The AM Forum

Not wanting to thread-jack....

I just read W1AEX's amazing thread (Thanks!) about using a Flex-5000 on A.M. I'm still drinking from the fire hose so far as SDR goes, but one piece of data really jumped out at me, so now I will again display my on-going ignorance. There is a reference to using a Flex-5000 on A.M. with an Acom amplifier. My thought process says using any modern amp on AM would cause a whole bunch of heat and not be good for the amp (assuming the amp wasn't running at some ridiculously low level of gain).

If I run my TS-480 at 65W (SSB) into my ACOM, the output of the amp is right around 600W or so. I never even thought of trying it on AM at any power level as I was afraid of cooking the Amp.

So... am I all wet (again) or is there some modern amp fairy magic in SDR that makes it work?

73
Jack
WA2OLZ

Nothing magic about a Flex XXXX and any amplifer.  It's just a radio [from the P/A stage onward]

Regardless of the amplifier model you must pay attention to ratings and technical limitations (and understand them).  :)

If it is a surprise to anybody, many ham manufacturers play fast and loose with their output ratings, and fail to mention the modes, duty cycle, etc.

How are you measuring your power levels (input vs output)?  Are you using a peak reading power meter for these measured level (65 watts drive vs 600 watts output).

Be careful of using "rule of thumb" numbers.  You need in addition to a good power meter,  a scope to avoid flattopping on modulation peaks. I think we need more info at your end.

One of my AM setups uses a Flex 5000 with an Ameritron AL82 and am finding for my setup that a carrier level of ~14 watts  coming out of the Flex is about right.  I seldom exceed 200  to 250 watts of carrier coming out of the AL82.  With proper loading I am not seeing any flattopping..

Al

Additions in red are for clarification purposes

http://www.w8ji.com/am_linear_amplifiers.htm

Here is an introduction on AM operation with amplifiers from Tom W8JI (with lots of good links leading to more info).

Great information, that. Thanks!

-- Prepared this note but it failed to go since there was a response in the meanwhile --

Thank you, Al.

My less than scientific measurement consist of simply reading the power readout on the TS-480 and spinning the knob until it reads 65 watts. That does show ~65 watts on the dedicated wattmeter connected to my LDG Pro AT-1000 PRO-II. If I the enable the ACOM Amp, the silly LED idiot meter on its front panel indicates ~600W out and that also matches the LDG. Of course, neither has been calibrated against any standard.

Good point on the scope waveforms. I monitor the audio out of my Valiant that way but have never thought to do so on the ricebox. That would be interesting all on its own.

You used the phrase I couldn't think of in my first post. Al: "Duty Cycle". I would imagine the duty cycle on AM (always on) would generate the heat, at least as compared to AM or CW. RTTY, of course, would also push it, I imagine.

Which Acom Amp?

The original early 1010, what is now called a 1011. A pair of 4CX250Bs, as I recall.

From the Acom 1010 manual:

It provides over 700 W PEP of output power (or 500 W in continuous-duty operation) with less than 60 W of drive.

Single tube operation. A single Svetlana 4CX800A (GU74B) high-performance ceramic-metal tetrode with plate dissipation of 800W (forced air cooling, grid-driven) is used for maximum efficiency.

In the Acom 1011: Two 4CX250B (7203) ceramic-metal tetrodes with a total plate dissipation of 500W (forced air cooling, grid-driven) are used for maximum efficiency.

Select the RTTY mode to operate continuous-duty modes such as RTTY, SSTV, or other data modes. The LED indicator above the RTTY button illuminates and the amplifier operating parameters are changed to reduce tube dissipation. In the RTTY mode, the amplifier output power is reduced to a maximum of 500 W. There is no need to adjust tuning when changing between RTTY and normal modes.

Adjust the drive on the TS-480 as required.

Maybe, just maybe, I'll get enough guts to try it!

