Posts by SM6PGP
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..and yet another one, a Coaxial cavity feed like the OM6AA feed. The 2.4 GHz part is fed with two probes which simplifies the feeding compared to OM6AA feed. I only need one 90 deg hybrid , Anaren XC2500-3. Less prefect symmetry is the price to pay.
In the 10 GHz part I have vertikal and horizontal probes so I can easily switch between NB and WB transponder with a SMA-relay.My 10GHz RX setup is NOT based on an LNB - it is scratch built with SMD MMIC:s.
The feed is designed by SM6FHZ and is of course a compromise and not as efficient as the EME-feeds.
I use a 2.3 m dish, f/D = 0.31 , it is actually a1.8 m dish extended to 2.3 m.
https://sdr-radio.groups.io/g/…/0/S_X_Dual_Band_Feed.pdf
Any one else using something like this or OM6AA feed ?
73 - Hannes - SM6PGP
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Hi ! I used 20mW into my 2.3 m dish (estimate 33dBi gain) for CW QSO with good signals. Could not get down to the noise floor have to remove some gain. It is interesting to see how low it is possible to go with the power. In sweden we are limited to 100mW, but with a 2.3 m dish it is not a problem.
73 - Hannes - SM6PGP
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Hi !
Power control built into Up-converter.
I have a step attenuator in the RF chain in my up-converter.
The mixer is followed by som BPF:s and amplification an then fed into a HMC624, a 6 bit attenuator with 0.5 dB steps so max attenuation is 31.5 dB. Using 5 bits so I have 1dB steps. Up and down stepping is controlled by up/dwn counters (2 x 74HC193) feeding the HMC624 parallell input.
The upconverter (and down converter) will be mounted at dish focus behind the feed, so I have remote control of the attenuator by pulses to the up/down counter inputs.
Attenuator/counter setting is read by a DAC and feeding a DC-voltage back to the shack, 30V = 30dB attenuation.
Thus I can control my output power from 9 dBm up to 37 dBm without the need to change anything like at the IF rig like MIC gain/RF power. It will always be running the same settings. IF (TX) rig is IC7600 running at 28MHz + xverter to 144 MHz fed via 25 m cable to the up-converter at the dish.
At the power amplifier output I have a coupler feeding a log detector AD8313 with some signal conditioning so I get 5 V for 40 dBm, 4V = > 30dBm and so on, this will show the actual RF power feed to the antenna port.
73 - Hannes - SM6PGP