By: K5JXH ,
All issues with using a Panadapter, with my ICOM IC7200.                         

SDR or Software Defined RADIO's, used in my SHACK.
  (dealing with it)

Problems with ICom 7200, Send relays solved on this Panadapter page below, just one page.
My Icom has no "IF" strip,  tap jack making traditional Panadapters Impossible, I must go direct to my SDR.
The ICom IC7200 has 2  flaws, first is naming the both the SEND phone jack in the rear and then ACC pin3  SEND the same; Warning they are not the same one is a simple cheap transistor and other is a relay. (one is slow , other fast)
Lets rename them, to  the phone jack relay SEND_R,  and the Pin3, ACC pin 3 is true SEND.(faster)
The phone jack SEND_R can handle more current and for sure more voltage (it's just a small relay in the ICOM)
The ACC jack is the best SEND jack for most modern usage , but is  limited to 20vdc, and 200mA( it lands at the Q501 RF board transistor inside ,located just behind the ACC 13pin JACK) 
I do run the SB200 off the SEND_R relay (a real relay inside the ICOM) but my SDR radio is now gated with pin 3 ACC , true SEND line (early send PTT it is) and connected to the TR switch PTT pin.

I found this on the web, and is mostly not a problem running SSB, due to its suppressed carrier mode,  But you really should use the Pin3 ACC pin to give the external relays a chance to settle out. (sooner)
 The TR box relay is a  AXicom  #V2305a-5003-A201 RF communictions relay it is) I want this relay closed before RF hits the poor thing.
(SSB mode is safe but what if you had the dial set on the wrong mode, you  kiss off the SDR )
I had to study this page (scope) hard to learn what connections he used,  (top photos are the SEND_R Phone jack on the rear) the Bottom photos are the ACC pin3 SEND (early send) phone jack.
The Relay Phone jack is too slow. LATE. (that means the RF arrives way  too soon)

The Send fast pin 3  sends a more early send signal so the RF arrives later. (as seen in the below left bottom photo )
 Lifting the PTT mic button, the IC1 brain inside the Transceiver ends, RF fast, (100% electronically ended by the way)
I use the term brain, in the context and quote the famous (RIP ) Alan Turing ( Mr. Enigma machine from WW2) the brain controls Pin 3 totally after you key up, and nothing else. (we are told this time varies too, my guess on how busy the brain is!)




Thank you W7RY , for the nice scope images. (even better would be both sends at same time, I added a red line above, to show where it would land , but the time base in not the same, 1mS and 2Ms, thus the shift.
6mS is about 1/2 what most relays made need, by the way. (but lucky me , my very modern Comm relay in the TRbox  is 6mS spec per below cut paste.
In truth the relays beat their own spec.(it's only a max)
"Operate / release time max. 6ms/4ms
Bounce time max. 5 ms"
I bet this below relic takes like 50mS to close, depending on how many dead bugs and spiders are in that Pole gap , hihi ! (the slotted screws, age the part, 1960? )
one very old and relic TR switch, some even had 120vac 60Hz coils, wow. I'd bet the BNC is Receiver.
What Icom did not do and should have done is use only 1 high voltage (known as) a sold state relay, .  or just 1 high voltage and high current, power transistor here,  even with a snubber built in and  a GDT (gas discharge tube 90v on that line too)
They should end the practace of using relays at all. (but so can you, connect pin 3 to your own buffer box,  using  HV transistor. (MOSFET with VMOS or deep channel MOS have huge current ratings and low RDs(on) spec.)
Today this device ?, or this one , you could put one in a box and do that, with an optical  coupler as input. (see my Idea below)
The use of an OCR opical coupler (see my IDEA below link) on the input to the MOSFET and have 5000vdc isolation to the precious radio insides.
The trouble with driving relays   back EMF spikes up to 750v , lacking  a coil snubber, so use transistors with them built in (or zeners) and designed to be used with relays. (like cars use)
MODERN Nchannel MOS FET, some have super low on resistance, Drain to Source pin and allows for them to drive huge currents, and never overheat (P= I² x R) keep R low and heat is super low, and no heat sinks needed. (as old as Vmos this is)
The key parameters are HV drain, High current Drain to source and low RDs(on) the turned on drain resistance, (using Vmos or what others call deep channel and other names, that all boil down to a huge floating gate)

