NATIONAL RADIO ASTRONOMY OBSERVATORY

GREEN BANK, WEST VIRGINIA

ELECTRONICS DIVISION INTERNAL REPORT No. 194

A 2 TO 18 GHz SIGNAL SOURCE

FOR THE

GREEN BANK ANTENNA RANGE

J. R. FISHER AND W. D. KUHLKEN

OCTOBER 1978

NUMBER OF COPIES: 150

A 2 to 18 GHz SIGNAL SOURCEFOR THE GREEN BANK ANTENNA RANGE

J. R. Fisher and W. D. Kuhlken

Introduction

The signal source described in this report was built to improve the

accuracy and convenience of the Green Bank antenna range. In the past a re-

motely controlled HP 8690 sweep generator has been used as the antenna range

source, but its residual FM of a few tens of kHz added noise to antenna phase

measurements and often made it difficult to lock the receiver LO to the trans-

mitted signal. To cover the 2 to 18 GHz range four plug-ins were required

which could be a particular nuisance if an antenna under test overlapped two

plug-in frequency ranges. Although the new source does not cover the full 0.1

to 40 Gllz capability of the antenna range, It, along with the 1 to 2 GHz LO

multiPlier, provides a synthesizer derived signal for the most heavily used

portion of the spectrum.

The Antenna Range

The Green Bank antenna range has one movable and one fixed tower which

hold the transmitting antenna and the antenna under test approximately 8.4

meters above level ground. The distance between the two antennas can be varied

from about 4 to 16 meters. The antenna under test is mounted on a Scientific

Atlanta vertical axis turntable. The received signal is heterodyned at the an-

tenna and sent to the receiver hut at the base of the tower. The receiver is a

Scientific Atlanta Model 1754 phase and amplitude system which can operate from

0.1 to 40 GHz.

The minimum detectable signal below 18 GHz at the antenna under test is

-105 dBm, and the phase reference signal in an auxiliary receiving antenna

must be at least -60 dBm. With a 15 dB transmitting antenna gain at 18 GHz the

2

unknown antenna pattern can be measured to about 38 dB below an isotropic

reference pattern under ideal conditions with 1 mW of transmitter power. Under

the same conditions an auxiliary antenna with 7 dB of gain is required to meet

the -60 dBm phase reference signal requirement. The new signal source provides

about 2 mW of power at 18 GHz and over 20 mW below 8 MHz.

System Layout

The 2-18 GHz signal source is based on a voltage controlled YIG tuned multi-

plier which is driven by a signal anywhere in the 1 to 2 GHz band. The multi-

plier is packaged with its driver amplifier, D/A converters for frequency con-

trol, level monitoring circuitry, and associated power supplies in a single

chassis in the transmitter tower. The 1 to 2 GHz driver signal is generated by

the spare univeral local oscillator (ULO) system in the lab building and is sent

to the multiplier chassis via semirigid and RG 214 coaxial cables.

Both the ULO and multiplier frequencies are digitally controlled from the

receiver hut via multiconductor cables. The remote control panel also contains

multiplier drive and output power monitor meters.

The Multiplier Chassis

Figure 1 is the multiplier chassis schematic, and the details of the D/A

converter circuitry are shown in Figure 3. Some of the mechanical specifica-

tions and power supply requirements of the YIG tuned multiplier are shown in

Figure 2.

The YIG device requires up to one watt of 1 to 2 GHz drive power. Since

there is about 20 dB of loss in the coax between the lab and the antenna tower

a 30 dB gain amplifier is used to drive the multiplier. The drive level monitor

amplifier is designed for about 1 V output (meter full scale on X1 setting) for

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the Multiplier Chassis.

7

TABLE 1

Thumbwheel Switch Logic for Multiplier (13) and ULO (17)Frequency Controls

Truth Table 17Truth Table 13

COMMON CCONN. TO TERMINALS:

DIAL 1 2 4 80 551 •23 •

•,5 •6 0 •7 •8.9 5

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Standard Dial: 0-9

10 Positions

Series Symbol Part Number Terminations List Price

200 201 WL 17.00

300 0 378 S or DC1 6.00

* 315 S or DC1 7.00

3669 WW 8.00

3800 WW 9.00

700 701 S or DC27 10.00

701/107 S or DC27 1200.

* 715 S 12.00

* 715/107 S 14.00

8000 0 8078 S or DC8 5.00

* 8015 S or DC8 6.00

TRUTH TABLE 13 (continued next column)

COMMS. X (1103 & Y (COCONN. TO TERMINALS.

