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Which one should I buy for Apartment usage?


Eric Inloes
 

So, I'm trying to decide which version to buy.

It will be used in an Apartment and i wont be using it for VHF. Will be used with a SDRplay RSP2 and hopefully a SDRplay RSPdx down the road.

It does seem the VHF version offers more gain for 20m but i wonder how it compares to the VLF/HF version with a smaller loop. 

Thanks! 


WA8LMF
 

On 12/9/2019 10:26 AM, Eric Inloes wrote:
So, I'm trying to decide which version to buy.

It will be used in an Apartment and i wont be using it for VHF. Will be used with a SDRplay RSP2 and hopefully a SDRplay RSPdx down the road.

It does seem the VHF version offers more gain for 20m but i wonder how it compares to the VLF/HF version with a smaller loop. 

 

If you are NOT going to use the antenna for VHF, opt for the LF/HF version. 

1)   The gain is not going to be the limiting factor on what you can hear.     Local NOISE -- lots and lots of it - will limit what you can hear.   ANY antenna located in or near an apartment complex will be deafened by the broadband noise from household electronics:  Cheap cell phone chargers, computers, digital TVs, LED lights, home automation controllers, light dimmers, etc.   According to the (US) National Association of Broadcasters (NAB) concerned about the dwindling audience for AM broadcasting, the average noise level in the typical residence has increased over 20dB over the last two decades due to the proliferation of household electronic gadgets. This make AM broadcast RX at home now almost impossible - the main audience is now in cars. 

The only cure to this noise problem is to get the antenna farther away from the house!


2)   If you have high-power TV or FM broadcast stations nearby, the HF/VHF version of the amplifier is likely to overload on these VHF stations, creating splattery distorted inter-modulation products across the HF spectrum.  

[To users in the UK and Europe, the mode of VHF broadcasting in the US is sharply different from that on your side of the pond.    In EU, broadcasting tends to be lots of relatively low power transmitters, with many of them connected to a single program source in a major city.  In the US, TV and FM stations are mostly independent entities that transmit with a LOT of power from very high towers.   I.e. 50-100KW ERP on FM, hundreds of KW ERP on VHF-TV and MEGAWATTS ERP on UHF-TV.    This causes numerous problems.  Users install amplified receive antennas or mast-mounted preamps in an effort to get out-of-town stations.  If the local stations are closer than 10-15 miles, all that happens is that the preamp overloads on the local stations and makes distant reception WORSE!       Amplified antennas only work decently if ALL the stations are out of town.

Since digital broadcasting replaced analog a decade ago, the degraded performance is often not obvious at first.  Since the digital transmissions are a bit stream that sounds like white noise, the intermod just appears as  MORE noise smothering the desired signal. I.e. not an obvious mix of two or more signals.  ]


Stephen H. Smith    wa8lmf (at) aol.com
Skype:        WA8LMF
EchoLink:  Node #  14400  [Think bottom of the 2-meter band]
Home Page:          http://wa8lmf.net

-----   NEW!    60-Meter APRS!   HF NVIS APRS Igate Now Operating  ------
   <http://wa8lmf.ddns.net:14447/>



Live Off-The-Air APRS Activity Maps
   <http://wa8lmf.net/map>

Long-Range APRS on 30 Meters HF
   <http://wa8lmf.net/aprs/HF_APRS_Notes.htm>




Chris Moulding
 

I would recommend the VLF/HF version for apartment use if you don't need VHF.

One advantage of the loop antenna is that it is not sensitive to the electric noise field radiated by the electronic devices very close to the antenna especially if you add the common mode chokes we fit in the VLF/HF loop amplifier.

I'm planning to make a video of my workbench where I have the wire loop I use for testing hanging from a set of shelves with LED and fluorescent lights, PC power supplies, RF powered soldering iron, wires hanging down, everything live just inches away from the loop with perfect AM broadcast reception on the radio. I'll also cover near field and far field to explain what happens as the antenna interacts with the incoming radio wave.

I found out about the differences between the US and EU broadcast systems some years back.

One of the first customers for the HF Active Antenna lived in New York city in direct line of sight with megawatt EIRP VHF FM transmitters on tall buildings. We built a special version of the antenna for him with a low pass filter to reduce everything above 50 MHz. After that it was nicknamed the "New York filter" and if it was fitted to an antenna I wrote NY on the PCB.

Regards,

Chris


Eric Inloes
 

Thanks for the reply!

Slightly confused as to if the test loop wire is included with the head and base unit.

Also seems using the base unit with the HF/VHF results in more gain then being powered via Bias-T. Does the same apply to the VLF/HF version or is it the same here


WA8LMF
 

On 12/9/2019 5:36 PM, Chris Moulding wrote:
 
I found out about the differences between the US and EU broadcast systems some years back.

One of the first customers for the HF Active Antenna lived in New York city in direct line of sight with megawatt EIRP VHF FM transmitters on tall buildings. We built a special version of the antenna for him with a low pass filter to reduce everything above 50 MHz. After that it was nicknamed the "New York filter" and if it was fitted to an antenna I wrote NY on the PCB.

