Date   
Re: FDM Duo & Xiegu XPA125B

carrmccormackiii@...
 

A few minutes ago  I tried sending Andrew at RM Italy the following message

Hi Andrew,

I have been a part of a discussion on the Elad users group

https://groups.io/g/EladSDR/topic/fdm_duo_xiegu_xpa125b/34548160?p=,,,20,0,0,0::recentpostdate%2Fsticky,,,20,2,0,34548160

about solid state amplifiers and hot switching when operated  either semi or full break in. One of the other forum members recommended I contact you. I (and others) are interested  in your amps but have reservations abut T/R switching time and whether you recommend your amps for full break in CW operation. Any advice you might  offer would be deeply appreciated.

 

Warmest Regards

Carr McCormack III

KF4VAR


unfortunately the e mail bounced because of an invalid address.  Craig, I think what happened is the forum for some reason truncated the address. If you would be so kind to e mail me that address it would be deeply appreciated.
Regards
Carr KF4VAR

fdm duo r

neilcoley9@...
 

Hi all

New here 

I have 4 antennas connected to my duo r

antenna 1 port has 3 on 1 switch

antenna port 2 has single fed antenna

Please can you help me to switch from antenna port 1 to port 2 on the duo r?

also, running sw2 version 3.027 and cannoy get 2 channels to work


All help and advice appreciated 


Clint

Used FDM Duo

carrmccormackiii@...
 

Spotted this for anyone interested. I might make a run  at this one but am waiting on information on what I have to pay import duties living in Ecuador on the FDM Duo. Here is the link.

https://swap.qth.com/view_ad.php?counter=1460765


Regards & 73
Carr KF4VAR

Re: External audio in standalone mode

Neil Smith G4DBN
 

Good call. A line-level analogue input would be a nice addition.

I use an old Behringer Xenyx 1002 mixer which lets me select between a Heil headset with dynamic insert, a Shure SM58 boom mic, and multiple line inputs. It is bigger than the DUO and not very convenient.  I use a 600 ohm isolating transformer on the output, along with an attenuator and blocking cap. It is very useful when doing two-tone tests from analogue sources and for injecting end-of-transmission tone pips and suchlike.  It also lets me mix in Zello audio and CW sidetone from my keyer for Stone Age mode when using SW2 for transmit in a remote mode.

Neil G4DBN

On 17/10/2019 14:37, Andy G4JNT wrote:
I've just tried to connectt up a standalone SMT-Hell generator using the Duo in standalone mode, and realised there is no option for line-level audio in.   I know people  use a PC and the internal soundcard for most applications, but just this once, and possibly when using the transceiver with various test signal sources, it would be nice to be able to feed directly in.

Now I've got to find a surplus ethernet cable, chop off a connector and mess about with a potential divider to feed into the mic socket.

Perhaps consider on later upgrades, make the aux audio socket on the front panel bidirectional.   After all, audio out only needs one connection of a stereo connector leaving the ring for input.


External audio in standalone mode

Andy G4JNT
 

I've just tried to connectt up a standalone SMT-Hell generator using the Duo in standalone mode, and realised there is no option for line-level audio in.   I know people  use a PC and the internal soundcard for most applications, but just this once, and possibly when using the transceiver with various test signal sources, it would be nice to be able to feed directly in.

Now I've got to find a surplus ethernet cable, chop off a connector and mess about with a potential divider to feed into the mic socket.

Perhaps consider on later upgrades, make the aux audio socket on the front panel bidirectional.   After all, audio out only needs one connection of a stereo connector leaving the ring for input.

DUO-ART spectrum settings

Mark EI3KD
 

Hi,

The latest available manual for DUO-ART, Rev 1.6, doesn't match the visualisation settings available in my DUO-ART, SW ver 1.61 - i.e. menu 40 is different and menu 45 is new.

Consequently, I'm not sure about one of the settings and whether what I'm seeing is an error: Using menu 40, it's possible to change the "Offset" value for the spectrum (per band), but only with a positive value from zero to some high number, certainly greater than 200. In older software, this was a value from -200 to +200. I actually need to set a negative number to make the ART spectrum match the levels I see on my FDM-DUO more closely, but this no longer seems possible?

