Grace:
Putting the pre-amp directly on the antenna is the best way to use a pre-amp, and the calibration data is what tells you if the system is good enough for what you need. Assuming you can trust the manufacturer’s data, look at the sensitivity (the minimum discernable field strength) that the combination of the antenna design and the pre-amp design yields. Of course, the noise floor is determined by the pre-amp’s first stage. Remember that you still will have to adjust for cable loss between the pre-amp output and your analyzer input. Be cautious about overloading the pre-amp, both in-band and out-of-band (just because the 3115 is a 1 GHz to 18 GHz antenna doesn’t mean that it also isn’t a 300 MHz antenna; it is, it’s just a poor 300 MHz antenna). Lindgren cautions you about that. I wonder how the amplifier handles fast pulsed or transient RF? I’m surprised that the manufacturer provides data only for the combination of the antenna AND pre-amp; I could often want to use the antenna without any pre-amp. If I sent this out for periodic re-calibration to an antenna cal lab, I would request antenna factors for the bare antenna and the antenna plus pre-amp. In fact, unless you are digging for the last few dB of sensitivity, it’s good practice to not use the pre-amp. Always try for simplicity in measurements. Remember that you always pay for bandwidth with sensitivity. Sure, it’s nice to cover 1-18GHz with one antenna, but I found those broadband antennas often were very inefficient at their band edges. My choice was to use a 3115 style antenna only from 1-12 GHz, and then switch to a K-band traditional pyramidal horn for 12-18 GHz. The 3115-style antenna AF starts to climb badly above about 15 GHz. (I always used octave-band horns above 18 GHz, so I don’t have any experience with the 3116-style antennas. However, the same cautions apply.) Before I would buy a broadband antenna and pre-amplifier, I would study what’s available by using several antennas to cover that range. True, this slows you down, and that is also money, but only you can assign what that means to your decision. BTW, that’s a honking big external box for the pre-amp. I certainly hope that the box shields the pre-amp from any possible stray RF pickup. Lindgren vaguely mentions an “AC-DC power supply” and that tells me that the big box doesn’t have an internal battery. Well, I can picture a wideband, K-band pre-amp about the size of a ceramic postage stamp, so Lindgren must use that box for something (maybe they need that area to dissipate the heat). And remember that you will be tied to that power pack, so that means an extra wire snaking up to your antenna. There likely will be some times when that extra dangling cable could cause you some measurement issues (like worrying how a strong 300 MHz field might couple into the pre-amp via its DC power cord). It also makes field use of the antenna a problem (unless maybe you build yourself a battery pack). Lastly, how do you do a head-end validation of the measurement system? Do you plan to face the new antenna into some standard emitter, or do you plan to inject a signal into the pre-amp input? I didn’t see if Lundgren uses an SMA, N or something exotic between the antenna output and the pre-amp input; you might need a couple of coax adapters. Ed Price WB6WSN Chula Vista, CA USA From: Grace Lin [mailto:graceli...@gmail.com] Sent: Sunday, September 20, 2015 3:45 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: [PSES] 3115-PA & 3116C-PA Horn Antennas with Pre-amplifiers Dear Members, Does anyone have experience using the 3115-PA and 3116C-PA? http://ets-lindgren.com/3115-PA http://ets-lindgren.com/3116c-PA More specifically, does the amplifier work good with the antenna? The design eliminates a cable between the antenna and the preamplifier. Thank you very much and I look forward to hearing from you. Best regards, Grace Lin - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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