JPS61244144A - Privacy telephone set - Google Patents

Abstract

PURPOSE:To reduce a rounding error and to increase an arithmetic speed by obtaining the same privacy telephone set characteristics by a small number of arithmetic elements when the same sampling frequency is equal. CONSTITUTION:A speech signal input terminal 4 is branched into two and one is inputted to a multiplier 6 which inputs the output of an oscillator 5 of oscillator frequency fm as the other input to extract a low frequency component through a low-pass filter 7; and this is inputted to one input terminal of a multiplier 8 and the output of an oscillator 9 which outputs a frequency fK is inputted to the other input terminal to extract a high frequency part through a high-pass filter 10. Then, the high frequency part is inputted to one terminal of an adder 13 through a multiplier 12 which inputs the output of an oscillator 11 having an oscillation frequency fm. The other part of the speech signal, on the other hand, is inputted to a multiplier 15 inputs the output of the 1st oscillator 14 having an oscillation frequency fK+fm, inputted to the other terminal of the adder 13 through a delay circuit 16 having a necessary delay time, and passed through a low-pass filter 17 to obtain a desired reverse rotational spectrum.

Description

【発明の詳細な説明】 （産業上の利用分野） 本発明は秘話装置、殊にスペクトル反転回転形秘話装置
の改良に関する。DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to an improved encrypted communication device, particularly to a spectrum inversion rotary encrypted communication device.

（従来技術） 通信内容の秘密保持方法として従来から種々のものが提
案されているが、その一つに伝送すべき信号の周波数ス
ペクトルを所要数の区間に分割して並べ変え或は反転せ
しめ反転回転スペクトルとして送信するものがある。(Prior Art) Various methods have been proposed to maintain the confidentiality of communication contents, one of which is dividing the frequency spectrum of the signal to be transmitted into a required number of sections and rearranging or inverting the frequency spectrum. There is something that is transmitted as a rotating spectrum.

このスペクトル反転回転方式は他のものに比較して復調
音質に優れかつ回路の実現が容易である反面単純な反転
回転方式では秘話強度がやや低い欠点及びこれを実現す
る装置に製作困難な帯域フィルタ金製すると云う問題が
あった。This spectral inversion/rotation method has superior demodulation sound quality compared to other methods and is easy to implement as a circuit. However, the simple inversion/rotation method has the drawback that the secret signal strength is somewhat low, and the device that implements this method requires a bandpass filter that is difficult to fabricate. There was a problem with it being made of gold.

このため従来例えば特願昭５９年ＩＫ２１１４８（秘話
装置）或は特願昭５９−４４１４１（秘話方法及び装置
）に示されるように、スペクトルの反転周波数位置又は
回転組合せを任意に変更すると共に帯域フィルタに代え
比較的製作容易な低域フィルタで代用しうるようＫする
ことによって秘話性を高めかつコスト低域全はかった方
法が提案されている。For this purpose, conventionally, for example, as shown in Japanese Patent Application No. 1988 IK21148 (Secret Communication Device) or Japanese Patent Application No. 59-44141 (Secret Communication Method and Apparatus), the inversion frequency position or rotation combination of the spectrum is arbitrarily changed and a bandpass filter is used. A method has been proposed in which a relatively easy-to-manufacture low-pass filter can be used in place of K, thereby increasing confidentiality and reducing cost.

本発明の理解を容易ならしめるために以下に前記従来方
法について少しく説明する。In order to facilitate understanding of the present invention, the conventional method will be briefly explained below.

第２図（ａ）及びｌｂ）は従来の反転回転形秘話装置を
示すブロック図及びその動作全説明する信号のスペクト
ル図である。FIGS. 2(a) and 2b) are a block diagram showing a conventional reversal-rotation type private communication device and a signal spectrum diagram illustrating its entire operation.

先づ第２図（ａｔに示した装置構成を簡単に説明すれば
、同図（ｂｌの（イ）に示す如＜ｆＬからｆＭ（ｆｔ、
（ｆｍ）　　の帯域制限を施した音声信号１１／ｃ２分
岐し一方を直接加算器２の一入力端に、又他方をローカ
ル周波数ｔｆｌとし混合出力のうち両者の和のみを出力
する周波数変換回路３を介して前記加算器２の他の入力
端に入力し該加算器の出力端に箪２図（ｂｌの（ロ）に
示す如く前記音声信号ｌを周波数音シフトし隣接して２
つ並べたスペクトルを得る。First, to briefly explain the device configuration shown in FIG. 2 (at), as shown in (a) of FIG.
(fm) band-limited audio signal 11/c2, one of which is directly input to one input terminal of the adder 2, and the other is set to the local frequency tfl, and the frequency conversion circuit 3 outputs only the sum of both of the mixed output. The audio signal l is inputted to the other input terminal of the adder 2 via the adder 2, and is inputted to the output terminal of the adder by frequency-shifting the audio signal l as shown in (b) of Fig. 2 (bl).
Obtain an array of spectra.

