ARRL FMT Tonight -- getting the most accurate frequency

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Tonight is the ARRL Frequency Measuring Test (FMT) where you can test your skills, and the capabilities of your radio, measuring an on-air signal with the best accuracy you can muster:

http://www.arrl.org/frequency-measuring-test

The FLEX-6000 radios are well suited to perform in the challenge, but there's some important information you should know before having a go at it.  I apologize in advance that this will not be a complete "how to" guide and I hope that some others may be able to answer questions on what I've written as they arise.  I've been meaning to post this for several weeks and just haven't had the time.

In a direct sampling radio like the FLEX-6000, there is an Direct Digital Synthesizer (DDS) or Numerically Controlled Oscillator (NCO) performing the tuning of receivers in the digital domain.  In the FLEX-6000, there is a complex set of DDSs and mixers that control the final output frequency of the radio.  We've not previously exposed how all this works in the radio and so the opaqueness of this part of the radio makes competing in the FMT hard.  So this post will provide enough information to get a much more accurate measurement for those that are interested.  The capabilities here were developed for a government customer of ours and have been shown to get frequency results within a few hundred microHertz (yes, microHertz).  It is important to point out that doppler shift in the ionosphere and other considerations will affect your on-air accuracy, but the FLEX-6000 should get you closer that any other amateur radio I know of.

Note that for best results, you will need to have a FLEX-6500 or FLEX-6700 with either the on-board GPS option or a 10MHz reference that is derived from a GPS locked oscillator (or cesium, rubidium, hydrogen maser, etc).  A FLEX-6300 will simply not have the same level of accuracy, but you can have a go after using the WWV calibration built into the radio.  Incidentally, if you are using a FLEX-6500 or 6700 that is locked to a reference, ensure that you have your frequency offset setting set to ZERO.

THEORY
When a DDS is tuned, it is supplied with a frequency tuning word (FTW).  The frequency tuning word is limited to a set number of bits and most of ours in the radio are 30-32 bits.  Every frequency cannot be represented with 32 bits, of course, and the error in any given DDS can be calculated by taking the sampling radio divided by 2^<# of bits>.  In our case, this would be 245,760,000 / 2^32 = 57.22mHz (millihertz).  This means that the radio can be off as much as 57mHz at any time.  Some changes were made a few months ago that limit this to +/- 28.61mHz (SmartSDR v1.10.9 and later).  In addition, a new API command was added that will actually report the error for both the receiver and transmitter:

http://wiki.flexradio.com/index.php?title=TCP/IP_slice#GET_ERROR

So you can tune a receiver and then connect to the radio using the API and request the error.  Then you can use available software to measure the audio frequency of a tone in your passband and make the adjustment provided by the get_error command.  Details on using the API are beyond the scope of this quick posting so you'll have to look around to get that information.  The short version is that you find your radio's IP address, use a telnet client to telnet to it and then issue the get_error command after you've tuned your slice receiver.

I hope this helps someone use the FLEX-6000 in the FMT and I'd be glad to answer questions as I have time.  Again, our military customers use this to get within a couple hundred microHertz so you should be able to do very well in the FMT by applying this information.
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Steve - N5AC, VP Engineering / CTO

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Posted 2 years ago

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Photo of Ria - N2RJ

Ria - N2RJ, Elmer

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Thanks Steve. Man, this is making me regret not getting the GPSDO option, but the good news is I can always acquire one later on. This is my first FMT, as I didn't have a rig capable enough. Now I do. :)
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Mike va3mw

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Ria, you can do it with a 6300 and be darn close.  It just means you'll have to work at it a bit, while the others will just crack another beer!

I'm doing it the old fashion way with the FMT code that comes with WSPR.

73
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David Warnberg

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I can't even get to the ARRL site currently... anyone else having an issue or is it just me?

Thanks
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Ria - N2RJ, Elmer

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It's down.

http://www.isup.me/www.arrl.org

LoTW and other sites on that server are up, however. 
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David Warnberg

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Thanks I just got in...  I have plenty of time does not start till 8:00 pm EDT or 00:00 UTC
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Neal - K3NC, Elmer

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Ria, thanks for posting isup.me You are a gift that just keeps giving!
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roger na4rr

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Hi Ria    thanks for the link  Does it do more than just ping the site? 

roger
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Ria - N2RJ, Elmer

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I believe it uses servers in different part of the country (may be AWS, I'm not sure) and tries to curl the site. PING is unreliable as many sites block ICMP traffic for security reasons. 

There are a few many others
http://downdetector.com
http://www.isitdownrightnow.com/
http://currentlydown.com/

etc etc

Basically a lot of bored/creative programmers etc who like creating useful things for public consumption. 

AND it's not limited to websites. There are toolbars, browser extensions, and even access via REST APIs. 

