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

Wed Oct 31 17:56:34 EDT 2018

Jim

Instead of internet, don't you mean Ethernet?

Just wondering.

73

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.
> 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/>
>
> ---------- 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.
>
> 73,
>
> Jim W8ZR
>
>
>
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