Loading coil antenna for HF reception - Page 1
Forum section: electronics / rf-microwave

author: prabhatkarpe4
author_rank: Contributor
timestamp: September 08, 2024, 12:44:06 pm
content: I need to know whether a loading coil antenna would work better than a random wire antenna for receiving HF band of 21 meters?Will it able to receive all the shortwave broadcasts (1.7 - 30 MHz)?

author: Andy Chee
author_rank: Super Contributor
timestamp: September 08, 2024, 01:07:44 pm
content: No.Random wire antenna will work better for receiving.

author: A.Z.
author_rank: Super Contributor
timestamp: September 09, 2024, 05:43:59 am
content: Quote from: Andy Chee on September 08, 2024, 01:07:44 pmright, loading is used to shorten a resonant antenna, wiling to shorten a wideband receiving antenna we may consider to use a resistive termination and try a T2FD to obtain an acceptable impedance match over a pretty wide frequency range

author: Juri 69
author_rank: Newbie
timestamp: September 09, 2024, 06:25:38 pm
content: What specific frequency range are you interested in? And why exactly frame?

author: wasedadoc
author_rank: Super Contributor
timestamp: September 09, 2024, 07:06:59 pm
content: Quote from: Juri 69 on September 09, 2024, 06:25:38 pmDid you read the OP? Who mentioned "frame"?

author: Juri 69
author_rank: Newbie
timestamp: September 09, 2024, 08:21:38 pm
content: Sorry, the translator translated it incorrectly. Did you mean - with a load in the form of a coil? )))

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: September 09, 2024, 08:27:18 pm
content: A typical length of wire used as an antenna can pick up a lot of electrical noise, unless you are lucky enough to live in a remote rural location.Many of us use an active antenna mounted well away from the house, the PA0RDT type uses 2 transistors and is straightforward to make and install. Beware of useless versions on eBay, check this write up:https://www.dl1dbc.net/SAQ/Mwhip/Article_pa0rdt-Mini-Whip_English.pdfA commercial/military one is this, which is not hard to make either:https://www.dst.defence.gov.au/sites/default/files/publications/documents/DST-Group-TR-3522.pdfAll good stuff!SJ

author: vk4ffab
author_rank: Frequent Contributor
timestamp: September 09, 2024, 11:51:18 pm
content: Quote from: prabhatkarpe4 on September 08, 2024, 12:44:06 pmDefine better? The best antenna is the one you can actually erect. For reception of broadcast shortwave, you do not actually need a lot of antenna because you are mostly listening to stations that have very strong signals because they have massive transmission power and massive antenna systems and no one wants to listen to a AM broadcast that is fading in and out and is marginal and more noise than signal. So, pick your favorite SW broadcast station and put up enough antenna for good reception of it and for all the rest, just wait for good propagation to overcome the antenna impediment.As for me, if all i cared about was RX, i would install a fat monopole. 8 wires about 6m long each, to form a vertical cylinder about 2 to 4m across. will give very broadband performance across most of HF. The one pictured is 8m tall and 4m across and has a 2:1 swr bandwidth from 7mhz to 40Mhz and is a killer receive antenna for weak signal reception.Do not over think it. NIKE, just do it.

author: rf-fil
author_rank: Regular Contributor
timestamp: September 10, 2024, 03:40:20 am
content: OP, there isn't enough detail in your question. There are too many variables. What application is this for? Also, what is 21meter band? There is no such broadcast band, and the nearest ham band is 20m (14MHz).If it's for HF broadcast, why not just try? You can hook up a few meters of wire to your radio and see what happens. The longer and higher the wire is, the better the signal is.. but if it's too long, your radio may get overloaded and stop working. And if your wire is high up above ground, you should add protection for static discharge and for lightning.BTW, I find a 1-meter magnetic loop really good for receiving HF in noisy urban areas. It produces strong enough signal with just a tuning / matching circuit and a good radio. The disadvantage is that the antenna requires re-tuning for each different frequency.

author: vk4ffab
author_rank: Frequent Contributor
timestamp: September 10, 2024, 05:10:38 am
content: Quote from: rf-fil on September 10, 2024, 03:40:20 amIts probably a typo and he meant 22m band, which is a shortwave broadcast band used throughout Eurasia. OP is Indian and India is part of Eurasia.

author: A.Z.
author_rank: Super Contributor
timestamp: September 10, 2024, 12:05:24 pm
content: just in case the OP never heard about the T2FD or "his google is broken", the image below shows a short T2FD along with the pattern at 13.5 MHz and other data, willing to boost the gain it will be easy to add an LNA, since the antenna thanks to the 16:1 BalUn (galvanic transformer) and the terminating reistor will offer a good match over a wide frequency range; the 800 Ohm termination may be obtained connecting some resistors in series/parallel to obtain the needed value, ideally the resistors should be non-inductive ones, but for RX only that isn't strictly mandatory, the resistors and the 16:1 can be either built or easily sourced, even from AliExpress if desired, the SWR curve shows a good match between 1 and 31 MHz, but the antenna will work even at higher/lower frequencies, not the best antenna in the world, sure, but one which can be easily built at home and will offer quite acceptable performance; notice that if space is constrained the antenna can be installed in "inverted V" configuration, also, having more space the overall spread of the arms may be increased, in such a case, willing to optimize the impedance match, the resistor value should probably be adjusted

author: radiolistener
author_rank: Super Contributor
timestamp: September 10, 2024, 09:58:17 pm
content: Quote from: prabhatkarpe4 on September 08, 2024, 12:44:06 pmThe inductor or capacitor is needed to achieve resonance between the antenna wire and the inductor/capacitor. This allows the system (antenna wire + inductor/capacitor) to accumulate energy at a specific frequency. As a result, it works like a filter that cuts off unwanted frequencies.However, a proper connection between the receiver and the antenna system is also necessary. This connection is called the transmission line or feeder. It needs to account for the impedance of both the antenna system and the receiver, and the transmission line (e.g., coaxial cable) must have the correct impedance.If there is an impedance mismatch, you need to use a matching circuit to match one impedance with another.So, it will look something like this: Antenna wire => Matching circuit => Coax cable => ReceiverIt also may need matching circuit between coax cable and receiver to get better signal, but for receiver it's less critical.When everything is properly taken into account and connected together, you will get the best signal level at the receiver.Since you are still a beginner in this, you can start by using a1:9 balunas a matching circuit. It allows you to match the high impedance of an improperly selected piece of wire with a coaxial cable. The matching won't be perfect, but it will be sufficient for you to start with.Also, keep in mind that an antenna always consists of at least two pieces of wire - the radiator and the counterpoise. So, connect a two pieces of wire to each terminal of the balun.But there is also another issue - noise and interference from nearby equipment.The effect of this interference can be reduced by installing anRF chokeon the coaxial cable.