This article describes an add-on to a MFJ-993B auto ATU to provide an audible alarm when reflected power exceeds a set threshold. A deficiency of the original design IMHO.
The solution uses the generic heating / cooling controller (hcctl) configured for its alarm function only, including a function to silence the alarm.
Above is the directional coupler part of the MFJ-993B. The REF test point is designed to present voltages within the range 0-5V when used within the stated power ratings. Continue reading Reflected power alarm for the MFJ-993B
This article describes my build of a Radio-Kits SWR meter (v1.1) and post implementation review.
- HF coverage – 1.8-30MHz
- Displays VSWR, forward power, reverse power and supply voltage
- Peak reading power meter
- Bar graph or numerical format
- Reverse power alarm with adjustable threshold
- Auto turn on in presence of RF – sensitivity about 1 watt
- Optional turn off after preset time – 10-240 seconds
- Backlit LCD display with variable brightness
- Reverse polarity protection
I purchased the kit some years ago, and on receiving it and reviewing the circuit I formed the view that it was likely to have unacceptable Insertion VSWR on 1.8Mhz, and probably 3.5MHz bands… so I lost interest in assembling the kit. However, I have belatedly constructed the kit, calibrated and tested it.
The kit is supplied as a PCB and parts, no casework is supplied.
The board was difficult to solder, the strain relieved ground plane connections of components have very little donut to contact for heat transfer and are much harder to solder than the other pads. The strain relief is a dubious feature that makes soldering difficult.
Above, the kit assembled in a die-cast aluminium box. An opening for the LCD was milled into the box, and holes drilled for the rest of the fit up. The kit does not lend itself to this boxing as the buttons out the top and display out the front are a problem to fit up. A poor mechanical design.
Above is the interior of the box showing the LCD display and the external BNC connectors fitted (substituted for the ubiquitous UHF connectors supplied with the kit). Continue reading Radio-Kits SWR meter – build and review
The term Effective Radiated Power or ERP appears frequently in ham discussions, antenna literature and regulatory documents. Continue reading Effective Radiated Power (ERP)