TopBand: RX noise figure and gain

[K3BU]

In a message dated 98-04-10 11:30:08 EDT, K2WI writes:

<< I have never found it necessary to use a preamp on a Beverage, from the
 standpoint of noise figure.  I have always heard the noise level go up when
 attaching the Beverage to the receiver. >>

Preamps can be usefull on 160 & with Beverages in number of situations:
1. Preamps with tunable input help to eliminate out of band QRM, like BC
stations.
2. If you use rig like TS870 that can switch Beverages and TX antenna (with
famous K3BU diode mod.), preamp can bring up Beverage signals to the level of
TX antenna, then with attenuators and AIP it is possible to level the signals
so they sound more less same strength. Saves goofing with controls when quick
switch/check needed. (Similar effect can be had by using attenuator plugged
between the TX antenna on receive and RX ant. switching) The best results are
usually with RX gain set at the point when the band noise is about starting to
move Smeter. 
3. When Beverages (without preamp) "die" with sunrise (almost no signals) at
VE1ZZ, preamp brings them back to life, and quite often they beat 4 square in
hearing the weak one.
4. It is good to have the preamp, in case you need it. Another option in QRM -
weak signal digging arsenal.
5. Can be used with weird antennas like 40 m beam, TV antenna, Dog Loop, etc.
to bring the signal up when all other antennas don't.
   I picked up Palomar Engrs. preamp at the fleamarket, and is the the #1 used
here. It appears to have good high Q tuned circuit and smoooth gain control.
But I want to build my own, with multiple hi-Q tuned stages. Also looking for
that high gain/low noise super device and super circuit.

Yuri K3BU, VE3BMV

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