| Nowy mobilny ryżowiec QYT KT8900 |
| A jak tam odbiornik? Ze zdjęć w sieci wynika, że to w zasadzie Baofeng o większej mocy z jaki filtrem. edit: rewelacja  Sensitivity: ≤;; 0,25 μ;;V (wide) / ≤;; 0,35 μ;;V (narrow) Jest i co na temat filtra: It seems there are two (8-pole?!) low pass filters on the circuit board. The antenna signal is split in two ways and switched by PIN diodes. Therefore the VHF and UHF path should be able to suppress harmonics. I used the computer program ELSIE to determine what suppression should be able to get on VHF. I designed a 7-pole Chebycheff low pass filter for 148 MHz with a passband ripple value of 0,1. The component values are rounded to the nearest real world values. The suppression for 290 MHz is 55 dB, at 435 MHz 82 dB and at 580 MHz is the suppression 100 dB. If there is no loss at the carrier, the dB values can be considered as a negative dBc value. Since the third (theoretical strongest) harmonic is the strongest for real, it's possible the applied low pass filter doesn't work what it's designed for. My plan was to bridge the VHF low pass filter en measure the results and do the same measurement without the filter bridged (original configuration). Than it could be determined if the filter is working at all. I tried this and without success. It's likely the replacement of inductor (L) and capacitor (C) components will fix the problem. Since the crappy quality I decided not to spend more time on this rig. But I guess a replacement filter will work and solve the spurious radiation problem. Replacement filter sketch:  http://www.amateurtele.com/print.php?artikel=213 |
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