LAA ++ & Large (horizontal) loops


Jack
 

I’ve seen elsewhere that people have built large horizontal loops as antennas (10s of meters). Can the LAA ++ be used for that? What restrictions are there for antennas on the LAA ++? I assume that end-fed, dipole, tuned circuits are all out and that any kind of passive loop is in.

jack
m7eas


Simon
 

Hi Jack

Large horizontal loops do not need a preamp.infact adding an amp will degrade the big loop. So no.also its designed to work with small, read SMALL rx
loops..ie 1m dia.

There are sometimes instances when a preamp is needed on large horizontal loops, but not the laa, and that is ie a
log antenna ( google)

Regards Simon g0zen


Chris Moulding
 

The Loop Antenna Amplifier ++ is designed to match and amplify the signal from small loop antennas typically smaller than 0.1 wavelength.

Usually on HF you don't need the extra gain with large loops. More often than not you are having to reduce the front end gain or add attenuation to get the background noise floor below the AGC threshold for more comfortable listening.

I can think of one exception. One of our customer uses the LAA++ with a large thick loop to give demonstrations of pre-1930 receivers such as crystal sets and valve regen receivers. These would usually need a long wire antenna but he uses the loop antenna to give live demonstrations without a big antenna.

By the way Simon should have said that the log antenna you are looking for is the Loop On the Ground antenna. Our Beverage Antenna Amplifier also matches that.

If you just search for a log antenna you will probably find log periodic antennas which are a wideband directional antenna usually used at VHF and UHF.

Years ago I build a HF log periodic antenna that covered from 21 to 144 MHz. I think that it was probably the best HF antenna I ever made but it may be because it was tested at the peak of the sunspot cycle. I could transmit on the 15m amateur band and hear my signal echoing around the world at least three times due to chordal hop propagation!

Regards,

Chris


David Cutter
 

Chris

I remember those days of HF echoes. 


I had a very severe case a few years ago when the echo time coincided with the spaces between characters and all I heard was a long tone till conditions changed. That was on T32C

73 David G3UNA 

On 19 March 2022 at 15:47 Chris Moulding <chrism@...> wrote:

The Loop Antenna Amplifier ++ is designed to match and amplify the signal from small loop antennas typically smaller than 0.1 wavelength.

Usually on HF you don't need the extra gain with large loops. More often than not you are having to reduce the front end gain or add attenuation to get the background noise floor below the AGC threshold for more comfortable listening.

I can think of one exception. One of our customer uses the LAA++ with a large thick loop to give demonstrations of pre-1930 receivers such as crystal sets and valve regen receivers. These would usually need a long wire antenna but he uses the loop antenna to give live demonstrations without a big antenna.

By the way Simon should have said that the log antenna you are looking for is the Loop On the Ground antenna. Our Beverage Antenna Amplifier also matches that.

If you just search for a log antenna you will probably find log periodic antennas which are a wideband directional antenna usually used at VHF and UHF.

Years ago I build a HF log periodic antenna that covered from 21 to 144 MHz. I think that it was probably the best HF antenna I ever made but it may be because it was tested at the peak of the sunspot cycle. I could transmit on the 15m amateur band and hear my signal echoing around the world at least three times due to chordal hop propagation!

Regards,

Chris


WA8LMF
 

On 3/19/2022 11:47 AM, Chris Moulding wrote:
Years ago I build a HF log periodic antenna that covered from 21 to 144 MHz. I think that it was probably the best HF antenna I ever made but it may be because it was tested at the peak of the sunspot cycle. I could transmit on the 15m amateur band and hear my signal echoing around the world at least three times due to chordal hop propagation!

Regards,

Chris


About 35 years ago, I had this experience on 15 meters with a Kenwood TS-520 and a Hy-Gain TH-3 Jr tri-band beam.  I was just talking across town to a friend about 5 miles (8 KM) away when we started hearing triple echos of each other. Taking into account the total time span of the echos, I realized we were hearing our signals make three round trips around the world.   The freak propagatoin lasted about 90 minutes.

I actually measured the delay by having my friend send single CW "dits" about 5 secs apart while monitoring the audio from my receiver with an (old at that time) Heathkit scope set to a very slow sweep rate.  I figured that at the speed of light (186,000 mi/sec) that three round trips around the planet's 25,000 mile circumference (75,000 mi) should be just under half a second. The scope confirmed exactly this!


Log periodics are great!

