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Author Topic: on FT-8 if my signal is not getting through can I turn on the amplifier?  (Read 2479 times)
K1YTG
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« on: October 24, 2017, 12:46:08 PM »

What precautions should I take if I try to use an amp on FT-8?

What power output should I aim for?

It is a low power mode but more power would help, I assume for DX.

Thanks, Norm
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N6YFM
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Posts: 502




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« Reply #1 on: October 24, 2017, 01:20:21 PM »

What precautions should I take if I try to use an amp on FT-8?

What power output should I aim for?

It is a low power mode but more power would help, I assume for DX.

Thanks, Norm

1.   If I try to use an amp on FT8?      DON'T!!

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

Seriously, all stations use an average power of somewhere from 10 watts to 35 watts.
That is why most signals on the waterfall look ~approx. the same intensity.
When someone comes along and transmits 300 watts, it desenses EVERYONEs receivers,
turns the waterfall solid red, and makes more than several dozen people curse.

If hundreds of stations, some using low wires and loops inside their apartment can hit
psk reporter for thousands of miles, I might suggest looking into what else is wrong
instead of using an amp and destroying the band for all other FT8 users in a 2,000 mile radius.

For example;

1.   What does your output wattmeter show?
2.   What does an antenna analyzer say about your feedline and SWR?
3.   Is your audio drive level just at the point of showing ALC action but
      backed off a tiny bit?


Can you explain what you mean by "not getting out"?
Does this mean that you see output power on your meter of approx. 25 watts,
and you can monitor your audio level and it sounds clean, undistorted, but
that psk-reporter is not showing you received anywhere?

Please get into specific detail and people here will try to help.
The math behind FT8 (and all JT type modes) does not require more than
5 to 40 watts to hit multiple continents....

Lets get you set up correctly instead of turning to an amplifier, which is
this case will only amplify the problems for everyone.

Cheers,

N6YFM


2.
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AA6YQ
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« Reply #2 on: October 24, 2017, 01:36:16 PM »

When necessary, I run about 800 watts of RF output power on FT8. With its high duty cycle, amplifier power limitations are comparable to those when using RTTY.

I've made several QSOs on 160m FT8 that could not have been made without QRO; this is the relevant criterion for deciding whether or not to turn on your amplifier.

Whatever mode you're using, do be certain that your signal is clean.
« Last Edit: October 24, 2017, 01:38:41 PM by AA6YQ » Logged
AA4PB
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« Reply #3 on: October 24, 2017, 02:59:58 PM »

"The math behind FT8 (and all JT type modes) does not require more than
5 to 40 watts to hit multiple continents...."

It seems to me that this depends on the band and the conditions at the time. You just can't accurately make flat statements like that. For example, I work mostly 6M with FT-8 and I can assure you that most of the time you won't hit multiple continents with 5 to 40W (or even 1500W).

I have a station about 10 miles from me who often puts in a 10/9 signal here. That doesn't stop me from working other weaker signals.

Now I'm not proposing that everyone run 1500W to a 3el Yagi at 60 feet on 20M. However, a reasonable increase in power to compensate for a limited antenna or a band with poor propagation seems acceptable to me.
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Bob  AA4PB
Garrisonville, VA
AA2UK
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Posts: 308




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« Reply #4 on: October 24, 2017, 03:07:39 PM »

Depending on the mode the duty cycle is 50 to 95%.
If you are running VHF and up digital modes it's very common for stations to run 500 to 1000 watts even LL.
HF is entirely different and I don't operate HF so I can't comment.
MSK144 transmission cycles are generally 15 secs on 15 secs off. This is repeated until a contact is completed.
Some operators prefer 30 sec sequences on 2 meters and up.
One 222MHz MSK144 (meteor scatter) contact took longer than 1 hour to complete.
"SH" is normal for contacts on 2 meters.
Make sure your driver (the rig) and the amplifier have proper cooling. Also RF relays can get pushed to their limits.
There seem to be different rules of the road for VHF and up operation and HF operations.
Bill AA2UK

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N2NL
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« Reply #5 on: October 24, 2017, 03:35:55 PM »

The official answer is "Use the minimum power necessary" up to the legal limit allowed.

