The problem faced by VU VHF homebrewers is the non availability of variable VHF inductors. Designs with fixed coils and variable caps seem best for us.
73 Raj
--- In HamBrewers@yahoogroups.com, "prabakaran.D" <medianetworkcoin.hams@...> wrote:
>
> This receiver is a six channel crystal controlled design. An AFC facility is available on two channels, since the doppler frequency shift on the 2 meter beacon is about + /-3 kHz which will cause a significant degradation to the signal if a fixed frequency receiver is used. The AFC range is just sufficient to cope with the +/- 15 kHz doppler shift found on the 70cm beacon. A suitable low noise 70cm converter was described in reference (5).
>
> The low noise figure and high gain of the 3SK88 RF and mixer stages are exploited to give the receiver a sensitivity exceeding O.15uV (-l24dBm) for 12dB SINAD. The heart of the receiver is an MC3359/ULN3859 IF IC, which is a tidied-up and slightly improved version of the MC3357. The use of this IC simplifies the design of the IF considerably, and helps achieve the overall excellent price/performance of the unit. A nine times multiplication is used in the local oscillator chain to give the required range from the VXO - which also means that a readily available crystal may be used.
>
> Refer http://radioshop.co.uk/tech_articles/2m_rx_circuit.jpg
> http://radioshop.co.uk/tech_articles/2mrx.htm
>
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