Sadly the settings used to be correct (i.e. with negative numbers in the Offset fields, I guess previously set with an older version of software) but I reset all the values and now can't set them back.

Am I doing something wrong?

Thanks, Mark

Re: FDM Duo & Xiegu XPA125B

carrmccormackiii@...
 

Neil
Thanks for the great information I am going to look at the 122G Project.  30+wpm  for full QSK is impressive!

Also somewhat off topic I downloaded the apk for the FDM DUO  and can run it in demo  mode on my tablet.  For those (as I )  who have an aversion to all things Android, I am running a Samsung  Note 8 with a version of Android that is hacked to the point where it doesnt have the Google bloatware framework present.  The apk  is BlueDuo and if you are running the Duo in standalone mode you get the waterfall and what appear to be a number of other control options. FDM Duo looks like an awesome radio.  Thought I might share this.....
Carr
KF4VAR

Re: FDM Duo & Xiegu XPA125B

Neil Smith G4DBN
 

Off-topic, but the 122GHz devices have antennas for rx and tx embedded into the chip.  The dipoles are 1.67mm apart. The chips run full duplex at 144MHz split.  The VK team have found that a duplexer cavity 4mm wide and 1.6mm tall gives good result without any changeover into a 2mm diameter (oversize) waveguide. Marvellous stuff.  I'll be using one of my DUOs as the IF.

An actual changeover is easy enough, you just mount the transceiver on a translational plate with spring steel flexures and a cam to move the entire transmitter 1.67mm, using some standard 1 x 2mm waveguide fixed 0.1mm above the chip.  When I say "entire", the chip is 5mm square, so the thing is not large.

Join in the fun at The122GProject@groups.io

I retrofitted vacuum relays in my 2 x 3-500ZG HF amplifier, it can do full QSK at 30+wpm.

Neil G4DBN
http://g4dbn.uk


On 16/10/2019 22:52, carrmccormackiii@... wrote:
First- Craig-- Thanks very much for the kind information  and supplying the e mail to  RM Italy. Klaus, you are  more knowledgeable in this than am I but if  everyone would like I will write Andrew outlining the questions we raise here. Again Craig thanks very much for this

Klaus- I want to learn enough to do moon bounce. Some of the things you talk about with the tech is absolutely fascinating......Neil Smith G4DBN's web page.... I wonder what the T/R  switching device looks like for a 122GHz setup......

Years ago a German friend and fellow ham who lived in Mexico had a home brew 1KW amplifier with a vacuum relay.  I have never owned  such an amp but was amazed at the lightning response he got from that......

Agreed completely  about the attenuator. Xiegu, PAY ATTENTION!!

As far as any of this being esoteric I agree with you Klaus. Its not.  However in amateur  radio these days like in  computers, since the advent of the GUI --and in amateur radio, the advent of LSI.... make the user more of an appliance operator with less understanding of the underlying technology. No rant intended but everything is expected to be plug & play when many times its not.

From this end. The understanding I had when I moved here to Ecuador is that I had a one time duty free import of  whatever I wished.  I learned today that to take advantage of that, it must be applied for and accomplished within the first 6 months  here --with the start time being the date one applies for the residency visa. No one tells you that when you apply --and I have been here  for a couple of years without importing anything.  Greedy )$/#"#s, governments, arent they...... So some time next week I will find out what it will cost to import an FDM Duo and an amp.

Carr KF4VAR

Re: FDM Duo & Xiegu XPA125B

carrmccormackiii@...
 

First- Craig-- Thanks very much for the kind information  and supplying the e mail to  RM Italy. Klaus, you are  more knowledgeable in this than am I but if  everyone would like I will write Andrew outlining the questions we raise here. Again Craig thanks very much for this

Klaus- I want to learn enough to do moon bounce. Some of the things you talk about with the tech is absolutely fascinating......Neil Smith G4DBN's web page.... I wonder what the T/R  switching device looks like for a 122GHz setup......