更に、この信号を２分岐し、２つの乗算器ＭＵＬＴＩと
ＭＩＪＬＴｚとの間に低域ｆ波器ＬＰＦ　ｌを挿入した
第１の直列回路ルートと、同様に２つの乗算器ＭＵＬＴ
ｓとＭＵＬＴ４との間に第２の低域ｆ波器ＬＰＦＺを挿
入した第２の直列回路ルートの夫々を介して第２の加算
器４に入力すると共に前記ＷＬ１の直列回路ルートに属
する乗算器には９０°移相器を介し又第２の直列回路ル
ートの乗算器には直接に発振器Ｏ８（、＋及びＯ２０２
出力をローカル周波数として夫々の前置乗算器と後置乗
算器に共通に印加することによって前記第２の加算器４
の出力に第２図（ｂ）（／ｉに示す如く反転回転し九音
声スペクトルを得るよう構成したものである。Furthermore, this signal is branched into two, and a first series circuit route in which a low-frequency f-wave filter LPF l is inserted between two multipliers MULTI and MIJLTz, and a first series circuit route in which a low-frequency f-wave filter LPF l is inserted between two multipliers MULTI and MIJLTz, and a first series circuit route in which a low-frequency f wave filter LPF l is inserted between two multipliers MULTI and MIJLTz,
A multiplier that is input to the second adder 4 through each of the second series circuit routes in which a second low-frequency f-wavelength filter LPFZ is inserted between S and MULT4, and also belongs to the series circuit route of the WL1. through a 90° phase shifter and directly to the multiplier of the second series circuit route.
said second adder 4 by commonly applying the output as a local frequency to each pre-multiplier and post-multiplier.
The output is inverted and rotated as shown in FIG. 2(b) (/i) to obtain nine audio spectra.

このように構成すれば製作困難な帯域ｆ波器を不要とす
ることができるが、更に前記ローカル発振器Ｏ８Ｃ１又
は０８Ｃ２のいづれか一方にコード発生器を付加し所定
の規則に従ってローカル周波数を変化せしめたのち所望
の通信回線を介して伝送すればより一層秘話性を高める
ことができる。伺これを受信する際には前記コード化規
則と同期をとりつつローカル発振器を制御して復調すれ
ば原音声信号を復元することができる。With this configuration, it is possible to eliminate the need for a band f-wave generator, which is difficult to manufacture, but after adding a code generator to either the local oscillator O8C1 or O8C2 and changing the local frequency according to a predetermined rule. Confidentiality can be further improved by transmitting via a desired communication line. When receiving this signal, the original audio signal can be restored by controlling and demodulating the local oscillator in synchronization with the encoding rule.

しかしながら、このようなスペクトル反転回転処理はア
ナログ信号そのままでも可能であるが、これに用いる回
路素子は一般に大型かつ複雑となるから一層アナログ／
デジタル変換（ＡＤ変換）後デジタル処理するのが通常
であり。However, although such spectrum inversion/rotation processing is possible with analog signals as they are, the circuit elements used for this are generally large and complex, so analog/
It is normal to perform digital processing after digital conversion (AD conversion).

斯くすることによって装置自体を簡素化することが行な
われる。By doing so, the device itself can be simplified.

然かるに、上述した従来の秘話装置はＰ波器３個９乗算
器５個及び加減算器２個合計１０個の演算素子を最低必
要とするからこれをデジタル化する場合種々の不具合を
生ずる。However, since the above-mentioned conventional secret communication device requires a minimum of 10 arithmetic elements, including 3 P-wave units, 9 multipliers, and 2 adders/subtractors, various problems occur when digitizing this device.

即ち、一般にデジタル演算に於いてデータ全表示するビ
ット長は有限であるから該ビット長に逆比例して丸め誤
差も切捨て誤差とも云う）を生じ、あたかも雑音が混入
した如く作用する。That is, since the bit length for representing all data in digital calculations is generally finite, rounding errors and truncation errors (also called rounding errors and truncation errors) occur in inverse proportion to the bit length, and act as if noise had been mixed in.

