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[N8NK]

Back-to-back Schotky diodes will eliminate any Rx front-end input damage.
Many will disagree with me-
and they will be wrong.
Chuck, N8NK, Blowzo the Humbe Ham has spoken.
dit dit

[KA4WJA]

Del,
1)  The short answer is, with ~ 200' distance (or more), that you should have no issues....and, even if your antennas were a bit closer, it's also darned unlikely that you'd have any issues with receiver damage. 

And hence, in my opinion, many are over-thinking the issue of possible receiver damage.

But, for "operational" reasons, I'd recommend you orientate your antennas such as to maximize the isolation between them (distance, pattern/heading, and polarization, can all be used to maximize the isolation)....and make your choice of receiver to use for WSPR, taking into account some actual receiver specs that would apply to your situation.  This way your two stations can operate simultaneously without issue.

Of course, you're unlikely to find a manufacturer spec of "max receiver input" except for what they'll say publicly to cover their asses....but, figure +20 to +30dbm....but, more importantly, also knowing how well your WSPR receiver will be working when you're on-the-air with your other rig/antenna, would be good....so knowing the rigs' BDR, and its RMDR / in-band noise-limited operating range....and, of course, knowing your local HF receive noise levels needs to be put into the final calculation / decision, as well!

(If you've got the time....have a read of my longer answer...)


2)  The slightly (hi hi) longer answer is....
In addition to what Mike, K6AER and Peter, G3RZP wrote..

Most modern HF receivers will handle +20 dBm of signal with out permanent damage. Do note that anything much above -20dBm will be causing serious intermod in the receiver electronics.

  Disagree with your point about "serious intermod" if it's above -20dbm (that's only S-9 +53), if its out-of-band, or at least in another part of a band, like at Field Day, etc....if that's what today's standards are, we need to get better receivers, hi hi....but, that's not really pertinent at the moment... 

Over 70 years ago, the  RMS Queen Mary (GBTT) ran full HF Duplex on AM with rx and tx frequencies in the same HF marine band - those  at 2, 4, 8, 12, 16 and 22 MHz. (The 6 MHz marine was too narrow to accommodate R/T) The separation between receiver room and transmitter room was around 400 feet: they had around 400 watts of carrier, suppressor grid modulated. So it can be done.....The receiver room was fully screened and leads to it filtered. Marine receivers for HF had to withstand 30 volts EMF of carrier on any frequency for 15 minutes without damage: Marconi Marine used a  germanium diode voltage doubler rectifier and a 2 transistor Schmitt trigger to drive a reed relay.

So the problem is by no means insurmountable.

....most modern (and even 40 - 50 year old) HF receivers of either "amateur radio" design, or "commercial/maritime" design, will not only handle +20dbm just fine (most will handle +30dbm, without damage), assuming you're operating your other radio > = 100khz away from your WSPR freq, many can actually operate without much de-sense, or depending on your local HF receive noise-level without "noticeable" noise level increase...

On a side-note to Peter....although, I'm not sure if even my TR-7 would enjoy that 30v (9 watts into 50 ohms, yes?) into its mixer (Peter, thanks for lodging that image in my brain now), I think the mixer would survive for a bit, but assume some of the other components (LO amp?) might be stressed...{but, when I sent my original TR-7 into Drake to be cleaned/aligned/upgraded (to TR-7A), they did add the only upgrade I hadn't done, the "receiver input protection" for static discharge....so, maybe it would survive that 30v test?  But, I'm not going to test it...hi hi.}

But, for the heck of it, let's look at some rec numbers I have of my old fav, the venerable Drake TR-7.....She's got a 100khz BDR = 146db....and a MDS (@ 3db S/N) = -134dbm....you could hit the TR-7's receiver with a +12dbm signal 100khz (or more) away from your WSPR freq, and not only never have any damage, you'd not cause de-sense....and, depending on the freq separation, probable that you'd never even get a rise in the TR-7's background noise.....of course, even if you have a fairly low HF noise level in your rural area (assume it's rural, 'cuz you mention having a barn 200 feet away from your HF vertical and Windom?), it's doubtful it is as low as -134dbm on any bands below the 10m band [ITU "quiet rural" is above -130dbm below 24mhz]....so, you're not likely to run the WSPR receiver gain wide open, and depending on the band and your noise-levels you may actually use an attenuator, so you can add that into the mix here.  (and, btw....the '7300 is a good rig, but wondering why $pend a grand for a rig that you'll put out in a barn, for WSPR, when you can spend < 10% that on a dedicated WSPR receiver?)

