KVN and VERA Array

Brief Summary of VERA Receiving System

Each VERA antenna has the receivers for 4 bands, which are S (2 GHz), C (6.7 GHz), X (8 GHz), K (22 GHz), and Q (43 GHz) bands. For the common use in 2009, the K band and the Q band are open for observing. The low-noise HEMT amplifiers in the K and Q bands are enclosed in the cryogenic dewar, which is cooled down to 20 K, to reduce the thermal noise. The range of observable frequency and the typical receiver noise temperature () at each band are summarized in the Table 5 and Figure 5 .

table 5:Frequency range and of VERA and KVN receivers.
Frequency Range $t_{\rm rx}{}^{a}$
Band [GHz] [K] Polarization
VERA
K 21.5-23.8 30-50 LCP
42.5-44.5 70-90 LCP
KVN
K 21.25-23.25 30-40 LCP/RCP
Q 42.11-44.11 70-80 LCP/RCP
(40-50 for Ulsan)
Receiver noise temperature

Figure 5:Receiver noise temperature for each VERA antenna. Top and bottom panels show measurements in the K and Q bands, respectively. Horizontal axis indicate an IF (intermediate frequency) at which is measured. To convert it to RF (radio frequency), add 16.8 GHz in the K band and 37.5 GHz in the Q band to the IF frequency.

After the radio frequency (RF) signals from astronomical objects are amplified by the receivers, the RF signals are mixed with standard frequency signal generated in the first local oscillator to down-convert the RF to an intermediate frequency (IF) of 4.7 GHz-7 GHz. The first local frequencies are fixed at 16.8 GHz in the K band and at 37.5 GHz in the Q band. The IF signals are then mixed down again to the base band frequency of 0-512 MHz. The frequency of second local oscillator is tunable with a possible frequency range between 4 GHz and 7 GHz. The correction of the Doppler effect due to the earth rotation is carried out in the correlation process after the observation. Therefore, basically the second local oscillator frequency is kept to be constant during the observation. Figure 6 shows a flow diagram of these signals for VERA.


Figure 6:Flow diagram of signals from receiver to recorder for VERA.

KASI logo image

KaVA ( KVN and VERA Array )