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Author Topic: on FT-8 if my signal is not getting through can I turn on the amplifier?  (Read 2505 times)
AA4PB
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Posts: 14335




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« Reply #15 on: October 25, 2017, 11:42:19 AM »

AGC is not processing. AGC is the receiver Automatic Gain Control. It is intended to prevent strong signals from overloading your receiver and creating distortion products inside the receiver. If you turn the AGC off then there is the possibility of the stronger signals overloading the receiver and causing even more problems receiving weak signals. If you do turn AGC off then be prepared to control the receiver gain manually with the RF gain control. Personally, I leave the AGC on and I've not had an issue with receiving weak FT-8 signals. FT-8 seems to have plenty of dynamic range so that weak signals are still decoded even when a strong in-band signal is causing the AGC to reduce the receiver gain. PSK31 is another matter. My solution there is to place the weak signal inside a narrow (50Hz) filter so that the strong signal does not impact the AGC. An alternate option is to place a notch filter over the strong signal.

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Bob  AA4PB
Garrisonville, VA
AA2UK
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Posts: 309




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« Reply #16 on: October 25, 2017, 11:57:23 AM »

AGC or Automatic Gain Control is a receive function. Generic radios have fast, normal and slow.
When using MSK144 you want AGC either turned off or set to fast. Slower AGC's will result in lower signal reports, sometimes missed meteor scatter decodes.
All other modes AGC can be custom tailored.
Bill, AA2UK
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WC4R
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WWW

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« Reply #17 on: November 06, 2017, 06:07:06 AM »

Oh, I didn't address this, but others did, I see so many very dirty FT8 signals.  I have tracked down, and telephoned several operators and helped them set their audio levels.  I would rather see a loud but clean FT8 signal than some of the horrible but not all that strong signals I have seen lately. I have seen some that were putting almost as much energy in their spurious signals as they had in their fundamental.

If you get a phone call from me, it is meant in the spirit of ham friendship, and my intent is to help you.

As a new FT8 op here, THANK YOU for checking up on us new folks. We may think we are clean but a second opinion out a ways is always nice.
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K0UA
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Posts: 1371




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« Reply #18 on: November 06, 2017, 07:05:52 AM »

Oh, I didn't address this, but others did, I see so many very dirty FT8 signals.  I have tracked down, and telephoned several operators and helped them set their audio levels.  I would rather see a loud but clean FT8 signal than some of the horrible but not all that strong signals I have seen lately. I have seen some that were putting almost as much energy in their spurious signals as they had in their fundamental.

If you get a phone call from me, it is meant in the spirit of ham friendship, and my intent is to help you.

As a new FT8 op here, THANK YOU for checking up on us new folks. We may think we are clean but a second opinion out a ways is always nice.

I have had to do some pretty serious detective work to track down a phone number for some guys.  I wish everyone ran with JT alert so I could text them instead of spending time tracking them down them in whitepages.  Real interesting when the phone is in the wife's name.  I can usually find them too, but it can take some time.  Of course a lot of people won't take phone calls from someone they don't know either.
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K6BRN
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« Reply #19 on: November 07, 2017, 11:28:48 AM »

One problem with "Dirty" FT8, JT-65, JT-9 signals, is that many are not "dirty" at all, but rather the result of an ignorant user on the RX end not adjusting their RX sound card levels, WSJT-X levels (they are separate adjustments) and rig RX gain appropriately.

On strong signals, the sound card interface ADC, WSJT-x processing bitwidth or rig front  will begin to saturate, the spectral plots bloom like Outback onions and duplicates of signals multiply like Tribbles.  And all this can be caused by nearby neighbors or "spotlight" propagation over driving improperly adjusted RX settings.

Many new (and even some experienced) users of the FT and JT modes don't set TX or RX levels very well and have problems on one side, the other, or both.  Lots of goofy "lore" on how to do this on line, especially concerning AGC action.  So its really not that simple for a beginner to master.

So, first, before complaining like HOA graveyard committee members about someone else's signal, make sure your own computer, sound card and rig are configured properly.  In fact, you might want to buy a spectrum analyzer and RF coupler to do this and learn how to use them (this is almost biblical - "throw the first stone-ish").  And then, when you see a "dirty" signal, try and mentor the user and walk them through adjustment rather than rip them a new one.

Brian - K6BRN

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W6UV
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Posts: 792




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« Reply #20 on: November 08, 2017, 07:53:52 PM »

2.   What power should I aim for?        25 to 35 watts.

Wow! 25-35 watts? It's been proven that it's possible to make world-wide contacts with 1 milliwatt of power, so why is everyone using such excessive power levels like 25-35 watts?

I took math in school before "new math" became popular, so perhaps you can explain to me how this new math behind FT8 mandates low power.
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VA3VF
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« Reply #21 on: November 08, 2017, 08:09:53 PM »

2.   What power should I aim for?        25 to 35 watts.

Wow! 25-35 watts? It's been proven that it's possible to make world-wide contacts with 1 milliwatt of power, so why is everyone using such excessive power levels like 25-35 watts?

I took math in school before "new math" became popular, so perhaps you can explain to me how this new math behind FT8 mandates low power.

The 25-35 Watts has more to do with the safe operation of a typical 100W transceiver, than range. Weak signal operation is not necessarily low power, and high power is ok, if that is what it takes to complete the contact, and the equipment can handle it.

