Topics

SNA or VNA up 2.4Ghz

iz oos
 

Hi folks, so far I have been impressed by Antuino! It is really a cool tool! I could tune some filters much better than before, FM broadcasts notches, a 2m mag loop, and even a helical filter on 432Mhz. I wish something similar for UHF, I mean in the range 430mhz to 2.4ghz. I have seen 50usd nanoVNA up to 1ghz. Is it there something similar up to 2.4ghz not costing a leg?

Ashhar Farhan
 

Unfortunately, nothing really. The trick lies in getting a stable pll that goes that high. 
A spectrum analyzer at 2.4 ghz will need an IF of 3.6 ghz. The vco will have to span 3.6.ghz to 6 ghz with better than 1 ppm stability! The rest can be ordered from mouser.
- f

On Tue 29 Oct, 2019, 3:53 PM iz oos, <and2oosiz2@...> wrote:

Hi folks, so far I have been impressed by Antuino! It is really a cool tool! I could tune some filters much better than before, FM broadcasts notches, a 2m mag loop, and even a helical filter on 432Mhz. I wish something similar for UHF, I mean in the range 430mhz to 2.4ghz. I have seen 50usd nanoVNA up to 1ghz. Is it there something similar up to 2.4ghz not costing a leg?

Marcus Gustafsson
 

Erik has done a lot of great work in that area, check out https://groups.io/g/HBTE/message/388 for instance.

Br
Marcus

Ismo Väänänen OH2FTG
 

MAX2870 from Maxim has the same footprint as ADF4351, but goes from 23.5MHz to 6000MHz. 
Unfortunately optimal layout for either requires a 4-layer board.
For example, all of the black eBay adf4351 I have measured have significant sidebands at +-2x reference frequency due to the sub-optimal two layer board layout. 
Still delightfully cheap and very usable for many things.

Another problem with a wide band spectrum analyzer would be the expensive first mixer and the expensive or annoying to design first IF filter.

All that just means that while doable, it would not be 100usd/pcs for the first revisions. 

One cheap adf based example are the ~50usd 137-4400MHz "simple spectrum analyzer" on ebay end aliexpress. Cheap active mixer as frontend and the IF problem dealt with by using a fixed lowpass filter at the mixer output.
Essentially making it a direct conversion receiver with around 300kHz IF bandwidth. 
The IF is then fed to an ad8307 logamp we know and love.

Ashhar Farhan
 

Interesting observation, ismo,
An individual constructor has some advantage over the commercial builders here, one can get by with cavity and other kinds of strip line filters that are unsuitable for commercial production.
Yet another avenue is to programmatically remove mirror images from readings using software hacks rather than complex frequency manipulations.
On the other hand, it is feasible to build a high quality spectrum analyzer at home. I built one for the HF range. You will find it on the net. The Antuino is a cut down version of that idea.
Wes, W7ZOI's two part article published on the QST and available from his site are a huge wealth of information.
- f
73, f

On Wed 30 Oct, 2019, 11:40 AM Ismo Väänänen OH2FTG, <ismo.vaananen@...> wrote:
MAX2870 from Maxim has the same footprint as ADF4351, but goes from 23.5MHz to 6000MHz. 
Unfortunately optimal layout for either requires a 4-layer board.
For example, all of the black eBay adf4351 I have measured have significant sidebands at +-2x reference frequency due to the sub-optimal two layer board layout. 
Still delightfully cheap and very usable for many things.

Another problem with a wide band spectrum analyzer would be the expensive first mixer and the expensive or annoying to design first IF filter.

All that just means that while doable, it would not be 100usd/pcs for the first revisions. 

One cheap adf based example are the ~50usd 137-4400MHz "simple spectrum analyzer" on ebay end aliexpress. Cheap active mixer as frontend and the IF problem dealt with by using a fixed lowpass filter at the mixer output.
Essentially making it a direct conversion receiver with around 300kHz IF bandwidth. 
The IF is then fed to an ad8307 logamp we know and love.

erik@...
 

This is what I build

https://groups.io/g/nanovna-users/message/4344

Combined 35mHz to 3GHz VNA  and 0-2GHz SA 
The 2.016GHz cavity filter proved to be simpler to build then expected. I learned some nice tuning tricks
The stiched FFT RBW filters where fun to program
The resistive bridge is the limiting factor in the VNA