Tag Archives: QRM

Advice on cancelling locally generated noise

An SWLing Post reader recently contacted me with the following question:

“What devices work well to cancel out local RFI? I’ve been told that both the Timewave ANC-4 and a number of BHI products are all worth considering.”

Unfortunately (or fortunately, for me) I’ve no experience with outboard DSP or noise cancelling devices because I live in such an RFI-free area.

I know this reader already has a Wellbrook Loop, but he’s looking for a way to even increase noise mitigation further at his home listening post.

Post Readers: Can you help guide him?  Please comment with your experience. Is a product like the Timewave or BHI the next logical step? If not, what is?

Urban DXing: testing the Bonito Boni whip against a 30 metre longwire & the Wellbrook ALA15030

Hi there, if like me, you live in an urban environment, chances are QRM is having a negative impact on the quality of the signals you’re receiving at home. The presence of electrical noise makes antenna choice very important, particuarly if you’re planning to spend more than a few £££s on something more sophisticated than a length of wire. Recently I was considering the the purchase of a second compact antenna, for use at home in my shack and out and about on DXpeditions. I already had the excellent Wellbrook ALA1530 H field antenna, but at more than £250, it’s very costly and thus it seemed rather extravagent to buy a second one, if I could find something with similar performance for less expense. Space is at a premium at home and of course I take much of my equipment out on DXpeditions, so the Bonito Boni whip active antenna appeared to be an ideal choice. A wideband active antenna (from 20 kHz to 300 MHz) operating from 12 to 15V DC, with a very compact form-factor definitely ticked all the boxes. Furthermore, with reasonable second and third order intercept points of +55 and +32.5 dBm respectively, the Boni whip, on paper at least, looked like a pretty good buy at around £100.

 

Now, clearly, an E field antenna such as the Boni whip is not going to match the SNR provided by the H field Wellbrook ALA1530 in a noisy, urban environment. I have uploaded a few reception videos to my YouTube channel to demonstrate this, making a direct comparison of the two. However, what about the performance of the whip versus a simple longwire in an urban environment? Is there a delta in performance? The value proposition of the whip is primarliy in it’s performance, coupled with portability I suppose, but that must be considered a secondary requirement. The whip might be 10 or 15 times more expensive than a reel of cheap equipment wire, but will the reception justify the cost delta?!

Text links follow directly below, with embedded videos thereafter; you will find 3 reception videos comparing the whip and a 30 metre longwire, on shortwave and one each for LW and MW. At the end of each video there’s a section with the Wellbrook loop, just to calibrate where the longwire and whip are in terms of a much more effective H field antenna. The result? Well, there’s not much to separate the longwire and Boni whip, except on LW, where the whip prevails. A friend told me recently, if reception is rubbish at home under a blanket of QRM, don’t blame the antenna, the noise is the real problem. He was right. So, the next tests are to be undertaken out in the field, where the whip has a real chance to shine. I’m rooting for it because to have an antenna that performs as well as, or close to my loop out in the woods, yet can be packed away into a small case would be brilliant. Thanks for reading/watching/listening.



Clint Gouveia is the author of this post and a regular contributor to the SWLing Post. Clint actively publishes videos of his shortwave radio excursions on his YouTube channel: Oxford Shortwave Log. Clint is based in Oxfordshire, England.

Why good antennas need to be fed with good coax

Dennis Walter, of Bonito Radio in Germany, has just posted an excellent article on his blog regarding the importance of quality coaxial cable to fight local radio interference.

Click here to read his post, “Why even good antennas need good Coax cable.”

 

Fred Lundgren: “What happened to AM radio”

We all read articles about the utility and the demise of AM (mediumwave) broadcasting. In this short article via the Huffington Post, Fred Lundgren (Founder and CEO of KCAA) discusses “What Happened To AM Radio (that’s NOT a question)”:

On Christmas Eve morning, the electricity went off at our house and panic quickly spread among our younger guests.

First, the TV sets went dark. Then, the desktop computers began to die as UPS back up batteries failed. For a while, we were reassured by the sound of familiar alarms, but then suddenly, total silence. Could this be the end times? Is this the onslaught of the apocalypse?

Smart phones were quickly deployed and guests began calling each other from room to room. The panic began to subside when several millennials volunteered communal usage of their wireless data plans. The kingdom would be saved…crisis abated.

[…]As the younger generation huddled around the smart phones with data plans, I began to think of the outage as an opportunity to listen to AM Radio, so I went to my office and dusted off my old RCA SuperRadio III.

I couldn’t remember the last time I replaced the batteries but to my surprise, it came to life with its signature popcorn sound when I pushed its big silver button. “IT’S ALIVE” WOW…the AM band was extraordinarily quiet and responsive.

