Austron 2100F LORAN-C Frequency Monitor

& 2100T Timing Receiver


Brooke Clarke, N6GCE

Front of Austron 2100F

Back of Austron 2100F

2100F Frequency Monitor
2100T Timing Receiver
2084 Multifilter
2042 Simulator
1290A 24 Volt Standby Power Supply
Manuals
Patents
Pickard & Burns Model 601 Loran-C Receiver 
Links

Background

The LORAN-C system was originally designed for marine coastal navigation but has since been used for other purposes.

Aircraft LORAN-C receivers added the low cost capability to fly directly from point A to point B.  Prior to LORAN-C most aircraft flew radials either to or from the location of a navigation aid.

Additional LORAN-C chains were added to the central U.S. so that users on land and on lakes could take advantage of this precise positioning system.

Prior to LORAN-C the highest quality frequency standard in the U.S. was the WWVB radio station on 60 kHz.  There are similar LF time stations on nearby frequencies in other countries.  Note that WWVB can be used both as a frequency reference and by decoding it's digital time signal can be used to set clocks and watches.  LORAN-C provides a much more stable frequency monitoring capability than can be had using WWVB and this is the application the Austron 2100F LORAN-C Frequency Monitor was built to serve.

The stock LORAN-C system currently does not have any digital data containing time or date information so can not be used as a way to set a clock.  But by knowing the epoch date and time of the LORAN-C system it is possible to know when the synchronization point on the station being received matches the UTC second exactly.  The Austron 2100T was designed for this Time Of Coincidence (TOC) application.

2007 - There is Enhanced LORAN (eLORAN) experimental work going on now.  Part of this is the LORAN Data Channel (LDC) that will add data packets to the existing LORAN-C stations.  It works by adding a new pulse after all  the existing pulses hence existing receivers will not notice the new one.  It's Pulse Position Modulation whrere the new pulse can be shifted to one of 32 (from memory) different time slots.  A bunch of these make up one data packet.  One of the data packets has the date and time information so you could set a clock, just like you can from GPS or WWVB.  Other packets have the Lon and Lat of the antenna and other ID info.  As of June 2007 these stations are broadcasting the Data Channel:

The stations listed below are capable of but not currently broadcasting the Loran Data Channel.

Another aspect of the eLORAN will be a change from the current Master -delay- Slave timing system.  This way of timing made sense in the old days since the quality of the position fix depended on the time delays and if the master station drifted it was not important.  But as the LORAN-C stations get upgraded to atomic standards corrected by phase micro steppers the timing can switch to a system based on UTC.  The existing single chain LORAN-C receivers will not be affected by the change, but it then opens up the possibility of an "All in View" LORAN-C receiver working in a fashion similar to GPS where all the stations that can be heard are used for the position or time fix.  I'd guess that if you throw a dart at a globe at that point you can receive all of one chain and maybe a station or two or more from adjacent chains, but not enough adjacent stations to get a fix from them alone.  So an all in view receiver will do better without adding any new transmitting stations.

Frequency Transfer

The 2100F works by comparing the external reference frequency with the selected LORAN-C station.  This is done by generating a pulse from the external reference at the GRI rate and noting the change in the time interval between it and the LORAN-C pulse that's being tracked.  The result can be seen either in terms of the time offset (O/FS) or as a stability number like E12   3.1.

2100F Operation

This 2100F Frequency Monitor does not have a built in oscillator and so needs a 1, 5 or 10 MHz input signal that is an accuracy of 1E-8 or better in addition to an antenna and power.  I'm using the AMRAD active LF whip and it works great.  My Stanford Research PRS10 GPS disciplined Rb oscillator is the source of 10 MHz fed into the 2100F.

After letting the 2100F receive the Middletown, CA station that is less than 1 degree of Lat and Lon from me (Status 2 Noise = 0) overnight the frequency offset displayed 1.0E-13.  I don't understand why this display jumps around to 4.0 E-12 because the phase error value (status 7) is 00.0 us.

There may be a need for the 2100F to run for some hours to stabilize temperature in order to track properly.  When first turned on it would quickly lock on Middletown but would not lock onto the chain master station.  After a few hours it would display something when "Advance Station" was pressed.

