UHF Receiver

This page covers the Range 1 to Range 4 receivers. The Range 0 is a newer (and easier to modify) design.

Basics

The basic receiver is pictured below. Note the UHF R1-R4 receivers have a preselector that's flush with the front panel and only 3 adjustment. This is a dead give away that you have a UHF R1-R4 from the front. Unfortunately there is not an easy way to identify it further than by part number.

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  UHF RX Front

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  UHF RX Back

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  UHF RX Case

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  UHF RX Internal

The receiver is a high side injection with the 1st Lo operating +73.35 MHz higher than the receiver frequency.

The SCM knows what type of module is inserted by reading voltage divider resistors on the u2600 A/D Converter. Some of these are on ports used for other things, Change Frequency and Lock and then A8 input is used for ID. Note the resistors have the same labels on the UHF boards but on other bands the same parts have different labels. The R2606 and R2607 form a voltage divider feeding the A8 input with the computed voltage in volts.

Range	R2449 Chg Freq	R2450 Lock	SPACE	R2606	R2607	A8 Volts
UHF R0	0	3300		5600	3300	1.9
UHF R1	0	0		1200	1200	2.5
UHF R2	0	3300		1200	1200	2.5
UHF R3	3300	0		1200	1200	2.5
UHF R4	3300	3300		1200	1200	2.5
VHF	R2413	R2415		R2812	R2814
VHF R1	0	0		2700	1200	1.5
VHF R2	0	3300		2700	1200	1.5
800/900	R2422	R2414		R2816	R2815
900	0	0		1200	4700	4.0
800	0	0		1200	2700	3.5

The service manual excerpt is in PDF and below.

UHF Receiver Models TRE6281-TRE6282-TRE6283-TRE6284 Service Manual Excerpt

In PNG format.

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  Schematic Sheet 1 of 4

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  Schematic Sheet 2 of 4

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  Schematic Sheet 3 of 4

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  Schematic Sheet 4 of 4

Note on the schematic the VCO high and Low are reversed. This seems to be a recurring theme in the Quantar manuals.

Reversed VCO's

As the VCO runs at 73.35 MHz higher than the intended receive frequency the VCO will expect to lock over the following ranges. The ideal spot for the VCO to opperate is between 2.5 and 7.5 Volts highlighted in pink below.

Range	Lower VCO					Upper VCO
Volts	0.8	2.5	5.0	7.5	9.2	0.8	2.5	5.0	7.5	9.2
UHF R1	462	467	479	491	499	478	491	499	506	514
UHF R2	498	511	519	527	536	514	527	535	543	552
UHF R3	528	543	549	555	564	541	555	561	567	575
UHF R4	553	567	574	580	589	568	580	587	593	601

The VCO is much like the VCO in the exciter, a sealed unit with no further diagram available from the factory.