Classic Broadcast

Rohde & Schwarz

all-purpose SK1

for 1 kW shortwave operation
in any mode (1,5mc - 30mc)

formerly BOS tx at various locations

built in the early 1970s

Rohde & Schwarz

heavy duty shortwave class A
amplifier VK20 (1,5mc - 30mc)

formerly Bundeskriminalamt Wiesbaden

runs in combination with
the antenna matching device HS 9128

20 kW permanent output in any mode

power supply 3ph 400V approx. 60kVA

built in 1977

RF Power, AF Response & Intermodulation
Measurements for Transmitter 20 kW, type SK 20/3904

Operational Data

	U_a (kV)	I_ao (A)	U_g2 (V)	U_g1 (V)
SK1	3,0	0,35	460	-40
VK20	8,2	2,6	1200	-160

Vacuum-Tubes:

RS 1072 C Ser# 3445 (SK1)
RS 1082 CL Ser# 234 (VK20)

For all measurement procedures the transmitter is terminated by the dummy load RBN 60/60 .

RF Power Output operating in emission mode A1

Rated value: 20 kW

Measured @ power stage 'II' by vacuum-tube voltmeter URU with insertion head after automatic self-tuning:

f (mc)	P_in (W)	U_out (kV)	P_out (kW)	I_a (A)
1,5	220	1,11	20,5	5,2
2,1	240	1,09	20,0	5,2
3,5	215	1,12	21,0	5,2
5,4	240	1,07	19,0	5,2
8,3	205	1,09	20,0	5,4
10	250	1,08	19,5	5,3
13	280	1,09	20,0	5,3
16	390	1,11	20,5	5,4
20	350	1,08	19,5	5,2
24	280	1,09	20,0	5,2
30	180	1,07	19,0	5,1

Indicated P_max with manual power setting @ decade exciter NO281 and adapting the anode overcurrent trip:

P_out = 30 kW @ 10mc for intermittent operation

Audio Frequency Response operating in emission
mode A3 with P_carrier = 7,5 kW

f (kc)	0,1	0,5	1	2	4	6	8,4	16,8
Rated value (dB)	≤ ±2,5	≤ ±2	0	≤ ±2	≤ ±2	≤ ±2,5	≥ -20	≥ -32
Measured value (dB)	-0,5	+1	0	+0,5	-1	-1	-60	> -70

Measured by RC Generator SRB & Millivoltmeter UVN

Spacing of intermodulation products 3rd & 5th order operating in emission mode A3J

Rated value: ≥ 41 dB vs. pep

Measurement procedure
The transmitter will be modulated by two audio signals with the same level which both @ a time drive the transmitter to 50% output.
After shifting down to the 10 kc stage the RF output signal will be recorded by the frequency spectrograph FNA.

f (mc)	f₁(kc)	f₂(kc)	2xf₂-f₁	2xf₁-f₂	3xf₂-2xf₁	3xf₁-2xf₂
			d₃(dB)	d₃(dB)	d₅(dB)	d₅(dB)
5	1,21	3,6	45	46	67	69
20	1,21	3,6	42	41	57	60
30	1,21	3,6	42	41	58	60