Ever wondered what your favorite website is running? This is an oldie but goldie:

http://toolbar.netcraft.com/site_report

Since I run a large website as my day job I spend half my day looking for tools to make my life easier (or I write my own when I don't find them). 
(Edited)
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David Warnberg

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So, since I am new to this and excited to give it a shot, what exactly am I listening for?  is this a simple CW tone, a SSB transmission tone, a beacon, what?

Like just now there was some weird looking pulsing signal at about 14.097.900

Thanks
(Edited)
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Steve - N5AC, VP Engineering / CTO

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Can you download PuTTY and try using it?  You should always get a response back -- if for no other reason that to tell you that your command was received and doesn't mean anything to the radio.  I used this command on my mac to access the radio:

screen telnet 192.168.1.58 4992

Here's my output:

Trying 192.168.30.58...Connected to 192.168.1.58.
Escape character is '^]'.
V1.3.0.0
H86C07A9A
M10000001|Client connected from IP 192.168.1.67
S86C07A9A|radio slices=7 panadapters=7 lineout_gain=46 lineout_mute=0 headphone_gain=50 headphone_mute=0 remote_on_enabled=0 pll_done=0 freq_error_ppb=0 cal_freq=15.000000 tnf_enabled=1 snap_tune_enabled=1 nickname=N5AC_Dev callsign=N5AC binaural_rx=0 full_duplex_enabled=1 band_persistence_enabled=1 rtty_mark_default=2125 enforce_private_ip_connections=1
S86C07A9A|radio filter_sharpness VOICE level=2 auto_level=1
S86C07A9A|radio filter_sharpness CW level=2 auto_level=1
S86C07A9A|radio filter_sharpness DIGITAL level=3 auto_level=0
S86C07A9A|radio static_net_params ip= gateway= netmask=
S86C07A9A|interlock timeout=0 acc_txreq_enable=0 rca_txreq_enable=0 acc_txreq_polarity=0 rca_txreq_polarity=0 tx1_enabled=1 tx1_delay=0 tx2_enabled=0 tx2_delay=0 tx3_enabled=0 tx3_delay=0 acc_tx_enabled=0 acc_tx_delay=0 tx_delay=0
S86C07A9A|eq rx mode=1 63Hz=10 125Hz=10 250Hz=10 500Hz=10 1000Hz=10 2000Hz=10 4000Hz=10 8000Hz=10
S86C07A9A|eq rxsc mode=1 63Hz=0 125Hz=0 250Hz=0 500Hz=0 1000Hz=0 2000Hz=0 4000Hz=0 8000Hz=0
S86C07A9A|client 0x86C07A9A connected
c1|slice get_error 0
R1|0|+19.073483,+9.536743
c1|jkdhsf sdkhf ksldf
R1|50000015|

Even the last command that is gibberish gets a response.  If you get nothing back, there's a problem with what the radio is (isn't) seeing from your client.  There's also a setting in PuTTY that allows you to specify how <LF> or <CR><LF> are handled that will make everything appear in a single line.
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Tim Taylor

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Steve,
I used my MAC and it worked perfectly. Thank you very much.
73,
Tim K8XS
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Tim Taylor

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Also used PuTTY and it worked fine. There must be something I am not setting in the Microsoft version. Thanks Steve. Another satisfied customer!!
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Ken - NM9P, Elmer

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Thanks for the hint, Steve.  
I had never thought about "puttying around" the 6500!
I tested a few simple commands with success.

I didn't realize exactly how easy it was to send TCP/IP commands via Telnet.
I have programmed information exchanges for the MIDI Control project that got stalled, but This has convinced me even more that all I need to do is learn enough to open up and read a serial port and a TCP port and I should be able to write a basic MIDI controller interface in C#.   Perhaps a summer vacation project.....
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Andrew Russell

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Steve,
I had some trouble with no response to c21|slice get_error 0 in telnet and PuTTY on
win7
Even after connecting to the radio on its local address and the correct port.
Just now tried PuTTY on win10 64bit.
Connected OK but no response on slice 0.
Though running on Slice A in one panadapter on the Maestro the initial screen reported 3 panadapters and 3 slices.
After bit of lateral thought I tried slices 1-4.
Got a response on slices 2 and 3 of R1|0| +0.000000, +8.010864
Slice A 1.8366 MHz running WSPR.
No response for slices 0, 1 or 4 (know that for the 6500 there  is no 4)
However c21|slice list (not l) returns R21|0|0
So no response if the slice numbers are wrong.
My radio must be a bit confused!

Why are RX and TX different?

Is there a simple math way of mapping any decimal frequency to an integer binary FTW?

Andrew VK5CV
(Edited)
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K1FR

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Any opinions re recommended/favorite windows programs for measuring the audio frequency of the tone in the passband?  Thanks.

And, thanks to Steve for posting the FMT info. Looking forward to the next FMT.

