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loss of RX sensitivity

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Rick Dwight

loss of RX sensitivity

Scott,
The problem you describe is actually quite common in electronics. In the telephone industry, especially in the “good old days” with wire cables, sometimes with many splices it was common to get drop outs. These could be due to a splice, wire wrap connection, oxidized relay contact or whatever, especially with only low level signals. If the circuit also had a DC voltage on it, the problem often did not exist. In fact it was common on critical circuits for the FAA or military, or whatever to sometimes just put “sealing current” on certain circuits just to be sure it was reliable. Often we used 24 volts DC or less with only a few ma of current. At one time I had many phased verticals which were controlled by many relays. Occasionally the received signal would drop by many S units. Sending a single dot, even with QRP or QRPP power always cleared the problem, sometimes for weeks or months. So it could be a connection in the antenna system, a plug on a circuit board, or even a relay. I have never experienced trouble with Elecraft relays personally. Sometimes PL-259 center pins are not correctly soldered, and can present similar symptoms. You could try a random wire, or even something like an 80 meter dipole on 30 meters, just to see if it was anywhere in the antenna system. Even a volt or two is often enough to punch through a poor solder or oxidized connection, but even something like a 0 dBm signal is just not enough. I have identified problems with BNC connectors and adaptors purchased at ham flea markets which are just not reliable and are probably factory rejects. So look into your antenna system before you dig into your rig. You could also hook a signal generator to the rig and see if it receives OK on all bands with something like less than an S9 signal. Be sure to not transmit into your generator, and/or set your tx to very low power. Good Luck Rick KL7CW

Sent from Mail for Windows 10

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rich hurd WC3T

Re: loss of RX sensitivity

I guess that’s the electronic equivalent of blowing through a tube to clear
the blockage. :)

On Mon, Sep 17, 2018 at 01:44 Frederick Dwight <[hidden email]> wrote:

> Scott,
> The problem you describe is actually quite common in electronics. In
> the telephone industry, especially in the “good old days” with wire cables,
> sometimes with many splices it was common to get drop outs. These could be
> due to a splice, wire wrap connection, oxidized relay contact or whatever,
> especially with only low level signals. If the circuit also had a DC
> voltage on it, the problem often did not exist. In fact it was common on
> critical circuits for the FAA or military, or whatever to sometimes just
> put “sealing current” on certain circuits just to be sure it was reliable.
> Often we used 24 volts DC or less with only a few ma of current. At one
> time I had many phased verticals which were controlled by many relays.
> Occasionally the received signal would drop by many S units. Sending a
> single dot, even with QRP or QRPP power always cleared the problem,
> sometimes for weeks or months. So it could be a connection in the antenna
> system, a plug on a circuit board, or even a relay. I have never
> experienced trouble with Elecraft relays personally. Sometimes PL-259
> center pins are not correctly soldered, and can present similar symptoms.
> You could try a random wire, or even something like an 80 meter dipole on
> 30 meters, just to see if it was anywhere in the antenna system. Even a
> volt or two is often enough to punch through a poor solder or oxidized
> connection, but even something like a 0 dBm signal is just not enough. I
> have identified problems with BNC connectors and adaptors purchased at ham
> flea markets which are just not reliable and are probably factory rejects.
> So look into your antenna system before you dig into your rig. You could
> also hook a signal generator to the rig and see if it receives OK on all
> bands with something like less than an S9 signal. Be sure to not transmit
> into your generator, and/or set your tx to very low power. Good Luck
> Rick KL7CW
>
> Sent from Mail for Windows 10
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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--
72,
Rich Hurd / WC3T / DMR: 3142737
Northampton County RACES, EPA-ARRL Public Information Officer for Scouting
Latitude: 40.761621 Longitude: -75.288988 (40°45.68' N 75°17.33' W) Grid:
*FN20is*
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Gwen Patton

Re: loss of RX sensitivity

Reminds me of having to blow on the contacts in a Nintendo game cartridge
to make it work in the console. ;)

On Mon, Sep 17, 2018 at 7:31 AM rich hurd WC3T <[hidden email]> wrote:

