Transceiver: injecting a tone - Page 1
Forum section: electronics / beginners

author: Crambone
author_rank: Frequent Contributor
timestamp: January 23, 2025, 02:10:08 pm
content: So if I want to inject a tone into a transceiver using a signal generator how is it done? For sake of discussion let’s say transceiver is on 7.000 MHz. I was given an HP 4432B, I see an RF Out 50ohms & LF Out. I see several settings under Am, FM, LF Out…1) Depth/ Dev2) Rate3) WaveformSo I guess I’m asking how to hook Signal Generator to Transceiver properly if using microphone to key radio and bnc to alligator clips from transceiver to signal generator.How to set Signal Generator for AM then SSB?Reason is I would like to see my Modulation on a scope via a sampler for Both AM & SSB.Figure it’s never too late to learn something for this old man.Drew

author: Terry Bites
author_rank: Super Contributor
timestamp: January 23, 2025, 04:37:52 pm
content: A very generous gift, some one loves you!Put a 50R termination on the generator output set to desired level. Say -90dBm (5uV in 50R). A very small cap ~3pF in line with the signal lead and the antenna input.

author: CaptDon
author_rank: Super Contributor
timestamp: January 23, 2025, 06:54:27 pm
content: Set the generator for 1KHz sinewave at about 50 millivolts. You will need the mic wiring schematic (probably available online) Normally the PTT keying line gets connected to ground to key the Xceiver into the transmit mode. Usually the microphone element is connected between Mic In and ground. Be aware the Mic In may have voltage on it for phantom Mic power, usually 5 to 9 volts coming through a series resistance of 2.2K up to around 10K is common. In This case you will want a series capacitor in line with the driving signal. You can look at the RF output of the transceiver with your scope. AM will have a definite waveshape of audio producing envelopes of RF. With a steady sinewave audio input and the transceiver set to SSB you will see a steady smooth RF carrier offset either above or below the carrier frequency as selected by the USB/LSB switch. Hope this helps.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: January 23, 2025, 11:53:30 pm
content: I have a microphone set up just for this for several common mic configurations,. Crambone's procedure is correct.I have a BNC connector set up in parallel to the element in the microphone and introduce the AF signal this way, When the PTT is engaged, you get a proper level AF introduced, Check your mic input in the radio manual. they tell you how to put an AF signal into the radio.You can make up a mic plug and use the MOX switch on the radio to turn on the Tx. It may be necessary to put a 1 or 10 mF cap in line if there is "phantom" voltage on the audio pin of the mic plug.However on SSB I use a 1.5 KHz signal rather than a One KHz signal.An AF signal of 50 mV is typical but your manual may call for a greater signal.Do you have an Oscilloscope or a Spectrum Analyzer?? I use a SA>On SSB you should see one peak 1.5 KHz from the center freq on a Spectrum Analyzer.On AM you should see the carrier and then progressively smaller peaks on each side of carrier at whatever audio freq you inject.You can also see the "deviation" of a FM signal on a spectrum analyzer. If you have a fancy Service Monitor it will give you a number for the deviation.On an Oscilloscope you will see a modulated "envelope"How do you plan on sampling the output signal? Are you going to use a load or use an antenna on the radio??With a Spectrum Analyzer you probably would do fine with a short antenna on the analyzer... With a Scope you probably would do well to wrap a few turns of wire around the radio antenna coax and attach your probe to that. There are "samplers" but that is not necessary to get a pattern.Giggle scope patterns of SSB and AM to see what you should have on the scope. Here is a start:https://www.ab4oj.com/test/peptest.html

author: radiolistener
author_rank: Super Contributor
timestamp: January 24, 2025, 12:13:55 am
content: To evaluate the performance of your TRX, it is recommended to apply a two-tone signal at the input, typically at 1800 Hz and 2250 Hz. Then, observe the TRX output on a dummy load using a spectrum analyzer. You will notice that the SSB signal exhibits additional parasitic frequencies around the two main peaks. These represent distortion products. Measure the magnitude difference in dB between the primary peaks at 1800 Hz and 2250 Hz and the distortion peaks. This difference value represents the third-order intermodulation distortion (IMD3) of your TRX.Higher value is better. The min required value is 60 dB (in some countries 40 dB).

author: Crambone
author_rank: Frequent Contributor
timestamp: January 24, 2025, 05:25:09 pm
content: OK thanks everyone great info!