Tag Archives: Filters

Radio Waves: Eugène Aisberg, Filter Design, ABC Workers Face Cuts, and Data via Web SDRs

Radio Waves: Stories Making Waves in the World of Broadcasting

Because I keep my ear to the waves, as well as receive many tips from others who do the same, I find myself privy to radio-related stories that might interest SWLing Post readers. To that end: Welcome to the SWLing Post’s Radio Waves, a collection of links to interesting stories making waves in the world of radio. Enjoy!

Many thanks to SWLing Post contributors Paul, Marty, and Michael Bird for the following tips:

Eugène Aisberg, Radio Writer (OneTubeRadio.com)

After a wartime absence, the January 1946 issue of Radio Craft carried an article by writer Eugène Aisberg. While that name might not be familiar to American readers, Aisberg was a prolific author in the early days of radio, and wrote some of the best treatises on radio for the popular audience. He was fluent in French, Esperanto, German, Russian, and English.

Aisberg was born in Odessa, Ukraine, in 1905, and lived most of his life in France. He was the director of the French magazine Toute la Radio and a prolific author of a number of books. His most popular book, which is still in print, is La Radio? Mais c’est très simple (Radio? But It’s So Simple!) The book, currently in its 29th edition, an extremely solid background covering all aspects of electronics, and is written in a popular, easy-to-read style. While the book was ultimately translated into several languages, it was apparently never published in English.[…]

Filter Design Software (Nuts and Volts)

If you’ve ever lived close to an AM broadcast station, you probably experienced the phenomenon known as fundamental overload. It occurs when a receiving device is functioning entirely properly but unable to reject a strong signal. The receiver might be a wireless telephone, a scanner, or even a TV or radio receiver. The AM signal is completely legal but just too strong, disrupting the function of the receiver or overriding the desired programming.

[…]Hams often experience fundamental overload on the 160 meter band (1.8–2.0 MHz) which is adjacent to the AM broadcast (BC) band (550 kHz–1.7 MHz). Antennas for those frequencies pick up a lot of AM band RF, overloading the input circuits and creating distortion or false signals inside the receiver. The usual solution is to install a high-pass broadcast-reject filter at the receiver input, attenuating the unwanted AM signals below 1.6 MHz while passing the desired 160 meter signals with little attenuation.

So far, so good, but a filter that doesn’t attenuate signals very much above 1.8 MHz while attenuating them significantly in the adjacent broadcast band is not a simple thing to design. There are tables and equations, but they are tedious to work with. Practically, you’ll need to build the filter with standard-value components as well, and that will affect filter performance too. Sounds like a job for some filter design software, doesn’t it?

There are several filter design software packages ranging from simple calculators to sophisticated CAD programs. Luckily for hams and other experimenters, there are plenty of free or low-cost programs to try.[…]

ABC workers face anxious wait over job, program cuts (The Age)

David Anderson did not mince words at a Senate Estimates hearing last October. “There will be job losses,” ABC’s managing director warned. “It’s not something I can quantify at this point in time. There’s still more work to be done.”

Towards the end of March, Anderson will reveal a five-year plan for the national broadcaster. To the frustration of staff, it’s unlikely to specify which parts of the organisation will bear the brunt of these cuts or how many workers they might lose.

Several senior sources spoke about the situation at ABC on the condition of anonymity, given sensitive funding negotiations are yet to be finalised.

“All these media reports claiming the redundancy numbers will be finalised in March are just wrong,” says one ABC executive. “What we need is some clarity [about long-term resourcing] from the government.”[…]

Receiving Data With Web Based Shortwave Radios (Nuts and Volts)

Your computer and the Internet give you free access to over 100 web based shortwave receivers that you can use as if they were your own. Unfortunately, employing these radios to decode data transmissions can be very difficult or impossible — unless you know the secret. So, read on and we’ll guide you through the details of how to do it.

Web based shortwave radios are an amazing new implementation of software defined radios (SDR). These SDRs are free to use and widely available on the Internet. Even more remarkable is that they are located in countries all around the world.[…]

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Mike’s low and high pass filter deals

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SWLing Post contributor, Mike Ladd, is an avid SDR enthusiast and an administrator of the SDRplay Facebook group. Mike contacted me about special pricing he has arranged for low and high pass filters through Rescue Electronics. Mike explains:

These filters retail for $70.00 each. I spoke to the builder. I told him who I was and what I do and got him to make a deal for anyone in the United States with these filters and a direct link to his site. I make zero dollars on this. I always try to give back to the hobby and the community any way possible.

You have 3 choices: a high pass filter, a low pass filter, or a combo package.

These are hand built one at a time by Paul W1VLF with your choice of SO-239 or BNC connections. Full details are below:

High pass filter $55 shipped anywhere in the USA

This filter will begin attacking the AM band at 1770 Khz and increase attenuation as frequency decreases.

You can see this in the screen capture of the swept filter below.

160 Meters and above is virtually left untouched, but below that is where the attenuation takes place.

The filter has attenuated 60 db by 960 KHz.

The AM band has some very large signals that can mix in the front end of your. A lot of these spurious frequencies can land in 160 meter band or above.

For instance, I have a big signal at 1080 Khz and another at 770 Khz, add these 2 together and you get a spur that falls at 1850 Khz

Picture this happening at multiple frequencies with multiple mixes and you have a raised noise floor in the 160 Meter band.

The filter is built into a 2″ x 4″ 1.25″ 1/8″ wall aluminum enclosure for excellent RF shielding

Low pass filter $55 shipped anywhere in the USA

The AM-2 filter has a cutoff at 520 KHz.

Then, and without a lot of fanfare it begins the attack on the MW band.

Purchase this filter if you are into NDB, DX’ing, Maritime Mobile, Navetex, FCC Part 5 600 Meter band.

Each filter is handmade and swept in my lab.

The AM -2 Low pass is equipped with BNC connectors.

The filter begins to roll off at 520 Khz and gives an ultimate rejection of around 80 Db.

The filter is built into a 2″ x 4″ 1.25″ 1/8″ wall aluminum enclosure for excellent RF shielding

Combo deal for both $100 shipped anywhere in the USA

Click here to view/purchase via Mike Ladd’s promotional page at Rescue Electronics.

Many thanks for sharing this Mike! During my presentation at the Winter SWL Fest last week, I spoke about the need for high/low pass filters for listeners who live in the presence of strong broadcasters and interference. Many of the inexpensive SDRs on the market do not have built-in filters and preselectors thus can overload under these conditions.

While filters can be homebrewed or built from kits, these filters seem to be a good deal for a quality shielded and tested product. Thanks for arranging this, Mike!

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A simple homebrew high pass filter

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Many thanks to Jon Hudson, of SDRplay, who posted the image above along with the following note on Facebook:

David, WA7JHZ has designed and assembled this neat 2.6 MHz high-pass filter (HPF) for use with SDRs. He says that this simple input band-pass filter (BPF) might be of interest to anyone suffering from strong AM broadcast stations that are causing overloads…..David suffers from three nearby AM radio broadcast stations that overload the front ends of several of his receivers, including the SDRplay RSP and this is an ideal, low cost solution. He built this circuit from junk parts and commented that Amidon T44-2 iron powder cores would have made a better design, but that he decided to keep costs down with this design.

This design is simple enough for almost anyone to build and could help your receiver’s front end from overloading. Many thanks to David for the design/schematic and to Jon for sharing!

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