High dynamic range broadband LNA for handheld transceivers
Design and implementation, SV3ORA

RLY

Rt

MMBT
4401
100pF		 >8V

MMBT
4401
78M05

BAT54

10		   Yellow

Blue
  10uF
6.3v		 4
 		 8
 

47k

100nF
 		 1uF
35v

>100uH

470nF

 10
 

100nF

47uF
6.3v

SW1
 

3.7V
Li-ion


Rprog		 5
 		 7
 		 1k
 

NC

ANT
470nF		 PGA
103+
470nF
68
470nF

1k

 2
 		 6
 

1k

100

100

 1
 		 TP4056
 		 3
 
RLY
 		 RLY
 
1N
4148		 1N
4148		 1N
4148		 1N
4148		 IN/OUT
 

SW1 is a SPST switch that switches the preamplifier ON/OFF. In this configuration, the battery can be charged and at the same time the preamplifier can be switched to on.

Relay contacts are shown in the energized position (relay ON). When the preamplifier power switch SW1 is OFF, relay is OFF and the preamplifier is bypassed both on receiving and transmitting mode. When in receiving mode and the preamplifier power switch SW1 is ON, relay is ON and the preamplifier is active. When in transmitting mode and SW1 is ON, relay is OFF and the preamplifier is bypassed.

The value of Rt has to be set so that when in transmitting mode (at minimum TX power) and SW1 is ON, the relay can be switched to OFF so that the preamplifier is bypassed.

The value of Rprog has to be set so that the TP4056 can provide the desired battery charging current. The charging current with different values of resistors is shown below.

Rprog Current Setting
RPROG (k)      IBAT (mA)
10             130
5              250
4              300
3              400
2              580
1.66           690
1.5            780
1.33           900
1.2            1000

However, since the battery is possible to be charged at the same time when the preamplifier is switched ON, this current must be quite high, so that the TP4056 can provide the charging current for the battery, as well as the current for the operation of the preamplifier and the relay circuit. On the other hand, you should not use too much charging current, in order to keep the battery, the TP4056 and the 7805 regulator cool. I guess a good charging current point would be somewhere around in the middle of the table above, depending on your battery capacity.

The battery I have chosen in my prototype was a 16340 size, TrustFire 880mAh 3.7V Rechargeable Li-ion, the variant that has an internal protection circuit (just to be safe). This battery was primary chosen as a balance between battery size and capacity. According to the seller, the battery has the next specs:

 

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