Years ago a German friend and fellow ham who lived in Mexico had a home brew 1KW amplifier with a vacuum relay.  I have never owned  such an amp but was amazed at the lightning response he got from that......

Agreed completely  about the attenuator. Xiegu, PAY ATTENTION!!

As far as any of this being esoteric I agree with you Klaus. Its not.  However in amateur  radio these days like in  computers, since the advent of the GUI --and in amateur radio, the advent of LSI.... make the user more of an appliance operator with less understanding of the underlying technology. No rant intended but everything is expected to be plug & play when many times its not.

From this end. The understanding I had when I moved here to Ecuador is that I had a one time duty free import of  whatever I wished.  I learned today that to take advantage of that, it must be applied for and accomplished within the first 6 months  here --with the start time being the date one applies for the residency visa. No one tells you that when you apply --and I have been here  for a couple of years without importing anything.  Greedy )$/#"#s, governments, arent they...... So some time next week I will find out what it will cost to import an FDM Duo and an amp.

Carr KF4VAR

Re: FDM Duo & Xiegu XPA125B

Klaus Brosche, DK3QN
 

Carr,

IMHO, it is a major (unconcious ?) design flaw of that Amp, which, btw,
could be resolved for less than 5 Chinese Yuan to make it RF power-compatible
with 5 watt RF output rigs.

From my understanding, that Amp was meant for 'upgrading' QRP-level
TRXs from low power (QRP=5 watts) to abt. 100 watts RF output power.

Adding an additional (switchable) 3 dB attenuator would probably add cost
in the 30 (max.) Yuan cost range.

So, cost-wise we are talking about 'pea nuts'.

My greetings to Xiegu and this hint is 'for free'.

Klaus, DK3QN
Friedberg, Bavaria


Am 16.10.2019 um 20:37 schrieb carrmccormackiii@...:

Klaus-
Since my last post watching a couple of the Youtube videos I see why you want an input attenuator -half a watt to a watt and depending on the frequency, the XPA-125 is at full output power. That is a pretty delicate adjustment.  The option to  build an outboard attenuator is there for between the radio and the amp but thats just another piece of something to fiddle with along with its accompanying cabling.

Carr
KF4VAR


Re: FDM Duo & Xiegu XPA125B

Klaus Brosche, DK3QN
 

Hi Carr,

I started to care about sequencing when I was in the process of putting together
a 144MHz EME station together with my friend Michael, DL2MHO, back in 2009.
We had this EME station active until 2013, when we ended this activity.

In such an evironment it is *key* to have a proper equipment sequencing in place.
Especially given the RF power levels of 1 KW +/-.

Care about proper sequencing is also quite important at lower frequencies and
power levels, as *weird* things may happen which might be able to shorten life
of components/units drastically.

Since that lesson re. EME activity, I have put a special eye on this sequencing
subject with all of my ham radio equipment and I would like to encourage
everyone to also care about it! It's just a matter of 'best practise', which is
in most instances *not* equal to the 'easiest way'.

Regarding the FDM-DUO working together with an Amp appropriately:

It's a matter of how fast that Amp will turn-over to transmit in a stable way,
relay switching time, plus Bias etc., after the DUOs PTT went 'low' and thus
making the Amp to switch to TX.

So-called 'open frame' relays will definitely *not* make it in time! Given the
pretty small time delay of the DUO between key closure (and assumably
PTT-out 'low' at the very same time) and RF-onset.

Unless using vacuum relays or reed relays with their quite fast switching
times, it is a matter of finding appropriate fast enough relays that provide
switching times in the order of 6 milliSeconds or so. But they exist.
It's then a matter of studying the corresponding relay data sheets, not
only looking at switching times but also at *bouncing* times, i.e.
the time gap it requires until the contacts have settled in a steady manner.

Some may judge my writing as sort of 'esoteric'. I can assure you: it is not!
I often hear those 'crappy' CW signals on the air, predominantely when
people are running Amps behind their TRX. Key clicks, broad-banded, etc.
An SDR TRX is your friend: you can even look at this sh..