The back to back zeners are ESD protection seen below:
The diode on the drain, is for driving coils as a switch.  (the device is even spec.'d out on how powerful the clamp diode is there )
Today there are vast numbers of makers of this class of device,  (see these FET 9 monsters here (.45ohms ON) (leaded parts are less choices, up to 12amps here, with out leads 75amps) For sure ICOM7200 designers had way less parts choices then.
As you can see in the year 2018 the TO-220 case (leaded)  is NOT DEAD.  Long live this case ! (and TO-3 too)
If you run any old PAs, seriously consider making  5000v buffer box as seen below. (for sure if that PA runs TUBES of any kind)   (my PA has a modern (added) PTT buffer modification seen here)
This part handles 600v, 25watts. put it in A BOX,  Here is my idea of cheap fast buffer, with 5000v isolation,(even with Miller effect compensation)


Please skip my FARADAYS laws here and below: (better is learn to use your scope and see the spike)
Back EMF happens on all coils of wire,  in this case the coil is charged say to 12vdc with huge magnetic field stands there in the metal core,, and when the transistor turns off this field collapses fast and per the induction principle.
Lenz laws: (as simple as can be, simple division expressed in Algebraic form.  (sure the coil has wire and turns matter  but I can not change the turns, but worse I have no idea the field strength nor the collapse time )
To make this simple consider only "dt" for a moment.  (this is totally unknown or stated by the relay maker) but we know that it matters, big time on induced BACK EFF. (not the minus sign here, the current reverses at the collapes)
As you can see for  given "d" mag field there, if the field dt , is time , if time is reduces (speed of collapses) then EMF goes higher, for sure with air core , coil. ("d" means delta time, "the change in time"
In our case the ,  is a  constant steady unkown magnetic  field. (relay is energized) so only the dt maters and is unknown by me or most anyone, but the faster d¤ goes (lower number is faster) the more induced EMF voltage happens.
That is why EMF can not be predicted here lacking the spec on the relay core of metal and copper wire turns. (and its magnetic properties,) so don't worry it, just use a  diode clamp that can handle maximum back EMF spikes.
However if a true curious and spirited person can use  scope and 12vdc power supply and measure the back EMF very easy, in like 5min work. OMG -1000 volt spike there. (Oh My Golly) How can  3cent 60volt transistor stand that, answer BOOM.
Seeing is believing,  that way you won't forget the snubber next time. (snubber, clamper or dampener, not matter what you want to call it)
The best snubber is a 24v zener with 12vdc relays at the drain to ground pin ,this makes the relay release faster .
Actually ,IMHO., the word flywheel is not so good, they only spin  forever in one direction, but if you ever saw  and old watch balance wheel below,  with spring, now that is more like a coil that oscillates.
A real mechanical watch, used from year 1657 to now. (I even have new one) see that action, that is what the snubber does, and then wastes the energy as heat.
(the hair spring above stores energy and in your RELAY the coil does that (and core ) (The same with and RF TANK circuit  L/C and stores energy and oscillates)
If you expand the scope horz. time base below, you will see the coil ring like a bell. Note the spike goes beyond 50v, here.  some go to 500 volts larger relays. (one can measure it easy with a relay, a toggle switch and 12vdc supply any your scope)
Most transistors just blow up with such back kicks, but not transistors used in CARS, for running its relays. (chose wisely)


Note how it took a full 100mS to recover.! (a very long time in the electronics world)

end BACK EMF issues.



Trouble #2 is RF arriving too soon and burning relay contacts hot switched that, on the fly. (or far worse blowing my SDR to hell for the same reason)
History of TR (nut shelled):
The Hayday of TR switches.(were common before Transcievers were born (HAM born not commerically) 1930s to 1970s for 50 long years common.
Back in 1959 Collins KWM-2 sold  for $1250 then, $10685 (adjusted cost now for inflation) and very unaffordable, but to the rich. (or my uncle that worked for them!)
Later Heathkit fills this void, as did others (Drake). with HW101 (hot water 101) in 1970 for Christmas. $399(kit form)
$3400 adjusted prices (2017).  Still not that cheap , but 40,000 were sold.
The early heathkits, like my SB401 has  TR-switch inside built in. (And near impossible to repair , I might add...)
Many hams for 50 years built their own, TR switches (or bought one as seen above)  so they could use say their much cheap SWL ("short wave receivers") found used for $50 back when.
Many hams then, built their own exicters, then later made their own PA from scratch. {real hams did that then}  (after all $3400 back then was serious bread!)
Guess what ? the SDR receiver brings back this need for a TR switch again. (and my mod's to it)
The below is my solution (all parts off the shelf)