The point I'm driving at is....there is too much paranoia regarding receiver damage....and, little thought / calculation being put into actual operational capabilities (de-sense, or noise-floor rise from reciprocal-mixing)...


Just as example of REAL close antennas, etc....on the boat, I run an Icom M-802 [green X] (with somewhat similar receive architecture of the 756ProIII, but with OCXO....up-conv IF-DSP super-het, with 15khz "roofing filter", but without a receive pre-amp....then a 6khz wide 455khz second IF filter, before going to 3rd mixer and the IF-DSP module)....a clean (low IMD) 150 watt CCS 100% duty-cycle PA (FSK, CW, SSB) output HF maritime rig (on 1.6mhz - 26mhz maritime, and 1.8mhz - 28.5mhz ham)....with the main transmit and receive antenna being an ~ 60' long [red line] remote-auto-tuner-fed [red box] base-fed, against sea water ground....and a secondary HF antenna being ~ 22' long base-fed sloping vertical [purple line], feeding both, the maritime rig's sub-receiver (dedicated DSC-FSK rec for 2, 4, 6, 8, 12, and 16mhz bands)....as well as feeding a second HF receiver for HF We-Fax (facsimile / weather chart) receiving [green X]....with this secondary 22' sloping vertical being only ~ 20' - 25' away from the main transmit/receive antenna!  (and, many years ago during initial installation/use, while waiting for other insulators...I temporarily used a 5' whip antenna just 5' - 6' away from the main transmit/receive antenna [dashed purple line]....and, occasionally I rig a temporary 12mhz/14mhz center-fed vertical dipole [dashed yellow and dashed blue lines], as a secondary transmit/receive antenna, that is only 16' - 20' away from my secondary rec antenna...)

To head off any "on-line" push back from my fellow hams, regarding these close distances....here are the pics, showing the antenna (and radio) positions...for distance prospective, it's a 47' sailboat with a 64' high mast...

(BTW, for those who question how this is possible, you may also want to notice the solar array, just an inch or two away from the main HF tx and rx antenna....unlike on ships like the Queen Mary, etc....those of us who sail on small boats learn quickly to not have RFI producing devices on-board, or how-to reduce/mitigate the RFI --- both rec RFI and transmit RFI --- this means dealing with lots gear/devices within inches/feet of radios, antennas, other electronic devices, etc....you think RFI is bad at your home station, when your antenna is 50' - 75' away, think about my solar panels being just an inch or two away from my main HF antenna, and my solar controllers being just six inches from my main HF radio....or how about my wi-fi bridge being just a couple feet away from my main HF tx and rx antenna...or 12vdc driven 3-phase refrigeration compressor controller being just feet away from my antenna / remote tuner....etc. etc. etc....you see, we know what both small signal RFI close-up can do to rec S/N, AND what 150 watt HF transmitter can do with the antenna just inches away from other devices....400 feet on the Queen Mary, heck my whole boat is only 47 feet long... hi hi













During transmit with 150 watts (either 150 watt FSK carrier, or 150 watt PEP SSB), with my HF We-Fax receive antenna being only ~ 20' away, I do find raised noise level (depending on the band and freq separation, it's an increase of 5 - 15db of noise level) on my HF We-Fax receiver, which can introduce noise into a few lines of the facsimile image....but has never caused any major reception problems....and certainly no damage to any receiver at all!

