Topics

receiver overload

John Sharpe
 

Hi all,

I just had a thought about new users of the uBitx and the Bitx40.

I have both of these fine rigs but with my good antenna - a ZS6BKW at 30 feet - the receivers are swamped by noise and big signals on 40 metres.

When I tested just now a 59+ 10 signal on my IC-7300 was unreadable on the Bitexes with the big antenna (which has a low SWR at 40 metres) because of noise. With an antenna of just 6 feet of wire in the shack the signal was readable (but weak) on the Bitexes!

I usually use a tuner beween the antenna and the Bitexes - that works fine to tame the noise. Also I have fitted an RF control to the Bitx40 that helps quieten big signals.

But if you have lots of noise in the receiver and no tuner - try a smaller antenna on receive (it will be no good for transmitting).
If that improves things maybe you need a tuner or an RF control.

73s John V2VOL

Jacob Farnes
 

The Bitx40 is my favorite radio to listen with once I did the RF gain mod via the two pin holes and cut the trace on the underside.

https://groups.io/g/BITX20/message/26490

I shouldn't have tombstoned the 10-ohm surface mount resistor. Just needed 2 wires and a potentiometer to be a variable resistor. Nice and quiet most days.

Michael Shreeve
 

I'm going to try ND6Ts new AGC version. He seems to think its the way to go. Its here. My MOSFET's are on the way. http://www.nd6t.com/uBITX/AGC.htm

On Thu, Apr 19, 2018 at 7:05 PM, Jacob Farnes via Groups.Io <kk6jtl@...> wrote:
The Bitx40 is my favorite radio to listen with once I did the RF gain mod via the two pin holes and cut the trace on the underside.

https://groups.io/g/BITX20/message/26490

I shouldn't have tombstoned the 10-ohm surface mount resistor. Just needed 2 wires and a potentiometer to be a variable resistor. Nice and quiet most days.




--
Michael Shreeve N6GRG

Jim Sheldon
 

It's sure worth the effort to build & install it.  Made an S9++ signal into one that didn't hurt the ears and an S2 signal was readable at the same setting of the volume control.  Thanks ND6T for a very workable AGC circuit!

Jim, W0EB



Jim, W0EB

On Apr 19, 2018, at 9:16 PM, Michael Shreeve <shreevester@...> wrote:

I'm going to try ND6Ts new AGC version. He seems to think its the way to go. Its here. My MOSFET's are on the way. http://www.nd6t.com/uBITX/AGC.htm

On Thu, Apr 19, 2018 at 7:05 PM, Jacob Farnes via Groups.Io <kk6jtl@...> wrote:
The Bitx40 is my favorite radio to listen with once I did the RF gain mod via the two pin holes and cut the trace on the underside.

https://groups.io/g/BITX20/message/26490

I shouldn't have tombstoned the 10-ohm surface mount resistor. Just needed 2 wires and a potentiometer to be a variable resistor. Nice and quiet most days.




--
Michael Shreeve N6GRG

Tim Gorman
 

I am using his new AGC circuit. It works well. You still get a slight
pop when an extremely strong signal first comes on but it is very short
and, to me at least, not annoying at all. You may want to lower the
1Mohm resistor to something smaller to decrease the pop, i.e. decrease
the attack time. The next time I open the case I'm going to try 500K.

tim ab0wr

On Thu, 19 Apr 2018 19:16:04 -0700
"Michael Shreeve" <@N6GRG> wrote:

I'm going to try ND6Ts new AGC version. He seems to think its the way
to go. Its here. My MOSFET's are on the way.
http://www.nd6t.com/uBITX/AGC.htm

On Thu, Apr 19, 2018 at 7:05 PM, Jacob Farnes via Groups.Io <
kk6jtl=yahoo.com@groups.io> wrote:

The Bitx40 is my favorite radio to listen with once I did the RF
gain mod via the two pin holes and cut the trace on the underside.

https://groups.io/g/BITX20/message/26490

I shouldn't have tombstoned the 10-ohm surface mount resistor. Just
needed 2 wires and a potentiometer to be a variable resistor. Nice
and quiet most days.


John Sharpe
 

Hi Jacob,

Yes, I have done the RF gain mod and it works well - but still the tuner still makes a big difference.