As licensed ham radio OPs, we should all care about proper signal quality
of our transmissions, in order to avoid any on-air harm to our fellow OPs
next to our 'channel'.

Klaus, DK3QN
Friedberg, Bavaria


Am 16.10.2019 um 19:07 schrieb carrmccormackiii@...:

First --I want to say what a great group there is here on the FDM-Duo site and how much I appreciate all of the knowledge and the willingness to share. Wonderful community! I wonder from looking at some other sites, whether  some (but not all) of the newer generation of amateurs have not become appliance operators with no real understanding of the equipment they operate.......

Klaus- the translation worked thanks for the link to the blog. The scope presentation looks pretty scary doesnt it.  Although the modification helped things  a bit the concern Anton expressed about the mod is interesting.
I sold my last station in 2012, my last amp  had a pair of 3-500Z's. I had an old Tectronix oscilloscope I would run with a sampling loop most times I was on the air. I dont ever remember rise time problems of this magnitude from a tube amp.....My knowledge of solid state RF amplifiers is pretty small. It looks like we may be talking about a number of factors causing  a slow response time when the amp is keyed- one of which is sensing for automatic band switching, another  how bias is applied to the output transistors to turn them on ; how quickly  the T/R relay is able to operate; another, with microprocessor  control how the interrupts are done. So if the time problem is causing the first dot or dash  to be truncated in CW, then I  assume  that the same switching problem  will be present  whenever the amplifier is keyed irrespective  of mode. In SSB  not that much effect on communications but in some digital modes would this not cause problems as well?  I am assuming this would be bad for the amplifier output stage regardless of the mode. I also wonder about creation of radiated spurious signals as well.

One of the first reviews of the XPA-125 I saw was done by AB5N on YouTube
https://www.youtube.com/watch?v=5dDo9ZJlXjo

After reading  the review I linked earlier from E Ham, I wrote AB5N about  the problem with switching.  His comment was
Sadly, the TX/RX turn-around time of this amp is slow. It is not rated for break-in CW.
The relay is too big to be that fast. Upside is that the relay will probably last forever.
 



Neil- In reading the propagation forecasts from hamqsl.com I see how during this solar minimum, most of the HF bands are in difficulty but many times EME is fair or excellent.  I looked at your site. Beautiful work, thanks very much for sharing this online-  I remember from my days of working on S band Raytheon shipboard radar, how much larger the waveguide and feed horns were -the 122 GHz feedhorn in the palm of one's hand is amazing. Of course in those days one only dreamed of 122GHz.

Carr
KF4VAR



Re: FDM Duo & Xiegu XPA125B

carrmccormackiii@...
 

Klaus-
Since my last post watching a couple of the Youtube videos I see why you want an input attenuator -half a watt to a watt and depending on the frequency, the XPA-125 is at full output power. That is a pretty delicate adjustment.  The option to  build an outboard attenuator is there for between the radio and the amp but thats just another piece of something to fiddle with along with its accompanying cabling.

Carr
KF4VAR

Re: FDM Duo & Xiegu XPA125B

Craig Williams KA6RWL
 

Carr and Klaus

Here is a contact at RM Italy who is a very responsive guy.


Maybe this question should be poised to them and see what their answer is for the HLA-150v  and HLA-305v amp models. They may have modified the design since if the review that was cited was in 2016. I would be curious to know their answer but think someone more knowledgeable of the question might ask a more complete question.

And yes I concur that the group on this thread are Both helpful and amazing with their knowledge on so many subjects that relate to the FDM-DUO.

73

Craig
KA6RWL 

Re: FDM Duo & Xiegu XPA125B

carrmccormackiii@...
 

First --I want to say what a great group there is here on the FDM-Duo site and how much I appreciate all of the knowledge and the willingness to share. Wonderful community! I wonder from looking at some other sites, whether  some (but not all) of the newer generation of amateurs have not become appliance operators with no real understanding of the equipment they operate.......

