It is currently Mon Nov 20, 2017 3:06 pm

Click the link below to visit the site sponsor

The Ham Radio Shop




Post new topic Reply to topic  [ 39 posts ]  Go to page Previous  1, 2, 3
 80m antenna for limited space. 
Advanced Member

Joined: Sun Feb 23, 2014 7:09 pm
Posts: 195
Location: Blackpool, IO83LT
Feedback: 3 (100%)
Reply with quote
Post Re: 80m antenna for limited space.
Thanks Steve

I take back the "much lower" lol.. Just different but I expect that, as you say :)

I didn't take actual measurements (should have) but my sweep is on page 1. I only use under 5 watts so I figured the 106 would be good enough to test it out.. On the other hand its all I had in a 26.

Cheers

Dave
M6XMA

_________________
Dave
M6XMA


Wed Jul 08, 2015 9:48 pm
Profile Send private message

 80m antenna for limited space. 
Moderator

Joined: Fri May 22, 2009 1:23 pm
Posts: 5646
Location: Northampton IO92ME
Feedback: 0 (0%)
Reply with quote
Post Re: 80m antenna for limited space.
One further experiment this morning:

I set up a calibrated Field-Strength meter and measured how much Tx power I needed on 80m to achieve a given field strength using the Type-26 unun. Then I swapped to the Type-2 unun and measured how much power I needed to get the same field strength. Results:

Type-26 unun: 11.6W
Type-2 unun: 2.7W

Difference 6.3dB

The Type-2 unun was 11 bifilar turns on two stacked T200-2 cores.

I tried the same thing on 160m, but the Type-26 unun overheated and the Tx tripped :cry:

Steve G3TXQ


Thu Jul 09, 2015 9:47 am
Profile Send private message WWW

 80m antenna for limited space. 
Moderator

Joined: Fri May 22, 2009 1:23 pm
Posts: 5646
Location: Northampton IO92ME
Feedback: 0 (0%)
Reply with quote
Post Re: 80m antenna for limited space.
Here are the figures for all bands 80m thru 10m.

Difference in power needed to achieve a given field strength with the Type-26 unun compared to the Type-2:
80m: 6.3dB
40m: 1.1dB
30m: 3.2dB
20m: 5.2dB
17m: 2.8dB
15m: 0.5dB
12m: 3.9dB
10m: 5.9dB

Steve G3TXQ


Thu Jul 09, 2015 10:23 am
Profile Send private message WWW

 80m antenna for limited space. 
Contributor 2017
User avatar

Joined: Tue Oct 09, 2012 1:09 pm
Posts: 7996
Location: West Midlands
Feedback: 82 (100%)
Reply with quote
Post Re: 80m antenna for limited space.
The loss was one of the main reasons I was making two of everything to try.

Now anything more than 1dB on the two, and it doesn't even get tested on the antenna.

Couple of years ago when playing with the snake oil vertical (Comet style unun) it became clear that a flatter SW curve didn't mean better results.

I could hear well, but sometimes couldn't be heard so well.

Changing to a 5:1, 9:1 or 4:1 gave better overall results.

I have commented that the coax intentionally acts as part of the antenna, by moving the clipons, it is possible to find a position that allows all bands to be tuned by the internal tuners.

So far I have found the type 43 cores give the best results, and some Chinese cores are also OK. They are marked with 50, 75, 100 and 120 which I assume I wrote on the label from the specs, and they were like "75 ohms at 100 MHz" though I don't know if that means anything. Can't find where I got them :(


All the antennas work, and at the time they are the best found, but it is always nice to find one that works better than you thought you were going to get, and that doesn't always follow the rules, or duplicate what some one else found, so all the experiments and trials are worth while.

_________________
===================
Gee Three Eee Jay Ess - RSGB, SARL, G-QRP, FISTS, EPC
===================


Thu Jul 09, 2015 11:38 am
Profile Send private message

 80m antenna for limited space. 
Moderator

Joined: Fri May 22, 2009 1:23 pm
Posts: 5646
Location: Northampton IO92ME
Feedback: 0 (0%)
Reply with quote
Post Re: 80m antenna for limited space.
There are some pretty complex issues here. For example, I measured the through-loss of the Type-26 unun with a 200 Ohm load as just over 1dB - not too bad. But then give it the complex load impedance of that vertical on 160m, and the loss rockets to 24dB!

Also, we have to remember the differential-mode loss in the coax. A lossy unun lowers the SWR on the coax and thereby reduces the coax loss, so there's some degree of "compensation"; there might also be some small improvement in tuner loss because of the reduced SWR. So, it's possible that an unun with slightly higher loss could produce slightly lower overall system losses. However the Type-26 unun is so lossy that it never produces a net improvement in this application.