John VK2VOL

On 20 Apr 2018, at 12:05 pm, Jacob Farnes via Groups.Io <kk6jtl@...> wrote:

The Bitx40 is my favorite radio to listen with once I did the RF gain mod via the two pin holes and cut the trace on the underside.

https://groups.io/g/BITX20/message/26490

I shouldn't have tombstoned the 10-ohm surface mount resistor. Just needed 2 wires and a potentiometer to be a variable resistor. Nice and quiet most days.

Michael Shreeve
 

Just reading this initial post again. I was confused by it because its so different from my experience. I might have different conditions though. My antenna is balance and is a loop. A full loop on 80 meters. For transmitting I have a tuner,  but with or without it, and with different feed methds, such as coax, 450 open line, and 4 to one baluns, I've had excellent results with this tuner. I am in a low noise area. But, your problems seem to all be related to high signal levels, and possibly high noise levels . If that is what your antenna is receiving, I've had lower noise with my full waive 265 foot loop than any other type of antenna. It an amazing way to go. Of course, a dipole would be a much less efficient version of my antenna, and could display the lower noise attributes. Its definitely the way to go. 

--
Michael Shreeve N6GRG

Tim Gorman
 

Usually a tuner will increase noise, at least atmospheric noise, as the
tuner creates a match between the receiver and the antenna. A matched
antenna shouldn't "tame" the noise. If that is actually happening then
a closer look at the system might be appropriate.

tim ab0wr



On Fri, 20 Apr 2018 11:39:39 +1000
"John Sharpe" <johsharpe@...> wrote:

Hi all,

I just had a thought about new users of the uBitx and the Bitx40.

I have both of these fine rigs but with my good antenna - a ZS6BKW
<http://www.nc4fb.org/wordpress/zs6bkw-multi-band-antenna/> at 30
feet - the receivers are swamped by noise and big signals on 40
metres.

When I tested just now a 59+ 10 signal on my IC-7300 was unreadable
on the Bitexes with the big antenna (which has a low SWR at 40
metres) because of noise. With an antenna of just 6 feet of wire in
the shack the signal was readable (but weak) on the Bitexes!

I usually use a tuner beween the antenna and the Bitexes - that works
fine to tame the noise. Also I have fitted an RF control to the
Bitx40 that helps quieten big signals.

But if you have lots of noise in the receiver and no tuner - try a
smaller antenna on receive (it will be no good for transmitting). If
that improves things maybe you need a tuner or an RF control.

73s John V2VOL

K9HZ <bill@...>
 

Unless the antenna is picking up a static charge and the antenna tuner is
acting like an impedance to ground draining that charge off. Don't laugh,
it happens.


Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ

Owner - Operator
Big Signal Ranch – K9ZC
Staunton, Illinois

Owner – Operator
Villa Grand Piton – J68HZ
Soufriere, St. Lucia W.I.
Rent it: www.VillaGrandPiton.com
Like us on Facebook!

Moderator – North American QRO Group at Groups.IO.

email:  @Doc_Bill

-----Original Message-----
From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Tim Gorman
Sent: Friday, April 20, 2018 8:42 AM
To: BITX20@groups.io
Subject: Re: [BITX20] receiver overload

Usually a tuner will increase noise, at least atmospheric noise, as the
tuner creates a match between the receiver and the antenna. A matched
antenna shouldn't "tame" the noise. If that is actually happening then a
closer look at the system might be appropriate.

tim ab0wr



On Fri, 20 Apr 2018 11:39:39 +1000
"John Sharpe" <johsharpe@...> wrote:

Hi all,

I just had a thought about new users of the uBitx and the Bitx40.

I have both of these fine rigs but with my good antenna - a ZS6BKW
<http://www.nc4fb.org/wordpress/zs6bkw-multi-band-antenna/> at 30 feet
- the receivers are swamped by noise and big signals on 40 metres.

When I tested just now a 59+ 10 signal on my IC-7300 was unreadable on
the Bitexes with the big antenna (which has a low SWR at 40
metres) because of noise. With an antenna of just 6 feet of wire in
the shack the signal was readable (but weak) on the Bitexes!

I usually use a tuner beween the antenna and the Bitexes - that works
fine to tame the noise. Also I have fitted an RF control to the
Bitx40 that helps quieten big signals.

