To: rsgb_lf_group@blacksheep.org
References: <09a39510-37a4-06dc-5fc8-05fe24d4e681@n1bug.com>
 <5B44A64A.1070307@posteo.de> <3d737f55-9e30-1c39-f34c-ea6f3c1c06af@n1bug.com>
 <5B44B5A4.6040401@posteo.de>
From: N1BUG <paul@n1bug.com>
Openpgp: preference=signencrypt
Autocrypt: addr=paul@n1bug.com; prefer-encrypt=mutual; keydata=
 xsFNBFqj1+0BEACggWlaH8oG/AiXSUG3CeQwZ1NrVEP4U7YsA9N9XEffjCDEsnTjHF2BJSgS
 2AicyomkmTGvghEHxrNFfFw07jwgJl97ae/VtNxpERPSE98mb4sPOMpJbwddioMazMDXwhKA
 wpg5fse+Ru8OrIT04KK919xL/pZuAP6pY6d2kVoizjJOfS71pHpiU6N6q3d9cl+w7d2LKhAE
 a3A1ZgDquPvn0WQlrN8K5D66xVrwTRhf1b5H4Ozl8/mMJzCeLG1ZIsDB3Pu2flwE81P8dCJA
 y1azwgY8pTEshVk4em/se9uRiZaDJr/qUSCf6hrV7AGa8g1jpAQDmdGpDNYMqyDqXen4jNi1
 8kNFVu1BMl2vjaI8skw/YPxIxlk/0ROHYhN6SuoDq1mt4AW4FryNa7k3A8dM8Bt7udBoTv0i
 uw4j9R/bmh2vl/QaHRUhDco0xn2z6geWvXkKqha++vzXDrEKUuqgB85SDZPs5W/phs9p0pz1
 xA61d1gn8FQJtpou5dQuAucqMo8eKQY5LUcbC+MH5pebH+M2wIuDCBmFPJHQDSPNepeaxJ4o
 G/HU1hrpzlgLiTTSKR8DcwtMQwYywnCTlm8MgL4jXuPzoGyKDMYyKIjC51G+3AAOJ6oXJAGR
 g0ehhCPtmnCGBaRlUIoUSpbgc4B+onqFKZmDiVm9CRNJhKIWrQARAQABzRZOMUJVRyA8cGF1
 bEBuMWJ1Zy5jb20+wsF9BBMBCAAnBQJao9ftAhsjBQkJZgGABQsJCAcCBhUICQoLAgQWAgMB
 Ah4BAheAAAoJECRS/J8srRGjPBsQAIh+Haz9gqrQJ0OlMI5xmQ0A5nsVWcatWF/Ea4mucNjL
 4n4jmW+Z4Ukn3OVss55chWwrOVMRNWU2d2zRc92ZF7yJhLCoJFV870bZfxNYwdJ3GEBLIu6/
 anmQYX0oXFx8UBsx5K6egNqbeflPA7zrLiQkWrz6JApECdiA1rHDjyJdS7PDxBCG9cKgr/5b
 r4Rn/JlUl9pRPnxlSwHXsV+J6JtFYtWI69MWIVD7Y7OY1wO9+684uOnzeDANzeIwpBDcSm6p
 0D5u0b1hfPl2TD0ozVs6P0NvxkMbimXUhRR1QD0FvydyxmZTLAo+XZDGR8GqWYrYrauoRZ1h
 3m23+bNT2T4AuoFnWekpsZu+sxIf0LKPtEZCa51O65jZ810ROpXg9Lx71gEoQD+kbjO69+kq
 9r7wjytDq/jyhpOGrGYV6kgcQrISY86t9YvkA9Of2HDzZLih3GwecW6fkeV1AO5w4RteE9nL
 zIs2siGw2YqavF6LpTH71Db7cUYyZWn5hkKpwfpLNnPEuqgZACovpH1WUHx+KMqqIL4rMVCH
 GcSLqnH2KF4cEDb6OeTbwuLfpGlN+I3j24eQnB2uz5rDa7/IBjsClLl8S/wdDTP8IikBGixX