> I guess that’s the electronic equivalent of blowing through a tube to clear
> the blockage. :)
>
> On Mon, Sep 17, 2018 at 01:44 Frederick Dwight <[hidden email]>
> wrote:
>
> > Scott,
> > The problem you describe is actually quite common in electronics.
> In
> > the telephone industry, especially in the “good old days” with wire
> cables,
> > sometimes with many splices it was common to get drop outs. These could
> be
> > due to a splice, wire wrap connection, oxidized relay contact or
> whatever,
> > especially with only low level signals. If the circuit also had a DC
> > voltage on it, the problem often did not exist. In fact it was common on
> > critical circuits for the FAA or military, or whatever to sometimes just
> > put “sealing current” on certain circuits just to be sure it was
> reliable.
> > Often we used 24 volts DC or less with only a few ma of current. At one
> > time I had many phased verticals which were controlled by many relays.
> > Occasionally the received signal would drop by many S units. Sending a
> > single dot, even with QRP or QRPP power always cleared the problem,
> > sometimes for weeks or months. So it could be a connection in the
> antenna
> > system, a plug on a circuit board, or even a relay. I have never
> > experienced trouble with Elecraft relays personally. Sometimes PL-259
> > center pins are not correctly soldered, and can present similar symptoms.
> > You could try a random wire, or even something like an 80 meter dipole on
> > 30 meters, just to see if it was anywhere in the antenna system. Even a
> > volt or two is often enough to punch through a poor solder or oxidized
> > connection, but even something like a 0 dBm signal is just not enough. I
> > have identified problems with BNC connectors and adaptors purchased at
> ham
> > flea markets which are just not reliable and are probably factory
> rejects.
> > So look into your antenna system before you dig into your rig. You could
> > also hook a signal generator to the rig and see if it receives OK on all
> > bands with something like less than an S9 signal. Be sure to not
> transmit
> > into your generator, and/or set your tx to very low power. Good Luck
> > Rick KL7CW
> >
> > Sent from Mail for Windows 10
> >
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:[hidden email]
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
> > Message delivered to [hidden email]
>
> --
> 72,
> Rich Hurd / WC3T / DMR: 3142737
> Northampton County RACES, EPA-ARRL Public Information Officer for Scouting
> Latitude: 40.761621 Longitude: -75.288988 (40°45.68' N 75°17.33' W) Grid:
> *FN20is*
> ______________________________________________________________
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>
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--

-+-+-+-+-
Jenny Everywhere's Infinite: Quark Time
http://quarktime.net
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Drew AF2Z

Re: loss of RX sensitivity

In reply to this post by Rick Dwight

I used that trick to keep my DSL line running for a couple of years when
Verizon was abandoning copper and no longer interested in doing
maintenance. Placing a resistor across the telephone line would draw a
constant small current, not enough to off-hook the line but enough to
"seal" the poor connection, wherever it was, and improve the noise margin.

Regarding the PL-259 center pin-- it's also important to check the
connection between the threaded shell and the body of the plug. That is
a common and overlooked connection point subject to poor connection.

Note that there is no electrical connection through the threads on the
plug body and the threads on the shell; these threads are merely a stop
to keep the shell from sliding down the cable when not connected to the
SO-239 on the equipment.

The electrical connection occurs through the lip at the back of the
shell which butts against the threaded region on the plug. The area of
this thin ring of contact is pretty small so it's important that the
mating surfaces are entirely clean and free of corrosion.

It may help to disconnect the cable, then hold the back of the plug in
one hand (where the cable enters it), then pull on the shell with the
other hand, toward the pin end, as if trying to pull it off the plug;
while maintaining this pressure, twist the shell vigorously. That will
help clean the mating surfaces, especially if the plug is not silver
plated but that cheap "shiny metal" stuff a lot of plugs have now. Also
do this with all jumpers between SWR meter, matchbox, etc.