TDs

Whent he Advance button is pressed the display is supposed to show the time difference between the master and the station being tracked.
But so far it does not add up. (LORAN-C station locations rounded to nearest second)
 
me Master W X Y
Ukiah, CA Fallon, NV George, WA Middletown, CA Searchlight, NV
39:11:24N
123:09:50W
39:33:06N
118:49:55W
47:03:48N
119:44:8W
38:46:57N
122:29:43W
35:19:18N
114:48:16W
miles @ degrees 233 mi @ 94.8 570 mi @ 16.5 46 mi @ 127.8 532 mi @ 117.5
code delay 0 15,700 27,000 40,000
emission delay 0 13,796.9 28,094.5 41,967.3
2100F "station advance" delay 0 15700 27064 43632
delay based on known location 1252 3064 247 2860

 Station Advance - when this button is pressed a number will appear if the 2100F has been able to see the master station pulse, if no master station then the display will show ------.  Each time you press <1> <station advance> a new number will appear indicating different stations could be tracked.  To change stations enter the number of stations to advance then press station advance and the receiver will go into acquire mode.

5 May '03 - After a few weeks of rainy weather where only the local station would lock up the receiver would not sync onto the chain master by itself.  But when <1><ACQ> is done for a new acquisition the master and other slave stations were found.  So it appears that this must be forced manually.  The stations are now 0 (Fallon master), 27100 (Middletown), 43668 (Searchlight), and today Geroge is not there, but may show up in a few hours.

Stations Received at 39N 123W:

chain 59900 George, WA  delay 27000
chain 96100 Bosie City, OK delay 0
                    Gillette, WY delay 13032
                    Searchlight, NV delay 25400
                    Las Cruces, NM delay 41600
chain 99400   Fallon, NV delay 0
                    George, WA delay 15700
                    Middletown, CA delay 27064
                    Searchlight, NV delay 43632

Scope

By using an oscilloscope that is triggered from the 2100F and displaying the raw received signal you can see the quality of the signal and by using the time base trigger delay function move the time window being viewed through the complete GRI space.  This allows other stations in the chain to be seen.  But the problem is this receiver is designed to receive only a single station and so it's gain is set for that station.  When receiving Middletown which is very strong the gain is turned down making it difficult to impossible to see weak stations.

When acquiring a GRI the first time it is not clear which station the receiver locks onto. It does not seem to always be the master or the strongest station.

Modulation

The amplitude of the signal has some form of amplitude modulation.  It is slow and can be seen in this 1.4 MB AVI file that lasts about 8 seconds.  In my browser after the file loades I see a still picture on a white background.  Clicking on the still plays the video.

10 Feb 2003 - I called the Middletown LORAN-C station and asked about this and they said no modulation like that was being done.  Some time ago there was a program to add modulation, but it was canceled for lack of funding.

This must be something caused by all my electronic equipment or is in the Austron receiver.

2100T Timing Receiver

NSN 6625-01-1434-580
4 Feb 2005

2100T Front Operating

Shown using FTS4060/S24 as reference source

Background

The timing version of the Austron 2100 receiver uses Time Of Coincidence to synchronize its 1 PPS output with the UTC 1 PPS edge.  Like GPS there are a number of corrections that need to be made to get the edges lined up and the manual suggests that rather than trying to account for all of them that a visit by an atomic clock be used to determine the offsets, not just for the current station being tracked for for a number of stations so that they would be available as backups. 

The Stanford Research Systems FS700 Loran-C receiver does NOT have Time Of Coincidence capability, it's more like the A2100F.

LORAN-C will survive GPS

When GPS became operational other radio based navigation systems, like Omega, were shut down and the fate of the LORAN-C system was uncertain.  But in Nov. 2004 the report seems to indicate that the LORAN-C system will stay on the air and be upgraded.  It provides a needed backup to the GPS system for mission critical applications like commercial aircraft landing systems.

Time Transfer

LORAN-C is a navigational system and does not send any time codes so you can not set a clock using Loran-C.  But the whole LORAN-C system has an epoch date of  00:00:00 hours (UTC), Jan. 1, 1958.  Each chain of transmitters has a Group Repition Interval (GRI) and so the Middletown, CA station is one of the slave transmitters in the chain with a GRI of 9940 (i.e. the period of the group is 99.4 mS).  So the time when one of these pulses falls exactly on top of a UTC 1 second transition can be computed if you know the current time to better than 99.4 mS in my case and you know how the total number of leap seconds since the epoch.

