DANIELS
ELECTRONICS LTD.
TM
VHF Enhanced Extra Wideband Receiver Instruction Manual IM10-VR3H040-AB
2-5
2.3.3
Minor Frequency Change
Changes less than ± 0.5 MHz (29 - 38 MHz) or ± 1 MHz (38 - 50 MHz) from a previously tuned
working receive frequency will generally not require any adjustment. Change the channel
frequency select switches (Section 2.2) and inject a standard signal at the new channel
frequency. Verify that the receiver sensitivity is
≈
-114 dBm for 12 dB SINAD. Slight
adjustment of the Front End tuning slugs (5) may be performed to maximize sensitivity at the
new frequency. Be aware that the preferred Front End tuning procedure (Refer to sub-manual
IM10-FE3H040) requires swept frequency response measurement of the Front End filter in order
to provide a maximally flat response over a range of input frequencies, with the primary channel
frequency centered in the filter passband (5 MHz wide). This alignment approach is not
mandatory for single channel operation.
A quick check of the Synthesizer module PLL control voltage at TP4, accessible through the
synthesizer top cover, is advisable at all programmed frequencies. The voltage at TP4 should
range b0.5 Vdc and +4.5 Vdc at all programmed frequencies. Measured voltages
outside this range indicate a possible "out-of-lock" condition and should be avoided. The Front
End module must be removed (but left connected) from the main receiver chassis in order to
access TP4. The synthesizer top cover foil label may have to be cut in order to access TP4. Fine
Frequency TUNE adjust trimmer capacitor C24 may then be adjusted to position the PLL loop
voltage (TP4) as close as possible to the n2.3 Vdc for all programmed frequencies. For
single channel operation, TP4 should always be set to +2.3 Vdc.
2.3.4
Major Frequency Change
Changes greater than ± 0.5 MHz (29 - 38 MHz) or ± 1 MHz (38 - 50 MHz) from a previously
tuned working receive frequency will require complete FE3H Front End and OSR-3H061
Synthesizer alignment as per section 4 in this manual. Changing a high band receiver (VR-
3H045-S) to a low band receiver (VR-3H035-S) or vice-versa requires a complete change out
and alignment of the Front End module (FE3H035 or FE3H045) in addition to OSR-3H061
alignment.