73,
Drew
AF2Z

On 09/17/18 01:44, Frederick Dwight wrote:

> Scott,
> The problem you describe is actually quite common in electronics. In the telephone industry, especially in the “good old days” with wire cables, sometimes with many splices it was common to get drop outs. These could be due to a splice, wire wrap connection, oxidized relay contact or whatever, especially with only low level signals. If the circuit also had a DC voltage on it, the problem often did not exist. In fact it was common on critical circuits for the FAA or military, or whatever to sometimes just put “sealing current” on certain circuits just to be sure it was reliable. Often we used 24 volts DC or less with only a few ma of current. At one time I had many phased verticals which were controlled by many relays. Occasionally the received signal would drop by many S units. Sending a single dot, even with QRP or QRPP power always cleared the problem, sometimes for weeks or months. So it could be a connection in the antenna system, a plug on a circuit board, or even a relay. I have never experienced trouble with Elecraft relays personally. Sometimes PL-259 center pins are not correctly soldered, and can present similar symptoms. You could try a random wire, or even something like an 80 meter dipole on 30 meters, just to see if it was anywhere in the antenna system. Even a volt or two is often enough to punch through a poor solder or oxidized connection, but even something like a 0 dBm signal is just not enough. I have identified problems with BNC connectors and adaptors purchased at ham flea markets which are just not reliable and are probably factory rejects. So look into your antenna system before you dig into your rig. You could also hook a signal generator to the rig and see if it receives OK on all bands with something like less than an S9 signal. Be sure to not transmit into your generator, and/or set your tx to very low power. Good Luck Rick KL7CW
>
> Sent from Mail for Windows 10
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
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>

Don Wilhelm

Re: loss of RX sensitivity

Drew and all,

I beg to differ, unless you meant something different than I read.
The threads on a PL-259 connector are the only thing that connects the
coax shield to the SO-239 jack.

That is why hand tightening of PL-259 connectors is not sufficient. Use
pliers to snug them up just a bit more to assure a good connection.

BNC and N connectors do not have a similar requirement. They will make
positive contact without being tightened.

73,
Don W3FPR

On 9/17/2018 12:20 PM, Drew AF2Z wrote:

>
> Note that there is no electrical connection through the threads on the
> plug body and the threads on the shell; these threads are merely a stop
> to keep the shell from sliding down the cable when not connected to the
> SO-239 on the equipment.
>
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Ian-2

Re: loss of RX sensitivity

Real easy to see on a spectrum analyzer with a tracking generator. The
trace goes wild as soon as you start turning the PL-259 connector by hand
(please don't use pliers on your SA).
73, Ian N8IK

On Mon, Sep 17, 2018 at 12:59 PM, Don Wilhelm <[hidden email]>
wrote:

> Drew and all,
>
> I beg to differ, unless you meant something different than I read.
> The threads on a PL-259 connector are the only thing that connects the
> coax shield to the SO-239 jack.
>
> That is why hand tightening of PL-259 connectors is not sufficient. Use
> pliers to snug them up just a bit more to assure a good connection.
>
> BNC and N connectors do not have a similar requirement. They will make
> positive contact without being tightened.
>
> 73,
> Don W3FPR
>
> On 9/17/2018 12:20 PM, Drew AF2Z wrote:
>
>
>> Note that there is no electrical connection through the threads on the
>> plug body and the threads on the shell; these threads are merely a stop to
>> keep the shell from sliding down the cable when not connected to the SO-239
>> on the equipment.
>>
>> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

Jim Brown-10

Re: loss of RX sensitivity

In reply to this post by Drew AF2Z

On 9/17/2018 9:20 AM, Drew AF2Z wrote:
> Note that there is no electrical connection through the threads on the
> plug body and the threads on the shell; these threads are merely a
> stop to keep the shell from sliding down the cable when not connected
> to the SO-239 on the equipment.

This is simply not true. The entire PL259 body and shell and the entire
mating body are part of the connection. What IS correct is that 1) the
connectors must be properly installed both to the coax and the
equipment, and 2) that the shell must be well tightened, often described
as "wrench tight," with the pins on the PL259 firmly seated in the
notches in the mating connector. I'm being generic about mating
connectors because it's equally true of SO239 and other connectors like
barrels, elbows, tees, and inter-series adapters.

73, Jim K9YC

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Bob McGraw - K4TAX

Re: loss of RX sensitivity

Yes, regardless of how good they look, always snug the PL-259 with a small pair of Channel Lock pliers. Finger tight is not good enough. Many of our connectors today are of inferior quality.

Also due to the use of jumpers, the flexing and pulling is prone to damage the connection between the coax and connector. Always suspect the jumper and icon doubt, replace it. AND if you find one defective or in question, immediately cut it in two pieces. Thus it won't be used or confused again.

