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Portable Vertical Antenna for 75m and 40m featuring Low radiation angle for DX, easy to install and to match 50 ohms

Constructing a Lindenblad antenna for 137MHz NOAA satellite reception involves specific design considerations for optimal performance. The resource details the use of 4mm galvanised steel fencing wire, 300-ohm television ribbon cable, and wood/plastic components for the antenna structure. Key dimensions for a 137.58MHz-resonant antenna are provided, derived from the ARRL Satellite Handbook, specifying s, l, w, and d as 42, 926, 893, and 654mm respectively. The antenna is designed for Right Hand Circularly Polarised (RHCP) signals, requiring the four folded dipole elements to be tilted clockwise by 30 degrees. A significant aspect covered is impedance matching between the antenna's 75-ohm impedance and a typical 50-ohm receiver input. A twelfth-wave matching transformer, constructed from 117mm sections of 50-ohm RG-58 and 75-ohm RG-59 coax with a 0.66 velocity factor, is described. The article also addresses coaxial cable and connector selection, recommending 75-ohm Type-N connectors for RG-6 cable in professional setups and F56/F59 connectors for general use, while strongly advising against PL-259/SO-259 connectors for VHF. Strategies for mitigating Radio Frequency Interference (RFI) are discussed, including antenna placement to shield from local TV transmitters and the use of commercial or DIY band-pass filters, such as cavity resonators or helical notch filters, along with ferrite chokes on coaxial cables. Antenna orientation is explored, noting the Lindenblad's 'cone of silence' directly overhead and its maximized sensitivity towards the horizon. An experimental vertical tilt of 90 degrees is presented as a method to improve overhead reception and reduce interference from strong horizontal signals, particularly relevant in high RFI environments like the Siding Spring Observatory site.

Presents a detailed construction guide for a **Quadrifilar Helix Antenna** (QHA) optimized for 137 MHz, specifically for receiving weather satellite transmissions. The resource outlines the author's experience building previous QHA designs, highlighting challenges with tuning and nulls, and then focuses on a refined design by John Boyer, documented by Steve Blackmore, which proved easier to build and yielded superior reception. The guide provides precise element dimensions, including 1.5m of 32mm PVC pipe for the mast and 8mm soft copper tubing for the helix elements. It specifies lengths for horizontal tubes (190mm, 90mm) and helix elements (903mm, 1002mm), along with instructions for drilling, assembly, and forming a **balun** by wrapping RG58 coax around the mast. The text emphasizes critical steps like ensuring elements are square and twisting in the correct direction to avoid phase issues. It includes references to original QST articles by Buck Ruperto (W3KH) and the WxSat program for decoding satellite transmissions, contextualizing the antenna's purpose. The article concludes with a sample NOAA 12 image from September 1998, demonstrating the antenna's reception capabilities.

Operating on the 2200m band (135.7-137.8 kHz) often presents challenges for amateur radio transceivers, which typically exhibit poor receiver performance at these very low frequencies. This project addresses the issue by providing a design for a dedicated 137 kHz antenna preamplifier, specifically tailored to improve signal reception for radios such as the _Yaesu FT-817_. The preamplifier circuit utilizes a low-noise FET input stage, crucial for minimizing self-generated noise and maximizing the signal-to-noise ratio from weak LF signals. The design includes a detailed schematic, component values, and construction notes, enabling homebrewers to build a functional unit. The goal is to achieve significant gain, making the faint signals on 2200m more discernible and improving overall band usability. Key design considerations include impedance matching to typical antenna systems and ensuring stable operation across the narrow LF segment. The circuit aims for a **low noise figure** and sufficient amplification to overcome the inherent limitations of general-purpose HF transceivers when operating below **200 kHz**.

Article describing how to homebrew a yagi antenna for 50 MHz, includes plans for a four and five elements yagi beam and details how how match impedence with a gamma match

137 kHz propagation analysis details ground wave and sky wave mechanisms, drawing heavily from **CCIR Rec. 368-6** for ground wave field strength predictions and **CCIR Rep. 265-7** for sky wave modeling. The resource presents field strength values for 1 W ERP at varying distances, considering ground conductivity and permittivity for ground wave, and ionospheric height (70km daytime, 90km nighttime) for sky wave. Key factors like ionospheric focusing (factor "D"), reflection coefficient ("RC"), and antenna ground pattern factors ("Ft", "Fr") are quantified for 137 kHz, enabling calculation of sky wave field strength. Practical coverage ranges are derived for 137 kHz, showing useful ground wave coverage up to 1600 km over seawater and 1100 km over average ground, assuming a -9 dBuV/m noise floor. Sky wave coverage extends beyond 2200 km during night-time and winter daytime, but is negligible during summer daytime at solar minimum. The document also compares ground wave and sky wave strengths, identifying crossover distances at 550 km (night-time), 750 km (winter daytime), and 1250 km (summer daytime), where interference fading can occur. Adjustments for solar maximum conditions are provided, indicating 2-11 dB higher sky wave values depending on distance and season.

A monoband delta loop antenna for the 7 MHz. This vertically polarized DX Antenna is a full wavelength sngle side antenna and has a total length of 42.3 meters (137,1 inch) Can be easily setup with a flag pole or fishing pole as center top mast. For optimal performance lower side should be at 2 meter above the ground. This antenna offers a low radiation angle and 1 DB Gain.

DF0WD/DL4YHF's Longwave Overview details amateur radio operations on the 135.7 to 137.8 kHz segment in Germany. The author outlines the "inofficial" European band plan, specifying segments for QRSS, TX tests, beacons, conventional CW, and data modes. Early LF activities at DF0WD began with a 20-watt CW transmitter, later upgraded to a homemade linear transverter capable of 100 watts, driven by an Icom IC706 on 10.137 MHz. The station's antenna system includes a 200-meter wire, approximately 10 meters above ground, supported by football field light-masts. Despite its length, the antenna's efficiency is noted as very low due to the immense wavelength of about 2.2 km. The author's experience highlights the significant challenge of achieving effective radiated power (EIRP) on LF, estimating DF0WD's EIRP at around 80 milliwatts based on field strength measurements from PA0SE. DF0WD/DL4YHF has successfully worked numerous countries on 136 kHz CW, including DL, F, G, GI, GM, GU, GW, HB9, HB0, LX, OE, OH, OK, OM, ON, OZ, PA, and SM. The author also mentions ongoing efforts to log contacts with CT, EI, LA/LG, and to complete a two-way QSO with Italy, demonstrating persistent activity on this challenging band.

The DIY 137 MHz WX SAT V-dipole antenna project details the construction of a specialized antenna for receiving weather satellite transmissions. It provides specific dimensions for the dipole elements, designed for optimal reception around the 137 MHz band, which is commonly used by NOAA and Meteor weather satellites. The resource outlines the materials required, such as aluminum tubing for elements and PVC for the support structure, along with the necessary coaxial cable and connectors. The article presents a clear, step-by-step assembly process, including how to form the V-shape and connect the feedline. It emphasizes practical considerations for mounting and weatherproofing the antenna for outdoor deployment. The design focuses on simplicity and effectiveness for amateur radio operators interested in satellite imagery. Key aspects include the precise angle of the V-dipole and the lengths of the radiating elements, which are critical for achieving the desired circular polarization response for satellite signals. The resource includes photographic documentation of the construction phases and the final mounted antenna.

A home made project for a 7 element yagi antenna for the two meters band based on the DK7ZB original desing.