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Author Topic: Modifying an MA-160V turning it into a great lowband DX antenna  (Read 4626 times)
KY6R
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« Reply #15 on: April 13, 2013, 06:17:30 AM »

Rich,

15 meter (50 feet) is very short for a 160m antenna.
See fig 9-48 (A), at page 9-38 of ON4UN's book. That is your antenna. Physical length 33 degrees, small top load (7 degrees). To get 90 degrees electrical length you need 50 degrees ''to be produced'' by an inductor.
Impedance of your 15 meter vertical is 3,2-j506 Ohm without top head and 4,8-j390 Ohm with the 8 spikes of 4 feet each.
Exactly what you can read in figure 9-48. If you have a coil with a Q of 200, the extra loss is 1,95 Ohm.
With a radialnetwork of 10 Ohms the efficiency will be {4,8/(4,8+1,95+10)}x100%=28,6%. Even worse then the 33% in my previous posting.
Making a bigger top load will help you a lot but your MA-160V is not strong enough.

If you look at fig 9-91 in ON4UN's book (inverted L) you see that with a vertical part of 15 meters you will be able to increase the radiation resistance to 14 Ohm.
You do not need 390 Ohm of inductance (with additional losses) to match this impedance to your 50 Ohm cable. Together with your 10 Ohm  you can even fix it with a 1:2 stepp-up transformer.
Efficiency will be {14/(14+10)}x100%=58% instaed of 28,6%.

My inverted L is a little longer then 1/4 lambda to bringing the point of maximum current in the centre of the vertical part and increasing the radation resistance a bit.

Kees

Thanks, Kees. I re-read the chapter, and I did find a table that confirms your calculations on efficiency.

Now, on 30M and 40M the antenna looks very good, because it is just over a half wave on 30M and about 3/8 lambda on 40M (more than 1/4 wl).

I think the spokes in the cap hat add up in length, meaning 8 * 4 = 32' added to the 50' vertical - giving roughly 1/4 lambda on 80M. Please correct me if I have this wrong.

So - the antenna looks quite good on 80 - 30M, and could be improved on 160M by adding a trap just above the cap hat and with a long wire extended as an inverted L.

I do have some base loading on 160M - making it resonant on 1.823 mhz, but it is quite narrow banded. I switch in a 500 pf door knob capacitor for 80M, and I also have a small amount of base inductance on 40M. On 30M - its a direct feed, and my KAT500 finds a match in the shack with ease (quickly) on all 4 bands. My KPA-500 has no problems on the bands above 160M, but I am limited to about 300 watts on 160M. I think this means my antenna as it is has less than 100 watts out - due to it being inefficient. Above 160M its fine.

I can only imagine that the MA-160V is no better. However, I have still worked 46 entities - including VK / ZL, Spratly, many Caribbean and SA and one of my favorites - South Orkney with ease in the last couple of years. But I think a 50' hatted vertical is the equivalent of a mobile antenna on 20M on a car or truck as far as efficiency is concerned.

I would expect adding a trap with wire would give me a more broad banded 160M antenna, and not degrade performance on 80, 40 or 30M.

Without such a trap, an inverted L on 160M does not look good at all on 80 or 40M, but OK on 30M.

If the trap above the spoked top hat keeps radiation from happening on the horizontal wire on 80, 40 and 30M, then this "combination" hatted and trapped inverted L would be a very good antenna. The top horizontal wire raises the TOA on 80 and 40M to end up being a cloud wrming NVIS antenna - great for Gene's favorite "Unkel Winky Hour DX and Jabber Jaw Net", but only for talking to the Net Control in the US - not the DX itself.

Again - please correct me if I am wrong.

« Last Edit: April 13, 2013, 06:26:24 AM by KY6R » Logged
PE5T
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« Reply #16 on: April 13, 2013, 10:48:45 AM »

I modelled your antenna and it is a good performer on 80, 40 and 30m with low radiation angle.
There is not a simple solution to add 160m and keep the good characteristics on 80, 40 and 30m. Traps could be a solution (you need 3 off them, however) but will add inductance and decrease efficiency on 160m.
Good vacuum relay (or two in series) with low capacitance to decouple the horizontal wire is a possible solution. The control line for the relays have to be decoupled at the base of the antenna with a good choke (high impedance especial on 30 and 40).

Kees

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K6UJ
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« Reply #17 on: April 13, 2013, 11:34:44 AM »

I have been following this thread with much interest.  Learning more about 160 meter antennas thanks to you guys.   I am planning a 160 meter inverted L or something similar myself.  Looking at ON4UN's book I noticed a T configuration also.  I can manage a 160 meter L or T which would be 75 feet vertical and then one horizontal wire or two horizontal wires in a T.  The horizontal wires would
have to slope down about 45 degrees.  I am trying to figure out the length of the T horizontal wires,
(presumably shorter than the L wire) and the advantage if any of the T top loading compared to the L
config.  

