Hewlett-Packard 117A VLF Comparator (WWVB)
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The HP 117 VLF comparator was used to compare a house standard aginst the 60 kHz WWVB transmissions from Fort Collins CO. There is a loop antenna that has filtering to reject near by RTTY stations and amplification.
The rack unit has a Tuned Radio Frequency (TRF) design, not a mixer type receiver. There is a meter and paper plotter to display and record the phase difference between the house standard and WWVB.
There are two versions of the antenna, one uses 2 each 13CW4 Nuvistors and the other uses FETs. The 117A puts out 27 VDC on the antenna connector to power the remote active loop. The 35 VDC fuse blows if you short the Antenna connector.
Dymec DA100 Active Antenna
The Plot (DA100_28Jul01.tif
The front panel 100 kHz output ( 117out100kc.tif
B&W 1.8-30 Antenna
Connecting gound and center toghther does NOT work. The raw signal coming from the antenna has only a 10 dB signal to noise ratio.
Apparently the 117A wants a better S/N. WWVB is not one of the 7 strongest signals in the 0 to 120 kHz frequency range. Amidon
This is the active loop that's part of the Bob Roehrig, K9EUI WWVB 60 KHz frequency standard published in the Jan, Feb and March 1994 issues of 73 Magazine. Material 33 is a manganese-zinc material having low volume resistivity. Used for low frequency antennas in the 1 KHz to 1 MHz frequency range. Available in rod form only. The above part umber is for a 1/2" diameter by 7.5" long rod. FAR Circuits