Topband: identifying noise source

[Maciej Wieczorek]

GM,

I recently have some strange, pulsating noise on all 300 deg / NA beverages. 
Maybe someone have already experienced anything like this  - what kind of 
device it can be? Here is a recording on wide filters in AM, around 3,4MHz 
(maximum signal).


https://drive.google.com/file/d/1zTWirLyNiD2aYd7oJQjt8HhG9rgttcvn/view

It's starts late in the evenings and can be heard till 8-9:00 AM. In 
daylight it gets stronger.


I actually have 2 different RX arrays for NA, the distance is abt 300m from 
each other, but the noise is abt the same level on both antennas. I guess it 
means the source can be even few km's away?


73
Mac SP2XF/ SN2M 


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Re: Topband: RX antenna switching - unused ports

[Maciej Wieczorek]

Hi Brad,

what I can say from my perspective - in the last 10 years I have tried both 
grounding and terminating through 75ohm resistor. With the terminating I see 
absolutely no pattern distortion on my Beverage's, which was not so obvious 
when direct grounding was used.


My Bev's often are crossed 45 deg, height is 1,8-2,0m.  I use only isolated 
transformers / separate windings.


73's
Mac SP2XF / SN2M

- Original Message - 
From: "Brad Denison" 

To: 
Sent: Thursday, June 08, 2017 1:54 PM
Subject: Topband: RX antenna switching - unused ports



All,

 I am working a homebrew RX antenna switch box for my beverages, flags and
shared apex loop array and am looking for design advice.  Can someone
educate me on the proper way to handle unused ports:

1)  Leave all unused ports open
2)  Ground all unused ports
3)  Terminate unused ports to 75 ohm


I have seen various commercially available switch boxes with all of these
configurations but it is not clear to me if any of these variations are
best, i.e does it matter?

Thanks,

Brad, W1NT
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Re: Topband: 160 vertical/L

[Maciej Wieczorek]

Hi ,

did anyone try to match such 160m vertical /L or /T on 80m?
How about efficiency?

After my 31m tall vertical broke last sunday (now it's 23m only) my idea is 
to add 2 x15m top loading wires, making a T-vertical. 160m is a priority in 
this case and I know it will work OK,  but I'd like to use it also on 80m.


TNX

73's
Mac SP2XF / SN2M


- Original Message - 
From: 

To: "topband" 
Sent: Wednesday, November 30, 2016 2:16 PM
Subject: Re: Topband: 160 vertical/L



Hi Mike,


An inverted-L with 50-60 feet vertical is a far superior choice than
a bottom loaded vertical. Its much more efficient, its bandwidth
is much broader and you don't have to deal with the very high
voltages at the base of the loaded vertical, especially if you're
running high power.


73
Frank
W3LPL



- Original Message -

From: "Don Kirk" 
To: "W0MU Mike Fatchett" 
Cc: "topband" 
Sent: Wednesday, November 30, 2016 12:32:26 PM
Subject: Re: Topband: 160 vertical/L

HI Mike,

I use a 68 foot based loaded vertical on 160 meters with 55 short buried
ground radials (2500 feet of ground radials). I only run 100 watts and
located near Indianapolis. I would prefer an Inverted-L over the base
loaded vertical on 160 meters (the L would be much more efficient), but
having said that I did acquire my 160 meter DXCC last year (all CW) and
most of the contacts were during years when 160 meters was in very poor
condition.
Note: I do use small pennant antennas for RX on 160 meters.

For starters it sure would be easy to temporarily install a base loading
coil to test out your full size 80 meter vertical on 160 meters versus 
your

33 foot vertical. You can use part of the loading coil you install on the
full size 80 meter vertical with a fixed high voltage silver mica cap to
form a simple L network (that's what I do and it works great). This would
allow you to easily compare your two TX antennas.
Note: neither end of my base loading coil is connected to ground (my base
loading coil is between the bottom of my 68 foot vertical and the center
conductor of my feedline. I use an MFJ 404-0669 air wound coil as my
loading coil / L network.

But if you can install an Inverted-L easily, than I would skip what I have
said above and just install the Inverted-L.

Don (wd8dsb)

On Wed, Nov 30, 2016 at 1:33 AM, W0MU Mike Fatchett  wrote:


I have a full sized 80m vertical and a Top loaded Cushcraft 33ft vertical
for 160. The Cushcraft gets out but not great.