I am using the transmitter in min ICOM IC7200.(with SB200 linear PA)
To use the ICOM ACC SEND pin 3  to drive my TR-Switch PTT line (X1-2)
Rule one, is to never connect any relay coil directly to pin 3 above only use the SEND_R phone jack to do that. (lacking and external buffer as see on my page later)
If you wire a relay to this line directly the coil has huge back EMF kick back  pulse ( 100-750v possible). (use  a diode clamp on all relay coils to dampen this pulse out or  zener clamp)
Also known as a snubber or the flywheel effect. (or a dampener)
The ICom book shows adding  a relay at pin 3, even further causing the RF to arrive sooner,  If the Relay added is 10mS activation spec, then it switches RF hot for 4 full mS,  per above scope view bottom left.
Do not add relays, in fact avoid them if possible, best are solid state relays or just 2 transistors with DC amps ,  as simple buffer. (or Send , signal is low true for transmit )
PTT logic inside: (PTT= Push to Talk)
The ICOM time delays are hard coded in to its own IC1 processor and can not be changed by me, they should have used a full 20mS delay from MIC PTT pin, to the internal "SNDS >>SEND" line. but did not, they used 5ms, and is way too fast for RF to go HOT.
The delay should have been programmable, but is not, so we can tune it for relic gear, or modern. (too bad they did not ask old Hams what to do first?)
As you can see this is not Microsoft® Plug and Play at all, not by a mile.
INSIDE the ICom7200 (behind the ACC jack pin 3)

The pin 3 SEND Q510 transistor (RF board) is 32vdc spec, and 1 full amp and 1 watt, but is ICOM guard banded this , to 20v and 200mA (wisely) the Pin 3 is also an input and the voltage limits are for that reason too.
Allowing huge EMF voltage spikes on this pin 3 will cause damage to the ICOM. ! (so very easy to do) If you do not understand transistor destructive breakdown, avoid pin 3., Use Send_R rear phone jack( it's a relay there).
I  am using Pin3 for my SDR radio TR switch.  (it is only 12vdc and only  1.2mA (tiny) and there is no back EMF spikes on PTT input below,  Q2 below eats them all for breakfast deep inside.
I got my EASY TR here.(I have no idea the insertion losses here)
D3 zener was added to the newest revision, do buy that.
Related to the above is RF fields:
SDR usage in the near field.  (70watt out Icom and 500w out SB200 to antenna 50' away) Worst case protections.
  • My SDR box is a toy grade ; plastic only box, ver A is conductive painted inside, but not mine,  So I wrapped it in aluminum foil , x2 and taped it, like EMP engineers do. (Faraday shields)
  • All wires to  the SDR are shielded coax. (it only has 2 jacks , USB   and SMA)  the USB jack will be lots of clock noise from the PC (use only CLASS-B FFC certified PCs or noise is for sure "birdies")
  • The USB cable can induct RF so use the #43 Toroid protectors, (clamp around coffin types, are easy but 6 times more $) I use DOnut shaped and put turns on it.
  • My custom TR box, is a solid die cast aluminum box. (I sourced) and all cables are coax, except 12vdc. Even my PTT lines are shielded with coax.
  • The TR box , is setup for max protection,  but not diode clamps because I fear they cause IMD .(can) But BAT41 diodes might work here.(2pF ) Note that SDRPLAY has them there,(seen below)
  • A Donut Toroid #43 on the USB cable to SRDplay and PTT line to TR BOX.
  • I am testing my SDRplay inputs using a scope for excessive RF leakage , ( 2 ways, open circuit and with a 225 ohm terminator, only ) before using it live or connecting it at all.  (the impedances are not 50 at all frequences)
  • The TR box i made is all cast aluminum, and will work great as a faraday shield. (tight fitting lids and small 2 inch gaps. that block HF intrusion.)
  • All my Transmitters are all using top grade, shielded coax to far out side the home. (vertical Antenna)  (no long wires running to my shack , only COAX)
Before using such a thing, SDRplay, I do all the above, then transmitting (to SB200 and real antenna at full power) valid transmitter test at full RF out.
What ever mode you use, most do that, but If using SSB you need to modulate fully the signal. ( to see induced effects)
SDRPLAY states, max. 10mW and if wiser, 1mW, is max.  but the limit is really the clamp diodes see below.
BAV99WTIG "CLAMPS" D1/D4, is rated at 200mW max; 1.6 mW/°C derated above 25c.
My wild guess, due to facts below is that the 10mW rating is to protect the Poly-band RF tuner deep inside (the secret chip with no real datasheet, not even maximum rating pages.... )
The max forward current in this CLAMP  , is  for 1 full second, is 0.5 AMPS. (a wise choice  is 100mA limits, on this device, with and unknown source and modulation)
Obviously the maker knows V forward drop(clamps) on the RF switch antenna does no damage to the input is all about not damaging the BAV99 clamp sets.
The limits would be worst case mode,  if the switches were active and set to the most weak path say to the Poly-band RF tuner,  then this may be the limit this mode, I sure don't know that nor ever will lacking datasheets on it.
The input cap (DC blocker) in the SDRPLAY is 100nF at 7MHz is Xc = 0.23 ohms not much help there for protection from overvoltage and working with the clamps when tripped. Max inputs are 1 to 1.4v.
 