The 5220333 patent widens the 99.4 mS time window by looking at two different chains since the Time Of Concidence for both chains will be much larger than for a single chain.

Setup

Toms' web page with Chapter 3.6 from the manual.

Tracking

Open front panel and set toggle switch to 1, 10 or 5 (left to right) to match reference frequency. (if this is not done the Tracking LED may blink Red and Green).  Then connect to:

 Master GRI

Key in the desired GRI (in my case 99400) and press "GRI".
Key in 1 and press Master.
Now the Acquire red LED turns on for awhile, then the Settle red LED for awhile, then the green Tracking LED is on.
At this point pressing "Track Data 8" will show "--E-----" indicating that the TOC has not yet been set.
Note the receiver is now tracking the master station for the entered GRI.

Time Constant

At this point I set the time constant to the longest possible value (0 Track Data 6) which is 3200 GRIs.

15 Feb 2005 - With the Time Constant set to 3200 GRIs I changed the C Field on the FTS4060 from 525 to 580, maybe a change of 5.5E-13 to 1.1E-12 and the Tracking LED started blinking alternately Red and Green.  Pressing <1> <SECOND>ary relocked the receiver to Middletown in about 8 minutes.

Slave Station

Now by entering the Total Emission Delay for the salve station (Middletown in my case is 28000 us) and pressing SEC TD to set the value, then key in 1 and press SECONDary to lock to that station.  In my case it took 8 minutes to lock up.  After the  green Tracking LED lights the display is showing the actual emmission delay, in my case 27072.  This can be brought back by pressing the SECONDary key.  Doing the slave lock also disables TOC tracking  so it needs to be re synchronized.

If the receiver is tracking a secondary station and  you press the MASTER button the display will show "--------", and when you press SECONDary the display will show the total emission delay, in my case ""27026   ". 

Tracking LED

This LED is green when tracking a station.  It slow blinks Red and green when the receiver can not track the local reference or it has seen a signal strength change of 10 or more dB.  This will happen if there is no local reference connected or if the local reference is drifting too fast for the Time Constant that has been set.

For a signal strength change the Red-Green can be reset to steady green by pressing 0  then Track Data then 8.

Ref Freq Offset

TOC LockJust after TOC lock in photo at left the stability is shown as E10 1.7.
The offset of the local reference can be displayed by using Track Data 4 which now is E12 9.4.  8 minutes later the display is E12 8.6 and it appears to be working it's way to lower numbers.  The minimum delta time interval measured for the Track Data 4 stability display is 0.01 uS (see this by pressing O/FS).  Thus to see 1E-14 would take 1E6 seconds or about 11.57 days.  This is where GPS with a 1 PPS accuracy on the order of tens of nanoseconds has a big advantage.

The next morning (about 18 hours running time) the Track Data 4 shows E13 3.7 but waiting more days the best it gets is in the 3E-13 area, maybe that's as good as the FTS4060 is set?

By pressing <0>, <Track Data>, <7> the O/FS value will be reset to zero.  Only zero can be set, not other values.
This is a good thing to do when adjusting a frequency standard, like the FTS4060 Cesium,  when a new setting has been made.
Note
LORAN-C may be as good as GPS for precision time transfer, and may have advantages over GPS.

1E-131.0E-13 Limit

There seems to be a limit of 1.0E-13 in the 2100T.  It may be that my FTS4060 never gets any better, but I think that's not the case.  For example the stability should drift into and out of the 1E-14 area, but the 2100T never shows anything better than 1.0E-13.  If you have seen better numbers let me know.




TOC

In order to set the internal clock an external 1 PPS input in needed that's within one GRI (and ahead of the second tick).  Or the slewable 1 PPS output can be connected to the EXT 1 PPS input, which I did for convenience.  Then the next TOC is keyed in and First TOC pressed to load it.  Then 1 is keyed in and Begin TOC pressed.  At this point the TOC LED will alternatly flash red nad green and when the TOC time occurs if all is well the TOC LED turns solid green.