[…]I scanned across the dial from 610 AM to 1590 AM. All the stations were as clear as a bell. Then, I decided to press my luck. I tuned to KTSA 550 AM in San Antonio and then I moved the dial slightly to the right and heard KLVI 560 AM in Beaumont, Texas. Every station was booming in loud and clear.

I felt like a child with a new toy. I dialed up and down the band, experiencing the clear booming sound of AM Radio without any noise or interference. It was a feast for the senses. It was beautiful.

After a few minutes, one of my daughters walked in and asked about the source of my entertainment. I pointed to my SuperRadio and said joyfully, “listen”. She looked at the big black box and asked “How can you listen with the internet and electricity off?” I responded, “It’s my portable SuperRadio III.” Before I could explain further, she shrugged her shoulders, closed the door and went back upstairs, convinced that her Dad was conducting some sort of high tech experiment.

In a manner of speaking, her assumption was correct. I was listening to AM Radio in a big city without the interference of computers, wireless modems and an overloaded electrical grid. For the first time in my recent memory, the “Senior Radio Band” sounded beautiful. Sadly, my experiment ended with preordained results when the electric power was restored.[…]

Click here to read Lundgren’s full article on The Huffington Post.

Guest Post: “Car Shack” Radio Listening

Many thanks to SWLing Post contributor, TomL, for the following guest post:


“Car Shack” radio listening

by TomL

My car is an unusual place to listen to shortwave radio but has interesting possibilities. Due to the obscene noise at my home QTH, I decided that I must try something away from this unfortunate situation. So I took my homemade 14-inch loop antenna and outfitted the appropriate ancillary equipment with DC power packs. My trusty Sony ICF-2010 is the radio “vehicle” to “drive” this experiment (LOL). And, seriously, this is a way to show the public that it is not that hard to have a portable radio listening setup. Believe me, if I can do this, anyone can!
The basic ingredients are pictured here with some variations (see text):

  • Homemade 14-inch Loop antenna + EF-SWL balun mounted backwards
  • Wellbrook amplifier powered by DC power pack of 10 eneloop AA batteries
  • KIWA Broadcast band (mediumwave) inline filter
  • Palstar preselector (active antenna) plugged into car cigarette lighter
  • Sony 2010 connected to a second DC power pack
  • Sony ICD PX333 digital recorder
  • Sennheiser earbuds
  • 7 inch Samsung tablet and 4G MiFi device to do internet schedule lookups

Illustration SEQ “Illustration” 1: Car Shack in operation.

An important finding was that anything that has a cheap IC circuit to regulate and/or convert DC power can be extremely noisy!  The pictured 16000 maH lithium brick would initially be quiet but after a while it would start spewing noise all over the bands.  Power cycling it sometimes helped but I decided that it is too unpredictable.  Also, converter cables that convert 5V to 12V for devices needing 12V also produce overwhelming amounts of noise.  Even a small 5V USB converter plugged into the cigarette lighter makes a modest amount of ubiquitous noise.  I am ditching the lithium power pack and converter cables and any cigarette lighter adapters!

So, the main radio power pack will use the internal Sony battery comparment consisting of nine 2700 maH NiMH AA’s inside three D-cell battery holders that can each hold 3 AA batteries in parallel.  This boosts the capacity to around 8100 maH for a modest cost (I already have NiMH chargers and the 4.5V requirement is not too high for the batteries in question).  Pictured are examples of a single D-cell AA holder of which I bought 12 and the silver-top Powerex 2700 maH AA’s from fleaBay.  The total voltage is slightly low (3.6V) but the Sony 2010 still works at a slightly lower performance (received signals are slightly weaker).  I run the Sony on Local sensitivity and crank up the Palstar active antenna to compensate.

In a further quest for clean, portable DC power without noisy IC chips, I have been researching lithium batteries and it is quite a large amount of work to sift through all the variables.  The Palstar active antenna and the Wellbrook amplifier both use external connections of 12V, 2.1mm (+ tip) plugs.  NiMH is not going to cut it, too many needed and getting too heavy.  Amongst the variables are things like:

  • Using a proper charger and not leaving it unattended or it could burn down your house
  • Chinese fakes being sold by the zillions that look exactly like the real thing
  • Initial cost being higher than current NiMH
  • Avoiding 1.5V step down batteries with noisy step down converter built-in
  • Learning the new terminology for sizes: AA = 14500 = 14mm diameter & 50mm length
  • Learning the differences between type of lithium: Lithium, Li-ion, LiFePo4, IMR, etc.
  • The difference between protected vs. non-protected batteries
  • How to avoid discharging the batteries too much which could render them completely useless (not just usage but also NON-usage as well)
  • How to physically handle Lithium batteries to avoid shock and temperature extremes
  • Learning how to compare maH’s of lithium to NiMH batteries
  • Finding out that most top rated 14500 Li-ion batteries are too long to fit into AA battery holders without risking damage to the protection PCB mounted at the bottom of the battery
  • and the list goes on and on…..

