Spectrum Analyzer antennas - Page 1
Forum section: electronics / rf-microwave

author: bson
author_rank: Unknown
timestamp: June 14, 2016, 05:54:10 pm
content: I just got a Signal Hound SA44B and I'm looking for suggestions for a few different antennas... preferably 50ohm, with SMA connector.An adjustable/telescoping 50ohm antenna for 360 degree surveys.An 2.4G ISM band antenna, 50ohm. (Tunable?)A directional survey antenna, perhaps 100M-2.4GHz? (Yagi?) To locate sources of interference in my lab.I'm not a ham or anything... so I'm kind of lost when it comes to the nitty gritty of finding suitable antennas.

author: retrolefty
author_rank: Super Contributor
timestamp: June 14, 2016, 06:05:44 pm
content: Quote from: bson on June 14, 2016, 05:54:10 pmYagi is a narrow bandwidth antenna so not a good choice. Directivety and wide bandwidth are mostly conflicting requirements.

author: Emo
author_rank: Regular Contributor
timestamp: June 14, 2016, 06:21:15 pm
content: If portability is also in scope, log periodic antenna made on printed circuit boards are quiet useful for broadband measurements.wa5vjb does sell these and are relative cheap.(400 Mhz - 11 Ghz).

author: tggzzz
author_rank: Super Contributor
timestamp: June 14, 2016, 08:22:53 pm
content: If you want a non-directional wideband antenna, discones are easy to make: SMA connector plus 5 wires of non-critical lengths and at non-critical angles

author: bson
author_rank: Unknown
timestamp: June 14, 2016, 08:24:41 pm
content: Quote from: retrolefty on June 14, 2016, 06:05:44 pmSo let's start with something suitable for the ISM band(s)...But a microwave yagi should be pretty small, so several could easily be combined in a single enclosure, no?

author: bson
author_rank: Unknown
timestamp: June 15, 2016, 01:46:47 am
content: Just ordered a handful of 2.4 stubbies and telescoping... let's see how this works out. I see a bad antenna-collecting habit coming on...

author: bson
author_rank: Unknown
timestamp: June 15, 2016, 01:49:22 am
content: Isn't it possible to use 2 2.4G ISM stubbies to locate a source? If I place them in parallel and 1/2 wavelength apart, won't the signal strength vary with their orientation to the transmitter?

author: AF6LJ
author_rank: Unknown
timestamp: June 15, 2016, 02:25:04 am
content: Quote from: bson on June 15, 2016, 01:49:22 amIt is not really that simple.Assuming a 50 Ohm system you need to build a phasing harness.That is done with 75 ohm cable from each antenna, odd multiples of a quarter lenght long, and tied together at the input of the analyzer. That will give you some directionality but you are far better with an LPA. (Log Periodic Antenna)Another thing that needs to be pointed out; keep your signal levels low, your analyzer will see signals levels from outside of the range you are looking at, too much total signal power into your analyzer will damage it unless there is some form of input protection.

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: June 15, 2016, 06:10:42 am
content: You should probably buy wideband Vivaldi or Log Periodic antennas made by etching tracks on PCB. Price depends mostly on lower frequency. Something 1.5 to 6 or 10 GHz on PCB should cost about $150-200 if you look at usual places online.I got two from AliExpress - pretty happy with them. You have to solder your own connector however. I used piece of semi-rigid RG405 cable with solder-on SMA connector. I use them with my spectrum analyzer.(http://www.aliexpress.com/item/Vivaldi-antenna-UWB-antenna-GROUND-PENETRATING-RADAR-GPR-antenna-0-92-8GHz-VG920-7G/32610727590.html?spm=2114.01010208.3.1.QvzynJ&ws_ab_test=searchweb201556_0,searchweb201602_2_10017_507_401_10040,searchweb201603_9&btsid=2d54e98f-5a1e-4f0d-ac49-19d4cf9d9a6c).There are other wideband PCB antennas but I only tried log-periodic and Vivaldi.RFSpace had good antennas, they sold them on Amazon, but they seem to be always out of stock now.http://rfspace.com/RFSPACE/Antennas.html