Bob
K6UJ
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KY6R
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« Reply #18 on: April 13, 2013, 02:24:28 PM »

I modelled your antenna and it is a good performer on 80, 40 and 30m with low radiation angle.
There is not a simple solution to add 160m and keep the good characteristics on 80, 40 and 30m. Traps could be a solution (you need 3 off them, however) but will add inductance and decrease efficiency on 160m.
Good vacuum relay (or two in series) with low capacitance to decouple the horizontal wire is a possible solution. The control line for the relays have to be decoupled at the base of the antenna with a good choke (high impedance especial on 30 and 40).

Kees



Thanks again, Kees. I think I will keep it as it is - 30M and 40M are much more important for me, and all I want to do on 160M is get to 100 entities. I got 46 entities in 2 winters here - and fully expect to get my 9BDXCC with this antenna. It is like a mobile antenna on 160M  Wink
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KY6R
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« Reply #19 on: April 13, 2013, 02:37:33 PM »

I have been following this thread with much interest.  Learning more about 160 meter antennas thanks to you guys.   I am planning a 160 meter inverted L or something similar myself.  Looking at ON4UN's book I noticed a T configuration also.  I can manage a 160 meter L or T which would be 75 feet vertical and then one horizontal wire or two horizontal wires in a T.  The horizontal wires would
have to slope down about 45 degrees.  I am trying to figure out the length of the T horizontal wires,
(presumably shorter than the L wire) and the advantage if any of the T top loading compared to the L
config.  

Bob
K6UJ

I like the T wires to be horizontal if possible - or, the cap hat as I have it. The reason - and especially with the cap hat - it rejects high angle signals, so when the "High Cholesterol Net" fires up - it doesn't interfere so much with your low angle DX from Kerguelin. Of course - that's why we use CW on 80 and 160 especially - to not get mixed up with Gene's Nets - like OMISS.
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WB3CQM
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« Reply #20 on: April 13, 2013, 07:27:14 PM »

I have been following this thread with much interest.  Learning more about 160 meter antennas thanks to you guys.   I am planning a 160 meter inverted L or something similar myself.  Looking at ON4UN's book I noticed a T configuration also.  I can manage a 160 meter L or T which would be 75 feet vertical and then one horizontal wire or two horizontal wires in a T.  The horizontal wires would
have to slope down about 45 degrees.  I am trying to figure out the length of the T horizontal wires,
(presumably shorter than the L wire) and the advantage if any of the T top loading compared to the L
config.  

Bob
K6UJ

If a T is used the top -loading wire, the horizontal (high -angle ) radiation from this top wire will be effectively canceled in the far field.

I believe the T is a more effective DX antenna than a L .

But a lot comes into play. Radials - Radials - Radials besides other things. I think at lest 65 radials should be used on a ground mounted vertical T . Mine now has 115 -130 foot radials.

How long the top wire ? My T is 64 foot vertical and the top wire is about 45feet 8 inch on each side of vertical section

Xs=0 at 1.835 I made it a little high.

If ground mounted and if you use radials on the ground the Top Wire is adjusted to find the Xs= 0 or resonance freq.

I would suggest you put your radial field in place before you build the T. If you build the T then the radial field , things will change on you.

If you use elevated radials then the Top hat is the missing portion of the vertical plus a % or the equal of the other half as I recall.
The Xs=0 is obtained by adjusting the 2 radials and not the Top hat.

 The Insulators at the end of the T or top wire should be very good . High Voltage is present at the ends.

For a discussion on the T verses the L go to Top Band reflector
http://lists.contesting.com/_topband/2008-10/msg00041.html

I use a 80 meter band  T vertical with 2 elevated radials and though I could improve it with a good ground screen below and perhaps 2 or more radials . I find the antenna is in general as good or better than the ground mounted 160 meter T. But the 80 T is elevated to 14 feet. And 80 meters is not 160 meters.

I have used a L and many many many hams use a L  with good success on Top Band, they do  work. From what I understand if you wanted to work more USA you might want the L over a T
 .
But for dxing , I will stick with the T for now. The claim is a T receives better than a L . I have no clue . I use lots of Beverage antenna but then again the T does receive signals very good.

I am no expert on this subject but this my understanding of the antennas and experience I have had.
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KY6R
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« Reply #21 on: April 13, 2013, 09:20:15 PM »

Rich:

I am also intrigued by this project.  This winter was my first on 160, and it was a blast -even with poor low band antennas here.  Hoping you put some pictures of this latest project on you web page soon.