Bob, K4TAX

Sent from my iPhone

> On Sep 17, 2018, at 2:44 PM, Jim Brown <[hidden email]> wrote:
>
>> On 9/17/2018 9:20 AM, Drew AF2Z wrote:
>> Note that there is no electrical connection through the threads on the plug body and the threads on the shell; these threads are merely a stop to keep the shell from sliding down the cable when not connected to the SO-239 on the equipment.
>
> This is simply not true. The entire PL259 body and shell and the entire mating body are part of the connection. What IS correct is that 1) the connectors must be properly installed both to the coax and the equipment, and 2) that the shell must be well tightened, often described as "wrench tight," with the pins on the PL259 firmly seated in the notches in the mating connector. I'm being generic about mating connectors because it's equally true of SO239 and other connectors like barrels, elbows, tees, and inter-series adapters.
>
> 73, Jim K9YC
>
> ______________________________________________________________
> Elecraft mailing list
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>

ke9uw

Re: loss of RX sensitivity

In reply to this post by Jim Brown-10

I've found that wiggling the body of the plug while tightening the threads makes the pl259 quite tight with the pins firmly seated in the notches. The motion allows the pins to find the deepest well of the notch.

Chuck Hawley
[hidden email]

Amateur Radio, KE9UW
aka Jack, BMW Motorcycles
________________________________________
From: [hidden email] [[hidden email]] on behalf of Jim Brown [[hidden email]]
Sent: Monday, September 17, 2018 2:44 PM
To: [hidden email]
Subject: Re: [Elecraft] loss of RX sensitivity

On 9/17/2018 9:20 AM, Drew AF2Z wrote:
> Note that there is no electrical connection through the threads on the
> plug body and the threads on the shell; these threads are merely a
> stop to keep the shell from sliding down the cable when not connected
> to the SO-239 on the equipment.

This is simply not true. The entire PL259 body and shell and the entire
mating body are part of the connection. What IS correct is that 1) the
connectors must be properly installed both to the coax and the
equipment, and 2) that the shell must be well tightened, often described
as "wrench tight," with the pins on the PL259 firmly seated in the
notches in the mating connector. I'm being generic about mating
connectors because it's equally true of SO239 and other connectors like
barrels, elbows, tees, and inter-series adapters.

73, Jim K9YC

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Chuck, KE9UW

Don Wilhelm

Re: loss of RX sensitivity

Chuck,

That is true, but is ignoring the fact that the threads of the PL259 are
providing the only contact with the SO239. They must be solidly tight
for reliable conductivity to the shield of the coax. All contact from
the SO239 to the coax shield is by pressure contact. Finger tight may
"work", but unless one has very strong fingers, that is not tight enough
to assure a good connection.

A parallel is putting a locking nut on a screw by using a 2nd nut -
often done if you want to use the screw as an axle, like putting the
screw through a hinge (think a trailer rear gate). If you put the 2nd
nut on the screw with only finger pressure, it will likely back off with
slight vibration and twisting nullifying the locking effect. OTOH, if
you fasten the two nuts together with a slight twist of the wrenches,
the two nuts will not move and will remain locked together. It is not
the friction between the 2 nuts that does it, but there is a slight
elongation of the screw threads that keeps significant pressure on the
two nuts to keep them together.

The same principle applies to a PL-259 to SO-239 thread engagement.

We may have "gotten away" with only finger tight in the past, but is one
possible cause of failure.

73,
Don W3FPR

On 9/17/2018 5:05 PM, hawley, charles j jr wrote:
> I've found that wiggling the body of the plug while tightening the threads makes the pl259 quite tight with the pins firmly seated in the notches. The motion allows the pins to find the deepest well of the notch.
>
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ANDY DURBIN

loss of RX sensitivity

In reply to this post by Drew AF2Z

" the threads of the PL259 are providing the only contact with the SO239"

In the connectors that you are mating how do you prevent contact between the end face of the PL259 body and the end face of the SO239 body? You would need an insulating spacer for your statement to be true.

73,

Andy k3wyc

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Don Wilhelm

Re: loss of RX sensitivity

Andy,

The PL259 to SO239 connector "end face" contact is provided only by
pressure - it is not a sliding contact as you would find in a BNC or an
N connector. The pressure is provided only by the tightening of the
threaded portion of the PL259.