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: June 15, 2016, 06:40:05 am
content: I found this commercial log-periodc quite useful when doing site surveys:https://www.linxtechnologies.com/en/products/antennas/db1-lphttp://www.digikey.com/product-search/en?keywords=DB1-LP

author: Electro Fan
author_rank: Super Contributor
timestamp: June 15, 2016, 02:47:18 pm
content: Quote from: AF6LJ on June 15, 2016, 02:25:04 amIf you had a small ham Log Periodic VHF/UHF portable antenna normally used outside, how could you determine it's normal sensitivity and overall performance outside so you could in turn determine how many dB of attenuation would be sufficient in an attenuator so you could select an appropriate attenuator for using the antenna safely inside or outside with an SA? (Only for receiving, not transmitting.) Any guess on how many dB's of attenuation this might turn out to be? What are the typical dB attenuation ranges for simple passive inline attenuators? What Watt rating would be sufficient? The SA is worth more than the antenna - just want to be cautious and conservative on this - better to be on the safe side to protect the SA. Is there such a thing as a fairly wide ranging variable attenuator? One last question, is there any reason to also use a DC Block in line with the attenuator to help further protect the SA?ThanksUpdate: I found and measured a couple items shown below. The first two photos show a Tektronix 011-0099-00; this model is a Terminator and not an Attenuator; it seems to provide about 3 dB of attenuation. The second two photos show a Tektronix 011-0059-02; this model is labeled as a 10X Attenuator and it seems to provide about 20 dB of attenuation. Moral of this story is don't confuse a Terminator for an Attenuator.I'm guessing the 011-0059-02 10x Attenuator might suffice for what I originally asked about in this post (although interestingly this Attenuator is rated for 2 Watts vs. the 50 Watt rating on the Terminator), but if anyone thinks differently about this please let me know. ThxPS, I'm guessing that even if I happen to tune a strong local FM broadcast signal on the antenna while watching the signal on the SA the most the SA is going to see is milliWatts so 2 Watts is plenty sufficient, yes? Thx

author: Emo
author_rank: Regular Contributor
timestamp: June 15, 2016, 02:59:23 pm
content: Hi,The log periodic antenna are very cheap in that range. wa5vjb charges 7 US$ see his websitehttp://www.wa5vjb.com. Just add a connector or a coaxial cable and it ready.

author: AF6LJ
author_rank: Unknown
timestamp: June 16, 2016, 11:19:20 pm
content: Quote from: Electro Fan on June 15, 2016, 02:47:18 pmGenerally speaking it is back practice to put a spectrum analyzer on an outside antenna without some bandpass filter to limit the spectrum to your interest.For example I live close to three AM broadcast stations, I recently put up an active loop antenna for HF in order to improve my signal to noise ratio on the low bands. I ended up with .3V peak to peak on input to my receiver. Thankfully for me the receiver has built in bandpass filters for the bands it covers. This is only a slice of spectrum just under 30MHZ wide.The input of your spectrum analyzer has no such bandpass filtering.And 3DB isn't where I would start, more along the lines of 10DB was my thinking.That band can be rather congested with WiFi and all.

author: Electro Fan
author_rank: Super Contributor
timestamp: June 17, 2016, 11:28:07 am
content: Quote from: AF6LJ on June 16, 2016, 11:19:20 pmI think the attenuator in the second set of photos does 20dB, and I think my log periodic antenna might be time deaf outside UHF/VHF but without seeing it on the SA it's hard to know for sure. So to be on the safe side the band pass filter sounds like a good idea. Any thoughts on this model?https://www.dxengineering.com/parts/hiz-bpfThx

author: AF6LJ
author_rank: Unknown
timestamp: June 17, 2016, 02:20:18 pm
content: Quote from: Electro Fan on June 17, 2016, 11:28:07 amI was under the impression you were interested in viewing the 2.4GHZ band

author: Electro Fan
author_rank: Super Contributor
timestamp: June 18, 2016, 04:13:30 am
content: Quote from: AF6LJ on June 17, 2016, 02:20:18 pmOh, no worries. For this "test" I was trying to look at VHF and maybe UHF receiving ham signals transmitted from nearby at 5-50 Watts. This is what I would like to use the attenuator for.I have another antenna that supposedly was designed specifically for Wifi frequencies that I use around 2.4 GHz; when that is attached to the SA the SA nicely and I think very safely displays Wifi bursts without an attenuator.

author: AF6LJ
author_rank: Unknown
timestamp: June 19, 2016, 02:34:21 pm
content: Sounds good.