[Top] [All Lists]

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

Subject: Re: [Amps] Fwd: Fwd: *** PGXL Questions on CW Operation
From: Jim <>
Date: Wed, 31 Oct 2018 16:56:34 -0500
List-post: <>

Instead of internet, don't you mean Ethernet?

Just wondering.


Jim W7RY

On 10/30/2018 9:48 AM, Jim Garland wrote:
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.
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.

Gerald Youngblood, K5SDR
President and CEO
FlexRadio Systems(TM)
Email: <>
Web: <>

---------- Forwarded message ---------
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.


Jim W8ZR

Amps mailing list
Amps mailing list
<Prev in Thread] Current Thread [Next in Thread>