Regards,

Chris


Is this still available?    I have had the same problem with the HF Active antenna for years.     I live about 2 miles (3.2 Km) from the Michigan State University transmit site for WKAR-FM  ( 100 Kw on 90.5) and WKAR-TV (1/3 Megawatt on US chan 33 UHF).  Both are on a 1000-foot (300 M) tower. 


On a related topic, the RF overload capital of the world (or at least the US!) is Los Angeles/Southern California; not New York.    The major broadcast platform for metro Los Angeles is Mount Wilson, about 15.5 miles (25 KM) NE of downtown, situated in the San Gabriel mountain range. The TV transmit site is located directly next door to the famed Mt Wilson observatory (where Edwin Hubble discovered that the universe is expanding in the first part of the 20th century) at over 5000 feet (4700 meters).  Several 200-300-foot towers rest on top of this. (Most of the city of L.A. is at sea level.)  

The Mt Wilson transmit site is home to over 20 VHF & UHF TV transmitters and 15 FM broadcast stations with transmit powers ranging from 50 KW to 5 megawatts ERP.       About 2 miles (3.2 KM) to the west on the same ridge line is Mt Disappointment where over 300 public safety and commercial low band, VHF, UHF and 800/900 MHz two-way repeaters and base stations share about 10 towers.  Mt Disappointment is shielded from Wilson by an outcropping that protects it's receivers from the 300+ megawatt onslaught from Wilson.   In the past, when analog TV was still operating, you would drive up the Angeles Crest highway from Pasadena down below to Mt Wilson, and start hearing TV sync hash in your car audio system a mile and a half from the sites.  With the car system turned off!   It was diode detection in the audio output stage power transistors.   Now with digital TV broadcasting, you just hear a faint white noise hissing.

Los Angeles is a roughly triangular area about 50 miles across surrounded by 4-5-6-thousand-foot-high mountains on two sides and the Pacific Ocean on the third.   There are literally thousands of two-way radio systems, located in all of the mountains surrounding metro L.A. , operating on practically every band from "DC to light".  All of these sites enjoy  minimum-loss  literal free-space line-of-sight paths to the population of 18 million people down below.   The result of all these thousands of transmitters going on and off the air constantly is a generalized broadband RF white noise that blankets the entire VHF-UHF spectrum.    This noise comes from the from the 70-80-90-dB-down-from-the-carrier wideband noise generated by transmitter PAs all over the greater L.A. area.  This white noise is what I call "RF smog". 

It renders high-performance low-noise receiver front-ends and external preamps completely useless, since the RF smog appears at FM receiver front-ends as 2-3 microvolts of noise on virtually any band or frequency.  I have driven around and beyond the metro L.A. area with an Icom AH-7000 discone antenna mounted to my trailer hitch on a 10-foot mast, connected to my IFR-1500 spectrum analyzer.   I would scan a frequency span from 100-1000 MHz.   30 miles (48 KM) north of L.A. in the Mohave desert on the way to Las Vegas, you are shielded from the RF mayhem in greater L.A. by ranges of mountains. It's a noiseless receive environment  Come off the high desert through any of the mountain passes, down to the L.A. basin below, and the base line "grass" of my analyzer will immediately jump 20 dB across the entire span, anywhere in greater L.A. !  



Stephen H. Smith    wa8lmf (at) aol.com
Skype:        WA8LMF
EchoLink:  Node #  14400  [Think bottom of the 2-meter band]
Home Page:          http://wa8lmf.net

-----   NEW!    60-Meter APRS!   HF NVIS APRS Igate Now Operating  ------
   <http://wa8lmf.ddns.net:14447/>



Live Off-The-Air APRS Activity Maps
   <http://wa8lmf.net/map>

Long-Range APRS on 30 Meters HF
   <http://wa8lmf.net/aprs/HF_APRS_Notes.htm>






WA8LMF
 

On 12/9/2019 5:36 PM, Chris Moulding wrote:
I would recommend the VLF/HF version for apartment use if you don't need VHF.

One advantage of the loop antenna is that it is not sensitive to the electric noise field radiated by the electronic devices very close to the antenna especially if you add the common mode chokes we fit in the VLF/HF loop amplifier.

 

Is there something fundamentally different between your one-turn 1-meter loop and the smaller (usually rectangular) multi-turn air-core loops provided as receive antennas for the AM tuners in AV receivers?      (I pick up a horrendous amount of noise from nearby devices with these small loops.)      Could the difference be that the typical stereo receiver loop is unbalanced, connected between a single-wire-in terminal and a chassis-ground terminal, while yours is balanced?   

[Before the power amps in stereo components went to class D switching mode, usually stereo tuners or receivers had a ferrite rod antenna for AM receive, inside the device.   Now all these devices come with the annoying external air-core loops dangling from the rear, presumably to  get away from the firestorm of digital noise inside the case of the device.]  