I spent two years in Viet Nam 1968-70. I was a hard core radio nerd, even then. The first year I was with the "MARS" (Military Amateur Radio System) program.  About a dozen MARS stations up and down what was then "South Vietnam" linked with state-side stations to  run phone patches from troops in VN to relatives in the states. [In that pre--satellite, pre-Intenet, pre-fiber-optic era, the only place in the country where a civilian overseas phone call could be made was in downtown Saigon.]  We used Collins "S/Line" ham gear on mil frequencies just outside the 20, 15 and 10 meters bands. The peak of the Viet Nam war neatly coincided with a very good solar cycle max - the upper HF bands were hot!     We were "pushing patches" nearly 24 hours a ;day just above 20 meters and even 10 meters was open 8-10 hours a day.

The second year in Viet Nam, I was with AFVN (American Forces Vietnam Network) radio-TV. If you have seen the movie "Good Morning Vietnam", that movie is literally a piece of my own life. The look and feel of GI life captured in the movie is absolutely real.  The stage sets in the movie are extremely accurate re-creations of the real thing.  AFVN was no 10-watt toy FM campus radio station. This was serious commercial-scale AM-FM-TV broadcasting with 7 TV stations and 10 AM/FM radio stations up and down the country at the peak in 1969.   The Saigon headquarters station was 50,000 watts on 540 AM, 100,000 watts ERP on 99.9 MHz FM, and a quarter-million watts peak on VHF TV channel 11.  
   The AM transmitted from a full-sized 1/4-wave (at 550 meters wavelength!) "stick" with it's 120 radials 6" under salt water at high tide.  The AM signal absolutely bombed!  The daytime signal was effortlessly heard over 150 miles (240 Km) away in the daytime on a cheap 6-transistor pocket radio, and all over southeast Asia and beyond at night. We routinely got reception reports from Indonesia, Australia, New Zealand, the Philiipines, India and Taiwan. I even heard it on a Panasonic AM/FM portable from my hotel room in Tokyo!   Our Army, Air Force and Navy pilots actually used AFVN 540 Saigon and 560 Pleiku as NDBs all over Viet Nam and the South China Sea. 

The standard equipment issue at the MARS stations in VN was a Collins KWM-2A, a 30L-1 desktop four-811s amplifier (500-watts out) and the Hy_Gain LP-1017 log periodic. This was a 13-element antenna that covered 13 to 30 MHz continuously.  The boom was about 30 feet long and the back (lowest freq) element was about 35 feet side-to-side.   These antennas were seen a lot at embassies and special forces bases as well as MARS stations. 
    At my MARS station in Bien Hoa (about25 miles outside Saigon) we manged to finagle a Henry Radio 4K floor-model amplifier.  We couldn't verify that it actually produced 4K PEP output (didn't have an RF wattmeter that would go that high!), but it DID totally peg the wattmeter on the Collins 312B-5 station console when driven by the KWM-2 .  
    The KWM-2'As design provided for nearly continuous coverage on HF outside the ham bands when the optional "general coverage" kit was used. This was a pack of about 100 additional crystals for the KWM-2's first-conversion oscillator and a pair of forceps to stick crystals into sockets inside the KWM-2's chassis.  [The KWM-2 had faded from the ham market by the late 1960s, but had an amazing 20-year "second life" as a light-weight paramilitary and diplomatic HF radio, thanks to the crystal kit.]   
    I decided to test the actual bandwidth of the log-periodic, by trying it, courtesy of the crystal kit, in every 200 KHz segment from 13.9 to 30 MHz.  It was amazing!  With the Collins wattmeter pegged at full-scale from the Henry 4K driven to max out on key-down CW,  I measured less than 5 watts reflected on ANY frequency in the range.


For over 50 years now, I have been telling the story of "Radio In Vietnam" at radio club meetings and ham fests, using some of the over 3000 Kodachrome slides I shot over those years, and some of the real-life audio recordings I made back then.
    I have reprised the AFVN AM and FM stations at gatherings of the AFVN Veterans group that has reunions every two or three years. I actually have 1 watt FM and 10-watt AM transmitters that I put on the air to broadcast vintage recordings and period music of the late '60s/eaarly '70s at these events.

Some of these pictures and recordings are on my website at:

    <http://WA8LMF.net/Vietnam>


Stephen H. Smith    wa8lmf (at) aol.com
Skype:        WA8LMF
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