The question to ask is this:  Are you confident that the station you are working cannot decode you, while calling in the clear, with lower power and this is not something due to your time sync, setup, or otherwise?  If he is working callers, it's possible he sees your call decoded on his screen, and he's just not gotten to you yet.  By running more power in this scenario, you will still show the same on his screen, granted possibly with a louder dB signal report, but otherwise the same as you were calling before.  The operator might avoid working you if he sees that you are "excessively loud" or wide in comparison to the band activity waterfall.

If you're on, say, 80m and the station you're calling is weak (and you have a low noise floor), you very likely will need to run more power.  You don't know the other station's noise situation and whether or not he is dealing with line noise, using a sub-par antenna, etc.

Everyone knows a better antenna gives you more performance than more power alone, but there is no law against running up to legal limit, assuming you are transmitting a clean signal.  I would argue that a station running 30W with a dirty signal to a large antenna (such as a monobander, high in the sky) will cause far more damage to other users on the band than the station running 300W to a dipole with a clean signal.

I was recently QRV as WH7AA from Hawaii in the middle of the Pacific running 100W into a three-stack of 5el monoband antennas on a 90ft tower.  The power was necessary to work EU, over the pole, where band activity (and subsequent QRM/noise floor) is much higher.  There were times when I wished I had more power as it would sometimes take 4 or 5 minutes to complete a QSO due to problems being heard in EU.  With an average opening lasting less than 60 minutes per day, time mattered.  I am also QRV as N2NL from my remote station in FL, with decent antennas on a 60ft tower.  From FL, 70W more than plenty to work anything on the higher bands, though I have had to run more power to work stations such as 4S, HS, YB, and other difficult paths, as well as QSOs on the lower bands (80/160).

73, Dave
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NN2X
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« Reply #6 on: October 24, 2017, 04:04:55 PM »

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..I guess you can send a signal off to some other distant planet! (Or another solar system)

Cheers, see you all on the bands

Tom, NN2X

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K0UA
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Posts: 1368




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« Reply #7 on: October 24, 2017, 04:51:16 PM »

I have never owned an HF amp, but I am not anti QRO.  As others have stated, on 6 meters running MSK144, I run 100 watts and that is QRP.  Yes I said QRP.  I am in the minority, and yes I make plenty of 6 meter MSK QSO, but I and my QSO partners have to work a lot harder, and wait a lot longer.  Most guys run from 300 to 1500 watts, with about 700 common. Bouncing signals off of meteor trails is hard work sometimes.

 Now on to FT8.  Well the propagation modes are much different on the the lower frequencies, although I do see some meteor pings on 10, but I don't think they do much good running FT8 as they are so brief. Many times running more power would not do much good as the other guy is probably not running much power either.  This may not always be true, and the lower bands like 80 and 160, are where a lot of power may be necessary to close the loop, as a lot more folks are running power on those bands.  They always have on CW and SSB to fight the noise level, so why should this digital mode be any different?  The point is, run the amount of power that you need to close the loop.  If that is 10 watts then run 10 watts. But use common sense,  If all your QSO partner's are -20 and they are all giving you +19 or something like that all the time, every qso, use common sense and turn down your power.  That illustration may be an exaggeration but you get the idea. Don't run any more power than you have to.

To sum it up, run what power you have to , and no more. If you antenna efficiency is in the toilet, and from the descriptions of some of your antennas lately, I believe this is more the norm than not, then you may need some power to be heard.  But still use common sense, if you aren't hearing anything either, what is the point?

You all should set up and run WSPR on each band and let it run for an hour or more, and check the results.  Start at 5 watts out +37dBm and go down for there.  It will open your eyes to what you can do with low power.  And don't forget that the majority of "getting out" is about propagation and antenna, not power. In any case you will get a baseline of what your station and its antenna system is capable of.

Good luck and have fun.   
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K0UA
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« Reply #8 on: October 24, 2017, 04:56:39 PM »

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.
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K5UNX
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« Reply #9 on: October 24, 2017, 05:28:03 PM »

What precautions should I take if I try to use an amp on FT-8?

What power output should I aim for?

It is a low power mode but more power would help, I assume for DX.

Thanks, Norm

Looks like you are getting out now according to hamspots.net. The list are stations that heard you on the air today. This isn't the complete list, check it out.

