one amplifier or more cascaded - Page 1
Forum section: electronics / rf-microwave

author: Simon
author_rank: Unknown
timestamp: October 31, 2022, 11:39:13 am
content: I'm taking various measurements for EMC tests. We could do with amplifying our aerial signals. Up to 50-60dB of gain would be good. Should I use one amp or is several in series going to give me the same result. I am looking at for example:https://www.nooelec.com/store/downloads/dl/file/id/103/product/334/vega_datasheet_revision_1.pdfwhich has 50dB of gain that is adjustable or:https://www.nooelec.com/store/downloads/dl/file/id/107/product/335/lana_hf_datasheet_revision_1.pdfwhich have 20dB of gain and I could cascade 2 or 3, the gain on these seems more consistent.

author: BigBoss
author_rank: Regular Contributor
timestamp: November 01, 2022, 11:05:00 pm
content: 50 dB Gain Amplifier seems having lower noise and much higher P1dB Output Level.I believe These parameters are important for EMC measurements. Being wideband may have an issue but this can be worked out by a filter.On the other hand, EMC tests will need very low kHz range signals so 20dB amplifier will be more appropriate.You just need few kHz to 300MHz amplifier with excellent flatness and high output level.https://www.minicircuits.com/WebStore/dashboard.html?model=ZHL-6A%2B

author: fourfathom
author_rank: Super Contributor
timestamp: November 01, 2022, 11:41:04 pm
content: Quote from: Simon on October 31, 2022, 11:39:13 amThat sounds like a ridiculous amount of gain -- what is your antenna? I suspect that if you think you need that much gain then your antenna signal will be below the noise floor of just about any amplifier.But I'm just guessing, and look forward to hearing from the experts.

author: Simon
author_rank: Unknown
timestamp: November 02, 2022, 07:25:20 pm
content: Quote from: BigBoss on November 01, 2022, 11:05:00 pmThe problems with EMC generally happen at under 150MHz, higher than that and the signal levels naturally drop off combined with more allowance in the test standard. I have in fact got 3 of the 20dB amplifiers.I am not sure why I would choose the one you recommend, very expensive and I do not need over 1W of power output.

author: Simon
author_rank: Unknown
timestamp: November 02, 2022, 07:33:25 pm
content: Quote from: fourfathom on November 01, 2022, 11:41:04 pmThe antenna is a Tekbox TBMA1;https://www.tekbox.com/product/TBMA1_Manual.pdfa lousy piece of shit but I feel I will get a no if I ask for another one that will do lower frequencies, lesson learnt, never ask the reseller to recommend something, especially Telonic, they are useless, I clearly said that I had to work in the 10's to around or a little over 100MHz and they sold me an aerial that is essentially made for 450MHz.So with a mere -33dB of gain, yes it needs a little amplification. I have used one 20dB stage and it has improved matters but yes it appears to be taking the noise with it.So the noise figure, is this on the input or output? if it's on the input then yes I see what you mean, the noise will be amplified as much as the signal, I guess a first very low noise even if not high gain amplifier would be best as that can then be amplified by other amplifiers that are not so good. I have the joy of having to put a 6dB attenuator on the aerial as the VSWR is atrocious at low frequency, I am not sure if this matters more in transmission than reception, my understanding is that everything is a 50omm source/load and it all warks both ways.