An LNB (as opposed to an LNA) downconverts - in this case from 10.5 GHz to 740 MHz (approx). This, together with the amplification, allows cheap co-ax to be used from the dish focus to the receiver. There are two types of oscillators used in LNBs, Dielectric Resonator Oscillators and Phase Locked Loops (locked to a crystal). The later type provides adequate performance for SSB/CW.
The Pluto can do the IF RX at 740 MHz and the TX at 2.4 GHz (both simultaneously). It has a 40 MHz TCXO which is useable on CW and SSB but is not great.
I suspect WiFi amplifiers have to be linear to cope with the complex modulation used in WiFi (but I’m guessing). The “8 Watts” should be taken with a large pinch of salt I suspect. The amp has to be slightly modified to override its TX/RX switch. See amp below.
It’s probably valid when the device is used as a Wifi amp as it will be switching between TX and RX very fast, the peak power maybe 8W. It is extremely unlikely it would do 8W at 100% duty cycle. I read about this just recently but due to the rapid onset of age related befuddlement I cannot remember where.
He would most definately pointed out that understanding relativity as key to SAT work. Its as a near a perfect example, time dialation for GPS, Not to mention a moon bounce.
To see and play with things like this make me happy, which is why I got a radio licence.
The “8W” WiFi amplifier uses two YP242034 devices which are rated for 34dBm each (P1dB). The pair is good for 5W+, but people have been reporting getting from less than 2W to over 6W from them. I think the internal DC-DC converter should be investigated if the output is low; nominal is 6V but some people have reported it dropping down to 5.6V or less under load.
I’m using one of those amps. I run it at +30dBm (1W) out for about +17dBm in. It’ll do that all day long. It will do 2W, but I don’t need that much with a 90cm wifi mesh dish antenna. 2.5W at a push, 3W max. Modded into permanent Tx with a 10k resistor.
Re filtering, I built a simple transverter and pulled two SAW filters out of a very old 80211b wifi access point. They roll off beautifully below 2.4GHz and get rid of the LO (an ADF4351 module) and image. I’m driving it with the FT-817 at 435MHz.
I have just modded my amp to feed the RF directly into the PA fets (alleged to give 4dB more gain). It was far from easy even with a fancy 150W JBC iron as the ground areas are very well connected (thermally) to the heatsink. EVAL-CN0417-EBZ on order to boost the output from the Pluto.
30dBm, 1W gives a nice SSB signal
20dBm, 100mW gives readable CW
10dBm, 10mW gives good FT-8 decodes and readable CW with narrow filter
0dBm, 1mW gives good JT-65 decodes
Which implies that with a very much smaller antenna and as little as 1W, JT-65 and even FT-8 should work.
I decided to conduct some real-world tests here after getting very poor results with the dual-band feed on my offset TV dish I use for the downlink, compared with the 2.4GHz wifi dish I was already using.
To my surprise, I found that placing a 2.4GHz feed just above the LNB is only marginally worse (1-2dB) than placing it in the focus.
Tested feeds were a single band LHCP patch, a bi-quad and a can (sorry, circular waveguide) with 1/4 wave probe.
The LNB was left in place and the 2.4GHz antenna held above it while transmitting a carrier and measuring the strength of the return signal on the downlink. The signal was also peaked by moving the feed towards or away from the dish.
The single band 2.4GHz patch came out best of course, slightly better than the wifi dish, but even the can was only a few dB down.
It’s very easy to try. It helps that the wavelength at 2.4GHz is more than 4 times the wavelength at 10GHz, so everything is at least 4 times less critical. Placing the 2.4GHz feed at the side of the LNB wasn’t so effective, so it is obviously a property of offset dishes.
The patch is getting waterproofed and mounted on the downlink dish when the weather permits.