Klaus- the translation worked thanks for the link to the blog. The scope presentation looks pretty scary doesnt it.  Although the modification helped things  a bit the concern Anton expressed about the mod is interesting.
I sold my last station in 2012, my last amp  had a pair of 3-500Z's. I had an old Tectronix oscilloscope I would run with a sampling loop most times I was on the air. I dont ever remember rise time problems of this magnitude from a tube amp.....My knowledge of solid state RF amplifiers is pretty small. It looks like we may be talking about a number of factors causing  a slow response time when the amp is keyed- one of which is sensing for automatic band switching, another  how bias is applied to the output transistors to turn them on ; how quickly  the T/R relay is able to operate; another, with microprocessor  control how the interrupts are done. So if the time problem is causing the first dot or dash  to be truncated in CW, then I  assume  that the same switching problem  will be present  whenever the amplifier is keyed irrespective  of mode. In SSB  not that much effect on communications but in some digital modes would this not cause problems as well?  I am assuming this would be bad for the amplifier output stage regardless of the mode. I also wonder about creation of radiated spurious signals as well.

One of the first reviews of the XPA-125 I saw was done by AB5N on YouTube
https://www.youtube.com/watch?v=5dDo9ZJlXjo

After reading  the review I linked earlier from E Ham, I wrote AB5N about  the problem with switching.  His comment was
Sadly, the TX/RX turn-around time of this amp is slow. It is not rated for break-in CW.
The relay is too big to be that fast. Upside is that the relay will probably last forever.
 



Neil- In reading the propagation forecasts from hamqsl.com I see how during this solar minimum, most of the HF bands are in difficulty but many times EME is fair or excellent.  I looked at your site. Beautiful work, thanks very much for sharing this online-  I remember from my days of working on S band Raytheon shipboard radar, how much larger the waveguide and feed horns were -the 122 GHz feedhorn in the palm of one's hand is amazing. Of course in those days one only dreamed of 122GHz.

Carr
KF4VAR


Re: FDM Duo & Xiegu XPA125B

Neil Smith G4DBN
 

I hope that the amp manufacturers are using intelligent detection circuits which will wait for the signal frequency to be detected, then enable the signal path using PIN diodes or another proigrammable attenuator which will allow a ramped soft attack.  That way, there won't be any hot switching, just the first symbol of CW (or MGM or the first few milliseconds of voice) will be clipped and then soft-started.

I am working on a delay-line approach to CW keying so that when I start sending, PTT is enabled, but a microcontroller delays the actual switch closures going into the DUO key input until there is a signal from the sequencer to confirm that all of the transverters and masthead relays or waveguide switches are in transmit position. I'll get the sidetone from my keyer, via an audio mixer.  The problem on 10GHz is that it does take quite a long time for the waveguide relay to clunk over. When scintillation is really bad with troposcatter, I have to drop to maybe 5wpm to send recognisable Morse, and that is too slow for the hang time on the DUO for normal use, so at the moment, I use the footswitch when running slow CW.

If the external amp uses a voltage level to switch bands, it is simple to make an interface looking at the IO port on the back of the DUO and use that to generate a suitable voltage or other command sequence.  Just needs a PIC or Arduino looking at the 9-pin socket data stream and maybe an op-amp if it needs more than 5V.

Neil G4DBN



On 16/10/2019 11:14, Klaus Brosche, DK3QN wrote:
'Hot switching' an amp (e.g. by means of an RF VOX circuitry) IMHO is not
'best practise' at all. It's sort of a work-around for the ease of connecting
an amp to a TRX.

It can create a variety of unwanted situations/issues due to the fact
that the driver RF signal is already at/in the amp before necessary
actions can take place. E.g. RX/TX relay switching etc.

To provide for a proper sequencing of all envolved stages, not only
the RX to TX sequencing needs to be looked at. Also the TX to RX
sequencing is of identical importance! This is especially important
if one runs CW in full-bk mode.
In semi-bk the 'tail-end' proper sequencing in general is provided
by the 'hang-time' at the end of CW words transmitted, e.g.,
and that 'hang-time' can be adjusted in a wide range in the vast
majority of transceivers.

