Message-ID: <164b344b028.marcocadeddu@tin.it>
Date: Thu, 19 Jul 2018 17:59:40 +0200 (CEST)
From: "marcocadeddu@tin.it" <marcocadeddu@tin.it>
To:  <rsgb_lf_group@blacksheep.org>
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Subject: R: Re: LF: TX > RX isolation test
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Hi Paul,

a "magic T" at the RX end will allow you to power a remote E-probe ;-) don't be worried of your 100m coax run: I live at first floor of my building and although the building is not a sky skraper, but a common italian condominium the closest antenna is 50m of coax away! On the other hand losses are quite small on LF / MF so for a proper matched antenna are negligible I guess your RG59 and RG6 are more than useful!

Keep on and do not worry if you feel to not understand something: you are not alone! :-) and the reflector should also be a room were more experts can explain to common (or almost common) people esotic tales ;-)

73, Marco IK1HSS  


----Messaggio originale----
Da: paul@n1bug.com
Data: 18-lug-2018 23.34
A: <rsgb_lf_group@blacksheep.org>
Ogg: Re: LF: TX &amp;gt; RX isolation test

Hi Stefan,

> Be happy to find some new challenges to expanse your knowledge spectrum.

I am, but I feel like a fool asking so many questions and sometimes
having difficulty understanding how things work at this part of the
electromagnetic spectrum.

> Here i have the same experience with Linux, a big struggle to me! :-)

I understand! I use linux every day but for routine things like
email, web browsing, etc. For this I do not need (and do not have)
much 'under the hood' expertise with linux.

>> In hindsight, the TX>  RX antenna isolation measurements I made the
>> other day make no sense at all to me. I now question whether the
>> results mean anything.
>>    
> Your measurements appeared meaningful to me.

Perhaps so but now I do not understand how the coupling can be only
-21 dB. The efficiency of the TX antenna is < 0.1% and surely the
little RX antenna is very inefficient also. How can I have only 21
dB loss of signal between them? What is the method of coupling or
signal transfer for antennas in such close proximity?

> But as far as i understand your main interest is to reach the best 
> sensitivity of the RX antenna when it is standing far away from the TX 
> antenna.

Yes, that's correct.

>> If the preamp is designed for 50 ohm input, why is a 50 ohm resistor
>> not a suitable 'dummy load' for receiver testing?
>>    
> It is. But do you think that the antenna and the 100:1 transformer 
> represents a Z=50+j0 Ohm load?

Ah. I see. In fact I have no idea what complex impedance it presents.

> All in all i would favour the JFET preamp solution but if you like, you 
> can also treat the RX antenna like a TX antenna and resonante it (using 
> a coil on a ferrite rod for example) to 137 kHz and then transform to 50 
> Ohm and connect your 50 Ohm preamp. Your transformer will have a winding 
> ratio of just 4:1 maybe, e.g. 20:5 turns.

I would like to continue using this antenna on LF and MF, at least
until I have more RX antennas installed. The preamp I use now is
(perhaps foolishly) band pass filter, preamp, and two way splitter
all in one box. This has been good because with the filter I can TX
will full power on 160m, HF, VHF without interference to my LF and
MF receivers.

If I understand correctly, one suggestion is to convert this antenna
into an e-probe by eliminating the transformer and putting a JFET
preamp at the antenna. It would be reasonably simple (maybe) to feed
DC power over coax. I don't have any RG58 but I have a lot of RG-59
and RG-6 direct burial cable. I use it for my 160m RX antennas.

One concern for me is that I don't make my RX situation any worse
than it was last winter. To address that, maybe I can leave the
existing RX antenna just as it is and make a new one with JFET
amplifier and power over coax feed at the more distant location
where this one failed to work. I don't know if that is a good idea.
Until now I did not see anyone use long coax runs with e-probe type
antennas. Loss is obviously not a concern, but common mode problems
could be. The coax to reach that location would be about 100m.

I see most people put e-probe antennas very close to their home with
short coax runs. I can try that and see what happens. I also read
the suggestions to find a quiet location for the antenna. My
experience at 160m is probably useless at LF, but I have always
found that any RX antenna in close proximity to my house (and
neighbor's house) was a disaster on 160m. Very noisy!

> Yes yes it is a good idea to use a directional antenna.
> But, a normal loop will also improve the situation and is easier to 
> build. the K9AY stuff is more complex/ advanced. But certainly a good 
> choice.