X   +2h   AD0QI   KS   United States   15   FT8   +6   0.6
X   +2h   AI4DD   FL   United States   15   FT8   -06   0.6
X   +2h   AJ9D   IN   United States   15   FT8   -12   0.7
X   +2h   K2LYV   FL   United States   15   FT8   -03   0.6
X   +2h   K3MA   PA   United States   15   FT8   +1   0.6
X   +2h   K4JT       United States   15   FT8   -16   0.6
X   +2h   K4MY   GA   United States   15   FT8   -12   0.5
X   +2h   K4SO   VA   United States   15   FT8   +5   0.8
X   +2h   K5CM   OK   United States   15   FT8   -08   0.8
X   +2h   K6SID   CA   United States   15   FT8   -07   -0.1
X   +2h   K7WLX   NV   United States   15   FT8   -18   0.6
X   +2h   KA4RSZ   GA   United States   15   FT8   +3   0.6
X   +2h   KB3FF   MD   United States   15   FT8   +7   1.3
X   +2h   KD2KW   TX   United States   15   FT8   -14   0.7
X   +2h   KE0HQZ   SD   United States   15   FT8   +13   0.6
X   +2h   KE0NOS   ND   United States   15   FT8   +2   0.8
X   +2h   KG5WR   TX   United States   15   FT8   -06   0.6
X   +2h   KK6ZIZ   CA   United States   15   FT8   -19   0.5
X   +2h   N1HRK   RI   United States   15   FT8   -02   0.6
X   +2h   N2NL   FL   United States   15   FT8   -03   1.5
X   +2h   N4CY   AL   United States   15   FT8   -11   0.6
X   +2h   N8DEA   OH   United States   15   FT8   -22   0.6
X   +2h   N8YSZ   VA   United States   15   FT8   -05   0.6
X   +2h   N9OJC   IN   United States   15   FT8   -15   0.5
X   +2h   VK2RT       Australia   15   FT8   -03   0.7
X   +2h   W0QL   CO   United States   15   FT8   -19   0.7
X   +2h   W2GPK   NJ   United States   15   FT8   -02   0.5
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W5DXP
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« Reply #10 on: October 24, 2017, 05:45:39 PM »

When someone comes along and transmits 300 watts, it desenses EVERYONEs receivers,...

What AGC setting should one use for FT8 and PSK31?
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VA3VF
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Posts: 802




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« Reply #11 on: October 24, 2017, 06:00:24 PM »

Looks like you are getting out now according to hamspots.net. The list are stations that heard you on the air today. This isn't the complete list, check it out.

I was going to mention Hamspots.net for the same reason. It's clear you are getting out.

An amp may help, but there are other 'variables'. In addition to the vagaries of propagation, the FT8 segments can be very busy at times. Stations TXing on top of each other is becoming too common. My rate of incomplete QSOs is increasing. I'm not sure higher power would have made a difference in most situations.

As mentioned already, use the least clean power needed, up to your license limits. JT modes are weak signal modes, not low power modes necessarily.

I'm talking about HF (80-10). Other segments may operate differently.
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VA3VF
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« Reply #12 on: October 24, 2017, 06:02:43 PM »

When someone comes along and transmits 300 watts, it desenses EVERYONEs receivers,...

What AGC setting should one use for FT8 and PSK31?

I believe AGC should be off for most digital modes. JTDX has an option to deal with transceivers that cannot switch off AGC.
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WB2KSP
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« Reply #13 on: October 25, 2017, 07:12:32 AM »

When someone comes along and transmits 300 watts, it desenses EVERYONEs receivers,...

What AGC setting should one use for FT8 and PSK31?

I believe AGC should be off for most digital modes. JTDX has an option to deal with transceivers that cannot switch off AGC.


AGC would be processing and I believe most modern radios allow the user to select AGC (or Proc) on or off. The ALC level should also be set as low as possible (preferably just outside of ALC range).
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K0UA
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« Reply #14 on: October 25, 2017, 10:10:04 AM »

When someone comes along and transmits 300 watts, it desenses EVERYONEs receivers,...

What AGC setting should one use for FT8 and PSK31?

I believe AGC should be off for most digital modes. JTDX has an option to deal with transceivers that cannot switch off AGC.


AGC would be processing and I believe most modern radios allow the user to select AGC (or Proc) on or off. The ALC level should also be set as low as possible (preferably just outside of ALC range).

Most of the newer radios won't allow the processor to be turned on when in the USB-D mode.  Of course some radios don't have a Data mode at all.  So yes make sure the processor is off.
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