Some of the configuration has been changed. It is preferable not to install anything between the Pick-up detector and the receiver. It is preferable to configure it with an ATT inside the detector and an ATT inside the receiver. 45dBATT+20dBATT=65dBATT, which is S9+35dB at 1KW transmission, so it is better to set the ATT to a smaller number for powers less than 1KW.

Any radio station needs a system that can monitor the transmitted radio waves in real time. When we first started our amateur radio station, we operated by shouting into the microphone on AM radio waves so that our radio waves would fly as far and strong as possible. Naturally, we did not have a monitoring system, and we operated without caring whether the emitted radio waves were distorted or were circulating radio waves. Decades have passed since then, and technology has advanced, and the frequency management of SSB radio waves has become more precise, and various methods have emerged, resulting in many radio waves called Hi-Fi-SSB. However, radio waves that are distorted or circulating can still be heard from time to time. If we had a system that could monitor such radio waves in real time, we could prevent this, and by doing so, we would be motivated to consciously improve the quality of radio waves. However, in a word, even if it is called an air monitor system, it is usually necessary to realize the monitor directly under the transmitting antenna, and various problems occur under such a strong electric field. Basically, I think it is possible if you clarify the route of the high-frequency current, eliminate the loop formation, and perform proper matching. I will introduce my own air monitor configuration.

composition

The signal is taken from the pick-up detector just before the antenna as a signal for the air monitor, and is supplied to the receiver at the required level. The monitor signal must be sufficiently isolated. Generally, when comparing the receiver output (audio signal) with ANT (dummy load) and the receiver output when ANT (real antenna) is emitted, differences will be found when checking and comparing with various measuring instruments. This varies greatly depending on the shielding and isolation method of each block. Apart from this, the phenomenon of wraparound is a separate factor. The way to check is to shunt the ANT input of the receiver when radio waves are emitted from a real antenna, and compare the S meter deflection value at this time (the one that is often called a ghost radio wave) with the S meter deflection value with the real air monitor signal when the input is open. The larger this ratio is, the more ideal the air monitor is. 45 dB BATT inside the pick-up detector, and from here, 30 dB BATT was initially added externally (on the way), but this has been stopped. Directly supplied to the receiver (internal 20 dB BATT). The optimum monitor signal is S9+30 to 40 dB. It is best to input as much as possible to the receiver input. Although it depends on the transmission power, it is best to use only the ATT inside the Pick-up detector. However, the receiver should have at least 20 dB ATT inside. In this condition, transmitting 1 kW will result in S9+35 dB.

Pick-UP detector

There are several ways to extract monitor signals, but I have experimented with the C-division method and the link extraction method using ferrite cores, and in the end I went with the link extraction method. The C-division method requires a high-voltage capacitor, and there are differences due to subtle differences in the production layout conditions, so if left as is, isolation problems will arise and this will be further complicated by link coupling. Therefore, I adopted the simplest link extraction method.

The ATT (first stage ATT) used inside the pickup can be either T-type or π-type, the resistor R1 is 2W, and anything else is OK. Anything is OK for the second and subsequent stages.

When communicating with a station whose signal is at the same level as the noise level, the monitor signal during transmission will have a deep AGC, and when switching to reception, the receiver's AGC is usually set to SLOW, so there is a time lag until the receiver reaches full gain, making it difficult to understand the first part of the signal. Therefore, in the monitor system, when switching from transmission to reception, the AGC capacitor is discharged for a period of ms, making it possible to instantly receive at full gain. 　Output    Receiver Input     S-Meter 　20W　   　-62.5ｄBm　    9+10.5ｄB 　200W　   -52.5ｄBm　　  9+20.5ｄB 　1KW　  　-45.5ｄBm　　  9+27.5ｄBm

There is a difference of about 5 dB between 3.5 MHz and 28 MHz, but this is for one S unit, so it will not cause any problems in actual use.　　　　　Pick-UP detector output

Some modifications to the receiver are required.

�@ A circuit is required to turn on/off the 20dB ATT on the ANT input for the transmission and reception signals from the transmitter. Install it inside the receiver.
�AModifying the AGC circuit The diagram on the right shows a typical AGC circuit, but the receiver sensitivity is at its maximum when the AGC voltage is +B value. The moment the system switches to receive mode, it needs to be at its maximum sensitivity, and the period is determined by the C/R time constant.
In the above example, the AGC voltage was at +B and the sensitivity was at its maximum. However, if the AGC voltage is at 0 and the sensitivity is at its maximum, the AGC capacitor must be discharged to 0 for a specific period (C/R). In this case,