Abstract

During instances such as the COVID-19 pandemic, access to necessary information is crucial for safety, but not everyone has access to information. Therefore, the goal is to develop a form of cheap and efficient communication that does not lack in quality so that anyone, regardless of income, may have access to important information. Multiple initial sketches and crystal radios diagrams were created. Prototypes of crystal radios were constructed upon created designs and out of both homemade and purchased materials. These prototypes were tested based upon three criteria: cost, range, and sound quality. Furthermore, an AM transmitter and crystal radio able to use regular headphones were created. The average base crystal radio costs roughly $10, an average range of 27.4 miles to 31.4 miles using a 15-foot antenna, each with acceptable audio quality. The crystal radio design with a transformer was able to utilize standard headphones rather than the earpiece and costs approximately $15. The range and quality was similar to the base crystal radios. The AM transmitter was able to broadcast a 1-MHz signal and was tested on multiple radios. The transmitter costs $16 with audio quality similar to that of regular broadcasting stations. It has an estimated range of 200 feet with a 10-foot antenna, which was not further tested due to the legality of transmitting radio signals. Crystal radios are inexpensive devices that may be able to be used as a method of communication for those who have financial issues. Prices may be different than recorded.

The infographic to the left lays out the basis of the project. The problem at hand pertains to communication issues, particularly during the COVID-19 pandemic. Even though technology seems to be extremely modernized in the current year and that everyone has widepsread access to information, particularly through the internet, it turns out that 10% of U.S. citizens do not use the internet. While this can be due to preference, further studies show that those with lower income are less likely to use the internet, showing a financial reason to the lack of internet. While other forms of communication are out there, and internet is not the only form, internet is undeniably a rapidly growing means of transferring information. Due to this, crystal radios, an old yet very cheap form of communication were looked at and created in my project.

To the left is another infographic regarding my project. Particularly, this infographic focuses on the methods and materials section of the project. Once research was completed, the first step to achieving my project was to first design and create crystal radio diagrams, both physical and circuit diagrams. Multiple of these were created, and with that necessary materials for creating crystal radios based upon these designs were collected. The collected materials were both materials that could be found at home and materials that needed to be purchased. Once purchased, these materials were used to create the cyrstal radios based off of previously created designs. With the creation of crystal radios, the crystal radios were tested upon three criteria: cost, range, and sound quality, with descending importance.

Analysis

The results of the Pearson’s r test on each yield that the two variables are greatly and positively correlated with a coefficient of correlation near 1. However, flaws exist in this testing, due to the relatively low sample size and range, this linear correlation may not hold as the length of antenna further increases. Beyond that, there exist a finite quantity of radio stations, meaning that the data set of stations is discrete, whereas the length of the antenna is continuous and can be measured. Sound quality of the crystal radios was the most difficult of the three to measure. Audio software was used to analyze the sound, however, due to the build of the piezoelectric earpiece, there were difficulties in properly recording the sound. How loud the actual crystal radio was versus how loud the recording was differed quite greatly. Despite difficulties, the crystal radios were still analyzed on sound quality. The crystal radios had quite some background noise present, with crystal radio #1 having the least presence of background audio, then following is the kit, then crystal radio #2, and #3 with the most background noise. The difference in background noise among all radios was not drastic, but did exist. The amount of background noise is comparable to that of an alarm clock with a built in radio. Direct listening of the radio with the earpiece is acceptable, although not being to the quality of radios out there in the market. Most stations received were intelligible and understood by the listener. The two iterations of crystal radios were also tested. The first of which, being the crystal radio capable of using non-piezoelectric earphones did not require much testing. This iteration came in at a cost of roughly $15, due to the $10 transformer, but also the negation of the piezoelectric earpiece’s cost, assuming one already has a pair of usable headphones. The headphones used in experimentation were able to receive sound from the radio, and the sound quality was comparable to the use of the piezoelectric earpiece. Range of the radio was unaffected by the change.The AM transmitter was tested upon three criteria similar to the original crystal radios, that being cost, range of transmission, and sound quality of transmission. With the cost of all parts summed, the transmitter cost in total roughly $16, not including the price of 4 AA batteries. This AM transmitted sent out signals at 1 MHz, and multiple AM radios, including crystal radios. were tested to see if they were able receive the aforementioned transmitted signal. The AM radios used in testing were able to receive the 1 MHz signal, and sound quality of the transmission was comparable to other stations received by each radio. The distance of transmission of the AM radio transmitter followed a correlation between the range and antenna length similar to that of the previous crystal radios. Range of transmission, however, was nowhere near the range received by crystal radios at tens of miles. Instead, at an antenna length of 10 feet, the transmitter was able to send off a signal that could be received only 200 feet away. Although increasing the antenna beyond 10 feet would likely increase transmission distance, testing halted at a range of 200 feet, due to the legality of transmitting signals without a ham radio license. Having an antenna as long as the one tested with the mere result of a 200 foot transmission does not seem acceptable; ways to improve the antenna beyond simply increasing length would have to be looked into. Below is the correlation between antenna length and transmission distance.

