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Radio receiver using the ZN414

2018-01-22 22:27  
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This is a project from the dim and distant past that has proven to be a real winner. I have used it as a basis for an 8 channel proportional R / C (AM) and 145MHz FM “chat box”. Recipients very simple and is shown below. This consists of a single transistor mixer then ZN414 radio IC to provide the gain and detection. An OP-AMP 741 is used as the final audio stage, but it can be replaced by LM380, if you want to drive a small speaker. The following is a schematic drawing:

figure 1 zn414 rx Radio receiver using the ZN414

The ZN414 is designed only for the PM, but the signal can be copied NBFM adequately by off-tuning the receiver slightly (slope detection). The ZN414 also be replaced with a newer ZN416 IC to provide more 18dB gain. I have to leave your pin number as they are available at Maplins (and other) catalogs. 2nd IF transformer was robbed of one more coil 465KHz-cheap’n evil $ 1.5 radio.

The OP-AMP 741 will drive 70 ohm headphones quite easy. 70 ohm headphones are cheap and available as a substitute for “Sony Walkman”, but with two wired headphones in seried (only using TIP and RING of 3.5mm connector). In the lab-book, I made a note to put the 560 ohm resistor between the output and the 741 ve supply. This is to force one of the O / P transistors to draw some current to prevent crossover distortion. OP-AMPS make good low-power AF amplifier, but they have their limitations.

The circuit shown above illustrates the antenna input circuit for 145MHz, but you can change the band whatever you want from 70 kHz to more than 200 MHz, with a suitable local oscillator, of course. Local oscillator can be HF / VHF Signal Generator, but if you want a self contained unit, the local oscillator must be custom built. The following is a schematic drawing:
figure 2 zn414 m1 Radio receiver using the ZN414

Provide diagrams 145MHz VHF oscillator circuit that can be used to receive the 2 meter band. Crystal is 8MHz type 2 meters (Kenwood 2200), but the 12MHz crystal will work well in this circuit. If you want to receive using the crystal 145.750 TX 145,250-145,300 (RTTY channel). IF Tweek two cans (change IF) to the top of the channel is required. The following is a schematic drawing:

figure 3 zn414 m2 Radio receiver using the ZN414

RX crystals was controlled for 27 MHz. Crystals are available. Here is the frequency of R / C band crystals.

26.995, 26.540 – Brown
27.045, 26.590 – Red
27.095, 26.640 – Orange
27.145, 26.690 – Yellow
27.195, 26.740 – Green
27.245, 27.790 – Blue

Get RX adjusted to the correct frequency by adjusting the IF transformers. Changing the IF frequency will change the RX RF frequency by about plus / minus 40 KHz.
Radio receiver using the ZN414 figure 4 Radio receiver using the ZN414

VFO is that you can include the frequency from 70KHz to like it more than 20MHz, but stability may suffer at high frequency. L1 and C1 you must choose the band you want. The 47pf and 100pf capacitors should always have the same ratio. SUM those of C1 / 2. If you are skilled in construction and can produce a stable VFO VHF there is no reason why you can not make tuneable VHF receiver with this circuit.

I hope that you have a lot of fun with this as recipients for many years. One of my next project will soon be posting soon will be used by recipients TX. I was lucky enough to live on a hill where the loss of my way to GB3PI only 109dB. This means that I can open off of GB3PI with 20uW only (no MICRO Milli)!! I modify the IF receiver coils (internal issue is the external capacitor and a hat) so that it 600KHz IF. Transmitter is also a local oscillator for the receiver! Transmitter provide above 1mW. The antenna switching is the only TX / RX switching is used, the TX is always left switched on. One thing about QRP – you do not have to worry about SWR!!

source: w1.859.telia.com


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