[hfsig] Antenna analyzer kit

Tue Mar 26 09:06:39 EDT 2019

Bruce, 

I got the picture in both versions of the email.

Ricardo

From: hfsig <hfsig-bounces at lists.tapr.org> On Behalf Of Bruce Raymond
Sent: Tuesday, March 26, 2019 8:41 AM
To: TAPR HF Modes SIG Mailing List <hfsig at lists.tapr.org>
Subject: Re: [hfsig] Antenna analyzer kit

Hi Guys,

I've not seen the picture of the prototype show up in my email, so I'm assuming that it's been chopped out. Here's a link to the file on a very crude server I put together that has the picture.

http://bnrstuff.duckdns.org/AntennaAnalyzerPrototype.png

I know there must be cloud stuff out there to share pictures and I've been using Dropbox for many years. I just haven't figured out how to send the picture without using everyone's email address (which I don't have). 

73 Bruce

Bruce Raymond wrote on 3/25/2019 4:20 PM:

Hi Guys, 

I ran into trouble with email size on the last blast-o-gram. I don't know if the picture came through, so I'll send the email again with a much lower resolution picture. Please ignore this email if the previous email made it through. 

Again, any and all feedback is welcome. 

73 Bruce/ND8I 

Bruce Raymond wrote on 3/24/2019 9:52 PM: 

Hi Ed and Ricardo, 

Thanks for the feedback. Much appreciated. 

My concept for the antenna analyzer is to combine an Arduino (computer), Si5351a board (oscillator, frequency set by the Arduino) and an LCD diisplay. The oscillator drives a simple resistor bridge with the antenna as one of the legs of the bridge. I'm using an AD8307 log amp to measure the voltage across the bridge. I've attached a picture of the prototype analyzer. 

The idea is to sweep a range of frequencies to find the resonant point and calculate and display the VSWR at that frequency. 

Initially I thought that I could also measure the bandwidth where the VSWR of the antenna is 2:1 or less. I wasn't able to get that to work. After some reflection I realized that there are reactive components once you get away from resonance that make measuring VSWR impossible with a resistive bridge. 

I've tried to keep the operation simple. After turning the power on, you turn the knob (rotary encoder) to set the center frequency of the sweep; that's shown as "IN:" in the photo. Each click of the knob changes the frequency by 1 MHz. Then analyzer sweeps from 0.5 - 1.5 times the center frequency. In the case shown (center frequency = 12 MHz), the analyzer sweeps from 6 MHz - 18 MHz. After you set the center frequency you push the knob to start the sweep. It's fairly quick - takes about 2 sec to do a sweep. The analyzer should work over a frequency range of 1-30 MHz. It's possible that the range can be expanded. 

My objective was to make something that's portable and relatively cheap, sorta trading accuracy for money. I think it will be accurate within 5%-10%. Actually, the frequency measurement seems to be accurate within 10 KHz and the SWR within ~0.1 at resonance. 

This is an open source project, so I'm planning on releasing the source code into the wild. I'm planning on shipping an preprogrammed ProMini with the kit so that you don't have to do any programming or loading of software. 

I have two AD8307 chips in the design. These are smd chips that I'm going to have presoldered to the pcb so the builder doesn't have to do that. Everything else is through hole/parts with leads. There are a couple of other smd chips shown on the prototype. These were part of another project (mag loop autotuner) and not part of the antenna analyzer. 

I'm planning on having the analyzer available to show at Hamvention/Dayton in May and have kits available through TAPR hopefully in July - if I can get the documentation ready  ;-) 

I'm interested in everybody's thoughts and comments. Any and all feedback is welcome. 

73 Bruce/ND8I 

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