I once had a Ramsey Electronics "Signal Magnet" AM receive antenna built from a kit. This device was a typical ferrite rod AM "loopstick" with  a longer-than-average rod (8-10 inches long).   The antenna could be peaked anywhere in the AM broadcast band with varying voltage (3-18 VDC) provided remotely to a varactor connected across the loop.   This whole thing was inserted inside a piece of plastic pipe with a layer of brass foil glued to the outside of the pipe. The brass had a slit down the length of the pipe to prevent it from becoming a shorted turn itself.   I.e. a kind of Faraday shield against electrostatic pickup.   A small (non-resonant) secondary coil) on the rod coupled the signal to a coax line that could be any length to the receiver.     This ant had incredibly low-noise receive, even amid numerous nearby digital gadgets.  I could quietly hear 500-watt AM stations 100-150 miles(160-250 Km) away.  


Stephen H. Smith    wa8lmf (at) aol.com
Skype:        WA8LMF
EchoLink:  Node #  14400  [Think bottom of the 2-meter band]
Home Page:          http://wa8lmf.net

-----   NEW!    60-Meter APRS!   HF NVIS APRS Igate Now Operating  ------
   <http://wa8lmf.ddns.net:14447/>



Live Off-The-Air APRS Activity Maps
   <http://wa8lmf.net/map>

Long-Range APRS on 30 Meters HF
   <http://wa8lmf.net/aprs/HF_APRS_Notes.htm>




Chris Moulding
 

Yes the loop has to be balanced so that it doesn't act as a electric field antenna.

In our Loop Antenna Amplifier we also add common mode chokes to isolate the loop as completely as we can from the coax feeder.

Using a very low input impedance in the VLF/HF version helps with this but you have to have a very low inductance one turn loop for best results.

Your description of the Ramsey Signal magnet reminds me of the very first antenna I ever made as a teenager (a very long time ago).

I made a frame aerial using several turns of wire on a wooden frame tuned with the variable capacitor from an old radio set. I could sit my transistor portable inside the frame antenna and tune for maximum signal. My first introduction to medium wave DX tuning into European and African stations.

I might try and make a modern version using ribbon cable and the varactor diodes we now use in the HF Preselector, It might make a useful product for medium wave and 160m listening.

Regards,

Chris


Tom Crosbie G6PZZ
 

I might try and make a modern version using ribbon cable and the varactor diodes we now use in the HF Preselector, It might make a useful product for medium wave and 160m listening.

 

Chris, I would love to know how to use a varactor diode in an old style frame antenna situation. I have yet to solder the connections inside my frame ATU and could add this in as an alternative before I screw the lid down. It might also be a better solution for my whisky box loop antenna.

 

Tom G6PZZ

 

 

From: CrossCountryWireless@groups.io <CrossCountryWireless@groups.io> On Behalf Of Chris Moulding
Sent: 10 December 2019 22:59
To: CrossCountryWireless@groups.io
Subject: Re: [CrossCountryWireless] Which one should I buy for Apartment usage?

 

Yes the loop has to be balanced so that it doesn't act as a electric field antenna.

In our Loop Antenna Amplifier we also add common mode chokes to isolate the loop as completely as we can from the coax feeder.

Using a very low input impedance in the VLF/HF version helps with this but you have to have a very low inductance one turn loop for best results.

Your description of the Ramsey Signal magnet reminds me of the very first antenna I ever made as a teenager (a very long time ago).

I made a frame aerial using several turns of wire on a wooden frame tuned with the variable capacitor from an old radio set. I could sit my transistor portable inside the frame antenna and tune for maximum signal. My first introduction to medium wave DX tuning into European and African stations.

I might try and make a modern version using ribbon cable and the varactor diodes we now use in the HF Preselector, It might make a useful product for medium wave and 160m listening.

Regards,

Chris


Eric Inloes
 

"We supply a 3m (10 ft) length of wire as a simple loop to make a first loop for testing." 

Unsure how I missed this but I got an answer to my question.

Thanks for your help! 


Oene Spoelstra
 

Don't underestimate the frame antenna. Very good results with it over here ! I also use the varactor method .

Op di 10 dec. 2019 23:59 schreef Chris Moulding <chrism@...>:

Yes the loop has to be balanced so that it doesn't act as a electric field antenna.

In our Loop Antenna Amplifier we also add common mode chokes to isolate the loop as completely as we can from the coax feeder.

Using a very low input impedance in the VLF/HF version helps with this but you have to have a very low inductance one turn loop for best results.

Your description of the Ramsey Signal magnet reminds me of the very first antenna I ever made as a teenager (a very long time ago).

I made a frame aerial using several turns of wire on a wooden frame tuned with the variable capacitor from an old radio set. I could sit my transistor portable inside the frame antenna and tune for maximum signal. My first introduction to medium wave DX tuning into European and African stations.

I might try and make a modern version using ribbon cable and the varactor diodes we now use in the HF Preselector, It might make a useful product for medium wave and 160m listening.

Regards,

Chris