Preamp Living Urban
In many 144MHz NAC contests I have to give a several S-units lower report than I get. Of course can this have several reasons. My QTH is only about 15m above sea level and the antenna is about 15m over ground. There are also mountains in some directions. My output power at 144MHz is about 600W. Maybe I’m a crocodile :)
PreAmp, could this be the way to go? I have built some different PreAmps for 2, 70 and 23 cm over the years. However I have blown some up at the antenna and some was not so good.
The PGA-103 has a high IP3 and high gain at 144MHz. The noise figure is about 0.5dB at 144MHz. It is very easy to build a good PreAmp with this MMIC. The chip does not cost much and complete boards are available at many soursers. I builded one into a little die cast box. The gain is 23.5dB. High gain and good reception is 2 different things though, however good reception and SNR is. I made a BPF which is located at the right in the picture (after PreAmp).
The shape of the filter, the tracking generator is set to -10dbm. The filter loss is 0.5dB.
Since I live in an urban region ( Gothenburg ), high gain will increase the noise floor. There are many radio/TV stations. And all the the noise that comes from switched devices must be huge. Other ham stations will of course also be a problem. One FM radio station is at 107.8MHz, STAR FM. The filter is quite sharp 107.8 is -48dB down.
Picture inside of the filter.
From a measuremet point of view should this PreAmp boost my reception. However on the air test will tell the answer.
Note, This is not a scientific measurement it only displays what the radio see.
I will use a local beacon SK6VHF as reference. The noise level measurement is my IC-9700 S-meter and in this test listen on 144.390. SK6VHF is at 144.406.
The length of the RG-213 is < 20m. This will give 1.5 to 1.7 dB loss. The PreAmp is located at the radio side in this test. This means that 1.5dB noise will be added, and the PGA-103 noise figure should be about 0.5dB.
Noise level is actually only current background. The 9700 is quiet even with the internal PreAmp on. With the PGA-103 connected the background rises with 3 to 5 S-units. From this test it seems not to be any benefit using the external PreAmp.
Here the band scope shows the noise when the PGA PreAmp is used. When using the internal PreAmp the band scope is almost black = low noise.
As for now the best setup seems to be only use the BPF. If other stations uses PA's and or PreAmps is not known. And S-units is not a precise measurement method and differs with brands and age of the radios.
In a NAC test (2020-01-07) I did get a 4:1 report from Germany and could give back 5:5. I used 900W into a 9-element Yagi. This means that it is not all the time I give the lowest report back :)
I will upgrade my old 9-element Tonna to a 10-element LFA Yagi. This will probably much better for my QTH.
Below a test of the performance of a LFA antenna by G0KSC.
And Owenduffy's reflections about the LFA antenna.
https://owenduffy.net/antenna/
And also about using PreAmp at 144 MHz.
https://owenduffy.net/rx/gt/144LNA/index.htm
Update 2023-10-16:
I have mounted pre-amps for 70 and 23cm at the antennas. It is a big difference when listening to weak beacons or during the NAC contests. The noise floor is higher at 144MHz, and the antenna is not easilly taking down. Therefore I have a pre-amp a bit down for now.
My 10 element LFA is finally on the roof. Seems promising, abote 1-1.5 S-units stronger signals. The coaxial cable is replaced with a low loss LMR-400 equivalent. My length is equal to 0.7db loss. Antenna gain is 14.7 dBi, F/B about 30dB. (a 13 element LFA is now mounted as well)
Link to antenna specifications:
Welcome
Welcome to sm6why.n.nu.
My Newsletter
Links