I ask you - just how much resistance can be expected if you just touch
two ends of wires together without further positive contact?

The "insulating spacer" is any oxidation on either the SO239 or the
PL259. That is why I like silver plated UHF connectors. They may look
a bit corroded, but the silver oxide is conductive even though it can
appear brown or black. If you are shopping for UHF connectors at
hamfests, avoid all those nickel-plated ones that a not Amphenol, but
flock to those that are oxidized, and silver plated with Mil Spec
designations on them.

73,
Don W3FPR

On 9/17/2018 6:39 PM, ANDY DURBIN wrote:
> " the threads of the PL259 are providing the only contact with the SO239"
>
>
> In the connectors that you are mating how do you prevent contact between the end face of the PL259 body and the end face of the SO239 body? You would need an insulating spacer for your statement to be true.
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Wes Stewart-2

Re: loss of RX sensitivity

In reply to this post by Don Wilhelm

This is one of those, "it depends" situations. Depending on the location of the
two center conductor insulators in the plug and socket, the serrated (toothed)
surface of the female connector might well contact the mating plug surface, if
there is a gap between the insulators. In fact the "tighten it with pliers"
crowd might actually be forcing this connection and mistakenly believing that
they are improving the connection via the threads.

Wes N7WS

On 9/17/2018 3:22 PM, Don Wilhelm wrote:
> Chuck,
>
> That is true, but is ignoring the fact that the threads of the PL259 are
> providing the only contact with the SO239.
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Wes Stewart-2

Re: loss of RX sensitivity

In reply to this post by ANDY DURBIN

Pretty much my point made in another post.

In fact, I often take a perverse view of these situations and ask myself, "Self,
if you wanted to screw these two things together without the faces touching, how
difficult would it be to do?" And of course the answer is, almost impossible.

Wes N7ws

On 9/17/2018 3:39 PM, ANDY DURBIN wrote:

> " the threads of the PL259 are providing the only contact with the SO239"
>
>
> In the connectors that you are mating how do you prevent contact between the end face of the PL259 body and the end face of the SO239 body? You would need an insulating spacer for your statement to be true.
>
>
> 73,
>
> Andy k3wyc
>
>

donovanf

Re: loss of RX sensitivity

In reply to this post by Drew AF2Z

If you have a vector network analyzer you'll discover that BNC
connectors aren't all that great at VHF and above, l oss and
impedance vary with connector axial alignment because the bayonnet
shell doesn't support aligh the connector body very well. Strain relief
is extremely important with BNC connectors. TNC connectors are
far superior but not widely used.

While professionally installed N connectors have superb RF
characteristics, all too often they're improperly installed -- even by
professionals -- leading to damaged connectors if the male pin is
misaligned, or unreliable contact if the pin or socket depth is just a
few millimeters less than the manufacturers specification. I use
only captive pin male N connectors, avoiding the most severe
problems. I never use female N connectors on cables, the N sockets
are much too fragile.

Its hard to beat high quality silver plated UHF connectors at HF and
6 meters. But its important to use a tool to tighten them. That's a
small price to pay for a very reliable connector.

73
Frank
W3LPL

----- Original Message -----

From: "Walter Underwood" <[hidden email]>
To: [hidden email]
Sent: Monday, September 17, 2018 11:45:10 PM
Subject: Re: [Elecraft] loss of RX sensitivity

The next time someone challenges me on why I only use BNC and Type N connectors, I’m going to send them this entire discussion.

wunder
K6WRU
Walter Underwood
CM87wj
http://observer.wunderwood.org/ (my blog)

> On Sep 17, 2018, at 4:41 PM, Don Wilhelm <[hidden email]> wrote:
>
> Andy,
>
> The PL259 to SO239 connector "end face" contact is provided only by pressure - it is not a sliding contact as you would find in a BNC or an N connector. The pressure is provided only by the tightening of the threaded portion of the PL259.
>
> I ask you - just how much resistance can be expected if you just touch two ends of wires together without further positive contact?
>
> The "insulating spacer" is any oxidation on either the SO239 or the PL259. That is why I like silver plated UHF connectors. They may look a bit corroded, but the silver oxide is conductive even though it can appear brown or black. If you are shopping for UHF connectors at hamfests, avoid all those nickel-plated ones that a not Amphenol, but flock to those that are oxidized, and silver plated with Mil Spec designations on them.
>
> 73,
> Don W3FPR
>
> On 9/17/2018 6:39 PM, ANDY DURBIN wrote:
>> " the threads of the PL259 are providing the only contact with the SO239"
>> In the connectors that you are mating how do you prevent contact between the end face of the PL259 body and the end face of the SO239 body? You would need an insulating spacer for your statement to be true.
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ke9uw

