[hfsig] Antenna analyzer kit

Bruce Raymond bruce at raymondtech.net
Tue Mar 26 08:41:27 EDT 2019

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.


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 

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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