Your alternative is to run barefoot with the Flex or TS-480 at roughly 25 watts on AM. Obviously, I would try it with the TS-480 first to get the feel (plus there's less things to diddle with). Familiarity with the Flex and PowerSDR and all the various parameters is not absorbed and mastered in a single sitting in front of the rig even before you would consider connecting it to an amplifier.

I've occasionally used the TS-480 barefoot on AM, Pete, just to do it. Generally end up reverting to the Valiant. The Flex will be in receive-only mode as I work my way through the features, menus and all the great tips I've been pointed to here and on the Flex Community.

The amp question was a reactionary query based on the other thread here on the forum. Gotta' keep learning, you know!

A Phlexx through an AMplifier will easily outdo a Valiant at similar carrier power level due to low modulation distortion and higher level of positive going modulation.

Lots and lots of air.............

There is some advantage with the flex, you can reduce the carrier some with the carrier control, and still keep the PEP.
It can help an amp a bit.

Amplifying AM (or running screen modulation) supplies lots of heat for the house.
I had four 4cx250b/4x150a's running screen modulation and they were good for about 250 to 300 watts carrier output.
In plate modulated service, they would do 1000 watts carrier running easy, 1600 volts and 800 ma for 1280 watts in, about 1000 out, 280 watts out of 1000 plate dis.

I built a grounded grid amp running four 813's at 3KV, 500 watts plate dis, good for about 150 watts out and lots of heat.

You need to consider the power supply as much as the tubes, the carrier is on all the time and most SSB amps have wimpy power supplies.

You may be able to run your amp at 100 watts out.
You could try running it at 75 watts carrier and 500 watts PEP....you would sound loud.
I can do the same thing with screen modulation, turn the carrier level down, and I have run 50 or 75 watts carrier out of a pair of 4x150's with 500 watts PEP and people reported me sounding better then at 100 watts carrier and 500 watts PEP.
Around 100 watts carrier is a fine signal on 40 meters and up, 80 meters early evening.


For a flex, a pair of 3-500Z's is a good starting point.
Three would be better.
Or a 4cx1500 or some such.

That is why I sold the flex stuff, a pair of 812's modulated by 811's will do more then a flex into a big amp.
A pair of 813's will loaf along at 650 watts of carrier out.

Good points, Brett.  I just couldn't part with my Flex receivers.  Come to think of it, that's the reason why I bought them in the first place.

I'm not a buzzardly transmitting type but I run around 250 watts carrier and have never noticed all that much heat from my AL82 - heat yes but quite "normal" to me.

Jack, I still urge you to add a good average / peak reading power meter, an inline RF sensor and the best scope you can afford.  Another excellent tool would be the REA modulation meter^[1] or equivalent mod monitor to properly manage your modulation level.

Al

---

^[1]  http://www.radioassociates.com/ (http://www.radioassociates.com/)

Yes, the receivers are great, and the ability to record and play people back at the click of the mouse is great as well, but its still a 25 watt radio.
Other sdr's can supply the receiver only.

Plenty of people run a flex and an amp, but it takes a big well made amp to get good power output.
It still rubs me the wrong way that I would need a pair of 3-500z's to get the same power output of three 4D32's will do with plate modulation, with very little heat and no fans/blowers.

  Some comments from a Flex 3000 owner concerning amplifier operation on AM.

* QRO with a SDR transceiver is more likely to get RF feedback than a normal station. The big difference is adding a computer. So with your 5K, an RF proof Fireware cable is a must. Ground the computer if a desktop. Use a wireless mouse and keyboard if RF is getting into the system from your hands on the keyboard or mouse while transmitting.

* The Flex software has provision for time sequencing the amplifier keying. Use that feature.

* There will be a need for lots of RF chokes. Preferably keep the antenna away from the shack, and have a good station ground.

* Don't run "resonant tuned" OWL into the shack.  :'(

* The amplifier should have a tuned input, and low SWR in the drive line. Sometimes the AM positive peaks are better using the Flex internal tuner.

* As already stated run the Flex at about ~ 14 watts carrier RF output. The positive peaks are much better here than at 25 watts carrier.

