RF Preamps for HF Receivers: Worth it?
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- čas přidán 16. 01. 2023
- We usually expect RF preamps to improve our ability to receive weak signals on HF. But do they? As you'll see, they can, but it depends.
By the way....the best solution for shortwave listening is a GOOD antenna. - Věda a technologie
Very good video. You are very detailed in your radio videos. Thank you!
Great content!!! Please make more videos!
In the 70's, I tried playing with the ham satellites that would pass overhead. The downlink was on 10M and all I had was a random wire pushed through a basement window and up into a tree about 25 feet. I lived in suburbia a few miles from NYC, so noise and interference was about as bad as anywhere on earth. I could hear the CW as the satellite passed over, but it was too weak to read. I added an RF preamp and it was like night and day. For my situation it was well worth the small investment I made.
My G4CLF based transceiver has no pre-amp and I don't miss much. Now adding 60m.
I compared it with an FT817 some years ago at a special event station and my h/b radio received signals at a lower level only on 10m. It was designed with no pre-amp.
It was a good test to see how well my receiver was working compared with a commercial one. Measured figure from the original article was 0.2 microvolt sensitivity.
G4GHB
Pretty good camera… nice quality video.
Very nice video! It explains very well what a preamp can offer. Makis, SV1AFN
good vid, very helpful, txn
For the typical high noise suburban location, indoor RF preamps are only worthwhile at upper HF, low VHF, and above. The indoor preamp, providing it is nominal 2 dB or lower NF, only lowers the noise figure of your radio (e.g. Icom). Hence assuming a R8500 receiver front-end NF is 8 dB at 35 MHz, the indoor preamp will lower it to circa 2 dB when in circuit. The catch is that external atmospheric, galactic, and man-made RF noise is typically above 8 dB. This means that high quality receivers such as the Icom R8500 and R8600 are already RF noise-limited. At my location a 35 MHz dipole generates a dramatic increase in RF noise when connected to an Icom R8500 at low VHF. My 35 metre length coax length to the house introduces 2.5 dB loss. But because the ambient external RF noise is sufficiently high, even 0 dB coax cable loss would not produce any discernible signal-to-noise (SNR) improvement. A better option is to position a nominal 2 dB NF preamp near the antenna terminals. But even that improved arrangement may not result in a discernible SNR improvement at HF and low VHF. During days of high power pole RF noise, it is not possible for preamps to improve SNR, even at 50 MHz VHF. RF preamps for HF receivers are mainly beneficial when operating in rural or coastal areas well removed from man-made RF noise.
Thanks for these videos! I am seeking an RF amplifier that can input 250mw and boost to 3 watts+. Frequency range is 470-480mhz. Do you have any recommendations? Do you take on custom work? Thanks!
Works even better with a passive preselector or antenna tuner inline.
Sounds like the best option is make sure you can easily switch it in or out as desired.
i bought a vintage american nippon premap, but i'm confused bc online they had 135db, woudn't that burn my RTL SDR?
the reason was bc after running a +10m long coax cable, i noticed a 10db drop in my signal, and the internal LNA or hardware AGC is noisy and produce lot of heat
I'm curious about if it would work better on the 3.3 MHz signal at night?
Very likely. Noise does tend to abate and propagation improves on the lower frequencies at night.
Anything that amplifies noise at the same rate as signal is effectively just extra signal loss. Spend the money on a better antenna