Once the TOC has been set, the second prior to a new TOC the TOC LED turns red then if the internal 1 PPS edge is aligned with the LORAN-C TOC the LED turns green again.

At power up the green 1PPS LED will have a random timing.  Because of this it's impossible to set the UTC to within one GRI.  But when an external 1PPS is input to the 2100T and an attempt is made to set the TOC, although the TOC setting fails, the green 1PPS LED is now synchronized to the external 1PPS thus allowing the UTC to be set.  The next TOC setting procedure will then work.

22 Apr 2005 - When using an external 1 PPS that's good, like from a GPS receiver, if you set a random time for First TOC and try to sync, it will NOT sync.  I tried this to get the 1 PPS in sync, but it didn't work, so now need to use an actual TOC to resync after a big sferics crash.

Once the receiver has the TOC locked it automatically computes when the next TOC will occur.  You can see it by pressing FIRST TOC (without first pressing 1).  One second prior to a TOC the TOC LED will turn red then at the TOC back to green.

Track Data

Pressing <Track Data> <n> will display the Track Data value.
Pressing <some number(s)> <Track Data> <n> will set the Track Data Value.
Sometimes only zero is a valid input number.

Track Data #
Function
0
Enable Front Panel
1
Lock Front Panel
2
Signal/Noise
4 = 9 dB
28 = 0 dB
224 = -12 dB
3584 = -21 dB
3
Receiver Gain in dB
4
Frequency Offset
5
Cycle number being tracked (S.B. 3.0)
6
Receiver Time Constant
0 = 3200 GRIs
1 = 1600 GRIs
2 = 800 GRIs
3 = 400 GRIs
4 = 200 GRIs
7
Accumulated phase shift (same as O/FS)
8
Receiver Status
MSB to LSB
E = acquisition Mode
E = TOC LED red
E = No TOC Sync
E = loss for reference
E = LORAN-C Blinking
E= tracking cycle more than 0.5 from 3.0
E= gain change > 10 dB
E = not tracking

9
Delta TIme Internal fixed - External 1 PPS

O/FS Button

Pressing O/FS (Offset) causes the LCD to show the difference between the local reference and the LORAN-C derived 1 PPS.  This receiver was designed for use with lab grade crystal oscillators and so the display can go to thousands of microseconds with a LSD of 10 nano seconds.  The minus sign is all the way to the left of the display and so can easily be missed when the display is something like 0.03.

IEEE-4388

Both of these receivers have the IEEE-488 option.

What Goes Wrong

Two 2100T receivers arrived in the same jiffy box from a Government Liquidation auction.  They were sold as condition code A1 (new) units and included a couple of manuals.  One unit had the left front handle bent inward which prevented the front panel from hinging down and is missing the right side panel attachment captured screw (since replaced with part from RAF).  It was DOA.  The other unit looks nice on the outside.

After reseating the LCD module in the bent handle unit and plugging in the front panel ribbon cable the unit operates properly.  The nice looking unit still has some type of electrical problem.

7 Feb 2005- Board swap troubleshooting

Moving the microprocessor board from the bad receiver into the good receiver causes the good receiver to show the same power up error (does not end up in time mode) as the bad receiver.  This means that there's something wrong with the microprocessor board.

Rear Top w/o CoverBut moving the microprocessor board from the good receiver to ge bad receiver also has the same power up error.  Why? Still a mystery since there was a bad IC on the microprocessor board, unless the loose screw & washer were causing a problem.

A short 2-56 screw and a #2 lock washer were found loose in the bad receiver.  Came from front panel PCB.

The large PCBs have edge connectors with 43x2 contacts.  With the front panel facing you looking down on a PCB the contacts are numbered /Y to A (left to right) The letters are: ABCDEFHJKLMNPRSTUVWXYZ and then again except with a bar over the letter like /A /B.../Y (no /Z).  The contact directly below A is 1 and below /Y is 43. 

The manual uses signature analysis as a trouble shooting method, so I have an HP 5004 Signature Analyzer and will be shortly testing the non working unit.