A loop is also in my plans. I have many plans, not enough time or
money. :-)

73,
Paul N1BUG


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Hi Paul,<br><br>a "magic T" at the RX end will allow you to power a remote =
E-probe ;-) don't be worried of your 100m coax run: I live at first floor o=
f my building and although the building is not a sky skraper, but a common =
italian condominium the closest antenna is 50m of coax away! On the other h=
and losses are quite small on LF / MF so for a proper matched antenna are n=
egligible I guess your RG59 and RG6 are more than useful!<br><br>Keep on an=
d do not worry if you feel to not understand something: you are not alone! =
:-) and the reflector should also be a room were more experts can explain t=
o common (or almost common) people esotic tales ;-)<br><br>73, Marco IK1HSS=
&nbsp; <br>
<br>
----Messaggio originale----<br>Da: paul@n1bug.com<br>Data: 18-lug-2018 23.3=
4<br>A: &lt;rsgb_lf_group@blacksheep.org&gt;<br>Ogg: Re: LF: TX &amp;gt; RX=
 isolation test<br><br>Hi Stefan,<br><br>&gt; Be happy to find some new cha=
llenges to expanse your knowledge spectrum.<br><br>I am, but I feel like a =
fool asking so many questions and sometimes<br>having difficulty understand=
ing how things work at this part of the<br>electromagnetic spectrum.<br><br=
>&gt; Here i have the same experience with Linux, a big struggle to me! :-)=
<br><br>I understand! I use linux every day but for routine things like<br>=
email, web browsing, etc. For this I do not need (and do not have)<br>much =
'under the hood' expertise with linux.<br><br>&gt;&gt; In hindsight, the TX=
&gt;&nbsp; RX antenna isolation measurements I made the<br>&gt;&gt; other d=
ay make no sense at all to me. I now question whether the<br>&gt;&gt; resul=
ts mean anything.<br>&gt;&gt;&nbsp;&nbsp;&nbsp; <br>&gt; Your measurements =
appeared meaningful to me.<br><br>Perhaps so but now I do not understand ho=
w the coupling can be only<br>-21 dB. The efficiency of the TX antenna is &=
lt; 0.1% and surely the<br>little RX antenna is very inefficient also. How =
can I have only 21<br>dB loss of signal between them? What is the method of=
 coupling or<br>signal transfer for antennas in such close proximity?<br><b=
r>&gt; But as far as i understand your main interest is to reach the best <=
br>&gt; sensitivity of the RX antenna when it is standing far away from the=
 TX <br>&gt; antenna.<br><br>Yes, that's correct.<br><br>&gt;&gt; If the pr=
eamp is designed for 50 ohm input, why is a 50 ohm resistor<br>&gt;&gt; not=
 a suitable 'dummy load' for receiver testing?<br>&gt;&gt;&nbsp;&nbsp;&nbsp=
; <br>&gt; It is. But do you think that the antenna and the 100:1 transform=
er <br>&gt; represents a Z=3D50+j0 Ohm load?<br><br>Ah. I see. In fact I ha=
ve no idea what complex impedance it presents.<br><br>&gt; All in all i wou=
ld favour the JFET preamp solution but if you like, you <br>&gt; can also t=
reat the RX antenna like a TX antenna and resonante it (using <br>&gt; a co=
il on a ferrite rod for example) to 137 kHz and then transform to 50 <br>&g=
t; Ohm and connect your 50 Ohm preamp. Your transformer will have a winding=
 <br>&gt; ratio of just 4:1 maybe, e.g. 20:5 turns.<br><br>I would like to =
continue using this antenna on LF and MF, at least<br>until I have more RX =
antennas installed. The preamp I use now is<br>(perhaps foolishly) band pas=
s filter, preamp, and two way splitter<br>all in one box. This has been goo=
d because with the filter I can TX<br>will full power on 160m, HF, VHF with=
out interference to my LF and<br>MF receivers.<br><br>If I understand corre=
ctly, one suggestion is to convert this antenna<br>into an e-probe by elimi=
nating the transformer and putting a JFET<br>preamp at the antenna. It woul=
d be reasonably simple (maybe) to feed<br>DC power over coax. I don't have =
any RG58 but I have a lot of RG-59<br>and RG-6 direct burial cable. I use i=
t for my 160m RX antennas.<br><br>One concern for me is that I don't make m=
y RX situation any worse<br>than it was last winter. To address that, maybe=
 I can leave the<br>existing RX antenna just as it is and make a new one wi=
th JFET<br>amplifier and power over coax feed at the more distant location<=
br>where this one failed to work. I don't know if that is a good idea.<br>U=
ntil now I did not see anyone use long coax runs with e-probe type<br>anten=
nas. Loss is obviously not a concern, but common mode problems<br>could be.=
 The coax to reach that location would be about 100m.<br><br>I see most peo=
ple put e-probe antennas very close to their home with<br>short coax runs. =
I can try that and see what happens. I also read<br>the suggestions to find=
 a quiet location for the antenna. My<br>experience at 160m is probably use=
less at LF, but I have always<br>found that any RX antenna in close proximi=
ty to my house (and<br>neighbor's house) was a disaster on 160m. Very noisy=
!<br><br>&gt; Yes yes it is a good idea to use a directional antenna.<br>&g=
t; But, a normal loop will also improve the situation and is easier to <br>=
&gt; build. the K9AY stuff is more complex/ advanced. But certainly a good =
<br>&gt; choice.<br><br>A loop is also in my plans. I have many plans, not =
enough time or<br>money. :-)<br><br>73,<br>Paul N1BUG<br><br><br><br>

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