* Run the Amplifier output at about 20% the tuned PEP setting to allow headroom for positive peaks in excess of 100-120%.

Your mileage will vary.

Jim
Wd5JKO

Just sold my Flex 5K to finance another big project. Many of the reasons why have already been echoed in this posting....but primarily I guess I just like knobs and tubes.

They make a very good receiver and an exciter for a big rig or two though.
Very high end receiver, stable output, two antenna ports (or is it three?), and RX antenna port.

Very nice for the price used...

A small flash for Jim 5JKO....RFI problems with a flex radio has been talked about on 160M. Someone in the group mentioned that the fix is to cut the ground wire from the mic. cable to the radio and connect that wire to the case of the Flex radio, instead of the ground of the mic circuit.

Which Flex rig? Which mike input  (Flex 5000 has three)?

    Yes, I have seen that type of fix on many rigs. My points were general, but coming from a Flex 3K owner. In my case I use the rear DB-9 to inject line level audio from a 1:1 600 ohm transformer about 6" away. The electrostatic shield on the transformer connects to the F3K with a short stout ground wire.

    My RFI susceptibility issues are two-fold.

   One is that the low level speech gear picks up the RF, and the magnitude of the problem, and the fix varies band to band. 160m to 40m I use fix A, and 20-10m I use fix B. Since this radio like most SDR's have a latency delay within, any RF feedback has a peculiar sound to it, kind of like a guitar amp howling when the tremolo is turned on. Smaller amounts of RF feedback add an echo sound to my voice.

    The other issue is when the RF disturbs the Firewire communication link between the Flex and the computer. I have resonant OWL coming into the shack from a small vertical loop. The output of the EFJ Matchbox is voltage fed, and a CFL lamp ignites 3" away from the OWL with just 50 watts carrier. The Computer is within 2' of the Matchbox, and the F3K about 3' away. If I key up the F3K with the amplifier, the Power SDR program instantly stops. It doesn't crash though. All I have to do is push the STOP button, then the START button, and all is fine.

    I can use the small loop with my Gonset G-76 station at 200 watts carrier and 1000 watts PEP with no issues. I use that loop on all bands 40-15m. I was using that vertical loop almost exclusively a few years back when I was pretty regular on the Monday night 14330 group. Its only 16' wide and 8' high and 8' off the ground. That is pretty small for 40m. I once used it on 75m too by adding additional reactance to the matchbox, and worked a Wednesday night CCA net when net control was in Colorado.

   Despite my rambling, my point is that an SDR setup is more likely to have RF feedback than a more conventional station. Adding the computer complicates things, and the type of feedback due to latency delay is quite different. That said, moving the antennas away from the shack should reduce or eliminate the problem(s).

Jim
Wd5JKO

   A bit of an update...

   I had some time to address the RFI issues where under certain PWR SDR would stop while transmitting...

Well I made it much worse, and to the point that it would happen barefoot. A sustained Yeahhhh on AM would not only stop PWR SDR but it would crash. This required me to reset the radio 13.8V, and restart PER SDR. All the while it was fine into a dummy load...even with the amplifier!

I almost tore the whole setup apart to start fresh while verifying every RF cable was built right.

For sure my setup is not optimal, but who's station really is? Many rigs will work just fine this way.

In the end I found the problem. The Firewire PCI Express card retaining screw to the computer cardcage was about 1 turn from tight. The Firewire cable had multiple ferrite clamp on beads over it too. This is the Crux of a lot of problems people experience with the Flex3K/5K. Speculation appears to suggest that the Fireware cable at the computer side needs a robust RF path to the computer chassis. How to to that is another question.

Thought I'd post this to help out the next guy who might have this issue.

The grass isn't necessarily greener going with the Anan equipment:
http://anan-100d.wikidot.com/100d-case
http://anan-100d.wikidot.com/100d-rfi

Jim
Wd5JKO

I never had a bit of trouble with my flex stuff with the antenna's right over the house, but used coax fed antenna's.
Never tried the upper bands, just 80 and 40, lots of clamp on filters all over everything and a good ground system.