1 March 2005 - Replaced U4 (74LS244) that the 5004 identified as bad and now the receiver powers up properly ending in the time display mode.
2 March 2005 - the repaired receiver is working just like the other one.  The HP 5004 Signature Analyzer pointed out the bad IC.  If you have an Austron 2100F or 2100T (or any equipment documented to use it) the Signature Analyzer is a good investment.

Some other possible front panel related problems from Chuck Harris:

Top Front w/o CoverThe 3 large PCBs plug into a bus and any one of them can be moved to the top or bottom position to get easy service access without using an extender card.

The 2 RF amplifiers (small PCBs) also are on a bus so one of them can be moved to the top for alignment.  The bottom small PCB 9DAC card) is always in the bottom slot.


2084 Multifilter

2084 FilterThe LORAN-C frequency of 100 kHz is surrounded by high power military digital radio stations.  By filtering out these stations the interference they cause can be reduced.  There is also a Sferics warning lamp on the front panel.  Filter #2 (they are numbered right to left when looking at the front panel) has a "peak" function.  The idea is to tune filter #2 for the maximum interfering signal and then tune one of the other filters to be on that frequency.
The A.C. power input connector looks like a standard american 3 prong plug recessed in a cylinder, so a special line cord is needed for power.  Made from an extension cord by cutting off a small nub.

Here is a 0 to 200 kHz  spectrum display with the output from both the DA-100 and the AMRAD active whip antennas.  You can see that there are a number of adjacent signals stronger than my local LORAN-C station.

60 - 160 Khz w/ and w/o Filters
After using the HP 4395A in both spectrum and network analyzer mode the filters were set and a comparison spectrum plot from 60 to 160 kHz was made.  The upper trace is w/o the filters set using rear panel switch.  The lower trace is with all filters set except number 2.

The Loran-c "triangle" has a peak (-80 dBm) that's maybe 50 dB above the noise floor (-130 dBm) becasue the Middletwon station is very close to me.  The RTTY station at 132.625 has been depressed by about 30 dB.

When testing in N.A. mode any power level higher than -24 dBm caused the Sferics lamp to turn on, so N.A. testing was done at -30dBm.

The station at the very left side (60 kHz) is WWVB-C.






I'm using the 2084 as an antenna multicoupler driving a couple of 2100T receivers with the filters turned on.  I've noticed that the Sferics white lamp flashes every now and then.

I notice that the green 1 PPS LEDs on the two receivers are not flashing at the same time, need to figure out how to synchronize them, i.e. get them correct.  This has been done, see TOC above for procedure.

Friday 22 April 2005 4 pm PDT N. Calif.- It's been high overcast most of the day and the Sferics lamp has been flashing and sometimes double flash.  Both 2100T receivers went into alternate red-green TRACK mode.  Pressing 0 - <Track Data> 8 cured the top 2100T, but the bottom receiver (has the top receiver's output as it's input) lost lock and would wasn't fixed by 0 - <Track Data> 8.  These problems are almost certainly being caused by Sferies.  Sometimes the Sferies lamp is flashing within seconds of a prior flash.  Maybe there's going to be a lighting storm?  The forecast is for rain tonight and maybe thunder storms tomorrow.  So there's probably a thunderstorm going on now that causing the Sferics.  The status indication was that the gain had changed by more than 10.  I'm very close the the 99400 station at Middletown (normal gain 40) and so the sferic must have been very strong to cause the gain (88) to change.

2042 Simulator

This appears to simulate a master station and two salve stations.  Although it has a whip transmitting antenna the signal strength must be very feeble, only enough to drive a very nearby receiver.  Thumbwheel switches to set the GRI and emission delay for each slave.
Manual or any info wanted for the 2042.

1290A 24 Volt Standby Power Supply

This is a battery backup supply for 24 volt timing instruments.  And for many years they have been 24 volt units.