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Series Symbol Part Number Terminations List Price

200 211 WL 18.00

300 311 S or DC1 10.00

3773 WW j 12.00

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29000 29011 S 4.501 29159/x P or WW 5.25

TABLE 2

D/A Converter YTM Control Alignment

1. Set "Multiplier Frequency" to 02.00 GHz.

2. Ground point A-

3. Adjust R 1 for zero volts at point B.

4. Adjust R2 for zero volts at point C.

5. Adjust R4 for zero volts at point D.

6. Remove ground from point A.

7. Set "Multiplier Frequency" to 18.00 GHz.

8. Adjust R3 for 9.942 volts at point D.

9. Set "Multiplier Frequency" to 10.00 GHz.

10. Record voltage at point D.

(Should be close to 5.000 V.)

Call this reading V1.

11. Set "Multiplier Frequency" to 11.00 GHz.

12. Record voltage at point D.

(Should be close to 5.625 V.)

Call this reading V2.

13. Compute V1 + 0.99 (V2 - VI) = V3.

14. Set "Multiplier Frequency" to 10.99 GHz.

15. Adjust R5 so voltage at point D is equal to V3.

16. Double check by going through 1-15 again.

9

1 W into the multiplier. The external level monitor sensitivity depends on

the external coupling ratio and detector, but at 18 GHz a 16 dB coupling ratio

(10 dB directional coupler and 6 dB pad) with an HP 8472A detector produces

about 0.5 V output with 2 mW of RF power from the multiplier. The drive or

output monitor signals can be used to automatically stabilize the output power.

The DiA converter circuit is designed to accept 4 digits of complementary

BCD data to specify the multiplier frequency in steps of 0.01 GHz. The YIG

filter has a bandwidth of about 0.03 GHz so the 4 digit accuracy is sufficient.

The multiplier tunes from 2 to 18 GHz with a 0 to 10 V control range so IC3 in

Figure 3 is offset for 0 V output with 02.00 GHz digital input and R3 is ad-

justed for about 10 V output with 18.00 GHz input. The exact gain depends a

bit on the individual YIG unit. The gain of IC4 is adjusted for 17 of the gain

of IC3 for the tenths and hundredths digits. The complete alignment procedure

is given in Table 2.

For automated operation the digital tuning data could be supplied by a

computer, but for now only manual local and remote control are provided through

thumbwheel switches. One set of switches is mounted on the multiplier chassis

in the transmitter tower and another set in the remote control panel in the re-

ceiver hut. The two sets are tied in parallel with common pull-up resistors

so one set must be dialed to "00.00" while the other is in use. Truth Table 13

in Table 1 shows the switch logic.

While the YIG multiplier tuning is nearly linear it is not perfect. The

linearity specification is ± 0.1% which translates into ± 0.01 GHz at 10 GHz.

The unit used here appears to meet this specification everywhere except the high

end of the tuning range. The control circuitry was aligned to minimize the

error over the whole tuning range, and as a consequence there is an error of

about + 0.04 GHz in the multiplier frequency setting. In any case the multiplier

10

stetting should be tuned over a few tens of MHz around the output frequency to

obtain the maximum output power.

Figure 4 is a plot of the multiplier output power measured every 0.5 GHz

over the tuning range with a drive level of 700 mW. There is quite a bit of

fine scale structure on the order of ± 2 dB in the YIG filter passband so the

output power is quite frequency sensitive unless it is controlled with an ex-

ternal leveling loop.

The Remote Control Unit

The complete schematic of the remote control unit in the receiver hut is

given in Figure 5, and a functional schematic of the ULO frequency control sec-

tion is shown in Figure 6. The remote multiplier frequency control and level

monitor circuits duplicate and are in parallel with their counterparts in the

multiplier chassis. The connector pin configuration for the multiconductor

cable between the receiver hut and the transmitter tower is called out in

Table 3. This cable passes through a terminal strip in the receiver hut.

At the present time the only synthesizer derived 1 to 2 GHz source avail-

able in the lab is the spare ULO system. This system uses an HP 5105 RF syn-

thesizer to generate a 250 to 500 MHz signal which is multiplied to the 1 to

2 GHz band by a tracking YIG tuned multiplier. The multiplier unit is des-

cribed in EDIR #167 by B. Mauzy, and the synthesizer frequency control interface

is described in EDIR #144 by D. Schiebel. The control interface was designed

for control of the ULO by the telescope computers.

There are 3 switch selectable, 10-digit synthesizer frequency control

registers in the control interface unit. Only one,"FLO"

is used with the

antenna range source. The 10-digit registers are loaded 4 digits at a time

through a BCD 16-bit input bus which uses TTL, 1 = Low, logic. The loading

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Figure 6. Functional Diagram of ULO Frequency Control Circuit from Figure 5.

