Topics

New member - installation


Virgil ZS1VBC
 

Hi, just purchased a used HF6V antenna. I am installing on a metal roof 4m above ground. I took off my wire 80/40/20 dipole and will use this as resonant radials on the roof. Any advice or recommendations will be welcome.

Virgil - ZS1VBC


Emil ZS1XB
 

Hi Virgil, When you have a metal roof the surface area maybe enough as ground plane. If your roof consist of tiles I would go for more radials. I have done this on a hotel roof in Ghana and 6 - 8 radial will definitly benefit the overall efficiency. At the moment I have installed a folded dipole on the 10th floor building in Ghana for the NCA. You may also run the radials in folded patern and not necesarily straight.


Virgil ZS1VBC
 

Antenna is on the roof now, SWR is way out on all bands???


Craig KC2BK
 

There is a tuning procedure that comes with a new HF6V - do you have the manual?


Siegfried Jackstien
 

what groundplane did you add?? STUB TUNED RADIAL KIT???

or did you cut resonant radials for each band?

dg9bfc sigi


Am 11.07.2020 um 16:54 schrieb Virgil ZS1VBC:

Antenna is on the roof now, SWR is way out on all bands???


Virgil ZS1VBC
 

Yes


Virgil ZS1VBC
 

Radials
80m = 2
40m = 2
20m = 2

I must check lengths of wire, don't think it is resonant on the bands


 

Virgil,
How big is the roof?  It is sloped, is it overlapping metal sections?  How far off is the tuning?  Don't make any real assumptions that the antenna is bad until you check everything again.  You might have bumped something putting it on the roof or the top section may have slid down.  The fact that it is used my indicate a problem with parts as well.
Al
WB9UVJ


Virgil ZS1VBC
 

Hi Al, I got the 80 & 40m right, 20m SWR still high.


Scott AC8DE
 

A flat bonded metal roof is the king of ground planes and will make the antenna boom.  Radials will do nothing for that sort of installation.

 

It's key you get the feed point close to the metal roof.  I assume the roof is fairly flat and not sloped, as you did not say otherwise?  You want the base insulator to sit on the roof in such a way that your feed point is less than 6" above the sheet metal roof.  Just making some sort of "cup" to hold the insulator from moving on the roof and gluing it in place on the roof and then guying the antenna is the best way to go.  Do not use the roof mount kit on a metal roof as it raises your feed point too high.  That is intended to be used on an asphalt shingle roof and be accompanied by radials.

 

How about creating a directory in the photos area using your call sign ad the folder name and giving us some photos, focusing on the base of the antenna and your connections.

 

73,

Scott AC8DE

 

From: Butternut@groups.io On Behalf Of Virgil ZS1VBC
Sent: Friday, July 10, 2020 8:17 AM
To: Butternut@groups.io
Subject: [butternut] New member - installation

 

Hi, just purchased a used HF6V antenna. I am installing on a metal roof 4m above ground. I took off my wire 80/40/20 dipole and will use this as resonant radials on the roof. Any advice or recommendations will be welcome.

Virgil - ZS1VBC


Scott AC8DE
 

You keep talking about these radials.  Are they in the air or laying on a surface?  If laying on a surface, you are wasting your time tuning them.

 

73,

Scott AC8DE

 

From: Butternut@groups.io On Behalf Of Virgil ZS1VBC
Sent: Monday, July 13, 2020 3:06 AM
To: Butternut@groups.io
Subject: Re: [butternut] New member - installation

 

Hi Al, I got the 80 & 40m right, 20m SWR still high.


 

Virgil,
I have to ask...you did add the 1/4 wave coax transformer in series with the feedline?
Al


Virgil ZS1VBC
 

Hi Scott, it is a flat metal roof, feed point is close to metal roof. I used my 80/40/20 inverted V dipole wires that I took down and spread it out on the roof.
Had rain last few days, will take photos as soon as I can and post

73,
Virgil ZS1VBC


Virgil ZS1VBC
 

Al,
Yes, 75 ohm coax to antenna and connected to 50 ohm feedline.

73,
Virgil ZS1VBC


Virgil ZS1VBC
 

Radial wire laying on metal roof.

73,
Virgil ZS1VBC


Scott AC8DE
 

Virgil,

 

I await seeing the photos.

 

You said your feed point is "close" to the roof.  How close?

 

If the flat metal roof is bonded from end to end, just get rid of the wires.  They are not doing anything for you in that instance.  And note that the metal roof detunes the wires anyway, making them ineffective.  What you need to do is bond the shield of your matching section to the bonded metal roof near the antenna base.  Once you do this, you'll find out that your tuning is VERY sharp on the lower bands and that the overall SWR will appear higher.  This is a good thing.  I know that is counter-intuitive.  Multiband verticals with great ground planes are going to exhibit slightly higher SWR's and lower bandwidth on each band because the "Q" of the system is much higher.

 

As far as not being in-band when tuning, this is not unusual.  The factory dimensions are just a starting point to get it so you can see the band dips on an analyzer.  It may well be that the tune is out-of-band on the stock dimensions.  Now if you can't see any dips, then you have a problem.  Note that getting 10M right is key is setting up the antenna.  This is why having a low feed point and good bonding to the ground plane is a critical first step, as you can't get 10M right if these things are not correct.