LORAN-C Receivers

Lorchron LORAN-C Timing Receiver LFT-504
Micrologic SportNav with MGRS - hand held with military MGRS cooridnates
PSN-6 - attaches to PRC-25 or PRC-77 military back pack tranceiver

LORAN-C Spectral Lines

If you tune in the 135.7 - 137.8 kHz range you will find spectral lines coming from LORAN-C stations.  The lines depend on the GRI of the station and have been complied at:  Loran Lines Visible in North America  For my local station at Middletown, CA 9940 they are:
135,699.195, 135,704.225, 135,709.256, 135,714.286, 135,719.316, 135,724.346, 135,729.376, 135,734.406, 135,739.437, 135,744.467, 135,749.497, 135,754.527, and many more.
Here is a 4395A  Spectrum Analyzer plot of 135.7 - 137.8 kHz showing maybe 36 loran-c spurs.  This is using the AMRAD LF active whip antenna mounted at ground level.
The marker peak serach finds the largest one at 137.6005 kHz and the list shows one at 137,600.604
Next peak search finds 136.8445 kHz at -122.56 dBm, but they are all about the same magnitude and so the peak jumps around.  The noise floor between peaks is about -139.45dBm/root Hz.

Pickard & Burns Model 601 Loran-C Receiver


Pickard & Burns
                Model 601 Loran-C Receiver
Pickard & Burns
                Model 601 Loran-C Receiver
Front
Back
This receiver, as is typical of LORAN-C receivers, has no frequency conversion circuitry.  The RF is filtered and amplified and comes out the output separated from adjacent signals centered at 100 kHz.  The functional boxes are:
  1. Preamplifier 601-10 for 102" whip
  2. Receiver 601-20
  3. Power Supply
The Preamp did not come with the receiver and power supply.  There are two options:
The manual was included that has schematics and parts lists.

My interest is in looking at the new 9th pulse that contains data.  This would make a nice front end for a micro controller based data decoder.  Maybe not as nice as the Austron 2000 series front end, but better than some others.

LeapSecond.com - Museum - Austron 2100 Loran-C Timing Receiver - Austron 2100F start procedure - Loran-C by oscilloscope (unfinished)  - 9940 TOC -

LoranView by DF6NM - Listening to all the worlds LORAN-C stations from Nuernberg

Manuals

 A CD-ROM with the following Austron manuals is available.  For ordering information see the product page.
1120 Oscillator (octal tube base) brochure & drawing 3 pg
1210D Clock  stiched, rotated, cleaned. 130 pg (prior to stiching more like >200 pg
1250 Frequency Standard. 33 pg
1250A Frequency Standard. 52 pg
1250B Frequency Standard. 51 pg
1290A Power Supply 57 pg
2000C Analog Loran-C receiver.  Good overview of Loran-C and how a receiver works.  253 pg
2010B Disciplined Oscillator - locks to an external reference 105 pg
2042 Simulator - a Master and two Slave stations make up a chain direct and antenna outputs 67 pg
2084 Filter & Multicoupler - also has Sferics lamp, great for feeding multiple Loran-C receivers 54 pg
2100F Loran-C Frequency Monitor uP based- includes Signature Analysis data 166 pg
2100R Loran-C Frequency Monitor 168 pg
2100T Loran-C Timing Receiver uP based includes locking to Time of Coincidence, S.A. test data 225 pg
Brochure of Austron Products 8 pg

Patents

5220333 Method and apparatus for determining universal coordinated time from Loran-C Transmissions,
Bruce M. Penrod, Jun 15, 1993, 342/389; 368/47
4839613 Temperature compensation for a disciplined frequency standard,
James A. Barnes, James D. Echols, Bruce M. Penrod, Jun 13, 1989, 331/69; 331/25; 331/176
4740761 Fine tuning of atomic frequency standards, Barnes; James, Rodrigo; Enrico, April 26, 1988, 331/3 ; 331/94.1,

4314378 Antenna low-noise Q spoiling circuit,
              
Clarence W. Fowler, Bruce M. Penrod (Tractor, Inc.), Feb 2, 1982, 455/291, 455/292 -
An input coupling circuit for detuning the Q of a high-Q ferrite rod antenna is disclosed. A high-impedence low-noise amplifier is used to amplify the output signal from the LC resonant tank of the rod antenna. A portion of the amplified signal is fed back directly into the magnetic circuit of the antenna tank. This negative feedback reduces the losses produced in the magnetic circuit due to the presence of nearby conductors. As a result of this reduction, an increase in the antenna sensitivity and a decrease in the cross-feed from other nearby antenna is produced.