Klaus, DK3QN


Am 15.10.2019 um 23:19 schrieb carrmccormackiii@...:
Klaus & Craig
Many thanks  for the great information much appreciated!
Klaus I am under the impression that from what you say even  in SSB & digital modes, hot switching can still happen, am I interpreting this  correctly??

Craig- will look at the rmitaly amps many thanks for the help in this.

Is there a way via the menu on the Fdm Duo,  to control T/R delay as is  on the Elecraft? I have not found this in the online instruction manual that I have access to.....  Klaus, from what i am understanding, even with longer TR delay set in the transceiver  that  it would still be a problem......  because the amp does not select the band until it receives the first bit of RF from the transceiver. As was stated in the review if this is done through polling and   the CPU scheduler has other things going on I can see the reason for the delay that the reviewer  found and moreover the variable delay times he talked about. Even with a direct interrupt I wonder  if it would be sufficiently quick to prevent hot switching.
Regards & 73


Re: FDM Duo & Xiegu XPA125B

Klaus Brosche, DK3QN
 

XIEGU XPA125B

Hi Carr,

Early August this year I contacted the EU distributor for Xiegu in Sweden
re. the XPA125B (the 'B' is important as there is also an earlier version
without 'B').

This is part of what I got back from him:
(quote)
Schematics are not available unfortunately.
The power is amplified by 2 x Mitsubishi RD100HF1.

There obviously (is) a microprocessor in the amp taking care of business,
but there is no automatic detection of frequency.
The voltages used to switch bands are described in the manual,
then of course you can also switch band manually. (end of quote)
...
I also asked him about the behavior of the Xiegu amp relative to a
certain other amp which he had also contemplated for his
distribution business and which he had put through his tests:
(quote)
The XPA125B is not acting like this. It's far more sophisticated in its
construction and much more reliable.
(end of quote)

That's what he said.
I cannot comment on the XPA125B performance/behavior yet,
because I have not yet ordered one so far. What kept me from
ordering one is the fact, at least my perception, that the
XPA125B does not have any provision for selecting a 3dB (or so)
input attenuator which would allow for using this amp with
some of my 10 to 15 watts medium level QRP rigs which have
no easy provision for RF output control.
If you watch XPA125B videos on YouTube, it can be seen that
the amp puts out full RF power (100 watts +/-) at input power
levels of around 2.5 to 4 watts, depending on band.

Klaus, DK3QN
Friedberg, Bavaria


Am 15.10.2019 um 23:19 schrieb carrmccormackiii@...:

Klaus & Craig
Many thanks  for the great information much appreciated!
Klaus I am under the impression that from what you say even  in SSB & digital modes, hot switching can still happen, am I interpreting this  correctly??

Craig- will look at the rmitaly amps many thanks for the help in this.

Is there a way via the menu on the Fdm Duo,  to control T/R delay as is  on the Elecraft? I have not found this in the online instruction manual that I have access to.....  Klaus, from what i am understanding, even with longer TR delay set in the transceiver  that  it would still be a problem......  because the amp does not select the band until it receives the first bit of RF from the transceiver. As was stated in the review if this is done through polling and   the CPU scheduler has other things going on I can see the reason for the delay that the reviewer  found and moreover the variable delay times he talked about. Even with a direct interrupt I wonder  if it would be sufficiently quick to prevent hot switching.
Regards & 73


Re: FDM Duo & Xiegu XPA125B

Klaus Brosche, DK3QN
 

'Hot switching' an amp (e.g. by means of an RF VOX circuitry) IMHO is not
'best practise' at all. It's sort of a work-around for the ease of connecting
an amp to a TRX.

It can create a variety of unwanted situations/issues due to the fact
that the driver RF signal is already at/in the amp before necessary
actions can take place. E.g. RX/TX relay switching etc.

To provide for a proper sequencing of all envolved stages, not only
the RX to TX sequencing needs to be looked at. Also the TX to RX
sequencing is of identical importance! This is especially important
if one runs CW in full-bk mode.
In semi-bk the 'tail-end' proper sequencing in general is provided
by the 'hang-time' at the end of CW words transmitted, e.g.,
and that 'hang-time' can be adjusted in a wide range in the vast
majority of transceivers.

