Question: Any recommendable frequency converters for spectrum analyzer? - Page 1
Forum section: electronics / testgear

author: Bicurico
author_rank: Super Contributor
timestamp: September 06, 2018, 05:52:18 pm
content: Hi,Affordable spectrum analyzer like the Siglent SA3021X only offer a range up to 2.1GHz/3.2GHz.Some applications like WIFI, drones, etc. work in frequencies up to 6GHz.Is there any "Low Noise Converter" that would down convert 3GHz-6GHz to 9KHz-3GHz?I was looking at eBay and found this:https://www.ebay.com/itm/Microwave-Radio-Frequency-Converter-Double-Balanced-RF-Mixer-40dB-LO-312-gbd/401466149073Here some further info:https://www.analogictips.com/3-ghz-20-ghz-double-balanced-mixer-performs-downconverter/And:https://www.digikey.com/en/product-highlight/h/hittite-microwave/hmc1081-and-hmc1048lc3b-double-balanced-mixersIt is not entirely clear to me how such a device is used. Where do I get the LO signal from? Could I connect the TG output to LO?Anyone tried it?Regards,Vitor

author: hendorog
author_rank: Super Contributor
timestamp: September 06, 2018, 06:34:33 pm
content: Simplest solution is this:https://www.crowdsupply.com/outernet/morfeusI have one and it can be powered from USB on the SSA makes it quite a neat solution.You lose the ability to measure absolute amplitude with this of course - unless you some other accurate source to use as a reference.And the LO in the Morfeus isn't locked to the SSA.But to simply see the signals up to 6GHz and a bit above, it will work fine.Edit: also see this thread for some other options:https://www.eevblog.com/forum/rf-microwave/extend-spectrum-analyzer-range-from-3-to-6-ghz-the-easy-way/Or some parts from ebay:ADL5801 board:https://www.ebay.com/itm/ADL5801-double-balanced-active-mixer-up-and-down-mixing-module-Barron-coupling/182167050037?hash=item2a6a009735%3Am%3AmeKpKil911bPWLoFDf5s4MA&var=483841563927And you need an LO as well:https://www.ebay.com/itm/ADF4351-35M-4-4GHz-RF-Signal-Source-PLL-Frequency-Synthesizer-4-9V-5VDC-im/182819753791?hash=item2a90e80f3f:g:v68AAOSwj9dZ3Dwqorhttps://www.ebay.com/itm/MAX2870-23-5MHZ-6GHZ-Phase-Locked-Loop-RF-Source-Signal-Generator-Frequency/263507911139?hash=item3d5a4ba1e3:g:UAQAAOSw3p1ai9OKorhttps://www.ebay.com/itm/ADF4351-RF-Sweep-Signal-Source-Generator-Board-35M-4-4G-STM32-TFT-Touch-LCD-New/173108661847?hash=item284e148e57:g:8FwAAOSwZrhaYcI6

author: tautech
author_rank: Super Contributor
timestamp: September 06, 2018, 07:31:55 pm
content: @BicuricoVictor, I'd endorse any recommendation hendorog has as he has my SSA3032X for experimentation and checks against his HP gear. Consider his as trusted advice.

author: Bicurico
author_rank: Super Contributor
timestamp: September 06, 2018, 07:45:01 pm
content: Thanks! I will give this a thorough look!It is not urgent by any means, but I have come across the need of getting up tp 6GHz. I fixed that with the HackRF and/or PlutoSDR, but I am not able to adapt my "VMA Simple Spectrum Analyser" software for those devices.A economic way to extend the frequency ranges of the SSA3021X and CMU200/CRTU would be great. So will definitely take hendorog's advise into account! (thanks hendorog!)Regards,Vitor

author: hendorog
author_rank: Super Contributor
timestamp: September 06, 2018, 07:54:50 pm
content: Cripes I better get it out and make sure the above works as I remember !Once I've finished me eggs and coffee

author: tautech
author_rank: Super Contributor
timestamp: September 06, 2018, 07:56:14 pm
content: Quote from: hendorog on September 06, 2018, 07:54:50 pmYou sleep in mate ?

author: Bicurico
author_rank: Super Contributor
timestamp: September 06, 2018, 08:05:28 pm
content: Sorry if this sounds silly, but I never used any of these mixers.RF IN -> The signal I want to analyze, for exampe a transponder at 4.5GHzLO IN -> A signal at a frequency that is mixed with RF IN: for exampe 2GHzRF OUT -> Will be the transponder at 4.5GHz-2GHz = 2.5GHzIs that correct? What I don't understand: is the LO a FIXED static frequency, or a swept frequency? What is the span of the mixer?Wouldn't I need to connect the Tracking Generator of the SSA3021X to LO in, in order to swipe the frequencies and mix them down accordingly?In the eBay link I read:"Output signal range: LF-600MHZ;"So to see i.e. 4GHz-6GHz downmixed at 1GHz-3GHz, this device would be useless, right?Regards,Vitor

author: ogden
author_rank: Super Contributor
timestamp: September 06, 2018, 08:32:37 pm
content: Quote from: Bicurico on September 06, 2018, 08:05:28 pmSometimes LO is fixed and sometimes not. It depends on radio architecture. In your case LO shall be fixed.QuoteNo.Information is all around the internet. You can start here:https://en.wikipedia.org/wiki/Heterodyne

author: technogeeky
author_rank: Frequent Contributor
timestamp: September 06, 2018, 10:52:21 pm
content: Quote from: Bicurico on September 06, 2018, 05:52:18 pmMy friend,I just wanted to bring to your attention this ultra-cheap method for doing downconversion. You canuse these $5 DirecTV downconvertersand basically remove the filtering, and power externally (or use a bias tee). It only involves removing components, no addition is necessary. Just some wiring.This would get you up near 4.5 GHz. Since you're not in a hurry, it may be worth a shot. You won't need to provide a LO with this solution. The amplitude flatness over frequency probably isn't great.I have two of them and have done the mod, but I never actually tested the performance myself. I could do so if you're interested.

