Tuning of ceramic antenna circuit without spectrum analyzer - Page 1
Forum section: electronics / beginners

author: miduchp
author_rank: Contributor
timestamp: July 17, 2017, 06:35:59 am
content: Hello,I'm working on devices based on Atmel micro controllers and HopeRF RFM69HW 433MHz radios. I've build couple of prototypes, now I've started to work on PCB for those devices. I would like to make them as small as possible.Major issue I'm having right now is the antenna. I wanted to use one of such antennashttps://www.johansontechnology.com/datasheets/antennas/0433AT62A0020.pdf.Are there any alternative ways to tune antenna circuit without spectrum analyzers (which are totally out of range due to it's prices) ?Thanks for help in advance.

author: Jeroen3
author_rank: Super Contributor
timestamp: July 17, 2017, 08:02:38 am
content: Aretheseout of budget as well?I bought a used one on eBay some time ago. Are they accurate enough?

author: miduchp
author_rank: Contributor
timestamp: July 17, 2017, 10:48:53 am
content: If I understand correctly, In order to tune the antenna you need to perform VSWR measurementhttp://j3.rf-explorer.com/43-rfe/how-to/139-sna-how-to-measuring-reflection-return-loss. In order to do this I would need to buy:- RF Explorer Signal Generator RFE6GEN- RF Explorer Spectrum Analyzer model for the required frequency- Directional coupler (Mini-Circuits ZHDC-10-63-S+)This in total still gives summary of around 500 USD which is way over my budget.Is there any other way to achieve this ? Can oscilloscope be used somehow to achieve the same results ?

author: miduchp
author_rank: Contributor
timestamp: July 17, 2017, 11:02:55 am
content: I've just spotted that i could use cheaper directional coupler. In total that would cost around 350 USD. Still a lot, but looks like an acceptable proposal.

author: Jeroen3
author_rank: Super Contributor
timestamp: July 17, 2017, 11:14:07 am
content: There are other SDR's around you can use. Your base frequency isn't that high.Likethese. But you'll go lower in specs and functionality with lower price, as you'd expect.Perhaps there are other ways to tune an antenna without expensive kit. The amateur radio fanatics here should be able to help you with that.(wait a day, timezones)

author: mikerj
author_rank: Super Contributor
timestamp: July 17, 2017, 12:18:53 pm
content: You could use a simple field strength meter to tune an antenna, provided you take care to make measurement conditions repeatable.

author: dmills
author_rank: Super Contributor
timestamp: July 17, 2017, 05:24:35 pm
content: A signal generator, a directional coupler and something to measure the power on the reflected port would seem to me to get her done, it is scalar rather then vector analysis, but we have lived with that for years in the ham world.Maybe one of those AD log amps (You can these on little boards with SMA connectors on ebay? Search on the AD8318), as a detector, about £10.A directional coupler can be a handful of resistors and a carefully wound balun on a small ferrite ring, or another little £10 board from ebay, not going to be great, but it would serve.You will need to make up a board with just the antenna and matching network terminated to a suitable connector (Probably SMA?) but otherwise having exactly the geometry you intend to use.Which just leaves the signal gen,you only need a few mW but it is helpful if the output impedance is reasonably close to 50 ohms.73 Dan.

author: miduchp
author_rank: Contributor
timestamp: July 18, 2017, 06:22:21 am
content: Quote from: Jeroen3 on July 17, 2017, 11:14:07 amThese seems to a good way to go!I found sample setup using on:-Airspy170 USD-Simple tracking source15 USD-SWR Bridge30 USDIn total this should close in 210 USD max, which is quite ok.What do you think about this setup ?

author: CJay
author_rank: Super Contributor
timestamp: July 18, 2017, 06:48:32 am
content: You've already got a signal source, those Hope modules will provide 100mW, that's plenty.So, a Pasternack directional coupler like this:https://www.ebay.co.uk/i/282442511097?chn=ps&dispItem=1&adgroupid=13585920426&rlsatarget=aud-295856144804%3Apla-142405569186&abcId=&adtype=pla&merchantid=114999362&poi=&googleloc=1006473&device=c&campaignid=207297426&crdt=0(Yes, I know the lower spec is 500MHz, but I'd be very surprised if it didn't produce useable results at 433MHz)and a log detector like this:https://www.ebay.co.uk/i/142407369388?chn=ps&dispItem=1&adgroupid=13585920426&rlsatarget=aud-295856144804%3Apla-142405610226&abcId=&adtype=pla&merchantid=115144912&poi=&googleloc=1006473&device=c&campaignid=207297426&crdt=0All for under $50