Now that I have some decent amplifiers, it is time to make a project to make good use of them. since they have a high gain it is essential to avoid over-driving them.
Here are some ideas:
The easiest modules to employ are the 2-400mW modules, as they only need a single, +15V power supply. The modules are rather small, and heat up quickly, so some kind of heat sink is necessary for those. Not unexpected when I saw the size, and they do have holes for mounting on a heat sink.
The 1-2W module needs a -12V and a +12V supply, as does the amplifiers in the up-converter module I have tested earlier. Those units *need* the -12V to be supplied before the +12V, so some kind of sequencing/safety circuit is necessary.
For this reason the first construction tests will be done with the low power modules. Here are some options for experiments.
1) a WBFM modulated DRO, such as a modified HB-100 module driving the amplifier. The HB100 module needs to be modified for use as an exciter for the amplifier, and a modulator is needed, too. The modification would consist in disconnecting the RX mixer circuit and the transmit antenna on the PCB, adding a semi-rigid cable at the "antenna output" and building the HB100 into a shielded box. One more thing is needed, an attenuator in order to avoid over-driving the amplifier.
Adding the attenuator has one more advantage, it provides some isolation of the DRO, giving less drift and external influences.
Such a transmitter can be used together with a satellite LNB and a WBFM capable scanner running in the 600-700MHz range. Separate antennas can be used for simplicity.
It could also be used as aWBFM test TX ("Beacon") when used with an audio frequency keyed system, e.g. with a microprocessor, such as the Arduino with a suitable program. Of course, this could also include a keyer input for manually keying the audio tone.
The range with such a transmitter will be significantly improved when compared to a simple system with the HB100 "stand-alone".
2) A set-up using a cheap 70cm transceiver as the source for the TX signal. This is a bit more involved, but some of the circuitry can be used for other experiments later.
The circuit needed is a frequency multiplier chain, for example 432x2 -> 864x2 ->1728x2 ->3456x3 ->10368MHz (x24 multiplication, so other orders of the multipliers could be useful). A bit of offset from 432 would be good, as I want to avoid running WBFM in the narrow band segment. The advantage of this will be the improved frequency stability, as the reference frequency is usually synthesized. Yes, an attenuator is needed after the 70cm TX, but that is not too difficult, since such a TX can run a power as low as 0.5-1W, and the load impedance is not overly critical for the TX.
Otherwise the multiplied and filtered signal can be used as in example 1 above.
This was all wideband, and this does have its limitations with respect to range, so I would like to use the amplifiers for narrow band transmission as well.
3) Narrow band CW (FM) transmitter. Using the multiplier from example 2 it is then a matter of generating a 432MHz signal with sufficient stability. For a simple, single frequency CW TX, e.g. a "beacon", I have some TXCOs running on 14.4MHz. As those oscillators are likely to generate a square wave, taking out the 5th harmonic on 72MHz and amplifying it should not be tricky. After that a frequency doubler, followed by a tripler will generate a signal on 432MHz. As I have done a bit of VHF construction before I would not expect this to be too difficult, especially as this comes after trying making the higher frequency multipliers. Good shielding and decoupling is a known construction technique for me. Keying can be done in one of the multiplier stages, and this can also be used as marker signals for 2m, 70cm, and 23cm.
200mW CW should be quite good from a hill top.
Because I do not know any people near me running WBFM, this might be a better option to make a first QSO on 10GHz, if I do not build a second simple WBFM set, or find someone who has one or wants to build his or her own.
Now, although I know some, not all people doing microwaves can do CW, so what comes next?
4) Up-converter from a VHF or HF station, so all modes are possible. The receive side can still be a satellite LNB (modified for better reference frequency), so here goes:
Among the stuff I ebay'd lately, there is also a 10-11GHz mixer circuit. The IF connector is not a standard SMA, so it looks like I am going to make a modification so that all three connectors will be SMA. Otherwise I can use the one from the up-converter I already have (and tested), modified, so that the DRO is removed and a multiplier chain (as above) is used in stead. I will probably need a new multiplier chain, but that should be doable, if I can get the first version (above) working. In the up-converter there is (what looks like) a decent band pass filter centered on about 10330MHz. This has to be re-tuned as 10368 is outside the band pass.The amplifier chain in the up-converter as it originally was, is quite bulky, and could be replaced by the 2-400mW amplifier. I suspect there will be sufficient gain.
All in all, it will be interesting to see what I can do with the surplus equipment/modules I have got now. A bit more is on the way, more on that later. There is enough work for quite some time with the speed I normally build stuff. For now, the HB100 modulator is back in the front again. I received some (SMD) 4001s, so the morse tone generator can be made, even if I need to use an adapter from SMD to "normal" (old fashioned) PCB soldering.
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