この不具合は固定小数点演算の場合著しく、従って用い
るべき演算要素は出来得る限り少ない方が望ましい。This problem is significant in fixed-point arithmetic, so it is desirable to use as few arithmetic elements as possible.

（発明の目的） 本発明は上述したような従来のスペクトル反転回転形秘
話装置の問題を解決するため釦なされたものであって、
前記従来提案された秘話装置の特長を生かしつつ演算要
素全減少せしめデジタル処理を行うのに適した秘話装置
を提供することを目的とする。(Object of the Invention) The present invention has been made in order to solve the problems of the conventional spectrum inversion rotary secret communication device as described above.
It is an object of the present invention to provide a confidential communication device suitable for performing digital processing by reducing the total number of calculation elements while taking advantage of the features of the conventional confidential communication devices.

（発明の概！’） この目的の念め本発明では、所要の帯域制限を受けた音
声スペクトル信号を２分岐した一方を、ローカル周波数
をｆｍとし混合出力のうち低域成分を抽出するよう構成
した第１の周波数変換回路と、ローカル周波数をｆＫと
しその混合出力のうちから高域成分を抽出するよう構成
しｆｃ第２の周波数変換回路と、ローカル周波数をｆｍ
とした混合回路とを直列に接続したルートを介し加算回
路の一入力端に入力すると共に、前記２分岐した音声ス
ペクトル成分の他方をローカル周波数をｆｘ＋ｆｍとし
た混合回路と所定の遅延回路との直列回路を介して前記
加算回路のもう一方の入力端に入力し、更に該加算回路
の出力を低域ｒ波器を介して所望の反転回転スペクトル
信号を得るように構成する。(Summary of the Invention!') To achieve this purpose, the present invention is configured such that an audio spectrum signal subjected to the required band restriction is split into two, one of which is set to a local frequency of fm, and a low frequency component is extracted from the mixed output. a first frequency conversion circuit configured to set the local frequency to fK and extract a high frequency component from the mixed output thereof;
A mixing circuit with a local frequency of fx+fm is input to one input terminal of an adding circuit through a route in which a mixing circuit with a local frequency of fx+fm is connected in series with a predetermined delay circuit. The signal is input to the other input terminal of the adder circuit through a circuit, and the output of the adder circuit is configured to obtain a desired inverted rotational spectrum signal via a low-band r wave generator.

（実施例） 以下本発明ヲ因示した実施例に基づいて詳細に説明する
。(Example) The present invention will be described in detail based on an example illustrating the present invention.

第１図は本発明の秘話装置の一実施例を示すブロック図
である。FIG. 1 is a block diagram showing an embodiment of the secret communication device of the present invention.

同図に於いて、４は音声信号入力端であって、これ金２
分岐しその一方を発振周波数ｆｍなる発振器５の出力を
一方の入力とする乗算器６に入力せしめ核部に生ずる混
合成分のうち低域成分を低域Ｆ’＠器７を介して抽出し
これを＠２の乗算器８の一方の入力端に又該乗算器８の
もう一方の入力端には周波数ｆＫｆ出力するｗＩ２の発
振器９の出力を入力し該乗算器８に於いて生ずる混合成
分のうち高域部を高域ｆ波器１０によって抽出したのち
これを発振周波数ｉｆｍとする第３の発振器１１の出力
を一方の入力とする５ｇ３０乗算器１２を介して加算器
１３の一方の端子に入力する。又、前記２分岐した音声
信号の他方は発振周波数をｆＫ＋ｆｍとする第４の発振
器１４の出力金一方の入力とした乗算器１５に入力し該
部出力金所要の遅延時間をもった遅延回路１６を介して
前記加算器１３のもう一方の端子に入力せしめ、該部用
カを低域Ｐ波器１７を経て所望の反転回転スペクトルを
得るよう構成したものである。In the figure, 4 is the audio signal input terminal, which is gold 2.
The output of the oscillator 5, one of which has an oscillation frequency fm, is input to a multiplier 6 which receives the output of the oscillator 5 as one input, and extracts the low-frequency component from the mixed components generated in the core part via the low-frequency F'@ device 7. is input to one input terminal of the multiplier 8 of @2, and the output of the oscillator 9 of wI2 which outputs the frequency fKf is input to the other input terminal of the multiplier 8. The high frequency part is extracted by the high frequency f-wave generator 10, and then is input to one terminal of the adder 13 via the 5g30 multiplier 12, which uses the output of the third oscillator 11 as the oscillation frequency ifm as one input. input. The other of the two-branched audio signals is inputted to a multiplier 15 which serves as one input of the output of the fourth oscillator 14 whose oscillation frequency is fK+fm, and is input to a delay circuit 16 having the required delay time. The signal is inputted to the other terminal of the adder 13 through a low-pass P wave generator 17 to obtain a desired inverted rotation spectrum.