73/DX de

Gavin W9YE

I have taken pictures of the new antenna farm - and a write up on my Wordpress Blog:

http://ky6r.wordpress.com/2013/04/14/post-honor-roll-antenna-farm/
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N4OGW
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« Reply #22 on: April 14, 2013, 06:52:32 AM »


....
I have used a L and many many many hams use a L  with good success on Top Band, they do  work. From what I understand if you wanted to work more USA you might want the L over a T
 .
But for dxing , I will stick with the T for now. The claim is a T receives better than a L . I have no clue . I use lots of Beverage antenna but then again the T does receive signals very good.

I am no expert on this subject but this my understanding of the antennas and experience I have had.


Basically the choice between a T and L is simple- they are both just shortened verticals. Go with the one that allows you to put up the highest vertical section. If you can put up either, go with the T.

Receiving isn't that important because you really want a separate directional rx antenna anyway.

KY6R: your web page says you had a dipole at 65 feet. Why not hang an inverted L from that tree?

Tor
N4OGW
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KY6R
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« Reply #23 on: April 14, 2013, 08:05:32 AM »

KY6R: your web page says you had a dipole at 65 feet. Why not hang an inverted L from that tree?

Because the squirrels constantly eat through the rope - and the wire antennas keep falling. I finally am giving up on that. I was also using one of the neighbors trees - a 70' Monterrey Pine that he is most likely going to cut down this summer as its starting to die.

But that 40M dipole up 65' was a very good antenna while it lasted . . .
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N4OGW
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« Reply #24 on: April 14, 2013, 04:43:22 PM »

KY6R: your web page says you had a dipole at 65 feet. Why not hang an inverted L from that tree?

Because the squirrels constantly eat through the rope - and the wire antennas keep falling. I finally am giving up on that. I was also using one of the neighbors trees - a 70' Monterrey Pine that he is most likely going to cut down this summer as its starting to die.

But that 40M dipole up 65' was a very good antenna while it lasted . . .

Yes, wire antennas in trees are a pain to maintain Smiley A tree-supported inverted L with 65 ft vertical can work well on 160- I used to have one up here and remember working 3B9 with it.

Tor
N4OGW
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NU1O
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« Reply #25 on: April 14, 2013, 05:12:38 PM »

You need to shock the squirrels a few times, probably many, many times. I used to have several bird feeders but I gave up because the squirrels were always eating most of the food. They are incredibly smart animals and I've seen them do some amazing things to get food. The squirrels usually win because they wear just plain wear you out.

73,

Chris/NU1O
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KY6R
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« Reply #26 on: April 14, 2013, 05:28:09 PM »

They love the "cottony downie fluff" in the middle of the rope. They take it and use it to make little squirrel pillows and comforters - or sumpin'.

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W9YE
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« Reply #27 on: April 14, 2013, 05:37:05 PM »

Thanks for the pictures and the excellent description.  The angle of the photo makes the MA-160 look mighty high on top of that push-up mast!

Gavin W9YE
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N2NL
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« Reply #28 on: April 14, 2013, 05:38:48 PM »

From KH2, I decided to go with top loading - initially a TEE vertical - which has since morphed into three top loading wires as it provides some additional support in the wind.  My 1st vertical was about 55ft vertical.  Current configuration is about 70ft vertical - the top loading wires makes the antenna resonant on 160.

I decided *against* an inverted L because the majority of the antenna would be horizontal - 80ft or so for a 50ft vertical.  This provides some higher angle radiation components.  From KH2, I want as low angle radiator as possible, since EU and NA are 6K plus miles away.

Under the antenna are about 90 radials, averaging about 100ft long.

The antenna works VERY well.  Bandwidth is quite narrow, but 30khz is about all you need to cover the CW portion of the band.  Also, I needed to add a hairpin match across the feed point.  Radiation resistance for a short top loaded vertical is quite low.  This results in some mismatch to a 50 ohm radio.  The hairpin match fixes this.  If you top load a short vertical, and find that the SWR is excellent with good band width - you have a lot of loss in your system, probably though ground losses.

I've worked more than 3K unique stations on 160m with this antenna, in all 40 zones.  

If I were stateside or in Europe, I'd probably go with an inverted L, especially for Topband contesting.  From KH2, 1500 miles from Japan, I wanted the lowest angle radiator and most efficient antenna possible.  A top loaded vertical over a good ground system accomplished both of these goals.

73, Dave KH2/N2NL
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KY6R
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« Reply #29 on: April 14, 2013, 07:05:28 PM »

Thanks for the pictures and the excellent description.  The angle of the photo makes the MA-160 look mighty high on top of that push-up mast!

Gavin W9YE

Thanks Gavin. Yeah - its about as high as I can go given the top hat has some weight - and I want to be able to raise this by myself.

I know that 160M is a real compromise with this antenna, but the design goal was to multi-band it. I achieved my goal - to retain the MA-160V characteristic while adding 80, 40 and 30M - and adding these as really decent performing bands.

I have no doubt that I will at least make DXCC on 160M, and the other bands are better than just "icing on the cake".
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