Re: loss of RX sensitivity

In reply to this post by Don Wilhelm

Trouble is I have to put adapters on the equipment and then go to bnc

Chuck Jack
KE9UW

Sent from my iPhone, cjack

> On Sep 17, 2018, at 6:46 PM, Walter Underwood <[hidden email]> wrote:
>
> The next time someone challenges me on why I only use BNC and Type N connectors, I’m going to send them this entire discussion.
>
> wunder
> K6WRU
> Walter Underwood
> CM87wj
> http://observer.wunderwood.org/ (my blog)
>
>> On Sep 17, 2018, at 4:41 PM, Don Wilhelm <[hidden email]> wrote:
>>
>> Andy,
>>
>> The PL259 to SO239 connector "end face" contact is provided only by pressure - it is not a sliding contact as you would find in a BNC or an N connector. The pressure is provided only by the tightening of the threaded portion of the PL259.
>>
>> I ask you - just how much resistance can be expected if you just touch two ends of wires together without further positive contact?
>>
>> The "insulating spacer" is any oxidation on either the SO239 or the PL259. That is why I like silver plated UHF connectors. They may look a bit corroded, but the silver oxide is conductive even though it can appear brown or black. If you are shopping for UHF connectors at hamfests, avoid all those nickel-plated ones that a not Amphenol, but flock to those that are oxidized, and silver plated with Mil Spec designations on them.
>>
>> 73,
>> Don W3FPR
>>
>>> On 9/17/2018 6:39 PM, ANDY DURBIN wrote:
>>> " the threads of the PL259 are providing the only contact with the SO239"
>>> In the connectors that you are mating how do you prevent contact between the end face of the PL259 body and the end face of the SO239 body? You would need an insulating spacer for your statement to be true.
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]
>
> ______________________________________________________________
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Chuck, KE9UW

Dr. William J. Schmidt, II

Re: loss of RX sensitivity

In reply to this post by Don Wilhelm

[[The next time someone challenges me on why I only use BNC and Type N connectors, I’m going to send them this entire discussion.]]

Unfortunately this is not perfect either. If you use an "N" connector on long runs of heliax in a cold climate, you must be aware that the coefficients of expansion of the center conductor and the shield can be different... and on several occasions, I have seen the center pin pull back from the connector (and essentially disconnect) because the center conductor contracted more than the shield. Nb. This does not happen with all "N" connectors. This is less of a problem with BNC connectors because the coax used is generally has a somewhat flexible shield.

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donovanf

Re: loss of RX sensitivity

Captivated pin N connectors completely resolve the problem of the
center pin pulling back in cold weather.

73
Frank
W3LPL

----- Original Message -----

From: "Dr. William J. Schmidt" <[hidden email]>
To: "Elecraft Reflector" <[hidden email]>
Sent: Tuesday, September 18, 2018 3:29:41 PM
Subject: Re: [Elecraft] loss of RX sensitivity

[[The next time someone challenges me on why I only use BNC and Type N connectors, I’m going to send them this entire discussion.]]

Unfortunately this is not perfect either. If you use an "N" connector on long runs of heliax in a cold climate, you must be aware that the coefficients of expansion of the center conductor and the shield can be different... and on several occasions, I have seen the center pin pull back from the connector (and essentially disconnect) because the center conductor contracted more than the shield. Nb. This does not happen with all "N" connectors. This is less of a problem with BNC connectors because the coax used is generally has a somewhat flexible shield.

---
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Wes Stewart-2

Re: loss of RX sensitivity

In reply to this post by donovanf

It's difficult to argue with Frank's experience and expertise. That said, fools
rush in...