以上の如く構成した秘話装置の動作ｆｔ第１図（ｂｌに
示した各部のスペクトル図を参照しつつ詳細に説明する
。The operation of the confidential communication device constructed as above will be described in detail with reference to the spectrum diagram of each part shown in FIG.

先づ、入力端４に同図（ｂ）（イ）に示す姿態の音声ス
ペクトル信号が入力するものと仮定する。同核スペクト
ルは上述の従来例に於ける原音声スペクトルとその姿態
が異っているが、同図（ｂｌ（イ）Ｋ示すのが一般的で
あるから本実施例に於いてはこれに従う。First, it is assumed that an audio spectrum signal having the configuration shown in FIGS. 4(b) and (a) is input to the input terminal 4. Although the homonuclear spectrum differs in appearance from the original speech spectrum in the conventional example described above, it is generally shown as shown in FIG.

分岐した上述の原音声信号は＠１の周波数変換回路に於
いて原音声信号の最高周波数ｆｍと同一周波成分と混合
されるから同図（ｂ）（ロ）の破線で示した混合成分音
生ずるがこのうち遮断周波数をｆｍとする低域ｒ波器７
によって同図実線によって示す低域スペクトルのみが得
られ、この信号は更に次段の周波数変換回路に於いてロ
ーカル周波数ｆｘ　（０（ｆｘ（ｆｍ）と混合され同図
（ｂｌ（ハ）の点線の如きスペクトルを生じ、このうち
次段の連断周波数をｆｍとする高域ｒ波器１０によって
同図実線で示すようにｆｍからｆｍ＋ｆＫの間のスペク
トルのみを抽出する。この成分は次段の周波数変換回路
によってローカル周波数ｆｍと混合されるから前記加算
器１３の一入力端には同図（ｂｌに）に示す如＜　　ｆ
ｍｏを基軸に左右対称の位置夫々にｆｍｏからｆｘｉで
及びｆ＝２ｆｍから２ｆｍ＋ｆＫに原音声スペクトルの
うちｆＫからｆｍまでの高域部スペクトルを配置した如
きスペクトルが入力される。The above-mentioned branched original audio signal is mixed with the same frequency component as the highest frequency fm of the original audio signal in the frequency conversion circuit @1, so that the mixed component sound shown by the broken line in (b) and (b) of the same figure is generated. Among these, the low-frequency r wave generator 7 whose cutoff frequency is fm
As a result, only the low-frequency spectrum shown by the solid line in the same figure is obtained, and this signal is further mixed with the local frequency fx (0(fx(fm)) in the next stage frequency conversion circuit, and is mixed with the local frequency fx(0(fx(fm)) to obtain the signal indicated by the dotted line in A high-frequency r wave generator 10 with the successive frequency of the next stage as fm extracts only the spectrum between fm and fm+fK as shown by the solid line in the figure.This component is the frequency of the next stage. Since it is mixed with the local frequency fm by the conversion circuit, one input terminal of the adder 13 has < f as shown in the figure (bl).
Spectra are input in which the high-frequency spectrum from fK to fm of the original audio spectrum is arranged from fmo to fxi and from f=2fm to 2fm+fK at positions symmetrical to each other with mo as the reference axis.

一方前記２分岐した原音声スペクトルの他方は発振器１
４及び乗算器１５によってローカル了 周波数をｆｍ＋ｆＫとし大周波数変換されその結果同図
（ｂｌ（ホ）に示すように原音声スペクトルをｆｍ＋ｆ
Ｋだけシフトしたスペクトルが得られ。On the other hand, the other of the two-branched original audio spectrum is connected to the oscillator 1.
4 and multiplier 15, the local frequency is converted to fm+fK, and as a result, the original speech spectrum is converted to fm+f as shown in the same figure (bl (e)).
A spectrum shifted by K is obtained.

