FET Audio Deviation Limiter

This applicationis a very high specification peak control limiter. It has fast become the essential deviation limiter for FM radio. Audio Limiter is a standard specification in broadcast world. This limiter can be set up as sound processor for fm broadcast.

The application divided into two parts :
1. Broadband Limiter


2. Splitband Limiter


Active component : FET 2N5457 and Ics NE5534, 2N5532, TL071 TL072.

Download schematic and component mounted in Coreldraw 12 Format.

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QRP FYBO Contest

Today I participated in the annual QRP FYBO (Freeze Your B___ Off) contest. See http://www.azscqrpions.org . It happened that we are into a little warm spell after several weeks of below freezing weather. The temperature was 40 at 10AM when I got started, rose to 46 around lunchtime and then dropped into the 30s by the time I got off the air at 3:15. I'm not a big contester. With on and off operating and marginal band conditions I made only 5 contacts on 40 and 20 CW for 800 points. Most hams I worked were relatively warm, only VE3RRP in Ontario was below freezing.

The FYBO Contest did give me a chance to get out of the basement shack. One of the neighbors interrupted a snowman build to find out why I was lounging on my deck in February. Even with temperatures hitting the mid 40s it is still winter in Minnesota.

I found the FYBO Contest a challenging and fun break from my regular winter boatanchor activity. I'll do it again next winter.

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100W Broadband UHF TV Power Amplifier

The TV amplifier has been tuned under class-A small-signal conditions and characterised under large signal class-AB conditions from 470 - 860 MHz. (All Datasheets)

Schematic Circuit Amplifier
The total description of the amplifier is given in Figs 6 and 7 and Table 8 (in datasheet). The amplifiers input and output matching networks contain mixed microstrip-lumped elements networks to transform the terminal impedance levels to approx. 25 W balanced. The remaining transformation to 50 W unbalanced is obtained by 1 : 2 balun transformers. The baluns B1 and B2 are 25 W semi-rigid coax cables with an electrical length of 45° at midband and a diameter of 1.8 mm, soldered over the whole length on top of microstrip lines.

To keep the circuit in balance two stubs L1 and L8 with the same length have been added. For low frequency stability enhancement the input balun stubs are connected to the bias point by means of 1 W series resistors. Large capacitors (C4 and C11) are added at the biasing points to improve the amplifiers video response.


Printed Circuit Board (PCB)
The printed-circuit board laminate utilised is PTFE-glass with an er = 2.55 and a thickness of 0.51 mm (20 mills).


Component Mounted


A complete TV transmitter amplifier has been designed and characterised based on the BLV861, capable of operating in full band IV and V with flat gain and high output power in class-AB. BLV861 is able to generate 100 W CW power and a power gain compression below 1 dB in band IV and V. Overall gain of the amplifier is >8.5 dB and an efficiency of ± 55%. TV-measurements have been carried out showing a 1 dB compression point above 120 W PO, SYNC at VCE = 28 V
and 150 W at VCE = 32 V.

• Amplifier shows an agreed linearity performance in class AB operation both under two tone and three tone conditions
• Biasing the amplifier at a VCE = 32 V results in a higher output peak sync power and a better linearity response.

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