73, Tom
K1FR
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George - AB4FH

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Congratulations to the Flex community for a good showing, overall.  Many who used 6500/6700 radios achieved < 1 Hz accuracy with many under 0.1 Hz.  Results are available by Googling "ARRL FMT Results"
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Norm - W7CK

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I wasn't able to make it.  Was it possible to test 2 meters as well?    My 6700 is WAY WAY off on 2 meters.
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Ria - N2RJ, Elmer

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The test was on 20, 40 and 80m only.
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Ria - N2RJ, Elmer

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Dave KD5FX

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I used my 6300 and DM 780. Before the contest I tuned WWV on 2.5, 5.0, 10.0 and 15.0 and offset my USB tuning by 500 hz to watch the beat tone on DM 780. That worked pretty good but I found that the calibration setting required varied a great deal from band to band. Can you explain why that would be?

Below is the chart I used to set my calibration in the FLEX S/W before each part of the FMT. I got pretty good results, under 1 HZ on 40 and a little over 1 HZ on the other bands.
The ppb numbers for the WWV freqs are exact numbers I discovered for those freqs and the other numbers are interpreted. 

Freq  ppb
2.5    9000
3.8    6750 80 mtrs
5.0    4500
7.5    3400  40 mtrs
10.0  2300
12.5  1950
15.0  1600  20 mtrs
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Dave KD5FX

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Steve - N5AC Can you answer my question above?
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k3Tim

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This is my first FMT and by dumb luck was within 0,38, 0.02 and 0.09. I had the 20 meter freq but due to Operror overwrote it, otherwise had a shot at the "green box". With Steve's information about the milli-hertz read_error API and this experience hope to do better in Nov.

k3Tim/6
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Bob Brown - N8OB

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I submitted my readings for the latest ARRL FMT and the results they printed are impossible to be anywhere near correct.  It says I was reading a frequency of 100 million.  If you subtract the reading for each band, my readings are very close to the transmitted frequencies.  Check it out...N8OB
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Bob Brown - N8OB

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It was submitted in HZ.  In the past, it would not accept the wrong info.
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Mike va3mw

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On the results page you entered frequencies around 92mhz. What did you mean to enter?
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Bob Brown - N8OB

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K5CM - 80  3598118.50
K5CM - 40  7064197.48
W8RKO - 80  3598215.73
W8RKO - 40  7064083.50

These were the readings I measured and thought I entered.
N8OB - Bob
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Mike va3mw

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This is what you entered.

It looks like 100Mhz on each field.  That must be a bug, so I would email them and ask them to update your entry.

Your results look great and about what I got with my 6300.  

73

(Edited)
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Bob Brown - N8OB

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I can't find an Email address to send to for them
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Ria - N2RJ, Elmer

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I got curious to find out what the transmitter was. Found this:

http://www.k5cm.com

K5CM FMT transmitting equipment:

A HP Z3801 GPS frequency source clocks a HP-3336B. A 10 db transistor amp follows and drives a 12BY7 / pair 6146. Then to the final amplifier running 300 to 400 watts out.  There are no mixers or any device in the chain of amplifiers that might impact the accuracy of the GPS frequency source.  As a reality check,  I periodically log the frequency source against WWV and other GPS referenced sources.  I monitor each transmission with a completely separate receive system to look for any instability or short term drift. The separate system is not locked to the GPS transmitting system.

I typically see considerably less than 1 mHz difference at 10 Mhz when comparing  two Z3801's or a Z3801 and a Tbolt, over a 10 second period. 

 

Antennas:

160 - Vertical 

80 -  Cage Dipole (favors East, West, and North) or Dipole slopping down from 140' tower.

40 - Dipole hanging between two 80' towers (favors East, West)

30 -  Dipole

20,17,15,12,10  - 4 element SteppIR 

 

 W6OQI FMT transmitting equipment:

My transmitting setup consists of a HP Z3801 clocking a HP 3336B which drives a Johnson Viking I transmitter, the output of which is attenuated by a 6 dB attenuator, to then drive an Icom PW-1 amplifier to about 500 Watts. The antenna is an inverted Vee which favors north and south from the Los Angeles area. The QTH is actually La Canada, CA at 2000 foot elevation on the mountains on the north side of the Los Angeles basin. The Rose Bowl in Pasadena is about three miles to the east.  


I am amazed that these guys went pretty old school for their transmitters. 

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Ria - N2RJ, Elmer

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The latest version of WSJT-X (1.8 RC) brings a GUI for the frequency measuring tools. Way cool. This is my 6700 (stock with OCXO) on 15 megs. 

(Edited)
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Mike va3mw

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That is cool.  I will have to see how my stock 6300 plays out.  I was getting used to the command line stuff too.  :)
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Ria - N2RJ, Elmer

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Mode > FreqCal.
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Bob Brown - N8OB

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I would like to see the same test with an installed GPSDO
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Ria - N2RJ, Elmer

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It's on my list of things to get. :)