{Yes, my "150 watts" is 8 - 9db lower than your mention of "1000 watts"....but I also ran ~ 600 watts on-board, for a while....and my antennas are only 1/10 of the separation of yours...years ago (2009?), during the solar minimum, for a few months I had an SGC SG-500, 500 watt amp on-board (with an SGC SG-235 tuner), and I tried using this on the ham bands some, mostly on 40m daytime (some 20m daytime) and 80m nighttime....and, even though I knew it's spec'd IMD wasn't very good (hence I never used it on the maritime bands), I thought if I fed it with a high enough voltage it might be "good enough"....but I found even when fed with 4' of 00ga, from 1100 A/H of batteries to a 100-amp breaker, and then just 12" of 2ga wire to the amp....the amp's IMD just wasn't very good...daytime on 40m, when I had solar charging the batteries, with terminal voltages of 13.5 - 14.5vdc, the SG-500's IMD (listening with another receiver) was about as good as many other barefoot rigs on the ham bands, but just not up what I thought was good enough....and since the sun don't shine at night, I finally just took it off the boat (the SG-235 tuner I have as a spare tuner....and the SG-500 amp is at my friend's house)....fyi, I did give a minor thought to installing a large SM "battery booster" like the ones from Harrison in Colorado, but fact is I didn't actually need the amp much (a full-size vertical antenna, floating in sea water is like having an amp), so I never pursued this further....but...but, since I did have another 6db of transmit power into the mix for a few months, just thought you'd wish to know there was still no major issues, and certainly no damage. }

 
Now, perhaps using the TR-7 as example above, is unfair, 'cuz it has one of the best HF receivers ever made in regards to its inability to "overload" (guys in Europe in late 70's up until about 10-15 years ago, when most of the big SW broadcast moved out of the 40m band, used the TR-7....one guy who worked at a SW transmitter site and lived just down the road, wrote a letter about the TR-7 being the only rig that allowed him to use HF from his house), and heck the TR-7 alignment calls for using +7 to +10dbm signal into the receiver for test/alignment, and should take +30dbm without issue....but, what about more "normal" rigs?

(okay, even though I love Rob Sherwood, I have said / I do say that we shouldn't rely on any "list" to make rig choices...but, I freely admit that I'm using his list data here, to easily grab these BDR and MDS specs!  But, this is not the same as choosing a rig 'cuz it's on the top of "the list"... hi hi)

Although our current measurement procedures for measuring BDR shows a disadvantage of SDR's, this isn't actually a significant difference, as the way the SDR handles the signals is different (just leave the pre-amps OFF, and the IP+ (dither and randomization) turned ON....and maybe dial in a bit of attenuation, just like you do with a super-het, and you should be okay....as long as you don't let the ADC clip (overload) you're good....fyi, with the pre-amps off and the IP+ on, you increase the '7300's MDS by 10 - 20db and improve your DR by ~ 20db....so, you could hit the '7300 with a 0dbm signal ~ 100khz away, and not get rec de-sense....and, from Adam Farson's testing, at ~ 25khz separation, it would be a -10dbm signal...)...but, while this doesn't mean that you'd damage the '7300 in the barn on WSPR, it does mean you might be (?) better off using a standard super-het rig, whether a normal/analog super-het rig, or an IF-DSP super-het rig (which some folks are now regurgitating the marketing BS of some manufacturers, and calling our IF-DSP super-het rigs "Hybrid-SDR" rigs), as this may provide you with better "operational" performance with better BDR (as long as you don't put in any old clunker with poor RMDR)...I cannot make a definitive statement on this last point, as it depends on the actual signal levels you'd have, which can be calculated based on your antennas, their  orientations, and distances...or you could do as others mention, put something up and measure the levels.

Looking at a few dozen rigs for examples / ideas.....in addition to my TR-7 (which doesn't have the freq stability for WSPR), you'll note the BDR (Blocking Dynamic Range) of some of these rigs are pretty good, and the ones that I highlight (in bold-type), in addition to having good BDR, they also have decent in-band / close-in RMDR (their dynamic range isn't "noise limited" or they're "noise limited" at 90db+ in-band / close-in)...

