Basic question about antenna/ariels.

Thread Starter

ApacheKid

Joined Jan 12, 2015
418
I used to enjoy DXing as a kid, I have a decent receiver here (Icom ICR-75) and about to put up some kind of horizontal long wire antenna after many years of not using this (and I'm setting up my new workshop etc).

The antenna will pretty much be this:

Dipole_receiving_antenna_animation_6_800x394x150ms.gif
So the radio is "R" above, but why must one of the leads be designated as "ground"? why does the manual say this (connectors 7 and 8):

1614629504142.png
Says the black connector on the back is to "ground" and the red goes to "long wire antenna".

I'd expect each lead in the first diagram simply be connected to the black and red connectors (7 and 8).

Why is one designated "ground"? the unit itself is not connected to the mains supply, it is driven by an external dedicated 13 V DC supply adapter - no ground.

The antenna diagram above implies there are two leads, is it expected that one of these goes to ground AND into the black connector too (7) ?
 

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Yaakov

Joined Jan 27, 2019
3,492
It says "500Ω longwire antenna". A longwise isn't like the dipole you have pictured, and it uses the ground as the other half of the antenna. The 50Ω input would use something fed with coax, and have two elements at the antenna.
 

Thread Starter

ApacheKid

Joined Jan 12, 2015
418
It says "500Ω longwire antenna". A longwise isn't like the dipole you have pictured, and it uses the ground as the other half of the antenna. The 50Ω input would use something fed with coax, and have two elements at the antenna.
You're right, this is what I get for not looking at this stuff for 25 years!

I should use the coax connector, for some reason I assumed that was only for the 50-odd MHz range, no reason for thinking that though, part of the reason is I've never ever had a decent antenna setup, always been on my wish list.
 

Yaakov

Joined Jan 27, 2019
3,492
You're right, this is what I get for not looking at this stuff for 25 years!

I should use the coax connector, for some reason I assumed that was only for the 50-odd MHz range, no reason for thinking that though, part of the reason is I've never ever had a decent antenna setup, always been on my wish list.
A good longwire with a tuner is probably better than a resonant dipole for multi band SWL, by the way.
 

Thread Starter

ApacheKid

Joined Jan 12, 2015
418
A good longwire with a tuner is probably better than a resonant dipole for multi band SWL, by the way.
Thanks, I think that should be my first step, I have a lot of yard space here and I'm just playing around for the time being. Would it be sensible to connect some coax to the long wire where it enters the wall, run that through the room itself and ensure the "black" connection is truly grounded and that that black also connects to the coax braid?

This will (I assume) act as shielding for any RF noise etc. that might get picked up within the building itself, along interior walls etc.
 

Yaakov

Joined Jan 27, 2019
3,492
Thanks, I think that should be my first step, I have a lot of yard space here and I'm just playing around for the time being. Would it be sensible to connect some coax to the long wire where it enters the wall, run that through the room itself and ensure the "black" connection is truly grounded and that that black also connects to the coax braid?

This will (I assume) act as shielding for any RF noise etc. that might get picked up within the building itself, along interior walls etc.
This might be helpful. Have fun, I have spent many, many (,many) hours listening.
 

Thread Starter

ApacheKid

Joined Jan 12, 2015
418
Oh, one more question, the ground, the "black wire" that must be connected to ground, is there any reason to not connect it to the house ground wire? like a wall outlet's ground?
 

Yaakov

Joined Jan 27, 2019
3,492
Oh, one more question, the ground, the "black wire" that must be connected to ground, is there any reason to not connect it to the house ground wire? like a wall outlet's ground?
It would be less than ideal. On lower frequencies it would be a source of noise, possibly quite a bad one. A ground rod is worth the trouble both for SNR and performance.
 

Yaakov

Joined Jan 27, 2019
3,492
OK makes sense I guess.

Let me start looking, "ground rod" you say...
Yes, a nice copper one. Readily available. Good low impedance wire is best, but practically, just the largest gauge you can manage. You can get the rods at home improvement stores with good electrical supply departments.
 

Thread Starter

ApacheKid

Joined Jan 12, 2015
418
Not sure about this, where I live in Arizona the ground is notoriously tough, digging is hard work, really hard work.

The ground is also dry, very little moisture so the conductivity will be less than a more moist environment.
 

Yaakov

Joined Jan 27, 2019
3,492
Not sure about this, where I live in Arizona the ground is notoriously tough, digging is hard work, really hard work.

The ground is also dry, very little moisture so the conductivity will be less than a more moist environment.
The rod is generally driven into the ground. If you wet the area (and you can even add salt) while you install it, you can make a decent connection. The rods are quite long.

The alternative is a counterpoise but it is much more elaborate.
 

Thread Starter

ApacheKid

Joined Jan 12, 2015
418
I'm seeing a lot of talk about electricity codes insisting that such additional grounds be tied back to the supply ground, so to be "legal" you'd just end up using the supply ground, all very confusing!
 

MaxHeadRoom

Joined Jul 18, 2013
23,619
Traditional ground rods are copper plated steel, 8ft long.
Just pour a bucket of water over it each day! :p
Do you have a metalic piped water supply?
 

MaxHeadRoom

Joined Jul 18, 2013
23,619
I don't get this one? " water supply piping is often made of a metal that's not optimal for radio work".
If it s copper, I would consider that 'optimal'
Max.
 

crutschow

Joined Mar 14, 2008
27,718
Would it be sensible to connect some coax to the long wire where it enters the wall,
Not really.
The longwire input is 500Ω but coax is typically 50 or 75Ω so there would be an impedance discontinuity and likely loss of signal going through the coax.
 

SamR

Joined Mar 19, 2019
3,490
The antenna diagram above implies there are two leads, is it expected that one of these goes to ground AND into the black connector too (7) ?
For the basic ole timey "long wire" antenna it is just that, a long wire hung as long and high as possible outside the house. No Coax, no balun, no ladderwire, just a long wire. To "counterpoise" the antenna you use earth ground. The easiet way is to drive a metal stake into the ground to connect to. All this was being done on batteries before the days of indoor plumbing and electric lights. The basic longwire was then impoved upon. One of the first improvements was ladderwire and eventually coax and baluns. It's an antenna ground, not a safety ground for the radio chassis, which stayed ungrounded, even using 110VAC, for many years.
 
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