### Welcome to our site!

#### Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Status
Not open for further replies.

#### bowser22

##### Member
Hi guys, i'm trying to construct this **broken link removed** as a proof of concept for spoofing radar guns. problem is i only know very little about microwave transceivers. In the article he modulates the output frequency using a varactor bias tuning pin on his transceiver, but most transceivers ive looked at dont have this. is there some other way to modulate the frequency in hertz?

#### jimlovell777

##### New Member
I think the linked project would qualify as the proof of concept. Depending on your country LASER might be the more prominent speed detection method, just something to keep in mind.

#### bowser22

##### Member
its mostly k band here, they only use lidar for stopped highway speed checks

#### bowser22

##### Member
well i wanna build it to spoof police radar lol i dont care ab a proof of concept i just thot i might get flamed regarding the legality

#### Hero999

##### Banned
well i wanna build it to spoof police radar lol i dont care ab a proof of concept i just thot i might get flamed regarding the legality

And rightly so, it's illegal and help with breaking the law is against the forum rules.

#### RCinFLA

##### Well-Known Member
There was an article and circuit in Popular Electronics magazine about 30 years ago. It just used a diode modulator in a resonate cavity with horn antenna. The incoming radar gun signal was received and modulated with an audio tone to match the desired doppler carrier frequency shift. It caused the radar gun to read out the speed corresponding to the modulated tone. There was no transmitter, per say, just a modification of reflected signal.

#### Ross Craney

##### New Member
Back in the early 70's when I was doing electronic engineering there was a fellow student who made a gunn diode microwave transmitter that transmitted a freq with doppler shift equivelent to 250kph. He mounted it in a driving light using the parabolic reflector & attached it to his morris minor van.

#### bowser22

##### Member
ive noticed it says "Since not all Gunnplexer's have varactor tuning/modulation pins, you may have to apply the audio modulation directly to the Gunnplexer's Gunn diode bias line. This method, and schematic, are shown in the various older copies (when it was good) of the ARRL's Handbook for the Radio Amateur, so it won't be covered here.
" can anyone explain how this method works or a basic schem.

#### RCinFLA

##### Well-Known Member
Just FYI, a gunnplexer will not likely do anything to a police radar gun.

#### bowser22

##### Member
i beg to differ, as much knowledge of radar i dont have i wouldnt doubt for a second that it could effect a police radar gun

#### RCinFLA

##### Well-Known Member
Suggest you put one together and test it by speeding through a known radar speed trap. A negative experience can be an indelible learning exercise. (just joking)

You might want to find answers to these questions.

1) what is the minimum and maximum RF freq a given police radar unit may be tuned at.

2) what is the maximum doppler shift for the highest tuned RF frequency range for, say, 120 mph.

3) what would be the police radar's demod low pass filter frequency corner to get best receive sensitivity based on highest doppler beat frequency needed.

4) what would be the approximate interference bandwidth based on this low pass filter.

5) what is the freq stability of a free running cavity tuned gunn diode oscillator.

Last edited:

#### atferrari

##### Well-Known Member
From my limited understanding of current technologies, I can say that any single design using just one frequency is doomed.

Just in case Google for articles showing the las developments that overcome that kind of cheating. I am affraid that your learning experience, if applied in the roads, would cost you dearly in terms of \$ and time behind the bars.

The way I understand it, you could cause interference but just sitting at a fixed point near the road. In motion they will beat you.

Do something else or choose to travel in a big country with long extensions of land with nobody there.

Locally, we have some places where the road was built in a straight line for more than 50 Km.

Speeding there has a different problem than what you could expect: no fines but falling asleep. It happens. Believe me.

Added bonuses: no mobile phone coverage and not so much people in dark hours. And there is winter too...

Last edited:

#### bowser22

##### Member
what do i need to measure the exact frequency coming from a gunnplexer?

Status
Not open for further replies.

Replies
1
Views
923
Replies
8
Views
1K
Replies
5
Views
2K
Replies
2
Views
1K
Replies
6
Views
1K