The  chip itself  below called U1, has ESD protection to 4kV MIL-STD-883 Method 3015.7, or 4000 volts (short duration and capacitance models, see mil spec) 
The minimum frequency is 100 mHz? and max input is, +38dBm at 800mHz 50ohms. (odd no?)
dBm is referenced to 1mW POWER levels, so is a finite value, at 50 ohms, and that equates to 17.7617v RMS , or 24v Peak (rounded off) or about 6 watts.
In fact this device, is designed for 6watt Cell phones, it is not and exclusive to only a , RF RX switch !
What that tells me, is that the 2 diode clamps explode way before the PE42641 RF antenna switch sees damage,  and damage is damage. 
The diode drops 1v at 100 ma forward drop. 70v reverse voltage break down. (not going to happen in this form)
 
They hint at 50 ohm input impedance (a transmission line actually) ( there is no readings with a DMM set to ohms, shows infinity) I will try my antenna analyzer on it. (seen below)
But app note #48 answers all this in beautiful style, as seen here.(see the last page for the , model equivalence of this device, nice !)
IMO, I think the maker (SDRPLAY) is focused on only SWL. after all, all they  says" is avoid near field transmitters", with not a word (or application guide) telling the HAM how to do that. (as you can see I have some ideas)
Sure, shielding and isolation and even clamps can be used. (if you pop the lid on ICOM 7200 you see the reciever is in a metal faraday can, not for good looks or giggles)
I wonder how a Cell phone with this chip survives near a HAM ,.AM/FM or TV broadcast system?, seems to me it is OK (just it). (after all it is (IC RF switch alone) tuned for only CELL frequency usage by its true maker)

The Chip can be damaged in the near field even if the SDRPlay is not being used. (oops) The maker does give that warning too,  but no cures not one. (sure shielding.)
A shielded box (added later in revision 1A, would be great, and input protection on the SMA jack and USB and sure enough  both have it.
What I don't know is if the PE42641 sends too much signal to the , next chip , nor how it behaves. (The LNA spec, may be,  21dbm max , 3.5v-peak)
 (the MS1001 Poly-band RF tuners, launched in 2006, has no REAL data sheet, at all (a trade secret?) , so no max inputs in LNA pins published (my guess is you must beg for that information  to Mirics company)
Nor how much signal, is induced in the traces inside with a plastic only case (toy grade, mine) on HAM bands HF . (6m or 2 meter might be worse)
The only real issue is if the clamp work (0.7v or 1.4v if 2 in series) actually work, I'd say yes for most induced RF fields ,but never for TX power fed to the box, no matter the excuse, even closing the relay late, excuse  you lose.
I've been in HAM shacks, that when the operator keyed up (PTT) the PA (full gallon) on CW, the turned off desk Florescent lamp just  glows.. (yah) Local Fields vary,,,,, YMMV or YFSMV, your field strengths my vary?

  (The RF switch see below right) The chip to protect most in my analysis is the Top left chip, MS1001, Poly-band RF tuner chip, (the LNA inputs may not all that protected , only BAV99 is the guards as are  ESD clamps.)



last is my Stark100 scans (atten.analyser) (SDRplay is connected to live USB but not SPR programmed yet, it is at its default power on state)  Z varies from 90ohms (6m) to 225 ohms (160m)


end SDR musings. (and my Systems Approach)



v1; 2-20-2018,  I do not have copyrights here, it is just my journal and free to all HAM's , I am nicely retired and lost the greed for money long ago.