PGXL and rtty contesting at legal limit - possible?

Lawrence Libsch

Hello all.

PGXL Product Description Overview states PGXL "delivers full legal-limit power at 100% ICAS duty cycles." This might seem to imply that full legal limit power during a rtty contest might be operating outside of specs. Many amps require reduced power for rtty. Before I buy one, I'd like to know that I can use the PGXL for full legal limit rtty contesting without power reduction or other limitation.

Please advise.

K4KGG, Larry

Robby

I have used the PGXL for RTTY contesting. The amp has three cooling profiles. Standard, Contest and Broadcast. I set the cooling for Contest. I have tried it at 800W, 1200W and 1500W. The temperature for the finals is about the same. The only difference is the fans run faster at higher power levels. At 1500W the amplifier is still only at 75% output. I dial it down because I know the RX station can't see much difference if any. Sometimes I turn it down more if there are too many stations calling.

1 KW is a nice output level that will get attention and keep the shack cool and quiet and should not stress components.

So to answer your question, you can contest at 1500W if you want but it is hardly necessary in my opinion.

I set the power out and then watch the temperature. The finals do not need to go above 60C. I have seen the temp go higher in a long SSB transmission.

RTTY in a contest is not 100% duty cycle over time. Messages these days are short. I am in receive 2/3 of the time.

Buy it Larry. You won't be disappointed.

73,

Robby

Mike-VA3MW

The PGXL will manage its own heat and if it gets too hot, it will dial back the power for you.

As Robby mentioned the difference between 1000 watts and 1500 in RTTY is pretty minimal even though it sounds like a big number. It is less than a 2db improvement in signal and as a test, get on the air and run both powers while a station is copying you and ask them to provide you with the difference in signal strength. It is less than 1/2 and S unit.

Like driving a car. Floor it when you need to. :)

K5XH

Found this on the web:

ICAS: "Intermittent Commercial and Amateur Service (ICAS) is defined to include the many applications where the transmitter design factors of minimum size, light weight, and considerably increased power output are more important than long tube life. In this service, life expectancy may be one-half of that obtained in Continuous Commercial Service. Under the ICAS are such applications as the use of tubes in amateur transmitters, and the use of tubes in transmitters where transmissions are of an intermittent nature. The term "intermittent" is used to identify operation in all applications other than amateur in which no operating or "on" period exceeds 5 minutes and every "on" is followed by an "off" or standby period of at least the same or greater duration." ICAS service specifies a 5/10 duty cycle, which is 50%.

This seems to apply to tubes. Maybe there is a more modern definition out there.

If you accept this definition then 1000 (or even 1500 for S&P) watts during a SO1R RTTY contest would be OK. In this case the duty cycle would be << 50%. I have run several RTTY contests using SO2R style and can say that at 1200 watts the fan can get really loud. The duty cycle can be much greater than 50% when operating SO2R. Other than the fan noise the amp has worked flawlessly even though I was violating the 50% duty cycle limit some of the time.

Mark K5XH

Lawrence Libsch

Robby, Mike,

Thanks for your replies. My antennas are all wire with no gain -dipoles and ground plane vertical. I need all the dB I can get to compete with the antenna farms and even the tribanders. 2-3 dB is significant to me. I expect to take the plunge.

K4KGG, Larry

Mike-VA3MW

@Lawrence Libsch

I often hear this reply when I get a question about the next 500 watts. Do not lose sight of the big picture when you have your foot mashed to the floor. :)

In 100 contacts, how many times will 1.5db make a difference?

John KB4DU

Yes, 400 watts is 1 s-unit over 100 watts, 800 watts is an additional 1/2 s-unit, and 1600 watts to get the second s-unit over 100 watts.

Lawrence Libsch

Mark,

Thanks. Your contest experience is what I wanted to know. The noise is not an issue for me. My other brand 1500 W amp is very loud also when running RTTY at 1500 W but does not roll back power even in WAE RTTY when exchanging QTC with fills. It's a beast and a workhorse but it can't do SO2R.

Mike, John,

Thanks for your replies. I know the math. My reading tells me many contesters will pursue improvements to their stations that result in improvements of 1dB or more even at considerable expense. My experience tells me the extra power does make a difference. You tell me how many times 1.5 dB will make a difference to a station with no gain antennas if I work 800 Qs in a contest. I don't think you know. I know I don't. I'm not ready to throw away 1.5dB. It's OK with me if others are.

