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Hi,

I'm quite new to the topic. I learned a lot about the bad design of commonly available antennas and have modified quite a number since then with the help of the Nano.

From what I understand, a VNA is also a receiver (of its own signals). Is there a way to use it like a "scanner"? I do occasionally have to deal with Chinese HF transmitter setups, that only say "UHF" or "VHF" but do not specify the frequency. Normally I go to the company's testlab and have it checked for me.

Is there any practical way to use the NanonVNA for that purpose?

Thomas

Read here:
/g/nanovna-users/topic/34079496#2165

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Erik, PD0EK

Is there a way to use it like a "scanner"?

Yes, CH1 is a receiver that looks for signals at the frequency (or harmonic) of CH0.
Keep in mind that nanoVNA steps, rather than sweeps,
so that if set for a wide span will probably miss a narrow bandwidth signal.

NanoVNA has receiver, but it cannot digitize receiver output with enough bandwidth to listen AM or SSB radio. You can try to connect your PC soundcard to SA602 outputs and use HDSDR to listen radio, but there is no low pass filter, so you will get a lot of images. And such modification will ruin VNA functions.

The NanoVNA, and most VNA's in general, use the fact they know their transmitted excitation frequency and its harmonics to pick out the desired receive signal to simplify the circuitry.

The RF synthesizer generates two different frequencies separated by a few KHz's. One provides the transmitted test excitation frequency (along with its harmonics) and one provides the local oscillator for its mixer down conversions. The down conversion output is the difference frequency of a few KHz's. As a receiver this mixing will down convert based on difference of the Tx RF excitation and the mixer local oscillator frequency. There is no RF filtering for down conversion image rejection as it does not need it because it knows the expected Rx frequency. This is the first issue for using it as a general receiver.

It can pick out particular harmonics by adjusting the down converter mixer local oscillator frequency slightly relative to the Tx excitation frequency so the difference down conversion frequency is always in the same low (KHz) frequency range. The measurements of relative amplitude and phase are made at the low down converted frequency signal. The narrow bandwidth of the down conversion improves the ability to measurement of the desired signal but limits the use as a general receiver.

Software Defined Radio (SDR) receivers use a direct conversion mixer also known as zero intermediate frequency down conversion. It actually consists of two down conversion mixers that are given local oscillator signals that are exactly 90 degrees out of phase. This produces two outputs that are called 'I' channel ( In phase) and 'Q' channel (quadrature phase) signals that can be mathematically manipulated to recover all types of signal modulation methods. The I and Q channels are also known as baseband signals which are ADC digitized and are low pass filtered to half the desired RF receive bandwidth. The SDR method could be used for VNA measurements but it would be overkill complexity. Modern spectrum analyzers use this method and some also provide VNA capability within the same unit.

Thanks for your comments! Based on these I was able to verify this functionality. There are two issues:

the bandwidth of a typical FM signal
the low sensitivity if the Ch1 input

With only 101 points on the display you have to look quite thoroughly for a 100kHz wide signal in a 50kHz — 900MHz scan. It is physically impossible to see. Only when I use 5MHz scan steps you can clearly see the signal. With only ?VHF“ given as frequency indication that required a lot of runs from 100 to 350MHz. I did find the signal from that wireless microphone at 251.6MHz.

In addition you had to hold that micro quite close to the antenna to make the nano register the signal. Supposedly it transmits with some 10mW which should be plenty of signal in a distance of 1 cm from the receiving antenna.

Regards

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ThomasR

Greetings Thomas,
Your best solution for a low-cost scanner is the RTL-SDR dongle, and some scanning software.
The best one (currently) is the RTL-SDR.COM V3, ($23) which has a very good TCXO, software-switchable direct-sampling mode (for freq range DC- 25MHz), input protection (diodes), aluminum case, and SMA input. It will receive in bandwidths up to about 2.56MHz, and there is software that'll step it along, so you can cover a sweep from 25-1800MHz pretty fast.
The only down-side is that rtl-sdr dongles have no bandpass filtering and will show spurious signals, so you just need to keep its RF gain set low enough that they disappear. They are greatly improved with addition of notch filters for AM and FM broadcast bands (~$10-20 each).
For (free) software, SDR# ("SDR Sharp") is probably the most popular, with many plug-ins, including a full-featured scanner plug-in. There is also software that'll step it along and generate RF heat maps.
I'm not advertising for them, but I know what works... I use mine as a "poor man's" spectrum analyzer and freq counter, and after software calibration to a freq standard, it works quite well.
Don't get a cheap plastic DVR-B dongle; they have terrible oscillator that wanders around all over the place.
73, --kv5r