 06v3k06tk/OF4UsfJ0cY/ASGP5+kjT4ASMZAIikwVMpKi5A5be77vecKNYlJQ2a6zsFNBFqj
 1+0BEACaujZXo3F17v7QTnub4DjjYvm+nr8J0uU5pPc1UMEz9eWjmtmITm15fx1hPKNtVW+I
 VlT+DG+ShNnYmO2M4CFBoc7PwkAOc70aDxfHz20kotvj1HhXG7oBiqPkN3TK4C7qWV1HUEPA
 V960qPdhsoCqmtkvNwj39w1T0ZR5qwwaqDogs9UwBib7zseQ3OXHG32xYYCMcxM35hgXGkkz
 R7wFL4ZnAPOeFb8LnWtZcrGpwXdsYkXuCxm+A+u9KlFY+w3ZCzZt1F9Ie+/PSZnFIUtbXt2i
 mfc+VkRwOLz5BDAeWuDL09TN81+gbrR3kXlymDcCbuduO/yHOQK085qzE3LuImdy+JNb7oDf
 1C/hvpRvtB02vVy33rzIXT8644SJzFY/mw/W39/BgHKCoL1FrBbfgf0UoIFw5M752i7jQwmv
 j5yFfnVAXIPpCuusMwWMGVpZcGV7QxJxh0HBEhYgOo9v3zKwzNIPm9V/LA67u/rj4a/MlCE0
 mpd6IHaePE1vXDaboPZHZdhAziru5/Jd7KQI0k+HmM/HRANPRNDZ4UeBpgj9PzS6hDN5GHlZ
 fRUbI8JAg9wSaQtEn0bjyaR7lw0yngZTvvjT1Qqt5zGwm1IAall2STes5xK0aS7p+UJJMVbf
 ydZ5VOnocvUkwYxbiqoyuVtGxi4tpWW9CRstYXMkAwARAQABwsFlBBgBCAAPBQJao9ftAhsM
 BQkJZgGAAAoJECRS/J8srRGjTDMP/18q7uhac/naxoFsOqhgXIlvaPgu6GX7s/QOh+bcSV1F
 y50lxo51P/C95H2TVME/CtCjk2xWQcNjWtXloMEsZpl7T3qWgJHvyZYkDtgh3M6UNY+zb08U
 K9E2+rR0AZ6zdMKio7Z1xA9BtbUpSZpvy2NgjoYVqo35NllUWMZJq0u+88PvE5WeCIqLipNI
 EZmUcG9UwolQbPkrRc42ReL+bFbuXGXDA5GbQ0RudXbugI8iUwaw3ftaKElIZtuHW0hw1VrU
 9tVHsxKyEoKgNNT1hr+dgRmvCHmA87Pi4R5cMV0ZkLVOYfPX1motedag7HmSNPi2PkYLts4z
 kyvPEJe2IvaPvjvK1ShRWWgje3uytrhfwyjUZcIuA76RWEfBbwT2Mbrn9O7LvrYtbTiTlsLo
 Zdk2uocuefBvPd2oI7mTn5eLy/VDy2JVnlb9vpZZhriXI4KtCcP6mYyuPxlxqj/30Kn1fU5b
 C4EpnKy6hW1CHM42DbwzT+ChjBpFbX9bfwT4qn6d42+T4mN5wkmfnBRHfcn8Wf1ezRSK3Ome
 Esa3ZDssj23CZHe11uec6Ln14qoB7JyRT9qM3Q99tzvAlmWFM3GrSsG94g4JponQjQWHmr8B
 eMYezwJHzSI7zWElJpzs/OuohstTYfYTy16FygUOEinc1K4ywjEklgRpXRtjKvqc
Message-ID: <4eba6794-e366-5244-c9a8-621cc215da05@n1bug.com>
Date: Tue, 10 Jul 2018 15:03:29 -0400
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.8.0
MIME-Version: 1.0
In-Reply-To: <5B44B5A4.6040401@posteo.de>
Content-Language: en-US
Subject: Re: LF: Receiver protection
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org

