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Can I increase the signal strength by combining two radio transmitters with an antenna? İt has only one oscillator and two transmitter circuit. Same signal. I connect antenna coil together in one antenna .

Murat Özen
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  • Maybe but maybe not legally. – Andy aka Nov 21 '20 at 11:05
  • But I work with a frequency that has never been used. And I don't think anyone will sue me for a patent for this frequency. – Murat Özen Nov 21 '20 at 11:09
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    Perhaps if you were more specific in your question about what EXACTLY you are doing. – jwh20 Nov 21 '20 at 11:21
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    If you don't get the combiner exactly rght there is a danger the two transmitters will cancel each other out and decrease the signal strength. –  Nov 21 '20 at 11:23
  • Why cancel each other ? There is two radio transmitter circuit. They are sending radio signal together . Shouldn't they send more signals?. Why cancel another ? – Murat Özen Nov 21 '20 at 11:43
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    @MuratÖzen Waves can combine to reinforce, or to cancel. You need to manage the path lengths between the single oscillator and the combiner. – Neil_UK Nov 21 '20 at 12:06
  • I will do a test with 4 same transmitter circuit and only same one oscillator this day . I will manage lengths. I wonder about it. – Murat Özen Nov 21 '20 at 13:54
  • "a frequency that has never been used"? Really? That sounds interesting... What frequency is that? – jcaron Nov 21 '20 at 14:01
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    @jcaron - Well, OP did say something about a "patent for this frequency" :-). – SteveSh Nov 21 '20 at 14:26
  • Just to be clear... In most countries, use of any frequency is subject to national or supranational regulations. Some frequency bands can only be used by the people who have a licence for those (e.g. bands used for mobile phones, analog TV, digital TV...). Some are reserved for the government or military. Others are usable without a license (the so-called ISM bands), but are subject to restrictions, usually in terms of modulations, spread-spectrum schemes, carrier sensing, and most importantly power. Most ISM bands have extremely low limits in many regions. – jcaron Nov 21 '20 at 15:09

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Lets use a contrived example. Say your transmitters are operating at 10 MHz. Wavelength at 10 MHz is 30m (meters). If we assume the two transmitters are phase together correctly, and if the path length (cable) distance from the transmitters to the antenna are different by 15m, this results in a 180 deg phase shift at the antenna between the two signals, which results in 100% cancellation of the signal.

At 10 MHz, obviously, you should be able to match the cable lengths much better than that so theoretically, assuming you combine the two signals correctly at the antenna, you should be able to achieve a 2X (3 dB) increase in output power.

Now let's go up in frequency to 10 GHz (radar territory). Wavelength at 10 GHz is now 0.02997m, or 1.18in. At this frequency the path lengths (assuming everything else is equal) needs to be matched to within a couple of tenths of an inch for the combining to work. If they differ by ~0.6 in, then the two signals will again cancel at the antenna due to the 180 deg phase difference between the two signals.

Note that in the RF/microwave world, it is very common to parallel amplifiers to achieve the needed power output. But a great deal of care is taken to assure that the signals combine in phase, which includes identical amplifiers and careful attention to the path lengths and the combiner.

SteveSh
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