The IC-7300 BDR = 123db....the IC-7610 = 122db....the Flex5000 = 123db....Flex6400 = 119db.....Flex 6600 = 116db....Elecraft K4D = 128db.....K2 = 118 - 123db.....ANAN-7000 = 126db....Yaesu FT-710 = 129db....FTdx-5000 = 127db....Perseus = 125db....Orion II = 130db....AOR-7030 = 130db.....Kenwood TS-590SG = 137db....Elecraft KX3 = 138db....Icom IC-751 = 138db....Icom IC-756ProII = 138db....K3 = 140db....Yaesu FTdx-10 = 141db....Icom IC-756ProIII = 142db....Kenwood TS-480 = 142db....Icom IC-765 = 143db....Kenwood TS-990 = 145db...Icom IC-761 = 145db....FTdx-101MP = 147db...Icom IC-7851 = 149db....Elecraft K3S = 150db....Kenwood TS-890 = 151db...

I'm just saying, if I wanted to put a rig out in the barn for WSPR reception (as well as have it available as a spare rig), I'd look for a nice clean IC-751 (w/ the CR-64 TXCO option), the IC-761 (which has the TXCO built-in), the IC-765, etc...but, if I really wanted to go cheap (and still have a spare), I think I'd look for a nice IC-735....although,as I wrote up front, I wonder about the logic of having a full transceiver out there, just for WSPR...so again why not just put a dedicated WSPR receiver out there?


I know there are a lot of numbers here....and, I'm not saying you should pick any of the rigs I mention here, just showing you how you can better make your own choice....and, especially since I started out by writing that many are over-thinking this (but, that's in regards to rec damage), perhaps my long-winded ramblings here might seem contrary.....but, understand the long-winded rambling is in regards to optimal operations... 

So, I do hope I helped some?   If not....well at least I tried. 

73,
John,  KA4WJA


P.S.  Peter, sorry.....my maritime HF radio experience doesn't go as far back as the Queen Mary.....but, back in the 1970's and 80's (and 90's) Gulf Bravo Tango Tango (GBTT) was the callsign of the QE 2....I used to hear them all the time on HF.... (and, one of the tech ops at WOM, said he knew the chief radio officer, and was supposed to arrange a bridge and radio room tour for me, but that never happened)

Alas....the old girls are no longer British registered.
https://cunardqueens.wordpress.com/tag/call-sign-gbtt/
Not sure if she's still afloat, but last I heard the QE 2 was a floating hotel in Dubai?

[KH6AQ]

Back-to-back Schotky diodes will eliminate any Rx front-end input damage.
Many will disagree with me-
and they will be wrong.
Chuck, N8NK, Blowzo the Humbe Ham has spoken.
dit dit

This can work. I did not suggest clamp diodes because the OP's question is "Does anyone know of any RF sensing circuit that I could use to ground out the receiver antenna when I was transmitting on HF?" Additionally, I was concerned about harmonic generation and subsequent antenna harmonic radiation.

Let's take a look at using a Schokky diode clamp with Schottky diodes as you suggest.

Diode Survival
I simulated twelve BAS40 diodes in a back-to-back clamp arrangement using LTSpice. The RF source mimics the 80 meter vertical placed 200' from a 1 kW transmitter at 3.5 MHz. It is a 70 Vrms source with a 50 ohm source resistance. The diodes clamp at 1V peak and dissipate a bit over 100 mW each. Given 357 C/W thermal resistance the diode junctions run 30 deg above ambient. They will survive.

https://www.mouser.com/datasheet/2/395/BAS40_SERIES_H2001-1918076.pdf

Capacitive Loading
The twelve diodes have a total capacitance of 50 pF. At 28 MHz this is -j113 ohms and is acceptable in this 50-ohm circuit.

