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Old 02-01-2011, 12:12   #1
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Zero Beat a CW Station with an M700Pro

I'm setting up my rig and haven't gotten my key yet, but in anticipation, I was trying to see how best to zero beat to another station when using CW.

I've got an M700Pro and switching the CW break-in mode -- one method -- requires turning the radio on and off. CW doesn't have a carrier wave, so I'm a little stumped and figured I'd ask others who may have the same radio what they do.

Sorry if this is a dumb question. I'm a new ham and still getting used to radio, so any advice would be more than welcome -- google wasn't any help.

thanks...
don
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Old 02-01-2011, 18:26   #2
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The break-in setting has nothing to do with zero beating. Full break-in allows you to receive between the dits/dahs that you send. That's my prefered method of operating cw but many ops do not like it. To operate cw on this rig you really need to install the 500hz filter. You cannot zero-beat exactly since you can only adjust your freq in 100hz steps but that's close enough for a QSO. You also cannot change the cw offset on this rig which determines the tone of the received cw when you are zero beat. Zero-beating is a bit of an art and many ops don't do it or don't know how or even care. It's a sign of a good operator in my opinion. There is no "spot" tone function with this rig as there is with most ham radio's nor can you quickly switch sideband mode (reverse cw) which is another method used with ham rigs. In order to truely zero-beat with this rig, you need a separate audio tone generator to do it with. I created a little web page about zero beating a while back.

Eric
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Old 03-01-2011, 06:01   #3
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Hi Eric:

Thanks, that' very helpful. I'll get my key soon and give it a try. Btw, another ham who uses Winlink suggested I get a 100hz filter for use with my Pactor modem to get email. What would you recommend? I definitely want to do CW, so would the 500hz filter be sufficient for both?

Also, not sure I understand what you mean by "separate audio tone generator."

thanks...
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Old 03-01-2011, 09:35   #4
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After looking around for filters, I realize my friend meant the FL-100, which is a 500hz filter, but instead of a typed 100hz filter. I think he just uses his for email anyway, which might explain the confusion. I'll order the FL-100.
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Old 03-01-2011, 10:09   #5
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I don't think you will want a 500 Hz filter active if you will be using Pactor 3, it requires more bandwidth than that. It would be OK for Pactor 2 but won't usually be helpful. Eric will correct me if I'm wrong! As for CW the filter can be very helpful, though you often won't need it unless the band is crowded.

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Old 03-01-2011, 10:57   #6
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Zero beating "on the fly"

Wow, I didn't know anyone was interested in this anymore. I was an ET in the Navy working on a high power HF site. One of the duties was to log in all of the transmitter frequency errors on the fly as they were on the air, SSB, CW, AM, and FSK. All are doable. The zero beat accuracy is, of course, dependent upon the time base accuracy (of your rig, in this case) and the assumed or known offset of the tone from the carrier. SSB is actually easy because the carrier is merely suppressed, not entirely missing.

You adjust your rig's freq. up or down in whatever minimum steps that you have listening to the resulting tone. The tone decreases as you match the incoming signal then rises again as you pass it by. It sounds like a drummer hitting the drum as the drum head gets softer. If you have a very small incremental change available to match the carrier you will hear the tone dissappear and then hear a "wah-wah" beat in the one-cycle-per-second or less range. You can get very accurate with this method. Obviously you must pay attention only when the incoming signal is there and be quick.

There is a physiological/psychological grasp of the signal required for you brain to recognize the sound in the midst of all the noise and it takes a log of practice. The brain can pick a signal out to zero beat far below the noise level much like modern correlation techniques today are used with sophisticated analyzers.

Good luck!
Rick
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Old 03-01-2011, 11:07   #7
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I just check with Icom to be sure, but the FL-100 500hz filter, when enabled, is only active in the CV/FSK modes, so it shouldn't a problem for Pactor III.
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Old 03-01-2011, 11:31   #8
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The 500hz filter in these marine rigs is only functional in cw or fsk modes. It doesn't do a thing in ssb. (I see you already figured that out while I was composing my reply :-))

The cw offset in these rigs is about 1000hz. This means that if a station is transmitting cw on say 14.050mhz and your dial is set to 14.050mhz, you will hear 1000hz tones. In a ham rig, you can adjust the cw offset to whatever tone you are comfortable with operating at. You can't do this with the marine rig other than just adjusting your clarifer control. The big problem with not using the filter for cw operation on the marine rig is that you will hear the received signal on either sideband. In other words, if a station is xmitting on 14.050mhz, you can hear it on 14.050 and 14.052, but which freq is he really xmitting on? If your just tuning around the band and come across someone calling CQ on 14.052 and then try to reply, he may very well actually be on 14.050 This does not occur on ham rigs no matter what your bandwidth filter setting. With the 500hz filter in the marine rig, you will only hear him on the correct frequency. You can zero beat with your ear pretty close once you get used to what 1000hz sounds like but to get spot on, you need a 1000hz tone to properly zero beat on. Ham rigs provide the proper tone (depending on your selected cw offset) but marine rigs do not. I have one of those little micro-recorders (separate audio tone generator) for recording conversations that has a folder with just tone files that I put in it. I can just play the 1000hz tone and use it to zero beat when using my M710 that I use in my shop for cw.

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Old 03-01-2011, 11:32   #9
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Hi Rick:

When were you in? I was in the Corps back in the 80's -- did 2 med floats out of Camp Lejeaune. On the floats, I was the CMS custodian, so I kept all the paper tapes for keying the crypto gear, but didn't know a thing about radios.

In fact, in boot camp, they had me take a morse code test, but did so poorly, I ended up in a scout/sniper section of a STA platoon -- I was a pretty good shot back then.

Anyway, thanks for the tip. I'll get my key any day now, and can't wait to try it out.

semper fi...
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Old 03-01-2011, 11:47   #10
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Hi Don,
You don't need a narrow filter to zero beat anything, yet it may make it easier in some cases once you identify exactly which signal you want to track, more difficult when you are looking for a signal.

BTW, I could actually identify a particular transmitter by the signature of the carrier and/or modulation after a few years of doing the checks and calibrations.

Was in between '62 and '66 on Mare Is. Calif with 63 transmitters having between 500 W and 100kW PEP. A lot of gear to work on. The antenna field was huge, considering that a half-wave rhombic antenna working on 2 MHz was almost two football fields across, yet those signals would work half way around the world reliably even when the higher freqs might not.
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