author: hendorog
author_rank: Super Contributor
timestamp: September 06, 2018, 11:08:46 pm
content: I had a quick play before work, and the Morfeus wasn't great up around 5.8GHz.I set the LO to about 5.4GHz and the IF was about 400MHz - I tried a few different frequency combinations.There was at least 30dB of loss - probably more like 40dB - I'm not sure if my unit is faulty in Mixer+LO mode or if I just did something dumb. I didn't have time to look up the spec. That amount of loss meant it was only useful when directly connected to a signal source.I'll also have a look with an ADL5801 and let you know what I see with that.

author: Kosmic
author_rank: Super Contributor
timestamp: September 07, 2018, 05:56:14 pm
content: Downconversion sound kind of simple but it's hard to do it correctly. Using just a simple mixer will generate a lot of attenuation and images in your signal (https://www.digikey.ca/en/articles/techzone/2011/oct/the-basics-of-mixers).What you are trying to do is adding a downconversion stage to your Spectrum analyser. The thing is that your spectrum analyser probably already have 1 to 3 downconversion stage internally. Adding another one will definitely affect performance (ex: IP3) but should be technically doable. One of the problem though is that you spectrum analyser is probably equipped with a attenuator and preselector before the downconversion stages. So by placing a downconverter before those devices (in the signal path) you mostly loose the functionality they were providing.Long story short, you could probably build a simple downconverter but you will probably need to use some attenuators, amplifiers, filters, mixer and VCO (to generate the mixer LO). Buying a new SA might be a simpler option.

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 07, 2018, 06:25:55 pm
content: last time i gave advice to get >= 6GHz SA/VNA, even used one, and nobody take it, no thank you they even gave excuses such as hobbiests dont go 6GHz and parts are expensive etc. now what? now we have to play with images and unknown attenuation of mixers and down converters, or probably invent some rf poorman method and theory. or wait until siglent/R&S come up with their latest 6GHz version, and then buy another one. well, this is unhelpful

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 07, 2018, 07:14:54 pm
content: Quote from: hendorog on September 06, 2018, 11:08:46 pmi think none are faulty nor you are dumb... from the mosfeus link you gave (see picture below)....i think mosfeus is just a module OP linked above with monitor added and programmable mixer chip and vco/lo and mcu and enclosure. ymmv.

author: Bicurico
author_rank: Super Contributor
timestamp: September 07, 2018, 07:38:11 pm
content: Hi,Thanks for all the input. I am glad that I am not missing anything. Would be a shame if there was a simple and cheap device to enhance the frequency range and I hadn't known about it.The reason I bought the SSA3021X and the R&S CRTU was:a) They fit the budgetb) The frequency range is more than enough for my typical applications (TV, CATV and SAT - 50MHz-2150MHz)It is just that I would like to explore a little beyond, as new applications arise (5GHz WIFI, 5G, etc.).Of course I can "see" the spectrum with the HackRF and PlutoSDR, probably will less issues than using a low cost mixer.But having a SSA like the Siglent for up to 6GHz would be really cool (especially if hacked from the 2.1GHz version).Unfortunately, due to human nature, one can never get enough. Next step would be the ability to go up to 20GHz and receive C-Band/Ku-Band/Ka-Band without down conversion using an LNB... (Ka-Band ones are really expensive!).Cheers,Vitor

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 07, 2018, 08:04:03 pm
content: Quote from: Bicurico on September 07, 2018, 07:38:11 pmyeah, but it will not fulfill (a) i got an Advantest R3465 for half the price of SSA3021X...Quote from: Bicurico on September 07, 2018, 07:38:11 pmby the time, be ready to break the bank for cables, pcb and simulator.btw, there is more proper dedicated device for what you need, but i will anticipate another 4 digit price tag...https://www.signalcore.com/6ghz_down.html

author: hendorog
author_rank: Super Contributor
timestamp: September 07, 2018, 08:18:30 pm
content: Quote from: Mechatrommer on September 07, 2018, 07:14:54 pmThanks, that goes a long way to explain why it was so poor up there. I also see they only spec the LO and Mixer to 4GHz, but the LO works up to 5.4GHz and the mixer is advertised as a 6GHz mixer. So perhaps the LO isn't able to drive the mixer properly above 4GHz along with other limitations.Its a shame as it is very convenient being USB powered.I'll do more tests with the Morefeus and other mixers I have here - the ADL5801 is the easiest to work with as it is wideband doesn't need much input power.I have some passive mixers as well, which I'll have a go with too.

author: hendorog
author_rank: Super Contributor
timestamp: September 08, 2018, 10:33:52 pm
content: The ADL5801 mixer works well and I could see a 5.8GHz signal I was transmitting from another room.I connected my SH Tracking generator as the RF source, and set it to 5.8GHz and -12dBm (that is its max output power)I found that reducing the LO down to 5GHz and increasing the IF to 1000MHz I see about 10dBm of loss. So not bad considering the IF port is only spec'd to 600MHz. The loss increased above that.So in conclusion, a cheap ADL5801 board from ebay is a good option for downconversion with the SSA, up to 6GHz, as long as you have an LO which can deliver -5dBm or more up to 5GHz.(Note: I measured the output of the Morfeus, and it does struggle to deliver more than -5dBm over most of its range.At its max frequency of 5.4GHz it is down around -9 dBm and that isn't enough to drive this mixer properly.)I also took the top off the Morfeus and it has one of these in it:https://www.qorvo.com/products/p/RFFC5072Datasheet:https://www.qorvo.com/products/d/da000735