Discussion/Conclusion

The testing procedure of crystal radios did have some flaws. Most of these flaws came from the testing of range, even though there were great results showing a strong positive correlation between antenna length and reception distance. One issue is the fact that although the two variables tested, antenna length being independent and reception length being independent, are continuous, there does not exist an infinite amount of radio stations, meaning that there are intervals of distance where radio stations are not present. This partially hinders the data for range, per se there was a radio station 20 miles away and one 30 miles away. If the antenna length for exactly 20 miles was slightly increased, there will be no recorded difference until an antenna length for 30+ miles is recorded. Another potential issue with the range data is that only antenna lengths up to 15 feet, in mostly intervals of 2 feet, were recorded. The data may not follow such a linear trend for longer antenna lengths. As for data regarding cost, home materials were roughly estimated, although that estimation likely does not impact the results greatly. Additionally, prices compared to radios in the market were not intensely analyzed. Regarding audio quality, recording audio was difficult, which resulted in a quieter and not entirely accurate recording. Additionally, the software used was not the best software for analyzing the recordings and preferred software was not available. Some subjective testing was also used, which is not necessarily bad, but more objective data is preferred. Crystal radios are inexpensive communication devices, coming in at around $10 for constructed crystal radios. Despite being cheap, they have quite the range, as well acceptable audio quality. Although results yielded that crystal radios were not to the level of other general radios in terms of performance, they are by far cheaper than the vast majority of radios out in the market. For the problem at hand, crystal radios certainly appear to be an effective low-cost solution to communication issues. Nearly every individual is financially able to afford a crystal radio in terms of cost, and beyond that crystal radios can be constructed by anyone with the necessary materials. The AM transmitter also allows for a radio that is able to transmit and receive in conjunction with crystal radios, working in some ways as a ham radio. Although the transmitter has a short range, it is interesting to see how AM signals can be transmitted at a low cost. Looking beyond the purpose of the project, crystal radios are also able to be used as educational devices in learning radios. Their simplicity in structure, yet complexity in how they work make them fascinating devices. There certainly is more to this project than what has been conducted. Something that can be looked into in the future is how to improve the antenna, particularly for a low price. While increasing the antenna length can increase reception, it becomes impractical to have a very long wire. This is primarily important for the AM transmitter, as with a 10-foot antenna wire, it can only transmit 200 ft, which may not be necessary for this project, as there are legal issues with transmitting long distances, but it is certainly one thing that can be improved on, not only to increase transmission/reception distances, but to also improve the sound quality. This project did not look into comparing the prices of radios in the market to the crystal radios to an extensive degree. A full-scale analysis of radios on the market could be an objective to further insinuate that crystal radios are low-cost in comparison to other radios. Looking into how to make purchased pieces from raw materials may also help decrease the price of the radio. Diodes can be made from pencil lead and a piece of metal, such as a razer, held over a flame unil blue, but diodes are quite cheap in the radio. The earpiece takes up about half of the price of the radio, looking into how a makeshift piezoelectric earpiece can be made could reduce costs. Moreover, AM data channels may be an interesting and useless advancement with crystal radios, as more than sound can be received by the radio; however, information out there on AM data channels seems to be limited. Although this project has established quite the amount on crystal radios and their low-cost, much more can be done regarding the radios.

References