Here are some of the web pages I read to try to understand this technology:

So, to cut to the chase, I have decided to order this one from XTARDirect because:

  • I can order from a USA distributor who orders from the factory in Shenzen China
  • The price is very reasonable for “protected” lithium ion batteries
  • They actually should fit into typical AA battery holders without damaging it

Illustration SEQ “Illustration” 2 XTAR 14500 800 maH Li-ion

They are not the highest rated in terms of capacity, load drain, amp surge ability, etc., but they seem to have enough positive statements from users that indicate it gets the job done. Since I don’t have the lithiums yet, I am using some temporary 10-cell AA holders with good old Eneloops – good enough for now.  And I am buying this discontinued charger at a discount to recharge lithiums:

Illustration SEQ “Illustration” 3: Nitecore i4 original version

I will make two power packs made from these items pictured.  The wire is fragile so I super glue the insulation directly to the DC power plug housing (avoiding getting any glue onto the bare wire inserted at the back).  I will use three sets of lithiums (9 batteries) plus one set of Eneloop Pro’s (3 batteries) per power pack in the aforementioned parallel AA holders.

Illustration SEQ “Illustration” 4: 4X D-Cell battery holder.

Illustration SEQ “Illustration” 5: “9V” Snap connector.

Illustration SEQ “Illustration” 6: 2.1mm x 5.5mm DC power plug.

Other items of note: The umbrella stand is optional since I found I like to move the antenna around and even tilt it to get slightly better directional signal.  More importantly, I found that if I cut the Sony 2010 sensitivity from DX to Local, and then crank the Palstar preselector’s amplifier, I get a cleaner sound with less background noise. Also, the KIWA mediumwave filter is essential due to overloading.

One of my favorite stations is Radio Educacion (XEPPM) on 6185 kHz.  A 1 kW station near the foot of Vulcan de Guadalupe in Mexico City, it is so weak that I almost never hear it and their wonderful selection of music representative of regional & cultural heritage.  It is also 1675 miles distant according to Google Earth.  Now, if I want to bother, I can go out and listen in my car at locations less noisy than home.  So far, the safest places have been the parking deck at work (only two stories high) and the local grocery store parking lot.  What I would really like is a very tall parking deck whose owners let me stay up on top long into the evening without harrassment (not sure I want to risk security personnel questioning me about the strange contraption and equipment – paranoia reigns these days)!

Sample of XEPPM, moderately good propagation from the work location:

Click here to download MP3.

Of course, the Brazilian station is booming next door at 6180 kHz (thank goodness for SSB-selectable Sync detectors):

Click here to download MP3.

Unexpected reception happens with this experiment.  I mounted the antenna in the back, away from the engine and against the rear side window.  Was traversing the local restaurant drive-through lane to get a hot dog, and turning the corner next to the long empty brick wall, the reception became dramatically stronger and clearer!  Apparently, the brick wall blocked some interference as well as enhanced the signal coming from the Northeast.  You can hear the effect starting at 25 seconds into the recording of RRI:

Click here to download MP3.

Also, not recorded from a previous evening at the grocery store location, 6135 kHz Radio Santa Cruz in central Bolivia, a 10 kW station playing Spanish rock music and a clear ID near the top of the hour.

More experiments to do, like

    • Mount the antenna as high I as dare with PVC pipe (too cold out now and I would rather not open any windows but I am itching to mount the umbrella stand and antenna on a 3 foot PVC pipe on the roof of the car, the increase in received signal strength is significant)
    • A bigger backpack to carry all this equipment away from the car
    • If Elon Musk has his way and builds the Gigafactory (and competitors follow suit), there could be many more experiments with lithium type batteries in the future
    • Perhaps get an SDR and cheap laptop computer to replace the Sony radio

PS: I found out that the three-AA battery holders do not make contact at the (+) tip of the XTAR lithium batteries I purchased. I just gently lifted up the contact inside the battery holder to allow it to reach the battery tip, that’s all that is needed. Whatever you do, do not put an extra piece of metal inside the battery holders! I accidentally damaged the outside skin of two of the batteries with a common piece of copper metal and the batteries immediately started to get HOT. I took them out as soon as I could and the batteries cooled down. So, don’t use any extra metal surface inside the battery holders; lithium batteries do not tolerate any kind of short circuit!

Cheers from Noizey Illinoiz,

TomL


Thank so much, Tom, for sharing your experiences and your ongoing experiments! Lately, I’ve been doing NPOTA activations with a portable loop antenna on top of my vehicle. I completely understand what you mean about getting strange looks from passers-by! We look forward to hearing about your future experiments fighting RFI.