But if you have lots of noise in the receiver and no tuner - try a
smaller antenna on receive (it will be no good for transmitting). If
that improves things maybe you need a tuner or an RF control.

73s John V2VOL



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Tim Gorman
 

I'm sure it happens. But not consistently. You need wind and something
to create the charge like blowing dust. If the tuner is dissipating the
charge why doesn't the rig itself do it, at least with an unbalanced
feed?

tim ab0wr

On Fri, 20 Apr 2018 08:47:00 -0500
"K9HZ" <@Doc_Bill> wrote:

Unless the antenna is picking up a static charge and the antenna
tuner is acting like an impedance to ground draining that charge
off. Don't laugh, it happens.


Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ
PJ2/K9HZ

Owner - Operator
Big Signal Ranch – K9ZC
Staunton, Illinois

Owner – Operator
Villa Grand Piton – J68HZ
Soufriere, St. Lucia W.I.
Rent it: www.VillaGrandPiton.com
Like us on Facebook!

Moderator – North American QRO Group at Groups.IO.

email:  @Doc_Bill



-----Original Message-----
From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Tim
Gorman Sent: Friday, April 20, 2018 8:42 AM
To: BITX20@groups.io
Subject: Re: [BITX20] receiver overload

Usually a tuner will increase noise, at least atmospheric noise, as
the tuner creates a match between the receiver and the antenna. A
matched antenna shouldn't "tame" the noise. If that is actually
happening then a closer look at the system might be appropriate.

tim ab0wr



On Fri, 20 Apr 2018 11:39:39 +1000
"John Sharpe" <johsharpe@...> wrote:

Hi all,

I just had a thought about new users of the uBitx and the Bitx40.

I have both of these fine rigs but with my good antenna - a ZS6BKW
<http://www.nc4fb.org/wordpress/zs6bkw-multi-band-antenna/> at 30
feet
- the receivers are swamped by noise and big signals on 40 metres.

When I tested just now a 59+ 10 signal on my IC-7300 was unreadable
on the Bitexes with the big antenna (which has a low SWR at 40
metres) because of noise. With an antenna of just 6 feet of wire in
the shack the signal was readable (but weak) on the Bitexes!

I usually use a tuner beween the antenna and the Bitexes - that
works fine to tame the noise. Also I have fitted an RF control to
the Bitx40 that helps quieten big signals.

But if you have lots of noise in the receiver and no tuner - try a
smaller antenna on receive (it will be no good for transmitting). If
that improves things maybe you need a tuner or an RF control.

73s John V2VOL



---
This email has been checked for viruses by AVG.
http://www.avg.com



Jerry Gaffke
 

The stock uBitx provides a DC path to ground.
During receive, that would be K3-12,14, K1-12,14, L1,2,3,4,  and T2.

Don's AGC fix adds AC coupling, there is no DC path:
    http://www.nd6t.com/uBITX/AGC.htm
Perhaps a 1k resistor from antenna to ground is in order there.

Jerry


On Fri, Apr 20, 2018 at 02:04 pm, Tim Gorman wrote:
I'm sure it happens. But not consistently. You need wind and something
to create the charge like blowing dust. If the tuner is dissipating the
charge why doesn't the rig itself do it, at least with an unbalanced
feed?

tim ab0wr
. . .

 

On Fri, 20 Apr 2018 08:47:00 -0500
"K9HZ" <@Doc_Bill> wrote:
Unless the antenna is picking up a static charge and the antenna
tuner is acting like an impedance to ground draining that charge
off. Don't laugh, it happens.

Don, ND6T
 

The principle idea of my AGC mod is built around the potentiometer RF gain control. It is meant to work in concert with it. As such, that potentiometer works as a static dissipation device to ground. My antennas here are both end-fed random wires (one 175 feet long, the far end up 100 feet) and are excellent static accumulators unless provided a path to ground. A 10 Megohm resistor will do that, by the way. I cannot overemphasize the desirability of a manual RF gain control, even with an AGC. I think most operators, even with the fanciest of rigs, use that control extensively. Best noise reduction device ever! 73, Don 

K9HZ <bill@...>
 

That is not where you want static charges dissipating! Chokes to ground, resistors, at the antenna. All a better place for it (the fire) to happen.


Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ

Owner - Operator
Big Signal Ranch – K9ZC
Staunton, Illinois

Owner – Operator
Villa Grand Piton – J68HZ
Soufriere, St. Lucia W.I.
Rent it: www.VillaGrandPiton.com
Like us on Facebook!

Moderator – North American QRO Group at Groups.IO.

email: @Doc_Bill

-----Original Message-----
From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Tim Gorman
Sent: Friday, April 20, 2018 4:05 PM
To: BITX20@groups.io
Subject: Re: [BITX20] receiver overload

I'm sure it happens. But not consistently. You need wind and something to create the charge like blowing dust. If the tuner is dissipating the charge why doesn't the rig itself do it, at least with an unbalanced feed?

tim ab0wr

On Fri, 20 Apr 2018 08:47:00 -0500
"K9HZ" <@Doc_Bill> wrote:

Unless the antenna is picking up a static charge and the antenna tuner
is acting like an impedance to ground draining that charge
off. Don't laugh, it happens.


Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ
PJ2/K9HZ

Owner - Operator
Big Signal Ranch – K9ZC
Staunton, Illinois

Owner – Operator
Villa Grand Piton – J68HZ
Soufriere, St. Lucia W.I.
Rent it: www.VillaGrandPiton.com
Like us on Facebook!

Moderator – North American QRO Group at Groups.IO.

email: @Doc_Bill



-----Original Message-----
From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Tim
Gorman Sent: Friday, April 20, 2018 8:42 AM
To: BITX20@groups.io
Subject: Re: [BITX20] receiver overload

Usually a tuner will increase noise, at least atmospheric noise, as
the tuner creates a match between the receiver and the antenna. A
matched antenna shouldn't "tame" the noise. If that is actually
happening then a closer look at the system might be appropriate.

tim ab0wr



On Fri, 20 Apr 2018 11:39:39 +1000
"John Sharpe" <johsharpe@...> wrote:

Hi all,

I just had a thought about new users of the uBitx and the Bitx40.

I have both of these fine rigs but with my good antenna - a ZS6BKW
<http://www.nc4fb.org/wordpress/zs6bkw-multi-band-antenna/> at 30
feet
- the receivers are swamped by noise and big signals on 40 metres.

When I tested just now a 59+ 10 signal on my IC-7300 was unreadable
on the Bitexes with the big antenna (which has a low SWR at 40
metres) because of noise. With an antenna of just 6 feet of wire in
the shack the signal was readable (but weak) on the Bitexes!

I usually use a tuner beween the antenna and the Bitexes - that
works fine to tame the noise. Also I have fitted an RF control to
the Bitx40 that helps quieten big signals.

But if you have lots of noise in the receiver and no tuner - try a
smaller antenna on receive (it will be no good for transmitting). If
that improves things maybe you need a tuner or an RF control.

73s John V2VOL



---
This email has been checked for viruses by AVG.
http://www.avg.com



Don, ND6T
 

Don't let it get to that potential. If you are talking about lightning and such, yes, short it to ground outside. I am referring to those gentle breezes and what I call static charges. Nothing major, just enough to be annoying. -Don

Jerry Gaffke
 

The AGC writeup does mention that the RF gain control is assumed,
but the diagram just says "To K3 pin 14" where I assume it should say "To Wiper of RF Gain Pot"
    http://www.nd6t.com/uBITX/AGC.htm
Better yet, include the pot in the drawing.
Perhaps it should also mention the need for static discharge.
Regardless, by all accounts, that's looking like a simple and effective AGC implementation.

We get lots of thunderstorms blowing through, and I generally just try to unplug antennas
when I see them coming.  I believe I recall reading once that simply using coax offers adequate protection
if you give the braid a good earth ground.  Not sure how bulletproof that is, but my braid does have
a good earth ground. 

On p48 of July 2002 QST, it recommends something like this device:
    https://www.dxengineering.com/parts/ppr-is-50ux-c0
which costs more than a Bitx40.  Is there a cheaper alternative?

Gas discharge tubes (GDT's) are often used for lightning protection on phone lines.
Seem to be available with capacitances down to  5pf, so should work at RF.
    https://www.mouser.com/pdfdocs/bourns_gdt_white_paper.pdf
Might well be what's in that device above.
Perhaps there's also a fuse of some sort between the antenna wire and the GDT?

