Electronics > RF, Microwave, Ham Radio
making my own antenna analyzer
djacobow:
I'm thinking of building my own simple antenna analyzer. There are some examples out there, like the K6BEZ example and its variations. They use an AD9850 module or similar as a signal source and a SWR bridge and a diode detector. It sounds, though, like the diodes are operating right at the beginning of their conduction, so the response is nonlinear and not so good. One variation uses an AD8307 or similar to function as a detector instead. The AD I would use would be the standard 8-10-12 bitter available on a cheap MCU.
I'm pretty new to RF. What are the gotchas I need to worry about in making a half-decent instrument? Do I have to do anything special with the impedance of the antenna traces? I'm guessing no since the distances on the board are small fractions of the HF wavelengths I want to work with.
What else can go wrong?
I believe the AD9850 has a sine wave output, but some other parts that can go faster (SiLabs 54xx) generate a square wave. I'm correct in assuming that the harmonics will have different SWRs and so they will just mess up a the reading. In that case, I'll need an array of filters and the ability to switch between them depending on the band. That seems like a fair bit of extra complexity I'd like to avoid if I can.
-- dave j
Theboel:
--- Quote from: djacobow on December 05, 2016, 04:07:11 am ---
I'm thinking of building my own simple antenna analyzer. There are some examples out there, like the K6BEZ example and its variations. They use an AD9850 module or similar as a signal source and a SWR bridge and a diode detector. It sounds, though, like the diodes are operating right at the beginning of their conduction, so the response is nonlinear and not so good. One variation uses an AD8307 or similar to function as a detector instead. The AD I would use would be the standard 8-10-12 bitter available on a cheap MCU.
I'm pretty new to RF. What are the gotchas I need to worry about in making a half-decent instrument? Do I have to do anything special with the impedance of the antenna traces? I'm guessing no since the distances on the board are small fractions of the HF wavelengths I want to work with.
What else can go wrong?
I believe the AD9850 has a sine wave output, but some other parts that can go faster (SiLabs 54xx) generate a square wave. I'm correct in assuming that the harmonics will have different SWRs and so they will just mess up a the reading. In that case, I'll need an array of filters and the ability to switch between them depending on the band. That seems like a fair bit of extra complexity I'd like to avoid if I can.
-- dave j
--- End quote ---
Hi Dave,
Nothing wrong with Your plan, depent with your requirement. but there is a "mature" project in HF range (0-60Mhz) in "kits" version or DIY if You insist
or ready for use up to UHF range.
N2PK
www.makarov.ca
VNWA
www.sdr-kits.net
"something more conventional"
http://www.changpuak.ch/electronics/Arduino-Shield-TOBI.php
VNWA
VK5RC:
Have you seen the VK5JST analyser? http://www.ahars.com.au/about/kits/
I think the construction notes also contain a theory of operation. If I recall correctly a lot went into getting the oscillator to be very constant output across the frequencies.
Towger:
K6BEZ has designed a new version in conjunction with the Ham Radio 360 podcast. He was on it a few weeks ago talking about the design and the possibility of increasing its range up to cover the 2m band. I have also seen a 3rd party version which used a graphical display rather than the two line lcd which would be an interesting improvement.
Bud:
You need to understand that power detector ICs are wide band, and will sum together all of the power at their inputs, so the output will have a sum of the signals you measure (your DDS) and everything else that makes its way to the detector input. Basically that means your measurements will be off depending on the ratio of the useful and stray power. It is one''s guess by how much and will depend on a particular environment. You could mitigate the issue by using an LPF at the detector input. This is often overlooked in simple designs. Tuned detectors do not have that problem.
Navigation
[0] Message Index
[#] Next page
Go to full version