この信号は次段の遅延回路１６を介して前記加算器１３
のもう一方の入力端に注入され核部に於いて上述の他ル
ートヲ介して入力する信号との加算混合が行なわれる。This signal is sent to the adder 13 via the next stage delay circuit 16.
The signal is injected into the other input terminal of the signal and is added and mixed with the signal input via the other route mentioned above in the core section.

尚前記遅延回路の存在理由は前記２分した原音声信号が
夫々通過する２つのルートは回路構成が異るため互いに
位相遅れが異なる。故にこれを補正し両信号が前記加算
器１３に到達する時間を一致させるためのものであるか
ら、核部の遅延時間は両ルートの時間差を勘案して決定
する。The reason for the presence of the delay circuit is that the two routes through which the two divided original audio signals pass have different circuit configurations and therefore have different phase delays. Therefore, the purpose is to correct this and make the times at which both signals arrive at the adder 13 match, so the delay time of the core is determined by taking into account the time difference between the two routes.

このようにして夫々位相ヲ調整して同時に到着した２つ
の信号に）及び（へ）を前記加算器１３にの 於いて加算すると両者の和を信号金得るがこれｔ一連断
周波数１ｆｍとする低域Ｆ波器１７に入力すればその出
力には同図（へ）Ｋ示すように反転回転したスペクトル
信号を得ることができる。In this way, by adjusting the phase of each signal and adding () and () to the two signals arriving at the same time in the adder 13, the sum of the two is obtained as a signal sum, which is a low frequency signal with a continuous cutoff frequency of 1 fm. If the signal is inputted to the F-band filter 17, an inverted and rotated spectrum signal can be obtained at its output as shown in FIG.

以上の説明から明らかな如く本発明の秘話装置によれば
演算器としては乗算器が４個、Ｆ波器が３個及び加算器
が１測針８個で済むから上述し九従来のものが計１０個
必要としたのに比して２個減じることができる。As is clear from the above explanation, according to the confidential communication device of the present invention, only four multipliers, three F wave units, and one adder and eight pointers are required as arithmetic units. Compared to the total of 10 required, this can be reduced by 2.

更に、上述の実施例に於いて秘話性を高めるために前記
ｗＪ２の発掘器９の周波数ｆｔを所要のコード化信号に
よって変化するよう構成してもよい。Furthermore, in the above-described embodiment, the frequency ft of the excavator 9 of the wJ2 may be changed depending on a required coded signal in order to improve confidentiality.

この際前記発掘器にコード発掘器ＣＧを付加すればよく
、このようにローカル周波数ｆＫＱ変化すれば最終的に
得る前記低域Ｆ波器１７の出力、即ち同図（ｂｌ（へ）
に於ける反転回転の周波数位置が変化することになり前
記コード化信号が知られない限り秘話性を確保すること
ができる。At this time, it is only necessary to add a code excavator CG to the excavator, and by changing the local frequency fKQ in this way, the output of the low-frequency F wave generator 17 finally obtained, that is,
Since the frequency position of the inversion rotation in the signal changes, secrecy can be ensured as long as the coded signal is not known.

又、このようにスペクトルの反転回転周波数位置ｆＫの
変化範囲金Ｏから原音声の最高周波数ｆｍまでとすれば
このときの標本周波数（サンプリング周波数）ははＮ４
ｆｍ程度に設定すれば受信側復調周波数の忠実度を所望
のものに保ちうろことが実験的に確認できており、リア
ルタイム処理が充分可能であるから例えば電話回線等の
秘話装置として適したものとなる。Also, if the range of change of the inverted rotational frequency position fK of the spectrum is from gold O to the highest frequency fm of the original voice, the sample frequency (sampling frequency) at this time is N4.
It has been experimentally confirmed that if the setting is set to around fm, the fidelity of the demodulation frequency on the receiving side can be maintained at the desired level, and since real-time processing is sufficiently possible, it is suitable for use as a secret communication device for telephone lines, etc. Become.

同上述の実施例に於ける各発振器のうち同−周波数音も
つものは同一発振器を共用することが可能であり又ｆｍ
＋ｆＫなる和の周波数の発掘器１４はｆｍとｆＫとを発
振する発掘器５及び９の出力を別途設けた混合回路及び
ｆ波器全弁して注入することによって省略してもよいこ
とは側段説明を要しないであろう。Among the oscillators in the above-mentioned embodiment, those having the same frequency sound can share the same oscillator, and fm
It should be noted that the excavator 14 with the sum frequency of +fK may be omitted by injecting the outputs of the excavators 5 and 9 that oscillate fm and fK into a separately provided mixing circuit and f-wave generators. No further explanation is required.