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TABLE 3

YIG Multiplier Control and Monitor Cable(Receiver Hut to Transmitter Tower)

FunctionReceiver Hut

ControlPanel

Receiver HutTerminal

Strip

MultiplierChassis

P2-J2 P2-J2

MSB A 1 A

A B 2 B

E 3 E

F 4 F

4-Digit L 5 L

BCD M 6 M -

Multiplier R 7 R

Frequency S 8 S

Data W 9 W

X • 10 X

AA 11 AA

BB 12 BB

CC 13 CC

DD 14 DD

JJ 15 JJ

LSB NM 16 MM

Gnd NN 17 NN

Pl-J1 Pl-J1

Drive Level A 18 A

Gnd B 19 B

Ext. Level C 20 C

Gnd D 21 D

14

TABLE 4

Synthesizer Remote Control Cable(Receiver Hut to Lab Building)

FunctionP3-J3

ReceiverHut

TwistedPair

Cables

TerminalStripsin Lab

ULOPlugs

-A-MSB R Red 1 R

I

ST

Green 23

S TBlack

4-Digit U Green 4 UBCD V Black 5 V

Frequency W Blue 6 WData X Black 7 X

Y Yellow 8 YZ Black 9 Za Brown 10 ab Black 11 bc Orange 12 cd Red 13 de White 14 e

ir f Black 15 fLSB h Red 16 h

j Black 171 White 18

-B-+5 V E Red 1 F,H,L

F Green 2Gnd MM Black 3 MM,A,B,C,Ii.Gnd NN Green 4 NN,E,J,K m

bo

Load- k Black 5 k 0,-

Load+ 1 Blue 6 1 as

Reset- r Black 7 E coReset+ s Yellow 8 F 7Gnd A Black 9 MM 1_ (1)

Gnd B Brown 10 NNC Black 11D Orange 12H Red 13J White 14L Black 15M Red 16N Black 17P White 18

15

sequence is as follows:

1) Transmit a reset pulse to set the loading counter to zero.

2) Put the 102, 10 1 , 10° 10-1 MHz digits of the first register

on the 16-bit bus,

3) Transmit a load Pulse.

4) Put the 10-2_

103

10- and 10- MHz digits on the 16-bit bus.

5) Transmit a load pulse.

6) Continue until 9 words of 4 digits each are loaded. When the

ninth word is loaded the commanded frequency is presented to the

synthesizer. Note that the last two digits of the third, sixth,

and ninth words are ignored since they do not fit in the 10-digit

registers.

Since 0.04% frequency resolution is sufficient for the

4 non-zero digits are transmitted from the remote control unit. Referring to

Figure 6, the synthesizer frequency loading sequence is started by the "Set

Frequency" button on the remote control panel. The output pulse from IC5 ap-

pears on the "reset" line at the same time that it strobes the BC D information

into latches IC1-4 which have their complementary outputs connected to the 16-

bit data bus. (See Table 1 for thumbwheel switch logic.) After the latch

strobe and ULO reset pulses have terminated, a sequence of 9 load pulses are

initiated by clearing counter IC8 which starts the IC7 generator. The load

pulses came from this generator, and after the first pulse the latches are

cleared so all zeros are transmitted in the last eight words. After IC8 counts

to 9 the load-pulse generator is turned off.

The connector pins for the ULO control cables between the receiver hut and

and the lab are called out in Table 4. These cables go through two terminal

antenna range only

strips in the lab building.

16

Results

The noise on the amplitude and phase pattern plots made with the new signal

source appears to be by about a factor of 4 less than that produced by the HP

8690 generator at around 15 GHz even though the latter had a somewhat higher

output power. With the synthesizer derived source the receiver locks to the

transmitted signal more quickly and shows no sign of losing lock as it often

did with the HP 8690.

Figure 7 is an example of the phase and amplitude accuracy obtainable with

the new system. The horn used to generate these patterns has a gain of approxi-

mately 10 dB over isotropic. Thus, the noise on the pattern becomes important

in Figure 7 at about 26 dB below the isotropic reference. This is 14 dB above

the ultimate receiver sensitivity predicted in an earlier section. Some of the

noise in the pattern is undoubtedly due to parasitic currents on the antenna

support structure.

FEEDFREQ, 14.0 GHz

E-PLANE PLOT No111.H-PLANE DATE: 917178 REMARKS:

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ifflitiffiliiiilill IINEFINOkliiiuuuuuuuuuuuuuuuiuuFigure 7. Typical Amplitude and Phase Patterns at 14 GHz with the YIG Tuned

Multiplier Signal Source.