NATIONAL RADIO ASTRONOMY OBSERVATORYGreen Bank, West Virginia

Elec-xonics Division Internal Report No. 5

750 MC AND 1400 MC RECEIVER FRONT ENDSAT THE 300 FOOT TELESCOPEBy Bert Hans son and Dewey Ross

December 1962

NUMBER OF COPIES: 25

Reran June 4, 1963: 50

A thermal calibration made October 1, 1962, shows the calibration noise tube

to be 12. 04° on 750 Mc and 9.75° on 1400 Mc. Another thermal calibration on

October 11, 1962, shows the calibration noise tube to be 11. 1° on 750 Mc and 8.75° on

1400 Mc.

A tunnel diode amplifier (Micro State Model NC 1402, Serial No. 1) was added

to the 1400 Mc system and tested in the lab.

Measurements on Tunnel Diode Amplifier, Novrnt? ,er_14, 1962

The noise temperature of the tunnel diode amplifier was measured as a func-

tit n of temperature between 0 °C and 45 °C.

°K

1200 -

1000

800

600

400 Room0 10 20 30 40 C Temp.

The curve shows a relatively strong temperature dependence of the noise temperature

with a minimum around 36 °C. Since the gain as a function of temperature was not

measured, it is uncertain whether part of the change in system noise temperature is

a change in second stage noise contribution.

The noise temperature shown in the figure is the system noise temperature.

A noise temperature of 500 °I< was measured with an isolator between the first and

second stage. The noise contribution from the second stage was calculated to 50 °K

and consequently the noise temperature of the tunnel diode amplifier was 450 °K

BIAS1 1

-. 3 -

The noise temperature as a function of bias voltage was also measured. A

minimum occurred at 105 my (measured at the test point), the voltage recommended

by the manufacturer. Even in this case part of the change in measured noise tem-

perature could be caused by

variations in tunnel diode gain.

e in second stage noise contribution because of

TRop

700

600

50060 SO 100 140 MV

The battery voltage as a function of temperature was also measured. The

voltage was extremely stable over a temperature range of 0 - 50 °C.

In general, the optimum noise temperature of the amplifier was found to be

about 50'K higher than when first installed.

Front-End Removal

The following steps must be followed when removing either the 750 Mc or

1400 Mc front ends.

1. Remove the AC cable and the crystal current cable from the

terminal strips nearest the power supply and fasten them to

the terminal strip mounted above the power supply on the inner

box frame.

• Disconnect the following cables and secure them to the inner

box frame.

Input (to be disconnected at the directional coupler)

. Load (to be disconnected at the coaxial switch)

La cal oscillator (to be disconnected at the attenuator --

7 db for 750 Mc arid 12 (lb for 1400 Mc -- which is attached

to the mixer)*

IF (to be disconnected at the mixer)*

Noise tube power (to be disconnected at the relay chassis

and a cable clamp mounted behind the chassis must be re-

moved also)

Switch drive (to be disconnected at the switch and remove

able clamp).

Separate the steel cables attached to the top of each plate.

4. Rem ve the plate mounting bolts (6 on the 750 Mc plate and 5 on

the 1400 Mc plate).

5. Attach the winch to the steel cable located at the top of the plate

and lower assembly to the ground.

* The LO and IF cables for each receiver are clamped to the opposite plate

and the clamps have to be removed.

- -

Front End Block Dia ram and Cç t Lisn

103

Hai

Ta5ooHi LOAD

1 0ri5ONA OUT

1.5

750 Mc

Com onent Manufacturer m*del No. AUI __Ta No.

1. Directional coupler Narda 3001-20 1543

2. Coaxial Switch AEL SNB508B 2016

31 Mixer-Preamp LEL UCC -3 1373

4. Noise tube AIL 7010 133

5. Local oscillator GR 1361-A 1684

6. Power supply AC-DC 150-100 1883

7. Noise tube relay NRAO None

1400 Mc

8. Directional coupler Narda

9. Coaxial switch AEL

10. Mixer-Preamp LEL

11. Noise tube AIL

12. Local oscillator GR

13 Power supply AC -DC

14. Noise tube relay NRAO

3002-30

SNB508B

LAC-3

7010

1218-A

150-100

1422

2015

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55

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