>bottom end of the service monitor's range.
>
>FYI, Helper Instruments was sold several years ago to Zetron, which
>still sells some test equipment with the Helper label, but the SM-1000
>was discontinued just before the sale.
>
>73, Eric Lemmon WB6FLY
>
>antqradio at juno.com wrote:
>  
>
>>Greetings
>>First time post from a long time lurker.
>>I have the above and just received a copy of the operators's
>>instructions.  Now I should be able to properly operate this neat piece
>>of test equipment.  The generator has output, the meters seem to work OK,
>>so I assume it is working properly.  The problem is I don't have the over
>>all specifications, they aren't in the instruction manual.  Helper
>>doesn't list it as current production, in fact, it seems they doesn't
>>support it any longer.
>>
>>So, what are the SM-1000 capabilities?
>>What is the published frequency (XLO) stability?  Must be OK since it has
>>a crystal oven!
>>Is it OK to operate without the internal battery?  Mine was DOA so I
>>removed it.
>>
>>Inquiring minds want to know!
>>Jim
>>Hot Springs, AR
>>    
>>
>  
>