Is this normal?

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  • Updated 9 months ago
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Hi,

Wondering if this is normal.

I have a 6700 and sometimes listen to old time radio programs out of Canada at night.
If I shut down and ground my antenna on my Alpha Delta switch, I still can receive AM
broadcast signals. Switch to the ham bands and all signal disappear.
Bypassing the switch to the Palstar tuner and the signals are reduced if the tuner switch is turned to an unused port. But still can receive stations.
I have a Array Solutions coaxial lightning arrestor also in line. Bypassing that made no
difference. Again signals disappear on the ham bands, but not on the AM broadcast band.
Also this happens regardless of radio port. The only way to stop signals on the AM band is
to disconnect the coax from the radio.
I am thinking of getting an antenna disconnect actuator from Paradan Radio. Anyone try one
yet?
I am just concerned with the spring storms coming up. I do not want to get up the next morning and find the receive dead even though I had taken steps to ground things when I shut down for the night.

73, Jim N9VC
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N9VC

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Posted 9 months ago

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Bob Craig, K8RC

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In some situations, an AM broadcast signal can find it's way in to a sensitive receiver with only the center pin of a disconnected PL259 as an antenna.

My 6300 receives nearby WDJO and further away but 50KW WLW if a coax is connected on just the radio end.

Just as in your case, the only way to get a "clean" waterfall is to completely disconnect everything.
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N9VC

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Thanks Bob, I noticed the same but reduced behavior on an Icom transceiver.
But the AM broadcast band is attenuated on the Icom, which lacks the band
filtering of the 6700.
Just trying to get ready for the storms which will be here sooner than later.
Thanks again.

73, Jim N9VC
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Robert Lonn

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Not that unusual when it comes to the AM radio band. What did it for me was Grounding the antenna at the Antenna Itself as well as a good ground inside the shack.. When you have a Coax 50-75-100 feet long it makes a great low band antenna,, I used a 8' grounding Rod at both the  shack and at the antenna farm locations.. Grounding is a very subjective practice and a lot depends on soil condition, and how you ground the coax... I used a Transi-Trap Lightning surge protector from Alpha Delta Communications... GigAparts has this one for $45.00  ALPHA DELTA ATT3G50UHP
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N9VC

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Thanks Bob, I use an Alpha Delta surge protector on the noise pick-up antenna on my DX Eng NCC-2 with a coax switch between antenna and protector.
I use a Alpha Delta switch with surge protection between the radio and
amp, etc, that follows. I also have an Array Solutions coaxial lightning arrestor
between the radio and switch. Same unit as Tim said he uses. In the Alpha Delta,
I installed a high ohmage resistor inside the unit to bleed off any build-up
before the arrestor. It is only in a receive line so not concerned that it needed
to be high wattage. Grounding is extensive. Best bet for me is disconnect the
coax from the radio when I shut down at night and hope all protection does its
job when I have the equipment on.

73, Jim N9VC
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Bob Craig, K8RC

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Anytime you're talking lightning, you do the best you can. I spent most of my life tending a TV transmitter right underneath 1000' of steel tower. This is an environment where your antenna can get hit 3 or 4 times in an hour!

Which gives me an idea -

Starting with our 1978 Harris xmtr, the TV rigs have been equipped with a sensor that senses the rapid static buildup on the center conductor of the coax just before a strike. Then, it shuts down the xmtr, grounds the center conductor, counts to 5 then un-grounds and comes back up.

Since we have a transmit interlock on the Flex, we could fairly easily do the same thing. 

Hmmm.
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Doug K0DV

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I picked up two of these at Hamcation this year.
https://paradanradio.com/products/antenna-disconnect
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N9VC

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Thanks Doug. Yep, I said I was already looking at them. I have extensive grounding
here, but want to be sure that I am doing all I can, rather than wishing I would have
done something. I think it is just collateral pick-up from the shields.

73, Jim N9VC
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spopiela

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Jim
I’ve purchased the parandan antenna switch and found it to be acceptable. I installed it in place of the lightning arrestor outside and used the old arrestor ground. Wire to earth ground. This gave me a switch and arrestor without adding any more coax connections.. the antenna is an offset center dipole. The Swr sweeps on the 80 to 10 meter bands were good. I switch it on when the 6500 turns on thru the 12 v line.
Stan
N1THL
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N9VC

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Thanks for the review, Stan.

73, Jim N9VC
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Stan - VA7NF

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If A) The ground wire from your switch is more that a few metres or
B) The ground is weak then
There will be RF pickup on that ground wire and loop back through the outer shield to the Tx chassis and then continue back to ground, that ground should be the same shack grounding point.

That will leave the inner conductor to present a different level signal to the rig.
Providing your ground at the switch is good you will continue to have lightning protection.
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jerry stern

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Jim, I confirm your findings.  I also have an Alpha Delta switch right next to my 6700 and even with my dipole grounded, I can hear nearby AM stations coming in on my 6700 around -60 dBm so I question the isolation of the Alpha Delta switch when switched off (ground).  However my shack is on second floor and my "ground" is not an RF ground by a house electric ground.  Nevertheless, I also have the Paradan antenna disconnect about 30' away at the shack entry point and use this for more protection.  When I shut the Paradan off (with Alpha Delta switch still off), the AM signals drop below -120 dBm.  So, I think the Alpha Delta switch does not provide sufficient surge isolation.  BTW, i bought a remote control AC outlet extension just for the Paradan, about $30 at Home Depot, and I can turn the Paradan switch on/off remotely right from the station desk.  Nice thing is with an AC power loss the Paradan opens the antenna and switches it to ground.  Also at the shack entry, I have a 8' ground round bonded to  second 8' ground rod and that one is bonded to my service panel ground rod.  I also have an Alpha Delta arrester (TT3G50HP) on each ground rod grounding my outdoor coax run.  

73 Jerry NY2KW
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N9VC

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Hi Jerry,

Thanks for your input. You confirmed my findings and also thanks for
the input on the Paradan switch. I think that will be a worthwhile addition
to the shack. I have 3 ground rods all bonded together for the shack,
spaced and connected to the power entrance ground. According to what
you, and others, say. Everything is normal. I just have to make it more
normal. Which is a state my parents said I would never achieve.
Thanks again.

73, Jim N9VC