 

Tuned radials are only good in one situation; a true elevated vertical with no other ground plane.  For an antenna with a good ground plane (like a metal roof) or a ground mounted antenna, they do not help you.  The purpose of radial wires on a ground mounted antenna is to crate a current path and shield from the capacitance of the ground.  This is why more radials as long as about 25% longer than the antenna is tall is key to making a good system when ground mounted.  In the case of a metal roof, this is a big ground shield and current path, so the antenna cannot "see" the ground in such an installation.  It's a beautiful thing.  As far as an elevated non-metal roof install, that is when you need resonant radials, with 4 tuned radials per band giving the same performance as a 120+ radial ground mounted system, if you are least 1/4 wave above ground for the band being operated on. (VERY difficult to achieve.)  Another option that very few have accomplished in a lower elevated installation is to put in a very large number of elevated non-tuned radials in place.  This electrically approximates a metal roof and doesn't need to be resonant to work.  That is complex and pricey to achieve however, not to mention just a bit unsightly and not XYL approved usually.

 

What's your base shunt coil like at the moment?  It only affects 80 & 40 meter bands to any significant degree.

 

Also note that it is highly probable that you will want to put in at least 1 good common mode choke at the shack entrance.  Verticals tend to give your quite a bit of RFI, especially when the ground plane situation is not yet properly worked out and the installation is elevated.  I strongly suggest a toroidal wound version if homebrewing, otherwise a good commercial version on a ferrite core.  Without this, you'll find that your SWR will often look totally out-of-whack due to common mode issues.

 

Describe how your feed line is ran.  What kind of feed line are you using?  How far is the shack from the vertical?

 

73,

Scott AC8DE

 

From: Butternut@groups.io On Behalf Of Virgil ZS1VBC
Sent: Tuesday, July 14, 2020 9:30 AM
To: Butternut@groups.io
Subject: Re: [butternut] New member - installation

 

Hi Scott, it is a flat metal roof, feed point is close to metal roof. I used my 80/40/20 inverted V dipole wires that I took down and spread it out on the roof.
Had rain last few days, will take photos as soon as I can and post

73,
Virgil ZS1VBC


 

Virgil,
It is unusual for the 20 meter band to so off if everything else is correct, unless the 30 meter assy is not correct.
I should remind everyone that low SWR does not indicate tuning.  Having a SWR minimum shows where the tuning is at.  Lacking an antenna analyzer, one needs to use other tools.  With the antenna as designed, a 3/8 wave for 20, the tuning is very broad and is usually much wider than the 20 meter band even with a good ground system.   If the 30 meter assy is incorrectly placed and assembled, it could pull the antenna off frequency I suppose.
Since this antenna is used, it is possible that the previous owner replaced the 1/4 wave section with RG8.  Double check that the section is indeed RG-11.  The antenna at 20 meters is 100 ohms feedpoint impedance at resonance.  If you are showing an SWR minimum in the middle of the 20 meter band but SWR is high at the minimum, then this is likely the case.  RG-8 will not act a s transformer.
Al
WB9UVJ


Scott AC8DE
 

>RG-8 will not act a s transformer

 

Al is correct.  But RG-6 WILL act as a transformer, as it is 75 Ohm.  It just won't stand up to use with an amplifier, where RG-11 will.

 

73,

Scott AC8DE

 

From: Butternut@groups.io On Behalf Of Al WB9UVJ
Sent: Tuesday, July 14, 2020 11:40 AM
To: Butternut@groups.io
Subject: Re: [butternut] New member - installation

 

Virgil,
It is unusual for the 20 meter band to so off if everything else is correct, unless the 30 meter assy is not correct.
I should remind everyone that low SWR does not indicate tuning.  Having a SWR minimum shows where the tuning is at.  Lacking an antenna analyzer, one needs to use other tools.  With the antenna as designed, a 3/8 wave for 20, the tuning is very broad and is usually much wider than the 20 meter band even with a good ground system.   If the 30 meter assy is incorrectly placed and assembled, it could pull the antenna off frequency I suppose.
Since this antenna is used, it is possible that the previous owner replaced the 1/4 wave section with RG8.  Double check that the section is indeed RG-11.  The antenna at 20 meters is 100 ohms feedpoint impedance at resonance.  If you are showing an SWR minimum in the middle of the 20 meter band but SWR is high at the minimum, then this is likely the case.  RG-8 will not act a s transformer.
Al
WB9UVJ


Virgil ZS1VBC
 
Edited

I managed to get SWR right, question, is reception better ground mounted or roof mounted +- 3m?


 

Virgil,
There are a lot of variables in that question.  Remember that the antenna is designed to interact with the ground to form a lobe aimed at the horizon +15 degrees.  Roof mounting it with a good ground gets the lobe above surrounding objects.  However, when people talk about roof mounting, all roof types are included.  That includes sloping roof lines, roofs that are less than 1/4 wave at lower frequencies and flat roofs.  They may be covered in metallic sheet, asphalt with foil backing,  metal roof supports, or attics with HVAC duct, all of which will affect performance.  While the antenna may load up properly and have expected bandwidth, that does not mean that the lobe is formed at a good angle for DX.
--   Of course the same holds true for ground mounting depending on ground conductivity and contour.  Here in the Midwest, the ground is relatively flat, mostly clay, moderately moist but not great conductivity.  My antenna is ground mounted and in the early days, I had only four 33 ft. radials.  Then I added a few more eventually getting to 16.  My bandwidth was wide but I still made contacts.  When I had a chance, I laid down a new field of 64 radials, mostly 30 feet or longer and my bandwidth got narrower and my SWR changed a lot.  I also noted more stations in even bad conditions.  Right now, I can work some European stations on FT-8 and PSK31 at 5 watts.  I am sure I would get more QSOs with a beam at 30 ft. but I like this antenna and installation as it does not draw attention from neighbors or other people driving through the neighborhood.  I have way less than an ideal installation or location.  My antenna is mounted near a big silver maple, about 25 ft. from my house with a metal shed nearby in a yard that is surrounded by chain link fence.  I still get out and make my fair share of QSOs without high power, mostly QRP.  I am not a contester and this install works for me even though it is not ideal. 
Good hunting.
Al

Al
WB9UVJ