Harmonics
An FFT shows the 3rd harmonic current of 3.5 MHz to be 40 dB down from the fundamental. The short circuited (by the diodes clamps) RX antenna re-radiates 60 watts. The 10.5 MHz harmonic is down 40 dB which is 6 mW. This is equivalent to the 1 kW transmitter having a 3rd harmonic of -52 dB. The FCC harmonic limit is -43 dB and so the diode clamp does not cause the station to violate FCC spurious emissions under 97.307 (d).

(d) For transmitters installed after January 1, 2003, the mean power of any spurious emission from a station transmitter or external RF power amplifier transmitting on a frequency below 30 MHz must be at least 43 dB below the mean power of the fundamental emission.

[KH6AQ]

To make sure the IC-7300 can take the ~1V let thru voltage we can take a look at the schematic. On page 17, following the connector J1071 we follow the RXRF line. I see no components in the bandpass filter section that would be damaged by 1V from a 50 ohm source. I believe the signal exits that board on J1431.

Schematics   https://www.ab4oj.com/icom/ic7300/IC-7300_Schematic_Diagram_2.pdf

[N0GV]

I never knew receivers could feel pain....

Grover

[KK4GMU]

And I'm guessing most SDR receivers have <1/10th the RF capacity to withstand damage compared to most hardware receivers.  Am I close?

[K0UA]

Can someone explain how I have been able to use my two 7300's and my 7610 in my shack, often running all three radios at the same time? Must be a miracle. Haven't blown out the front ends yet. Sure some antenna/band  combinations (all antennas within a 100 foot circle) do give desense and interference and some do not. If the original poster wants my opinion, I would say he has nothing to worry about.

[KA4WJA]

Jerry,
Not really...but...
It not quite that simple.  (and, to be clear....except in some VERY rare and extreme cases, like antennas just inches, or a few feet, away while running legal-limit, etc....this is a NON-issue!)

And I'm guessing most SDR receivers have <1/10th the RF capacity to withstand damage compared to most hardware receivers.  Am I close?

You have two "specs" to consider...


1)  The original query here (and what you're asking about)....how much signal level can you subject your modern amateur HF rig's receiver to, without causing any damage?
This is governed by the components in the radio's "front end"....the specs of these components:

a)  In a super-het receiver, the "front end" (after the input filtering) is the first mixer...(and the other parts on the board that feed the mixer)
(or in the case of a receiver with a input pre-amp that you failed to switch-off / bypass, the specs of that transistor of the pre-amp). 
And, for today's mixers, they should all handle +20dbm (most should handle up to +30dbm)...


b)  In the case of a direct-sampling-SDR, the front-end (after the input filtering) is the A/D converter (or "ADC"), and any components feeding the ADC...
And, you'd need to read the schematic / parts list of some radio that you want to know about, and then look up the specs of that ADC in that radio....
Then you'd know what it's rated / spec'd at.
(I don't own an SDR, and don't have the time to look up the specs on the ADC's used in some of them....but, you can certainly do this...all it takes is an internet connection and the time to find-n-read the schematics/parts lists and then find-n-read the specs on the ADC)
But, to be clear, I highly doubt Icom, et al, would put in a wimpy ADC that couldn't handle at least +20dbm, or more....


2)  My major point....most receivers will handle +20dbm (and up to +30dbm) without damage, but how much signal can they handle (and at what freq separation) and still operate perfectly (or as good as you need them to operate), so that you can use both (or multiple) rigs at a time, such as at Field Day, or multi-multi contest stations. 
(actually antenna placement, cable runs, filtering, etc....as well as the rig choice/specs, are some of the most important design criteria of multi-multi stations!)

This second spec (#2) can be read from test reports of various rigs....and you can determine how far apart you'll need to space and how you'll orient your antennas accordingly.



3)  Use of well-designed super-het receivers allowed for much "operator error" and still have success....but early use of modern direct-sampling SDR ham rigs, showed that they are less forgiving to poor operators / mis-adjustments.

