DuneStar Model 504 Bandpass Filter Characteristics

By Bob Wolbert, K6XX


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The DuneStar 504 is a relay-selected bandpass filter array that allows operating two stations on different bands simultaneously--without blowing up your receiver front-ends. This model consists of five bandpass filters, one each for 160m, 80m, 40m, 20m, and 15m. The rig transmits and receives through the proper bandpass filter, which 1), reduces wideband phase noise radiated from the transmitter; and 2), prevents out-of-band power (and noise) from reaching the receiver. A band select signal from a manual switch or the radio selects the correct operating band. Coupled with the band select schemes described previously, the DuneStar filter array is completely transparent in operation. Besides its utility in protecting adjacent receiverís front ends, the filters also reduces TVI by a small amount (15dB to 20dB). Figure 1 shows the system block diagram of a dual-rig contest station employing autoswitching bandpass filters.


Figure 1. Block diagram of two radio contest station using automatically selected bandpass filters.


Filter Characteristics

The DuneStar 504 was evaluated with a HP 4396B Network/Spectrum analyzer. Table 1 summarizes the band-to-band rejection characteristics of the individual filters. Oscillographs for each bandpass filter follow.


Filter 160 80 40 20 15
4052 44 0.9 40 42
20 54 48 54 0.3 30
15 55 51 47 48 1
Table 1. Band-to Band Filter Characteristics of DuneStar 504 (Loss in dB)

Filter Oscillographs


160m Filter from 1MHz to 30MHz

160m Filter: Band-to-Band Characteristics

160m Filter: Broadband Characteristics to 150MHz

80m Filter from 1MHz to 30MHz
80m Filter: Band-to-band Characteristics
80m Filter: Broadband Characteristics to 150MHz
40m Filter from 1MHz to 30MHz
40m Filter: Band-to-band Characteristics
40m Filter: High Frequency Rejection to 150MHz
20m Filter from 1MHz to 30MHz
20m Filter: Band-to-band Characteristics
20m Filter: High Frequency Rejection to 150MHz
15m Filter from 1MHz to 30MHz
15m Filter: Band-to-band Characteristics
15m Filter High Frequency Rejection to 150MHz

E-mail: Bob Wolbert, K6XX
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