I have been thinking about getting something modern for all band use again, that would have good TX audio, and a good receiver, that could be used standalone, into an amp if I built one, or as en exciter.

I think the flex 6300 is the best bet, Ethernet and the design means NO delay through the system and almost any computer can be used.
Delay with firewire is an issue on anything but a very fast computer, the new flex radios have (much) lower phase noise, and since most of the work is done in the radio and not the computer, it should be more stable.

I look at any of the typical radios in the price class of the 6300 as garbage really, for one reason or another.

If I built an amplifier using four 4x150's I would have 1KW of plate dissipation and could likely get 300 watts out, 200 easy, at a low voltage (2kv).

Untuned (resistor) input, low voltage plate tuning cap, plug in copper tubing coil for 80 and up.

Would that work?

I had a 5000 (actually the one I purchased from you) and recently upgraded to the 6500 which I am totally satisfied with. On AM, especially receiving, the quality is so much better than the 5000 which I did not have any complaints about. Over the last few days the "flex-community" forum has been debating the latency of the 6000 series, the time from the spoken word to the actual moment it goes it on the air. The issue was introduced by contesters who claim the "amlost 100 ms" delay is costing them points and QSO's. Personally I think it's ridiculous, but, it does bring out the fact that even with a network interface there s some "delay".

If you monitor yourself, is there echo or delay?
I thought the delay problem was fixed as no one says its bad on CW like it used to be.
With a good computer and the right settings, I could get the delay very low, so you could monitor your audio without delay.

The 5000 on receive was very good, not sure how much better it could be....

I looked at the current Yeasu, Icom and Elecraft radios and you have to spend more then a 6300 cost to get a decent radio.
Was thinking about the ftdx1200 till I read the power output setting is in a menu, not on a knob.

CW operation is incredibly better - FSK works just fine.
On phone, you can hear a very slight delay, which varies depending on the filtering and processing you choose.
The new 6000 radios do all the processing in the radio, so the delay that was associated with the network connection and PC processing is gone.

I think the Flex haters, the "forum trolls", use such topics to simply stir the pot and try to cause controversy.

You mean Dick?

http://dilbert.com/strip/2015-04-02

"Stirring the pot" should not be a problem if there are valid reasons. Latency and various other delays were a known issue in the previous generation of rigs depending on your configuration and equipment. The current series has greatly reduced those issues, but for some, although reduced, is still a valid concern in their style of operating. Being passive and accepting what's not quite right doesn't bring about changes.

Hi Jim,

Nice job tracking down the loose retaining screw. Having run full legal limit from 160-10 meters with a Flex 5000 and now with an ANAN-100 I can say that I had a few adventures tracking down the causes of RF ingress. Once I bonded the SDR, the computer, and the external audio chain to a common point on the ground bar at the back of the bench most of it went away. I also found that using a 1:1 600 ohm transformer at the line input of the SDR helped to keep RF out.

One tool that helped me more than anything else was a field strength meter. I powered up the rig and amplifier, dumped around 500 watts onto an empty frequency and then held the field strength meter near every wire and cable that entered and exited the station. I found the last RF path into the station using that method. This one was quite a pain because on 160 meters my "touch control" Samsung monitor was powering down randomly while I transmitted. Of course this is more than inconvenient when you need the screen to see the operating software! At any rate, it turned that RF was flowing back to the operating desk along the rotor cable which terminated in the Rotor control box that sits neatly right under the "touch control" power button of the monitor. At the window threshold where the cable enters the station I looped the rotor cable several times and snapped a few big mix-31 ferrites over it. That cured it and I have not had a trace of RF feedback issues for several years now with the SDR stuff.

At any rate, I hope you can enjoy your Flex without any further RF ingress issues!

73,

Rob W1AEX

So can you listen to yourself in a mod monitor without sounding like you have brain damage?
I could get the flex 5k fine with a fast computer and small buffers...