As for the 1 mW of power, sure, how many QSOs per hour and the distances covered? If 1mW was the 'mandated' power for FT8, the mode would be dead. I'm a big fan of milliwatting, but to advocate that as standard operating practice is suicidal for the hobby, regardless of the mode.
« Last Edit: November 08, 2017, 08:12:08 PM by VA3VF » Logged
W6UV
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Posts: 792




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« Reply #22 on: November 09, 2017, 09:00:59 AM »

As for the 1 mW of power, sure, how many QSOs per hour and the distances covered? If 1mW was the 'mandated' power for FT8, the mode would be dead. I'm a big fan of milliwatting, but to advocate that as standard operating practice is suicidal for the hobby, regardless of the mode.

By advocating use of 1 mW for FT8 I was creating a straw man to battle that other straw man that says FT8 and the other JT modes are low-power modes..
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AA2UK
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« Reply #23 on: November 09, 2017, 09:06:10 AM »

As for the 1 mW of power, sure, how many QSOs per hour and the distances covered? If 1mW was the 'mandated' power for FT8, the mode would be dead. I'm a big fan of milliwatting, but to advocate that as standard operating practice is suicidal for the hobby, regardless of the mode.

By advocating use of 1 mW for FT8 I was creating a straw man to battle that other straw man that says FT8 and the other JT modes are low-power modes..
These modes are certainly not low power when used on 6 meters and up.
1mw/ 0dBm is often cited but rarely used and when so it's almost exclusively when using WSPR mode.
Bill AA2UK
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W6UV
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Posts: 792




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« Reply #24 on: November 09, 2017, 10:31:34 AM »

These modes are certainly not low power when used on 6 meters and up.

And they don't necessarily need to be on HF either. I use whatever power is needed to make a contact.

While I have sympathy for all the guys living in HOA areas who have to load up their rain gutter as an antenna and use low power to fly under the radar, you can bet that if P5 comes on FT8 tomorrow I'm going to be in there with 1500 watts and big beams trying to work them.
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K0UA
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Posts: 1371




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« Reply #25 on: November 09, 2017, 04:00:38 PM »

These modes are certainly not low power when used on 6 meters and up.

And they don't necessarily need to be on HF either. I use whatever power is needed to make a contact.

While I have sympathy for all the guys living in HOA areas who have to load up their rain gutter as an antenna and use low power to fly under the radar, you can bet that if P5 comes on FT8 tomorrow I'm going to be in there with 1500 watts and big beams trying to work them.

Truth be told a lot of guys are running some significant power now.  I managed to work Hawaii last night on 80 meters FT8, but it took 100 watts to do it with my low (35foot) OCFD antenna for 80 meters, and my report was only -21 at that.  Would a few more hundred more watts have helped?  yeah, probably, but of course getting the antenna up in the air would have helped too, but that isn't very practical here.  Hawaii was the last state I needed on 80, and just need 5 more on 10 meters to finish 5 band WAS. Would I use some power if I had it?  Yeah, if I needed it. And if I had it, which I don't.
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KM1H
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« Reply #26 on: November 09, 2017, 05:42:39 PM »

Quote
I find that is these modes like FT8 and JT65, are really binary when trying to close the link (On or off)..Meaning in most cases (Working DX), on lets say 15 meters, you can use 30 Watts (FT8) / dipole antenna, and if the band is not open you can use 1500 watts, and will not close the link.

In other words increasing the power (For these modes) usually does not gain much as the link will typically close with 30 watts, if more power is required this means the band is dead, and no more matter how much power you use (5000 Watts), it can change the fact that the ionosphere is not reflecting the signal.

If you think about it a bit you will see those statements are dead wrong. Going from 30 to 1500W is a 17dB difference and can make the difference between a contact or wasting your time on ANY mode. While youre believing in Martians or whatever, those with QRO and decent gain antennas are still working the world before the band really goes out...if it really does.

My preference is weak signal DX on CW, especially 160, 80 and 6M where I rarely waste time with 100W when 1200 will do the job often on a first call for a new DXCC counter or a contest multiplier. Or I can run a EU pileup on 6M for hours since most of EU is buried in man made noise. The 1200W + about another 17 dB of gain from the 8 el which includes ground gain is what it takes at times especially when the DX is weak and the path is marginal for 100W to a wet noodle. Working Japan and their 10W Novices on 10M is also interesting since their noise level is also horrendous. JT8 is a big boon to those hams restricted to low power and small antennas but it is also no reason to P&M about those in and out in a few seconds with a lot more ERP. My hilltop also hears better than someone in a concrete box with an indoor wire or a small yagi just above the roof in the burbs.

Carl
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W6UV
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Posts: 792




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« Reply #27 on: November 11, 2017, 02:20:12 PM »

I did an experiment: with the beam pointed to Australia I called CQ on 20M FT8 with 30 watts. After about five minutes I looked at pskreporter and saw that I wasn't spotted by any VK/ZL stations. I turned up the power to 500 watts out and called CQ again. This time pskreporter lit up with a dozen spots of my siganl in VK/ZL and vicinity. So power does make a difference.
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K0UA
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Posts: 1371




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« Reply #28 on: November 11, 2017, 04:21:44 PM »

I did an experiment: with the beam pointed to Australia I called CQ on 20M FT8 with 30 watts. After about five minutes I looked at pskreporter and saw that I wasn't spotted by any VK/ZL stations. I turned up the power to 500 watts out and called CQ again. This time pskreporter lit up with a dozen spots of my siganl in VK/ZL and vicinity. So power does make a difference.

It should have made around 12 dB positive difference in this case.
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