Back 50 years ago, they recommended building a spark gap for use as a lightning arrestor,
the older hams who wrote about it probably had fond memories of spark gaps.
Basically a homemade GDT, using locally available air instead of some exotic gas.

Anybody know what works?
Protection schemes for this sort of thing are inherently dangerous as they are generally
untested and might give a false sense of security.  Consequences can be considerable.
Unplugging antennas is still a good idea, will still have a rig if the house doesn't burn down.

Jerry, KE7ER


On Fri, Apr 20, 2018 at 03:07 pm, Don, ND6T wrote:
The principle idea of my AGC mod is built around the potentiometer RF gain control. It is meant to work in concert with it. As such, that potentiometer works as a static dissipation device to ground. My antennas here are both end-fed random wires (one 175 feet long, the far end up 100 feet) and are excellent static accumulators unless provided a path to ground. A 10 Megohm resistor will do that, by the way. I cannot overemphasize the desirability of a manual RF gain control, even with an AGC. I think most operators, even with the fanciest of rigs, use that control extensively. Best noise reduction device ever! 73, Don 

Tim Gorman
 

I agree! But if the problem here is static buildup then a tuner won't
help any more than the coax connector on the rig!

tim ab0wr

On Fri, 20 Apr 2018 17:37:45 -0500
"K9HZ" <@Doc_Bill> wrote:

That is not where you want static charges dissipating! Chokes to
ground, resistors, at the antenna. All a better place for it (the
fire) to happen.


Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ
PJ2/K9HZ

Owner - Operator
Big Signal Ranch – K9ZC
Staunton, Illinois

Owner – Operator
Villa Grand Piton – J68HZ
Soufriere, St. Lucia W.I.
Rent it: www.VillaGrandPiton.com
Like us on Facebook!

Moderator – North American QRO Group at Groups.IO.

email: @Doc_Bill



-----Original Message-----
From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Tim
Gorman Sent: Friday, April 20, 2018 4:05 PM
To: BITX20@groups.io
Subject: Re: [BITX20] receiver overload

I'm sure it happens. But not consistently. You need wind and
something to create the charge like blowing dust. If the tuner is
dissipating the charge why doesn't the rig itself do it, at least
with an unbalanced feed?

tim ab0wr

On Fri, 20 Apr 2018 08:47:00 -0500
"K9HZ" <@Doc_Bill> wrote:

Unless the antenna is picking up a static charge and the antenna
tuner is acting like an impedance to ground draining that charge
off. Don't laugh, it happens.


Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ
PJ2/K9HZ

Owner - Operator
Big Signal Ranch – K9ZC
Staunton, Illinois

Owner – Operator
Villa Grand Piton – J68HZ
Soufriere, St. Lucia W.I.
Rent it: www.VillaGrandPiton.com
Like us on Facebook!

Moderator – North American QRO Group at Groups.IO.

email: @Doc_Bill



-----Original Message-----
From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Tim
Gorman Sent: Friday, April 20, 2018 8:42 AM
To: BITX20@groups.io
Subject: Re: [BITX20] receiver overload

Usually a tuner will increase noise, at least atmospheric noise, as
the tuner creates a match between the receiver and the antenna. A
matched antenna shouldn't "tame" the noise. If that is actually
happening then a closer look at the system might be appropriate.

tim ab0wr



On Fri, 20 Apr 2018 11:39:39 +1000
"John Sharpe" <johsharpe@...> wrote:

Hi all,

I just had a thought about new users of the uBitx and the Bitx40.

I have both of these fine rigs but with my good antenna - a
ZS6BKW
<http://www.nc4fb.org/wordpress/zs6bkw-multi-band-antenna/> at 30
feet
- the receivers are swamped by noise and big signals on 40 metres.

When I tested just now a 59+ 10 signal on my IC-7300 was
unreadable on the Bitexes with the big antenna (which has a low
SWR at 40 metres) because of noise. With an antenna of just 6
feet of wire in the shack the signal was readable (but weak) on
the Bitexes!

I usually use a tuner beween the antenna and the Bitexes - that
works fine to tame the noise. Also I have fitted an RF control to
the Bitx40 that helps quieten big signals.

But if you have lots of noise in the receiver and no tuner - try
a smaller antenna on receive (it will be no good for
transmitting). If that improves things maybe you need a tuner or
an RF control.

