UHF Preselector

APR-546MPM8-01 : UHF Preselector

A typical UHF preselector consists of a frontend narrowband filter followed by amplifiers and signal conditioning elements like digital step attenuator.

APR-546MPM8-01 consists of a set of 8 -channel phase matched UHF receivers housed in a 19″ rack mountable chassis.

Each receiver channel has a high Q cavity filter that provides more than 60 dB out-of-band rejection. Low noise amplifiers are used to provide low noise and high linearity. Digital step attenuators are use to allow user to have 50 dB of user-controllable gain. All 8 receivers are optimized to provide a phase-matched of +/- 6 degrees from 514-578MHz.

A miniature lightweight version for airborne applications is available. Contact our sales team for more information.

< ± 8°[/av_cell][/av_row] [av_row row_style='' av_uid='av-1jdjp3'][av_cell col_style='' av_uid='av-54vtb']Power supply[/av_cell][av_cell col_style='avia-center-col' av_uid='av-1b3mdz']110 - 220Vac[/av_cell][/av_row] [av_row row_style='' av_uid='av-127on3'][av_cell col_style='' av_uid='av-3fhxr']Size[/av_cell][av_cell col_style='avia-center-col' av_uid='av-skebr']3U 19" rack mountable chasis IEC 60320-1 C14[/av_cell][/av_row] [/av_table] [av_promobox button='yes' label='Contact Sales' link='page,111' link_target='' color='theme-color' custom_bg='#444444' custom_font='#ffffff' size='large' icon_select='yes' icon='ue889' font='entypo-fontello' box_color='' box_custom_font='#ffffff' box_custom_bg='#444444' box_custom_border='#333333' av_uid='av-kwizz'] To get more information regarding our phase matched pre-selectors, contact our sales team. [/av_promobox] [av_hr class='default' height='50' shadow='no-shadow' position='center' custom_border='av-border-thin' custom_width='50px' custom_border_color='' custom_margin_top='30px' custom_margin_bottom='30px' icon_select='yes' custom_icon_color='' icon='ue808' av_uid='av-dgp0v'] [av_textblock size='' font_color='' color='' av_uid='av-afigv']

Antenna, Preamplifier and UHF-Pre-selector: The Basics

Back in the early ’70’s, the KRS AA-1 Active Antenna was sold all throughout Radio West, and was considered a good performer. However, the only thing wrong about it was the frequency response: It was about 200 kHz to 150MHz. In addition, the VHF pickup had the possibility to overload HF receivers. However, others may find it convenient to utilize the same antenna for shortwave and for the VHF/FM BCST band.

Power is then circulated to the antenna section through the coax cable, and gain can be enhanced by altering the turn ratio to T1 if there are no stations that can cause overloading/cross-modulation. Thus, this is where UHF pre-selectors, or other pre-selectors, come in.

What are Pre-selectors?

A pre-selector is an electronic device that links an antenna and a receiver. They impede trouble-causing out-of-tune frequencies from getting through from the antenna into the pre-amplifier; otherwise it would be directly linked to the antenna.

Pre-selectors works to improve the performance of practically any receiver; however, they are significantly helpful to receivers possessing broadband front-ends that are likely to overload, like scanners and consumer-market receivers.

How do they operate?

Generally, a pre-selector is tuned to have a narrow bandwidth, as the receiver’s operating frequency acts as the core. They pass through the signal it’s tuned with, only slightly reduced, but constricts other signals. It will then protect a sensitive receiver from damage caused by static input, voltage spikes and overloads coming from different signals or from other transmitters nearby. However, a pre-selector will not eliminate interferences originating from the same frequency that it and the receiver are tuned in to.

Extra filtering can also be useful in this circuitry because the first input stage (front-end) of the receiver starts with at least a single RF amplifier that has a limited scope (dynamic range). There are RF amplifiers that can strengthen all radio frequencies delivered to the antenna. Thus, off-frequency signals produce a wasteful load on RF amplifiers.

The amplifier circuitry also has a limited scope when it comes to the amount of incoming RF energy they can hold without overloading. In the event when the front-end overloads, receiver performance is significantly reduced, and in some intense cases it may lead the receiver to be damaged.

Applications and Other Facts

In situations like in noisy and crowded bands or where there are strong local radio stations, the receiver’s dynamic range can exceed in an alarming rate. Thus, extra filtering limits these frequency range and power demands that are utilized to every later stages of the receiver, and only loading it with signals within the pre-selected band scope.

A tunable antenna preamplifier may sometimes add in a front-end pre-selector circuit to further enhance functionality. The integrated device is both a preamplifier and a pre-selector and may be referred to either name. Although this vagueness may sometimes lead to confusion, still these two have the same function.

A passive pre-selector is known to contain zero power and has no internal amplifier, but it functions well with modern receivers with less signal loss. Plus, preamplifiers may no longer need an UHF pre-selector or any other pre-selectors when fed from a narrow-band source, like from a tuned-resonance loop antenna.
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