[Amps] Fwd: Fwd: *** PGXL Questions on CW Operation

[Jim Garland]

There has been considerable discussion on this group and elsewhere about 
the forthcoming FlexRadio Power Genius XL high-end solid state 
amplifier.  Some of us, myself included, have wondered about the new 
amp's CW performance, especially after learning that it uses plastic 
enclosed open frame relays, rather than vacuum relay or PIN diode T/R 
switching. I wrote Flex CEO Gerald K5SDR questions about the new amp's 
CW performance, and received the response below. Two interesting tidbits 
are that when using a Flex transceiver with the amp, there is no control 
cable between it and the transceiver. Both plug into the internet and 
all communication is via the internet. (Also, Flex transceivers time 
shift CW as it's sent to allow any other brand of amp to come on-line 
gracefully and to eliminate any potential latency. I don't believe other 
transceivers have this capability.) In addition, on CW the amplifier 
achieves about 70 percent efficiency, which allows it to run cooler than 
most solid state amps, thus allowing less fan noise.
73,
Jim W8ZR

Hi Jim,
Thanks so much for your questions and your interest in Power Genius XL.  
I asked the engineering team and their answers are provided in the text 
below.
73,
Gerald

Gerald Youngblood, K5SDR
President and CEO
FlexRadio Systems(TM)
Email: gerald at flexradio.com <mailto:gerald at flexradio.com>
Web: www.flexradio.com <http://www.flex-radio.com/>

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Dear Gerald,

I and my friends have been reading with great interest the updates on 
your new amp, and very much appreciate them. However, we do have a few 
questions about the amp's CW performance. It seems like a great deal of 
effort has gone into making the Power Genius XL an excellent SO2R 
amplifier, but I and my CW buddies are particularly interested in how 
the amplifier works on CW. As I'm sure you know, CW operators are vastly 
more numerous than SO2R operators, and many of them are curious about 
the new amplifier's CW performance. Looking at general contest 
participation (e.g., the CQ WW DX contests). there are many more CW 
participants than SSB/Digital participants, and nearly all of these 
participants are using amplifiers.

*Let me first state that Power Genius was designed by a CW op for XW 
ops.  4O3A is a top CW operator and has been running the amp in CW 
contests in Montenegro.  In CW mode, the amplifier operates near 70% 
efficiency based on the Maximum Efficiency Algorithm (Meffa).*

Here are the questions:

  1. The PG-XL evidently doesn't run QSK, which isn't a problem for the 
majority of CW operators who don't use QSK. However most of us (myself 
included) use a very short drop-out time when running semi-break-in (for 
me typically 150 msec), which can cause a lot of relay clicking of an 
amplifier's T/R relays. That raises the issue of reliability, which in 
turn leads to questions about relay sequencing and hot-switching. Does 
the PG-XL sequence its T/R relays to prevent hot-switching? For some 
transceivers, it is possible to set the TX Delay time long enough to let 
the amp's relays close before it receives RF, but many transceivers do 
not have this feature. For those operators, how is hot-switching 
prevented, and more generally, how does the amplifier handle relay 
sequencing? The proper sequence is to close the output relay first, then 
turn on the operating bias, and lastly close the input relay.

*While PG-XL is not designed for full QSK, it is designed for fast 
switching times as low as 10 ms. **We do NOT hot switch the relays.  The 
amplifier also provides an inhibit output that can be used with some 
radios that provide for that capability.  This is not needed with 
FlexRadio since all control and inhibit commands are sent over Ethernet.*

**2. The operating manual stipulates a 20 msec TX Delay time, which 
isn't a problem for, e.g., the FLEX  6000 series, which "remembers" 
whatever is sent during the first 20 msec and time-shifts the CW so that 
no dits are shortened. Most transceivers don't do this, however, so that 
whatever is sent during the first 20 msec is lost. With a 20 msec TX 
Delay and a short dropout time, this could lead to shortened or lost 
dits on almost every word or sentence. Is your engineering team aware of 
this potential problem, and if so how does the amplifier deal with it? 
I'm sure you know that 20 msec is a very long TX Delay time for CW 
operation.

*The current recommended transmit delay is 20 ms but we will drop that 
to 10-12 ms soon subject to further testing. **For FlexRadio only, this 
added delay is about to go away and will be incorporated into the 
handshake interchange, so any transmit delay is transparent to the 
customer.  For Flex radios only, the radio delays the start of the CW 
transmission, so no leading CW elements are lost. **For other brands of 
radios, we will soon see a shortening to less than 15 ms. Other brands 
of radios are not as sophisticated as to delay the transmit stream.*

  3. Much PG-XL discussion on the air centers around the fact that the 
PG-XL uses open-frame, plastic-encased DPDT relays for T/R switching 
instead of PIN diodes or vacuum relays. This is a curious choice for a 
$7000 amplifier and an important issue for potential buyers, who believe 
that general purpose relays have significant contact bounce, slow 
closing and opening times, experience arcing at the contacts if hot 
switched, and are noisier than vacuum relays or (completely silent) PIN 
diodes. How does FlexRadio address these concerns?

*The relays are rated for a maximum contact bounce of 7 ms.  That plus 
some time to control the relay we allow for 10 ms.  This is on the order 
of the fastest transceiver key down to RF out.  As stated above, the 
relays are not hot switched.  The relays are rated for 10 million 
mechanical cycles.  You can see the Finder 40.52 specification sheet 
attached. Contacts are AgNi.*

3. Who is advising your design team about the amplifier's CW operation? 
The CW deficiencies of the Flex 1500 series are well known, and these 
were entirely eliminated in the Flex Signature 6000 series, which are 
fabulous CW transceivers. It's important to the CW community that this 
same design care be carried over to the PowerGenius, so it would be 
helpful to know how your design team involved the CW community in 
designing the amplifier.

*Primarily 4O3A and K9CT. There are many others on the alpha team as 
well who are CW contesters.*

  4. Fan noise is a big problem with solid state amplifiers, especially 
with muffin-type fans which tend to have an irritating higher-pitched 
sound than, e.g., squirrel cage blowers. The Elecraft KPA-1500 is often 
criticized because of its whiny fan noise when running full output. Can 
you explain how the PG-XL deals with this issue?  A related issue is 
relay clicking noise, which many CW operators find bothersome, 
especially those who don't habitually wear headphones.

*We have significantly improved fan noise beginning with firmware 2.8.7 
or later.  CW mode operates at 70% efficiency and a fairly low duty 
cycle compared to RTTY and FT8 so fans typically will remain on the 
lowest speed in most CW operation.*

  Thanks very much Gerald, for considering my questions. I and my 
buddies are eagerly looking forward to leaerning more about your new 
amplifier.

73,

Jim W8ZR