73s John V2VOL



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This email has been checked for viruses by AVG.
http://www.avg.com








K9HZ <bill@...>
 

I guess that then assumes you have a very simple tuner (Cap-L leg)? No impedance transformers, inductors to ground, etc.


Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ

Owner - Operator
Big Signal Ranch – K9ZC
Staunton, Illinois

Owner – Operator
Villa Grand Piton – J68HZ
Soufriere, St. Lucia W.I.
Rent it: www.VillaGrandPiton.com
Like us on Facebook!

Moderator – North American QRO Group at Groups.IO.

email: @Doc_Bill

-----Original Message-----
From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Tim Gorman
Sent: Friday, April 20, 2018 8:18 PM
To: BITX20@groups.io
Subject: Re: [BITX20] receiver overload

I agree! But if the problem here is static buildup then a tuner won't help any more than the coax connector on the rig!

tim ab0wr

On Fri, 20 Apr 2018 17:37:45 -0500
"K9HZ" <@Doc_Bill> wrote:

That is not where you want static charges dissipating! Chokes to
ground, resistors, at the antenna. All a better place for it (the
fire) to happen.


Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ
PJ2/K9HZ

Owner - Operator
Big Signal Ranch – K9ZC
Staunton, Illinois

Owner – Operator
Villa Grand Piton – J68HZ
Soufriere, St. Lucia W.I.
Rent it: www.VillaGrandPiton.com
Like us on Facebook!

Moderator – North American QRO Group at Groups.IO.

email: @Doc_Bill



-----Original Message-----
From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Tim
Gorman Sent: Friday, April 20, 2018 4:05 PM
To: BITX20@groups.io
Subject: Re: [BITX20] receiver overload

I'm sure it happens. But not consistently. You need wind and something
to create the charge like blowing dust. If the tuner is dissipating
the charge why doesn't the rig itself do it, at least with an
unbalanced feed?

tim ab0wr

On Fri, 20 Apr 2018 08:47:00 -0500
"K9HZ" <@Doc_Bill> wrote:

Unless the antenna is picking up a static charge and the antenna
tuner is acting like an impedance to ground draining that charge
off. Don't laugh, it happens.


Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ
PJ2/K9HZ

Owner - Operator
Big Signal Ranch – K9ZC
Staunton, Illinois

Owner – Operator
Villa Grand Piton – J68HZ
Soufriere, St. Lucia W.I.
Rent it: www.VillaGrandPiton.com
Like us on Facebook!

Moderator – North American QRO Group at Groups.IO.

email: @Doc_Bill



-----Original Message-----
From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Tim
Gorman Sent: Friday, April 20, 2018 8:42 AM
To: BITX20@groups.io
Subject: Re: [BITX20] receiver overload

Usually a tuner will increase noise, at least atmospheric noise, as
the tuner creates a match between the receiver and the antenna. A
matched antenna shouldn't "tame" the noise. If that is actually
happening then a closer look at the system might be appropriate.

tim ab0wr



On Fri, 20 Apr 2018 11:39:39 +1000
"John Sharpe" <johsharpe@...> wrote:

Hi all,

I just had a thought about new users of the uBitx and the Bitx40.

I have both of these fine rigs but with my good antenna - a ZS6BKW
<http://www.nc4fb.org/wordpress/zs6bkw-multi-band-antenna/> at 30
feet
- the receivers are swamped by noise and big signals on 40 metres.

When I tested just now a 59+ 10 signal on my IC-7300 was
unreadable on the Bitexes with the big antenna (which has a low
SWR at 40 metres) because of noise. With an antenna of just 6 feet
of wire in the shack the signal was readable (but weak) on the
Bitexes!

I usually use a tuner beween the antenna and the Bitexes - that
works fine to tame the noise. Also I have fitted an RF control to
the Bitx40 that helps quieten big signals.

But if you have lots of noise in the receiver and no tuner - try a
smaller antenna on receive (it will be no good for transmitting).
If that improves things maybe you need a tuner or an RF control.