K4KGG, Larry

Neil D Friedman N3DF

Consider upgrading your antennas. Cheaper and more effective than an amp. Helps you on receive as well as transmit.

John K3MA

Dan-N7HQ

Contesting is like most competitive endeavors. For some, competing isn't (necessarily) about winning. Personally, I enjoy "the build" much more than the actual competition. But, if you want to squeeze every legal watt out of your station and that is your object - go for it!

The PGXL is one of the best, if not THE best, "stock" solid-state amp available to the amateur. It is designed for SO2R and to support sustained contest operations. The Lord knows, my PGXL has suffered from many more waves of abuse and **** antennas than any of our customers. The PA has never been on the repair bench.

However, it is still a part of "the build" and not a panacea. I read that is the main point here and akin to this:

You can drive a 4" speaker with a 1kW top-of-the-line audio amp - but it doesn't mean you can successfully use that setup at a rock concert.

73,

Dan, N7HQ

WX7Y

Not sure about RTTY but in my testing on FT-8 for this exact thing keeping a very close eye on all the metering and operating conditions the AMP is definitely not the weakest link and handles full legal limit with no issues.

RTTY is higher duty cycle then FT-8 so if no one from FLEX says for sure I would test using RTTY at full legal power very carefully.

What I ran into running this much power on FT-8 was the Antenna system!

Baluns, even constant mode chokes on your Antenna's, watch the SWR VERY closely and if you see the SWR start to rise gradually then the Balun/RF Transformer is being saturated and can't dissipate the heat, to protect your Balun etc. immediately unkey and let it cool off, If you see the SWR Jumping then there is a mechanical problem with the Baluns connections and arching.

Feed lines are a real issue too, make sure your using very good quality feed line and Teflon connectors properly installed and tight, (RG-Mini8 is a BIG no no). HINT (after a 5 minute RTTY session feel the COAX cable going to the Antenna's and see if it is getting hot). If you see the SWR Jumping then there is a mechanical problem with the Coax connections or arching between the conductor.

ONCE there is a carbon path created from arching your wasting your time trying to clean it well enough, best to replace the arched over parts.

JUST my opinion

Lawrence Libsch

Neil,

Gotta disagree that upgrading my antennas would be cheaper than an amp. Zoning restrictions do not permit a tower here without a legal battle I'm unwilling to wage. Without a tower no yagi at a useful height. If I could put up a tower it would generate much more expense than an purchasing an amp. An amp is absolutely my most cost effective solution.

Dan,

Thanks for your reply.

Bret,

Thanks for the advice. I've been running RTTY contests for years with my dipoles and verticals with legal limit power with none of the problems you describe. I built them with great care and they handle the power. But my amp can't do SO2R like the PGXL. My interest in the PGXL is not because I don't like the legal limit amp I have, it's because I want to do SO2R with my Flex 6600.

K4KGG, Larry

Doug Hall

For crying out loud, guys, Larry just asked if he could run the PGXL in a RTTY contest at 1500W. He didn't ask for help with antennas or baluns or feedlines or anything else. Didn't ask for contesting philosophy advice. Look him up on QRZ - he knows what he is doing, and just wanted to know what the PGXL will do.

K4DSP

Neil D Friedman N3DF

I feel justified in at least asking when a poster proposes feeding a $10,000 station into a $25 no-gain antenna.

Doug Hall

Sometimes it makes sense. I think if I were a top band contester or DXer it would be a no-brainer. How much does it cost to get 11.8 dB of gain over a 160M dipole? Even on 20M you're looking at a monobander on a decent tower.

But again, read his QRZ profile. He didn't want to fight the town over a tower variance. How much would that have cost?

Lawrence Libsch

Doug,

Thanks for your defense.

I'm just trying to make the most of the antennas I can have. It seems to me that's SO2R and 1500 amps. I can afford the purchase and just want to be sure the hardware an handle the challenge. The most challenging contest I work is WAE RTTY. TX there can be quite long when one works a station and then sends 10 QTC, especially if fills are requested. It's a challenge my other brand amp can meet, but many amps can't. I hope PGXL can meet that challenge without rolling back the power because it has gotten too hot.

K4KGG, Larry