但し、前記発振器１１の発振周波数は伝送する音声スペ
クトルの低域範囲を決定するものであるから希望する周
波数範囲に応じて適宜設定するものであって、前記発掘
器５とは別のものとした方が都合がよいであろう。However, since the oscillation frequency of the oscillator 11 determines the low range of the audio spectrum to be transmitted, it should be set appropriately depending on the desired frequency range, and is separate from the excavator 5. It would be more convenient.

（発明の効果） 本発明は以上説明し九ように構成し同一のす／ブリング
周波数の場合少ない演算素子によって同一の秘話特性を
得るものであるから、丸め誤差を減少すると共に演算速
度を早めた秘話装置をもたらすうえで効果がある。(Effects of the Invention) The present invention is configured as described above and obtains the same secret characteristic with fewer calculation elements when using the same S/Bling frequency, so that the present invention reduces rounding errors and increases the calculation speed. It is effective in providing equipment.

【図面の簡単な説明】[Brief explanation of drawings]

＠１図（ａｌ及び（ｂｌは本発明の一実施例を示すブロ
ック図及びその動作を説明するためのスペクトル図、第
２図（ａｌ及び（ｂｌは従来の秘話装置金示すブロック
図及びその動作を示すスペクトル図である。 ４・・・・・・・・・音声信号入力盤、　　　５，９，
１１及び１４・・・・・・・・・発振器、　　　６，８
．１２及び１５・・・・・・・・・乗算器、　　７及び
１７・・・・・・・・・低域Ｆ波器。 １０・・・・・・・・・高域Ｆ波器、　　１３・・・・
・・・・・加算器。@Figure 1 (al and (bl) is a block diagram showing one embodiment of the present invention and a spectrum diagram for explaining its operation, and Figure 2 (al and (bl) is a block diagram showing a conventional confidential communication device and its operation. It is a spectrum diagram showing 4... Audio signal input board, 5, 9,
11 and 14...Oscillator, 6,8
．． 12 and 15......multiplier, 7 and 17......low frequency F wave unit. 10......High frequency F wave device, 13...
...Adder.

Claims (4)

【特許請求の範囲】[Claims] （１）ｆ＿１なる周波数信号をローカルとし低域成分を
抽出する第１の周波数変換回路と、ｆ＿２なる周波数信
号をローカルとし高域成分を抽出する第２の周波数変換
回路とｆ＿３をローカルとする混合回路とを直列に接続
になる第１のルートと、ｆ＿１＋ｆ＿２なる周波数をロ
ーカルとする混合回路と所定の遅延時間を有する遅延回
路とからなる第２のルートの夫々に２分岐した音声信号
を通ぜしめたのち両者を加算し該加算成分のうち高域又
は低域成分のみを抽出送信するように構成したことを特
徴とする秘話装置。(1) A mixture of a first frequency conversion circuit that makes the frequency signal f_1 local and extracts low-frequency components, a second frequency conversion circuit that makes the frequency signal f_2 local and extracts high-frequency components, and f_3 as local. A first route connects the circuit in series, and a second route consists of a mixing circuit whose local frequency is f_1+f_2 and a delay circuit having a predetermined delay time. 2. A confidential communication device characterized in that the secret conversation device is configured to add the two components after adding the two components, and extract and transmit only the high frequency component or the low frequency component of the added components. （２）前記ローカル周波数のｆ＿１とｆ＿３とを音声信
号の最高周波数ｆ＿ｍと一致せしめたことを特徴とする
特許請求の範囲（１）項記載の秘話装置。(2) The private conversation device according to claim (1), wherein the local frequencies f_1 and f_3 are made to match the highest frequency f_m of the audio signal. （３）前記ローカル周波数ｆ＿３を伝送すべき音声信号
の高域又は低域周波数の遮断周波数に応じて決定したこ
とを特徴とする特許請求の範囲（１）項記載の秘話装置
。(3) The confidential communication device according to claim (1), wherein the local frequency f_3 is determined according to a cutoff frequency of a high frequency or a low frequency of an audio signal to be transmitted. （４）前記ローカル周波数ｆ＿２を所定の制御信号によ
って可変せしめることによって秘話性を高めたことを特
徴とする特許請求の範囲（１）（２）及び（３）項記載
の秘話装置。(4) The confidential communication device according to claims (1), (2) and (3), characterized in that communication confidentiality is enhanced by varying the local frequency f_2 by a predetermined control signal.