Patent Citations

Cited Patent Filing date Publication date Applicant Title
US1907653 * Feb 21, 1930 May 9, 1933 Telefunken Gmbh Short wave receiver
US2641704 * Aug 3, 1950 Jun 9, 1953 Rca Corp High-inductance loop antenna and system
US2774866 * Jan 30, 1956 Dec 18, 1956 Emerson Radio & Phonograph Cor Automatic gain and band width control for transistor circuits
US2787704 * Apr 19, 1955 Apr 2, 1957 Philips Corp Constant band-width input stage with high q antenna
US3005093 * Sep 16, 1960 Oct 17, 1961 Avco Mfg Corp Transistorized detector and automatic gain control circuit
US3077562 * Jan 7, 1960 Feb 12, 1963 Key Lee P High gain radio receiver
US3479609 * Jun 13, 1966 Nov 18, 1969 Us Army Attenuation circuit using a tuned amplifier whose q is varied by shunting resistors
US3495031 * Nov 1, 1967 Feb 10, 1970 Zenith Radio Corp Variable q i.f. amplifier circuit for a television receiver
US3510807 * Sep 29, 1966 May 5, 1970 Us Navy Electronic switch using a series string of two diodes,one zener and one conventional,and a capacitor in parallel with a resonant circuit as a q spoiler
US3528023 * Aug 29, 1968 Sep 8, 1970 Gen Dynamics Corp Amplifier
US3673523 * Oct 5, 1970 Jun 27, 1972 Electrohome Ltd Signal translating networks and control circuits for the tuners of signal receivers
US3786363 * Jan 5, 1973 Jan 15, 1974 Us Navy Voltage-controlled low-pass filter

Referenced by

Citing Patent Filing date Publication date Applicant Title
US4414690 * Jun 15, 1981 Nov 8, 1983 U.S. Philips Corporation Active aerial
US4442434 * Mar 13, 1981 Apr 10, 1984 Bang & Olufsen A/S Antenna circuit of the negative impedance type
US4805232 * Jan 15, 1987 Feb 14, 1989 Ma John Y Ferrite-core antenna
US4996484 * Dec 29, 1988 Feb 26, 1991 Atlantic Richfield Company Method and apparatus for cancelling powerline noise in geophysical electromagnetic exploration
US6809694 Mar 27, 2003 Oct 26, 2004 Andrew Corporation Adjustable beamwidth and azimuth scanning antenna with dipole elements
US6963314 Sep 26, 2002 Nov 8, 2005 Andrew Corporation Dynamically variable beamwidth and variable azimuth scanning antenna
US7158049 * Mar 24, 2003 Jan 2, 2007 Schlumberger Technology Corporation Wireless communication circuit
EP0392327A1 * Apr 4, 1990 Oct 17, 1990 Texas Instruments Deutschland Gmbh Damping circuit for the antenna resonance circuit of a radio transmitter-receiver
EP2541680A1 Jun 26, 2012 Jan 2, 2013 Roke Manor Research Limited Reduced Q low frequency antenna
WO1993001658A1 * Jul 6, 1992 Jan 21, 1993 Electronic Advanced Research Ltd Radio receiving circuits
WO2002093687A1 * May 13, 2002 Nov 21, 2002 Commissariat Energie Atomique Antenna quality factor self-adaptive device

Links

Table of US LORAN-C Stations
Patents related to Disciplined  Oscillators -
USCG - LORAN-C - Signal Specification - just U.S. LORAN-C - History page -
U.S. Naval Observatory - Time Service Department - LORAN-C Timing Operations - LORAN Times of Coincidence on line computation
International Loran Association - Links
Hyperbolic Radio navigation Systems by Jerry Proc VE3FAB
NTP use of LORAN-C -
SDR in action: The last LORAN-C receiver -
Locus - modern "All In View" (i.e. 40 stations) Loran-C receivers -
SDR in action: The last LORAN-C receiver - A $20 LF Loop antenna -
Loran-C Challenges GNSS: From a Quarter Nautical Mile Down to Meter-Level Accuracy -
The Case for e-LORAN by the UK

  All these have extensive bookmarks and the instrument manuals have a supplement with color photographs including inside.

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