Hello Audrius Merfeldas ,

Please, excuse my ignorance, but I do not see the relative motion between the source (transmitter) and the observer (receiver). Can you explain, for the RG readers, physically how the relative motion arises? For example, your 433 MHz CW signal, where is it coming from? Is it located on a moving transmitter, i.e., moving with respect to the four receiver antennas? Or is the transmitter stationary, but the target reflecting the signal from the transmitter is moving? I am assuming that the four receiving antennas are mounted on a stationary disk. Do you have a drawing showing the transmitter, receiver(s), and the moving target - if there is one?

Since you stated that your equipment is a direction finder, I suppose that the transmitter is at some fixed distance from the four receiver aerials on the disk. But electronically switching in or out these fixed receiving antennas does not look like relative motion to me, at least not to my understanding of the term 'relative motion'.

Regards,

Thomas Cuff

Dear Thomas,

Pseudo Doppler direction finder is a technique that imitates antenna rotation by rapidly switching between circularly arranged antennas. Commonly 4 antennas up to way much more. The structure often looks like https://www.everythingrf.com/news/details/4085-Europe-s-New-ATC-Radio-Direction-Finder-System-is-Based-on-Products-from-R-S

In my setup I have both stationary antennas, but "pseudo" motion should appear due to switching between antennas that physically are stationary, but while switched appears to be moved.

Hi Audrius Merfeldas ,

I did not find the link you mentioned to be very helpful, so I went in search of original source materials. I first tried Wikipedia: https://en.wikipedia.org/wiki/Doppler_radio_direction_finding . Their explanation of how pseudo-Doppler DF worked was that the technique used phase differences. They also referenced a 1987 book [1], which also mentioned on p. 122 that the technique, pseudo-Doppler DF, was also called "sequential phase" DF. Chapter 9 of this book shows one how to actually build such a DF, and it mentions a number of pitfalls when trying to get such a circuit to work: 1) multipath (p. 136), and 2) grounding of the non-active antennas (the non-active antennas must float, electrically, if they are grounded they tend to reradiate the incoming signal, see p. 130).

[1] also referenced a 1981 article by David C. Cunningham on designing and building a pseudo-Doppler DF, see [2]. The article also mentioned that Cunningham had patented his design. I looked up his US patent (granted on Novmeber 5, 1985), US Patent No. 4,551,727, on the following URL: https://ppubs.uspto.gov/pubwebapp/static/pages/ppubsbasic.html To obtain a PDF of a US patent, simply enter the patent number, without its commas, in the "Quick lookup" field at the top of the page, the link to the patent will appear in the list at the bottom of the page. Cunningham's patent cites the June 28, 1941 US patent, US Patent No. 2,414,798, by Horace T. Budenbom showing the rotating antenna DF - the word 'Doppler' was not used. The antenna at the edge of the rotating disk phase modulates the incoming signal. Cunningham's patent also cites the 1947 article discussing the square array of electronically commutated aerials [3], notice the title of this article.

[1] Joseph D. Moell, Thomas N. Curlee; Transmitter Hunting, Radio Direction Finding Simplified; TAB Books; 1987; see Chapter 9 Doppler DF Units, pp. 120-141; URL: https://archive.org/details/curlee-t.-n.-moell-j.-d.-transmitter-hunting-radio-direction-finding-simplified-1987-tab-books

[2] David Cunningham; DF Breakthrough!; 73 Magazine; Vol ...; No. ...; June 1981; pp. 32-46; URL: https://archive.org/details/73-magazine-1981-06

[3] C. W. Earp, R. M. Godfrey; Radio direction-finding by the cyclical differential measurement of phase; Journal of the Institution of Electrical Engineers, Part IIIA: Radiocommunication; Vol. 94; No. 15; March-April 1947; pp. 705-721.

Regards,

Thomas Cuff