Klaus, DK3QN


Am 15.10.2019 um 23:19 schrieb carrmccormackiii@...:

Klaus & Craig
Many thanks  for the great information much appreciated!
Klaus I am under the impression that from what you say even  in SSB & digital modes, hot switching can still happen, am I interpreting this  correctly??

Craig- will look at the rmitaly amps many thanks for the help in this.

Is there a way via the menu on the Fdm Duo,  to control T/R delay as is  on the Elecraft? I have not found this in the online instruction manual that I have access to.....  Klaus, from what i am understanding, even with longer TR delay set in the transceiver  that  it would still be a problem......  because the amp does not select the band until it receives the first bit of RF from the transceiver. As was stated in the review if this is done through polling and   the CPU scheduler has other things going on I can see the reason for the delay that the reviewer  found and moreover the variable delay times he talked about. Even with a direct interrupt I wonder  if it would be sufficiently quick to prevent hot switching.
Regards & 73


Re: FDM Duo & Xiegu XPA125B

Klaus Brosche, DK3QN
 

Hi Carr,

re: RM Italy HLA-150+ amp:

You can find a fully detailed analysis of the 'issue' (in CW mode) plus a possible user DIY solution
here:


It's in German language. Google translate should bring that into understandable English.

The DIY mod quoted on the website is from RM Italy and is in English language.

The key info is: the PTT-line only switches the relays on transmit/receive.
The Bias voltage for the power transistors is switched by means of RF-sensing.
The time-delay for this process obviously is the reason for truncated first CW code elements.
The modification gets rid of this delay.

There are Scope screenshots on the website (see above) which demonstrate the amps
CW behavior before and after the mod.

In its Transceiver product reviews QST shows the delay time between key closure (which
should be in synch with PTT-out closure) and RF onset.

For the FDM-DUO this time gap is pretty short, namely only 6 milliSeconds (QST review
May 2016).

For reference:
IC-7000: 8 mSec
FT-DX3000: 18 mSec
TS-590S: 14 mSec
FT-450D: 23 mSec
Elecraft KX-2: 13 mSec
All data from QST reviews.

73, Klaus, DK3QN
Friedberg, Bavaria


Am 15.10.2019 um 23:19 schrieb carrmccormackiii@...:

Klaus & Craig
Many thanks  for the great information much appreciated!
Klaus I am under the impression that from what you say even  in SSB & digital modes, hot switching can still happen, am I interpreting this  correctly??

Craig- will look at the rmitaly amps many thanks for the help in this.

Is there a way via the menu on the Fdm Duo,  to control T/R delay as is  on the Elecraft? I have not found this in the online instruction manual that I have access to.....  Klaus, from what i am understanding, even with longer TR delay set in the transceiver  that  it would still be a problem......  because the amp does not select the band until it receives the first bit of RF from the transceiver. As was stated in the review if this is done through polling and   the CPU scheduler has other things going on I can see the reason for the delay that the reviewer  found and moreover the variable delay times he talked about. Even with a direct interrupt I wonder  if it would be sufficiently quick to prevent hot switching.
Regards & 73


Re: FDM Duo & Xiegu XPA125B

carrmccormackiii@...
 

Hi Craig
Thanks very much  for the further information.

Regards & 73

Re: FDM Duo & Xiegu XPA125B

Craig Williams KA6RWL
 

I have not experienced the amp hot switching except when I change bands which I generally don’t do with the amp on. I tune the frequency with the amp off. Turn the amp on and on the first key it changes bands. Once the initial band change is made it stays on that band until you change bands. I have a PTT audio cable connected to the amp from the Elad FDM-Duo. I do not use this setup for CW so I can’t speak to delays on CW keying. 

My only complaint on the design of the amp is that there isn’t a ground terminal on the back but that is easily corrected by grounding the enclosure.

Best regards

Craig
KA6RWL