I was thinking about using an inverted L over the radial field that I use
for the 160. It is 30ish radials of various lengths or I have seen where
people have loaded the 80m vertical on 160. I think I recall people are
not overly excited about bottom loading the 80. The 80 is unguyed so the
top cannot support anything.

I can get the vertical part of the L up 50-60 feet.

Any feelings one way or another? I can make a switching system for the 80
vert if people think this is a reasonable transmitting solution. I have a
rcv array, so I am hoping to improve my xmit signal.

W0MU

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Re: Topband: Bandpass filters for receive antennas / LW 225khz rejecting

[Maciej Wieczorek]

GM All,

Can someone recomend me a simple high pass filter that will reject strong AM 
signal trasmitted at 225 khz?
I've just looked at Petr OK1RR website and there is nice filter, but rejects 
400khz-1600khz band, so will not work in my case...
This signal at 225 Khz comes from Polish Radio I AM station, located abt 
120kms away, but it puts  9+60db with ATT-30db turned on (IC 765) and it's 
quite spourius since abt 3 years (I know they changed something in the audio 
to make it "more readable"...).
In practice, I have QRM and harmonics on 160m (specially in daylight) and it 
makes impossible measuring any beverage antenna in my QTH, using MFJ or VNA 
analysers as you can see on this video:


https://www.youtube.com/watch?v=pEWTYrRPgjo

TNX for help and CU soon on the band
73's
Mac SP2XF (SN2M)

- Original Message - 
From: "Tom W8JI" 

To: 
Sent: Monday, August 31, 2015 8:43 PM
Subject: Re: Topband: Bandpass filters for receive antennas


Bandpass filters do nothing for in-band signals -- their only function is 
to reject OUT OF BAND signals. The primary reason for using bandpass 
filters IS for RX. A good 160M bandpass filter would be effective at 
reducing overload from AM broadcast stations. So would a high pass 
filter. There is a survey of bandpass filters for contesting at this 
link. http://k9yc.com/BandpassFilterSurvey.pdf


I use a high pass filter for rejection of the AM BCB band. Between 70 and 
80% of the net power (or voltage) into my RX system comes from distant AM 
BCB signals.


Without a small 5-pole highpass that starts to roll off at 1700 kHz, I can 
connect a  miniature 12V 50 mA incandescent lamp (like the MFJ 1025 uses 
as a fuse) and it illuminates a dull red.


This is with no attempt at matching power to the filament cold resistance.

My system can be bothered by the sum of all those thousands of signals, I 
add a BCB high pass, and then I can run 1500 watts and not bother my own 
RX when transmitting on 80 or 40 while receiving on 160. Of course I have 
500-2000 ft separation on antennas, but this still shows how a bunch of 
small signals can add up to disaster if they hit something non-linear 
before being filtered.


Always remember there are two problems. One is the absolute limit of 
in-band signal a receiver system can take. The other is the absolute limit 
of the sum of all the signals entering an overload sensitive point in the 
system.


Less than one volt peak line voltage is not enough headroom to prevent IM 
products in a reasonably good system. Back-to-back parallel diodes are 
fine for Sky Buddy receivers and FT101's. A single diode opposing another 
diode in parallel will clamp at about 6 dBm if your receiver looks like 75 
ohms. Almost all receivers will conservatively take 15-20 dBm, or 2-4 
volts peak, at the antenna port in band.


If you have a good system, you'll want something other than back-to-back 
diodes.


73 Tom
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Topband: IC 775 clicks

[Maciej Wieczorek]

GM/GE,

Has anyone ever seen any mod for IC 775 DSP, for getting rid of CW clicks? I 
mean, kind of solution that they have for FT 1000 Mark V..?

BTW, maybe I have a problem with my radio, with the signal S 9+30db on 160m 
(no amplifier) a friend located 30kms away was hearing my clicks for almost 
1,5khz up/dwn, with 400hz filter

I'm preparing for the CQWW 160m contest, so yesterday we made several tests and 
after puting the same power from IC 765 the difference is huge, almost no 
clicks and nothing detected if we go  +/-  0,5 khz  from the TX frequency...

73's
Mac SP2XF 
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