73s John V2VOL



---
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Tim Gorman
 

My braid is grounded at the entrance box to the house. I also made up
shorting plugs for when I unhook the antenna so the center conductor
and braid should both be at the same potential.

tim ab0wr

On Fri, 20 Apr 2018 16:55:25 -0700
"Jerry Gaffke via Groups.Io" <jgaffke=yahoo.com@groups.io> wrote:

The AGC writeup does mention that the RF gain control is assumed,
but the diagram just says "To K3 pin 14" where I assume it should say
"To Wiper of RF Gain Pot" http://www.nd6t.com/uBITX/AGC.htm
Better yet, include the pot in the drawing.
Perhaps it should also mention the need for static discharge.
Regardless, by all accounts, that's looking like a simple and
effective AGC implementation.

We get lots of thunderstorms blowing through, and I generally just
try to unplug antennas when I see them coming.  I believe I recall
reading once that simply using coax offers adequate protection if you
give the braid a good earth ground.  Not sure how bulletproof that
is, but my braid does have a good earth ground. 

On p48 of July 2002 QST, it recommends something like this device:
    https://www.dxengineering.com/parts/ppr-is-50ux-c0
which costs more than a Bitx40.  Is there a cheaper alternative?

Gas discharge tubes (GDT's) are often used for lightning protection
on phone lines. Seem to be available with capacitances down to  5pf,
so should work at RF.
https://www.mouser.com/pdfdocs/bourns_gdt_white_paper.pdf Might well
be what's in that device above. Perhaps there's also a fuse of some
sort between the antenna wire and the GDT?

Back 50 years ago, they recommended building a spark gap for use as a
lightning arrestor, the older hams who wrote about it probably had
fond memories of spark gaps. Basically a homemade GDT, using locally
available air instead of some exotic gas.

Anybody know what works?
Protection schemes for this sort of thing are inherently dangerous as
they are generally untested and might give a false sense of
security.  Consequences can be considerable. Unplugging antennas is
still a good idea, will still have a rig if the house doesn't burn
down.

Jerry, KE7ER

On Fri, Apr 20, 2018 at 03:07 pm, Don, ND6T wrote:


The principle idea of my AGC mod is built around the potentiometer
RF gain control. It is meant to work in concert with it. As such,
that potentiometer works as a static dissipation device to ground.
My antennas here are both end-fed random wires (one 175 feet long,
the far end up 100 feet) and are excellent static accumulators
unless provided a path to ground. A 10 Megohm resistor will do
that, by the way. I cannot overemphasize the desirability of a
manual RF gain control, even with an AGC. I think most operators,
even with the fanciest of rigs, use that control extensively. Best
noise reduction device ever! 73, Don

Tim Gorman
 

I assume a 10M leaded resistor from RF-in to ground is what you are
suggesting?

That will be a lot simpler for me to do than adding an RF gain control.
The front panel is getting pretty crowded!

tim ab0wr

On Fri, 20 Apr 2018 15:07:47 -0700
"Don, ND6T via Groups.Io" <nd6t_6=yahoo.com@groups.io> wrote:

The principle idea of my AGC mod is built around the potentiometer RF
gain control. It is meant to work in concert with it. As such, that
potentiometer works as a static dissipation device to ground. My
antennas here are both end-fed random wires (one 175 feet long, the
far end up 100 feet) and are excellent static accumulators unless
provided a path to ground. A 10 Megohm resistor will do that, by the
way. I cannot overemphasize the desirability of a manual RF gain
control, even with an AGC. I think most operators, even with the
fanciest of rigs, use that control extensively. Best noise reduction
device ever! 73, Don

Tim Gorman
 

Noise from static buildup varies with the weather and wind. If you
think you have static buildup then all you have to do is disconnect
your antenna, use a jumper cable to short each element to ground, and
then reconnect the antenna. If your noise level drops significantly
then you had static buildup. If not, then you are hearing atmospheric
noise and/or phase noise in the receiver. The two can be differentiated
by just disconnecting the antenna to see what kind of noise drop you
see.

Noise from static buildup is typically not static. It does not sound
like the white noise, more like a buzzing or popping, and sometimes
even like a musical tone.

A tuner, even one that is isolated by a capacitor from the antenna,
typically won't "tune" static buildup noise. The noise is basically
from small discharges caused by charge equalization. Can you use your
tuner to to "tune-in" or "tune-out" the noise from the static discharge
of a lightning strike? Mine won't. The "noise" from the lightning
strike comes through no matter where the tuner is set.