Case-in-point....many early users of the '7300 complained about its sensitivity to "overload" (the OVF light flashes or stays lit, indicating that the A/D converter is clipping / being saturated)....but, if the operator turned the damn pre-amps off, switched on the dither and randomization (the IP+), turned the RF Gain down a smidge, and/or switched in some attenuation (any, or preferably all of these things...just like we are all supposed to do, no matter what receiver-type we have)....then the '7300 is fine....

But, since direct-sampling SDR's take in a whole swath of the HF spectrum at once (within the band filters), they "test out" a bit differently ---- meaning that in order to see more "normal" results when subjected to the signal levels of BDR tests, etc.....then usually the SDR needs some "help" in the form of "dither" and "randomization", as well as not purposely hitting the ADC with high levels 'cuz you have your friggin' pre-amp on...

And, in actual operating (not just testing for "the numbers"), dialing back the RF Gain to better manage (match) your local HF noise levels....which is ALWAYS recommended, no matter whether you're running a standard/analog super-het, or a direct-sampling SDR....or an IF-DSP-super-het (which some are now marketing as a "hybrid-sdr")....

So...
So, Jerry, if the operator knows how to use the radio, there aren't great differences, and for > 95% of ham shacks, there would be no major difference in performance (again, assuming the operator knew how-to operate their radio....which, unfortunately is not the case for many hams these days!)....

But, if you wish to split-hairs, then yes...a well-designed super-het receiver can handle higher receive signal levels than the typical amateur radio direct-sampling-SDR....but, that's just a generality (see above for the specifics)...
{of course, now-a-days, we have super-hets with IF-DSP....and, they're good....but some are now calling them "hybrid-sdr's", which is confusing many new hams, and they're getting things a bit mixed-up....so, use caution when making generalizations, 'cuz you can't just use the advertising/marketing materials to do comparisons!}


Hope this helps?

73,
John,  KA4WJA


EDIT:  James, K0UA and I were typing at the same time. 
And, he makes a good point (that I have also stated)....this is a non-issue!
I'm not sure how/why/when, but it seems that some have started down this path and now it's a "thing" to worry about? 
Really, it isn't... 

73,
John,  KA4WJA

[KK4GMU]

RSPduo maximum RF input:

0dBm continuous
10dBm intermittent

[K6JH]

Can someone explain how I have been able to use my two 7300's and my 7610 in my shack, often running all three radios at the same time? Must be a miracle. Haven't blown out the front ends yet. Sure some antenna/band  combinations (all antennas within a 100 foot circle) do give desense and interference and some do not. If the original poster wants my opinion, I would say he has nothing to worry about.

are you using single band antennas? Or do you have multi and antennas like an R8 vertical and a fan dipole or multiband yagi? Can you be on the same band?

[K0UA]

Can someone explain how I have been able to use my two 7300's and my 7610 in my shack, often running all three radios at the same time? Must be a miracle. Haven't blown out the front ends yet. Sure some antenna/band  combinations (all antennas within a 100 foot circle) do give desense and interference and some do not. If the original poster wants my opinion, I would say he has nothing to worry about.

are you using single band antennas? Or do you have multi and antennas like an R8 vertical and a fan dipole or multiband yagi? Can you be on the same band?

Multi band antennas.  Fan vertical for 40, 20, 15  Inverted L for 160 and 30 vertical on same feed. Ma5B beam for 20, 17, 15, 12, 10.   OCFD for 80, 40, 20, 17, 12, 10, 6.   Moxon for 6M.  Recieve only antenna LOG. (Loop On Ground)

Absolutely NOT on the same band in any case.

Neighbor  KC0M is active on HF and is less than 1/4 mile away, and we can operate different modes on the same band without any interference. Line of sight too.

[K6JH]

BTW, Phil AD5X, has an article about building protection for a transceiver. Basically back to back diodes with a light bulb in series, with a gas discharge tube for good measure. A relay switches it out of line during transmit.

http://www.ad5x.com/images/Articles/FrontEndProt.pdf