One reason I did field strength tests and swapped ununs over was to take out all of those extra factors: same antenna, same coax, same tuner etc.

Steve G3TXQ


Thu Jul 09, 2015 12:19 pm
Profile Send private message WWW

 80m antenna for limited space. 
Moderator

Joined: Fri May 22, 2009 1:23 pm
Posts: 5646
Location: Northampton IO92ME
Feedback: 0 (0%)
Reply with quote
Post Re: 80m antenna for limited space.
For anyone who is interested in the full set of data:

Image

The first 3 blocks of data are the measured Antenna impedance, Type-26 unun winding impedance, and Type-2 unun winding impedance.

From those impedances I calculated the unun efficiencies shown in the mauve block.

I then used TLD to calculate the coax losses for each unun shown in the grey block.

Finally I calculated the expected net advantage of the Type-2 unun and compared it to the results from the field strength measurements - yellow block.

So, as an example, taking the 20m band data:
Antenna impedance = 1011-j1845
Type-26 winding impedance = 278+j301
Type-2 winding impedance = 585-j3430

Type-26 efficiency = 12.1%
Type-2 efficiency = 82.6%
Type-2 efficiency advantage = +8.3dB

Type-26 coax loss = 1.3dB
Type-2 coax loss = 3.7dB
Type-26 coax loss advantage = +2.4dB

Predicted Type-2 net advantage = +5.9dB
Measured FS advantage = +5.2dB

Reassuringly, the predicted differences in unun performance follow the same trends as the measured differences in field strength.

Steve G3TXQ


Thu Jul 09, 2015 1:54 pm
Profile Send private message WWW

 80m antenna for limited space. 
Advanced Member
User avatar

Joined: Tue Nov 26, 2013 11:55 pm
Posts: 419
Location: Lincoln QTHR
Feedback: 2 (100%)
Reply with quote
Post Re: 80m antenna for limited space.
Steve's experiments are excellent and show that for a compromise vertical antenna for the lower bands optimizing to minimize loss is very important. I would only add that if you want to get more out of your vertical compromise antenna, get as much 'earth' wire out as possible. In a small plot you should aim to get at least a few radials down, even if that means bending/wrapping them to fit the plot. You will notice the difference!


Sat Jul 11, 2015 10:28 am
Profile Send private message

 80m antenna for limited space. 
Contributor 2017
User avatar

Joined: Sat Jun 18, 2011 4:15 pm
Posts: 13339
Location: io65ga, Donegal
Feedback: 8 (100%)
Reply with quote
Post Re: 80m antenna for limited space.
What I'd like to know is, why when I asked earlier if measurements taken from the base of the antenna differed to those taken in the shack was I given misleading info :scratch:

Quote;
"We have taken SWR reading at the base and further afield. The aerial seems unaffected by coax length, height AGL, surrounding terrain etc etc etc. All of which is very good but all of which rather plays into the hands of the "snake oil!!" cryers.
We had one chap come up and quote text book references at us telling us why the aerial was a fake and would never work. Oddly enough the Asian stations I later worked with it hadnt read the same text books, so worked me anyway.
Like I say in the notes, we make no claims at all for this aerial, except that it works. They now operate in many countries and I have no one come back and tell me it didnt work as well as I say.
If you do play with one and make some interesting finding, do please tell us!

Regards"


Steve TXQ has just done that. ;)

I wonder how many of those Asian stations were on 80m & 160m. :scratch:

_________________
Even duct tape can't fix stupid, but it can muffle the sound.


Sat Jul 11, 2015 10:38 am
Profile Send private message

 80m antenna for limited space. 
Contributor 2017
User avatar

Joined: Tue Oct 09, 2012 1:09 pm
Posts: 7996
Location: West Midlands
Feedback: 82 (100%)
Reply with quote
Post Re: 80m antenna for limited space.
ei9ju wrote:

Steve TXQ has just done that. ;)





Yes, and in a polite, constructive and non-patronising manner.

_________________
===================
Gee Three Eee Jay Ess - RSGB, SARL, G-QRP, FISTS, EPC
===================


Sat Jul 11, 2015 11:30 am
Profile Send private message
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 39 posts ]  Go to page Previous  1, 2, 3


Who is online

Users browsing this forum: DJBlue and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
Powered by phpBB © phpBB Group.
Designed by Vjacheslav Trushkin for Free Forums/DivisionCore.