If noise in the receiver goes up and down as you operate your tuner to
find the best match between your receiver and your antenna it's because
it is actually working. It is highly unlikely that the noise you hear
going up and down is from static buildup on the antenna.

tim ab0wr

On Fri, 20 Apr 2018 20:21:25 -0500
"K9HZ" <@Doc_Bill> wrote:

I guess that then assumes you have a very simple tuner (Cap-L leg)?
No impedance transformers, inductors to ground, etc.


Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ
PJ2/K9HZ

Owner - Operator
Big Signal Ranch – K9ZC
Staunton, Illinois

Owner – Operator
Villa Grand Piton – J68HZ
Soufriere, St. Lucia W.I.
Rent it: www.VillaGrandPiton.com
Like us on Facebook!

Moderator – North American QRO Group at Groups.IO.

email: @Doc_Bill



-----Original Message-----
From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Tim
Gorman Sent: Friday, April 20, 2018 8:18 PM
To: BITX20@groups.io
Subject: Re: [BITX20] receiver overload

I agree! But if the problem here is static buildup then a tuner won't
help any more than the coax connector on the rig!

tim ab0wr

On Fri, 20 Apr 2018 17:37:45 -0500
"K9HZ" <@Doc_Bill> wrote:

That is not where you want static charges dissipating! Chokes to
ground, resistors, at the antenna. All a better place for it (the
fire) to happen.


Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ
PJ2/K9HZ

Owner - Operator
Big Signal Ranch – K9ZC
Staunton, Illinois

Owner – Operator
Villa Grand Piton – J68HZ
Soufriere, St. Lucia W.I.
Rent it: www.VillaGrandPiton.com
Like us on Facebook!

Moderator – North American QRO Group at Groups.IO.

email: @Doc_Bill



-----Original Message-----
From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Tim
Gorman Sent: Friday, April 20, 2018 4:05 PM
To: BITX20@groups.io
Subject: Re: [BITX20] receiver overload

I'm sure it happens. But not consistently. You need wind and
something to create the charge like blowing dust. If the tuner is
dissipating the charge why doesn't the rig itself do it, at least
with an unbalanced feed?

tim ab0wr

On Fri, 20 Apr 2018 08:47:00 -0500
"K9HZ" <@Doc_Bill> wrote:

Unless the antenna is picking up a static charge and the antenna
tuner is acting like an impedance to ground draining that charge
off. Don't laugh, it happens.


Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ
PJ2/K9HZ

Owner - Operator
Big Signal Ranch – K9ZC
Staunton, Illinois

Owner – Operator
Villa Grand Piton – J68HZ
Soufriere, St. Lucia W.I.
Rent it: www.VillaGrandPiton.com
Like us on Facebook!

Moderator – North American QRO Group at Groups.IO.

email: @Doc_Bill



-----Original Message-----
From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Tim
Gorman Sent: Friday, April 20, 2018 8:42 AM
To: BITX20@groups.io
Subject: Re: [BITX20] receiver overload

Usually a tuner will increase noise, at least atmospheric noise,
as the tuner creates a match between the receiver and the
antenna. A matched antenna shouldn't "tame" the noise. If that is
actually happening then a closer look at the system might be
appropriate.

tim ab0wr



On Fri, 20 Apr 2018 11:39:39 +1000
"John Sharpe" <johsharpe@...> wrote:

Hi all,

I just had a thought about new users of the uBitx and the
Bitx40.

I have both of these fine rigs but with my good antenna - a
ZS6BKW
<http://www.nc4fb.org/wordpress/zs6bkw-multi-band-antenna/> at
30 feet
- the receivers are swamped by noise and big signals on 40
metres.

When I tested just now a 59+ 10 signal on my IC-7300 was
unreadable on the Bitexes with the big antenna (which has a low
SWR at 40 metres) because of noise. With an antenna of just 6
feet of wire in the shack the signal was readable (but weak) on
the Bitexes!

I usually use a tuner beween the antenna and the Bitexes - that
works fine to tame the noise. Also I have fitted an RF control
to the Bitx40 that helps quieten big signals.

But if you have lots of noise in the receiver and no tuner -
try a smaller antenna on receive (it will be no good for
transmitting). If that improves things maybe you need a tuner
or an RF control.

73s John V2VOL



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