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<h1>Mast Head Preamplifier</h1>

<p>A MastHead Preamplifier (MHA) is used to compensate losses
at the BTS receiver antenna cable. Depending on the actual network uplink/downlink
balance, this feature allows an MS to use lower transmitting power and thus
increases the MS battery lifetime or simply increases the size of the cell.
The Nokia MHA provides gain in the range up to 12 dB. The BTS provides electrical
power for the MHA up to 150 mA at 11.5 V (11.1...12.4 V). DC power is provided
on the centre pin of the antenna port, positive with respect to the ground.</p>


<p>The MHA has a special RF bypass relay, which can be used
for two purposes. First, for the duration of the antenna VSWR measurement,
it is necessary to bypass the MHA for a correct result. Secondly, if a malfunction
is detected in the MHA, it can be bypassed with this relay. Thus the service
can continue with a reduced capacity until service takes place.</p>


<p>In case of receiver diversity but no duplex filter, both
receiver branches can have their own mast head preamplifiers. If duplex filter
is used, the MHA can be used only in the diversity branch. No hardware or
software modifications are required for the BTS because of the installation
of the MHA, only the appropriate entry into the hardware database.</p>


<p> Nokia has a selection of products for all frequency bands
that can be used in duplexed antenna line too.</p>
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