I own some network analyzers, 1) an N2PK which I built with type N connectors,
2) a DG8SAQ VNWA-3, supplied with SMA connectors and 3) a RigExpert AA-55 Zoom
with a SO239. Professionally, I've used analyzers with type N, 3.5mm (beadless
SMA) and K connectors. With the exception of the AA-55, which only goes to 55
MHz, all of these can be calibrated with "precision" calibration kits that can
cost thousands of dollars. So far, Frank is right, not a BNC in the bunch.

But that has changed with the introduction of the DG5MK's FA-VA5, one-port
vector analyzer. I am on the reserve list to buy one of these. The thing to
note is that it is supplied with a BNC connector. There has been a lot of
anguish, heartburn, etc about this on the VNWA Yahoo group but the consensus is
that it will be fine and BNC calibration kit has been developed and tested
without issue. https://www.youtube.com/watch?v=X8Z7veGV57o

There are tens of thousands of BNCs on oscilloscopes and other instruments and
I've seldom had an issue with them in 30+ years of lab work. For quick
disconnect I also use short jumper cables with BNCs to break the connections
between the hardline running to the tower and the cable entrance to the shack
during lightning season. Admittedly, I'm only running 500 W. When I can leave
them more permanently connected I revert to type N.

Wes N7WS

On 9/17/2018 5:04 PM, [hidden email] wrote:

> If you have a vector network analyzer you'll discover that BNC
> connectors aren't all that great at VHF and above, l oss and
> impedance vary with connector axial alignment because the bayonnet
> shell doesn't support aligh the connector body very well. Strain relief
> is extremely important with BNC connectors. TNC connectors are
> far superior but not widely used.
>
>
> While professionally installed N connectors have superb RF
> characteristics, all too often they're improperly installed -- even by
> professionals -- leading to damaged connectors if the male pin is
> misaligned, or unreliable contact if the pin or socket depth is just a
> few millimeters less than the manufacturers specification. I use
> only captive pin male N connectors, avoiding the most severe
> problems. I never use female N connectors on cables, the N sockets
> are much too fragile.
>
>
> Its hard to beat high quality silver plated UHF connectors at HF and
> 6 meters. But its important to use a tool to tighten them. That's a
> small price to pay for a very reliable connector.
>
>
> 73
> Frank
> W3LPL
>

donovanf

Re: loss of RX sensitivity

Hi Wes,

Thanks for forwarding the information about DG5MK's new FA-VA5
VNA. What is its current selling price?

If you use many BNC connectors, you'll notice a distinct difference in
connector quality especially above 100 MHz. Avoid using BNC male
connectors with weak tension when you turn the bayonette
to engage the connector. If the bayonette turns too easily it doesn't
maintain sufficient engagement force to keep the RF connections
in proper alignment.

73
Frank
W3LPL

----- Original Message -----

From: "Wes Stewart" <[hidden email]>
To: [hidden email]
Sent: Tuesday, September 18, 2018 5:51:45 PM
Subject: Re: [Elecraft] loss of RX sensitivity

It's difficult to argue with Frank's experience and expertise. That said, fools
rush in...

I own some network analyzers, 1) an N2PK which I built with type N connectors,
2) a DG8SAQ VNWA-3, supplied with SMA connectors and 3) a RigExpert AA-55 Zoom
with a SO239. Professionally, I've used analyzers with type N, 3.5mm (beadless
SMA) and K connectors. With the exception of the AA-55, which only goes to 55
MHz, all of these can be calibrated with "precision" calibration kits that can
cost thousands of dollars. So far, Frank is right, not a BNC in the bunch.

But that has changed with the introduction of the DG5MK's FA-VA5, one-port
vector analyzer. I am on the reserve list to buy one of these. The thing to
note is that it is supplied with a BNC connector. There has been a lot of
anguish, heartburn, etc about this on the VNWA Yahoo group but the consensus is
that it will be fine and BNC calibration kit has been developed and tested
without issue. https://www.youtube.com/watch?v=X8Z7veGV57o

There are tens of thousands of BNCs on oscilloscopes and other instruments and
I've seldom had an issue with them in 30+ years of lab work. For quick
disconnect I also use short jumper cables with BNCs to break the connections
between the hardline running to the tower and the cable entrance to the shack
during lightning season. Admittedly, I'm only running 500 W. When I can leave
them more permanently connected I revert to type N.

Wes N7WS

On 9/17/2018 5:04 PM, [hidden email] wrote: