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Fox Delta is a group of people formed a few years ago by Dinesh VU2FD. It deals with the development of kits for amateur radio needs. The entire documentation is available on the website so everyone can be inspired or build a kit from their own parts. The prices are really affordable, the selection is interesting, and those who are not quite skilled in assembling kits can order a finished product for an additional fee.
LCD SWR Meter with PIC16F877A
Jednou z ponúkaných stavebníc je aj dvojkanálový LCD SWR Meter s PIC16F877A. Autormi projektu sú Antonio I2TZK, Frank K7SFN a Dinesh VU2FD. Umožňuje meranie výkonu, odrazeného výkonu a PSV in the range determined by the sensor (HF/144MHz, 1-100W, 10-2000W). The measured data is displayed on a two-line LCD display or on a computer connected via a serial port (SWM3 version via USB).
I ordered and paid for the kit over the internet, and in about a week, I already had the package at home. The price was approx. 83EUR: SWM2 + Dual scale bridge sensor + shipping. And it could be assembled...
First impressions of the SWM2 kit
The first impression of the kit is greatly affected by the mechanical design of the boxes. Senzorová krabička má po hranách krytu medzery, rovnako pri konektoroch a hlavná krabička má pomerne veľké diery na LED, tlačidlá a konektory. Aj biela farba viac pristane kuchynským spotrebičom ako rádioamatérskemu zariadeniu. Toto som vyriešil čiernym sprejom a gumenými priechodkami a výsledok vyzerá lepšie. Senzor je možné umiestniť mimo dohľad alebo vyrobiť si vlastnú krabičku.
The dual-range KV sensor best suited my requirements. It is a classic PSV bridge with toroid and range-switched relays. Linearization is achieved by introducing diode bias. In principle, any design of a measuring sensor can be used.
Mounting the PCB is relatively simple, plôšky sú dostatočne veľké a tak sa spájkuje ľahko. Najprácnejšie je tak navinutie toroidu. V dokumentácii však chýba údaj o počte závitov! Skúmaním fotografií senzorov som odhadol počet závitov na 25, čo je pomerne reálne číslo. Toroidom prechádza kúsok tenkého teflonového koaxiálu. Výrobca síce deklaruje rozsah až 2kW, ale nie som si istý, či je to reálne.
Assembling the main PCB is also simple. Just follow the proven assembly procedure - from the smallest components to the largest, finally installing transistors and IO. Two smaller boards - display and control + LED - are connected to the main PCB via flat connecting cables with connectors.
The most interesting moment in devices assembled by hand is the first power-up. SWM2 started up, the display lit up after connecting the power supply. Adjusting the contrast on the main PCB with a trimmer was enough to prepare SWM2 for calibration. Calibration is described in the documentation and is similar to a standard PSV meter.
Screen remote station including power measurement and PSV software I2TZK
Connecting SWR Meter with PIC16F877A to PC
An interesting feature is the connection to a PC. To umožňuje zaznamenávať (logovať) namerané údaje pre ďalšie spracovanie a samozrejme zobrazenie aktuálne nameraných údajov na virtuálnych meracích prístrojoch (jednoručičkový, dvojručičkový či digitálny bargraf). Ukážkové video si môžete pozrieť na www.youtube.com
This function can also be used for a remote station, where the serial port is "extended" via LAN or the internet.
Calibration
Calibration is described in the document available on the FoxDelta website. There seem to be quite a few steps, but the setup is quick and takes only a few minutes. I did not verify the measurement accuracy, but it is likely determined mainly by the sensor (frequency dependency). When compared to the wattmeter built into the transceiver, I did not notice any deviation on any band.
Summary
The LCD SWR Meter FoxDelta is a useful addition to a ham shack for radio amateurs and, if one overlooks the construction, it offers features of meters that are several times more expensive. Even a not very technically skilled HAM can handle assembly from a kit.