Hi Stefan,

> I suggest to discuss along a concrete schematic that you could present 
> along with the question(s).

Here is a simplified description of the setup. RX antenna (at the
moment, but soon to change or have more than one choice)

http://www.n1bug.com/lnv.jpg

Then there is a two way splitter. One output feeds the LF RX system:
band pass filter, preamp, band pass filter, receiver. The other
output has the same line up but for MF.

The preamps, with diodes added at the input

http://www.n1bug.com/w1vd-pre2.png

Finally the receivers (one for LF, one for MF)

http://www.n1bug.com/srlite2.png

These receivers may look too simple but with the filters and preamps
have done quite well for me!

I was hoping for something better than the diodes to put there at
the preamp input. Something which would limit to a much lower level.

For HF, a company called ICE used to make RX protectors (ICE-196)
which use some kind of very small transformer on a ferrite core. I
think the idea was the core saturates to provide limiting. But there
were other parts, including diodes, resistor, capacitor. I have two
of these, one is permanently connected to the RX antenna input on my
FT-2000 transceiver. Unfortunately these do not work below 1 MHz.
The insertion loss becomes very high at MF and LF.

Probably the best, as many people have said, is to give up this
silly idea of limiting at the RX front end and use a fast relay to
disconnect RX antenna and put instead 50 ohm resistor on RX input.
This we can say is quite safe for the receiver. :-)

It's just some work. I have a FT-2000 which I use with home built
down converters for CW and digital QSOs on MF and LF. I think there
is 15 ms between FT-2000 PTT output going low and the beginning of
RF output, so with a fast relay it should be OK.

I also have a Ultimate 3S beacon transmitter. It provides +5V output
for external T/R switching, supposedly with a programmable delay. I
have it set to 50 ms now. I am sorry to say I do not completely
trust this as there are some things which do not work quite as they
should with this device. I don't know if the T/R delay is correct
and reliable. I will try to measure it.

The FT-2000 and all LF/MF receiving stuff is in one room, the ham
shack. MF and LF down converters, amplifiers, and U3S are in another
room, the lab or work shop. There was no more space in the ham
shack. ;-) It's really quite silly to call that little room the lab
or shop, because there is a ongoing radio construction project in
every room of my house! The whole place is a work shop!

Some time in the future I may be able to use my HP 3325B synthesizer
with a linear PA to TX Ebnaut. I don't have any idea how I will
provide proper timing to switch the RX input relay with that, but  I
will worry about it later.

For now I think I should just make the decision and do the work to
make both the FT-2000 and the U3S (if its T/R delay is reliable) to
switch a relay disconnecting the RX antenna during TX. Unless
somebody has a better idea about serious limiting at the RX...

>> I need to stop being lazy. ;-)
>>    
> Oh oh, i know what you mean. Good point :-) I can observe the same 
> behaviour here. Sitting in front of the monitor, watching grabbers, 
> watching the WSPR map, programming some Linux stuff, playing with 
> SpecLab can be quite comfortable and relaxing. When looking back, 10 
> years ago i have been more spontaneous in doing portable experiments.
> But can this tendency be stopped or is it hopeless? It could be helpful 
> to analyse the causes instead of 'fighting' against oneselve.

Sounds like fun! I'm a little bit tired from building. I built all
the LF and MF RX stuff including receivers, preamps, many filters,
splitters and so on. I built the U3S, TX converters, TX antenna,
variometers, transformers. I built a few LF and MF PAs before
finding success... and success came after many weeks of tracking
down trouble. Now I'm just finishing up the build of a power supply
for the new LF PA, also doing a lot of work to make new and better
cables to connect all this stuff together. I enjoy building stuff,
but I am ready for a little break. All this has been a bit of a rush
trying to get it all done as quickly as possible. After I finish the
power supply, RX protection, and new RX antenna maybe I can rest and
do some operating... ;-)

73,
Paul