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 Where has my RF gone ? 
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Post Where has my RF gone ?
Playing with end fed half wave. Wound a 49:1 matching transformer on a ferrite core, cut the length so it offers a very nice match on 80,40 and fairly good on 20. RX sounds very lively, but with noise which is much improved with choke in the feeder. Am getting very poor reports, with a similar power 5/9 station I get a S3 or S4 report. Adding a counterpoise or ground reduces the reports. SWR is 1.2:1, matching transformer doesn't get hot so where is the power going ?

Also how can I measure the current at the feed point ? A trusty old Avo8 on ac volts reports 750v to ground at the feed point at 10w drive. Assuming 2450 ohm that would be around 300ma which plainly is wrong. Measuring the voltage across a 100R in series with the feed point also produces nonsense value.


Sun Feb 28, 2021 5:58 pm
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 Where has my RF gone ? 
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Post Re: Where has my RF gone ?
My experience of transformer end fed antenna is the same as yours - they don't work.
Resonant circuit single band end fed are a different story - GWhip used to make good ones.

Maybe rewind as a 9:1 against earth and try as a inverted L ?

As far as measurements are concerned, ends of antenna are current minima, you are better off using a clamp on RF meter like the 'mousetrap'
http://www.ifwtech.co.uk/g3sek/clamp-on/clamp-on.htm

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Sun Feb 28, 2021 7:04 pm
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 Where has my RF gone ? 
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Post Re: Where has my RF gone ?
superb link, thanks.


Sun Feb 28, 2021 8:49 pm
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 Where has my RF gone ? 
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Post Re: Where has my RF gone ?
Where and what is the choke in the feeder?
Was there just one set of results, or were they a trend over a week or more? And where were the other stations?
Have you measured the power and SWR at the end of the coax?

I'm not sure the Avo 8 works properly at RF. I do remember when international telephones were on HF relays, they had special meters for the antennas, and the Avo 8s were used in the workshop and general use.

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Mon Mar 01, 2021 4:24 am
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 Where has my RF gone ? 
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Post Re: Where has my RF gone ?
You are right in assuming the Avo is not happy with RF but am not brave enough to connect any more modern devices. Choke is just a ferrite core with around 8 turns of feeder passed through it. Reports with and without it connected suggest no loss of TX power. Haven't measured SWR and power either side of it but a VNA reports just a tiny difference in tune with and without it. If RF is getting lost in the transformer or the choke I would expect them to get warm at least which they are not.

Reports have been over a week or so but with similar powered stations I would expect roughly comparable reports

I can only conclude that the radiation angle is so close to vertical that I am just warming the clouds


Mon Mar 01, 2021 12:10 pm
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 Where has my RF gone ? 
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Post Re: Where has my RF gone ?
G8WBO wrote:
You are right in assuming the Avo is not happy with RF but am not brave enough to connect any more modern devices. Choke is just a ferrite core with around 8 turns of feeder passed through it. Reports with and without it connected suggest no loss of TX power. Haven't measured SWR and power either side of it but a VNA reports just a tiny difference in tune with and without it. If RF is getting lost in the transformer or the choke I would expect them to get warm at least which they are not.

Reports have been over a week or so but with similar powered stations I would expect roughly comparable reports

I can only conclude that the radiation angle is so close to vertical that I am just warming the clouds



Where is the choke?

I wasn't meaning SWR and power either side of the choke, but either end of the coax. ie at the rig and at the antenna ends of the coax.

Yes, the transformer would get warm if that is what is causing the loss.

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Mon Mar 01, 2021 12:16 pm
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 Where has my RF gone ? 
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Post Re: Where has my RF gone ?
Choke is at rig end of feeder, feeder is only 5m long.


Mon Mar 01, 2021 1:15 pm
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 Where has my RF gone ? 
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Post Re: Where has my RF gone ?
G8WBO wrote:
Choke is at rig end of feeder, feeder is only 5m long.


Aren't half waves meant to have a longer feeder?

What is the SWR and power at the feed point?

How is the half wave mounted, ie how high is each end?
How was the counterpoise you tried arranged, and how long was it.

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Mon Mar 01, 2021 2:34 pm
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 Where has my RF gone ? 
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Post Re: Where has my RF gone ?
If you want a rf meter, there is a vk station who is well respected, who has the info on line to build an rf meter and a rf meter which also will show the balance with open wire feeder. Simple to build and works very well.
I built both a I usually use home made feeder. cannot remember the call now.

Look it up It is a handy tool. Also I have found that a 9to1 current balun works much better than a unun or a voltage balun that is usually recommended, much less noise as well. As well as a 84 ft doublet I use a 66ft wire with the current balun and one side down to earth, it forces the power up and out, A voltage balun do not.
The meter for the above can be any one available as there is a pot to to control the reading against the power.

Donald


Mon Mar 22, 2021 8:34 pm
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 Where has my RF gone ? 
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Post Re: Where has my RF gone ?
sedge wrote:
If you want a rf meter, there is a vk station who is well respected, who has the info on line to build an rf meter and a rf meter which also will show the balance with open wire feeder. Simple to build and works very well.
I built both a I usually use home made feeder. cannot remember the call now.

Look it up It is a handy tool. Also I have found that a 9to1 current balun works much better than a unun or a voltage balun that is usually recommended, much less noise as well. As well as a 84 ft doublet I use a 66ft wire with the current balun and one side down to earth, it forces the power up and out, A voltage balun do not.
The meter for the above can be any one available as there is a pot to to control the reading against the power.

Donald



First, it has been three weeks since the OP posted.


A 9:1 is better for a long wire multiband antenna, but the OP was asking about a half-wave antenna, for which the 49:1 is correct.

A 9:1 current balun in better in many regards, I use one, but having one leg "down to earth" will make it very dependant on the "earth" and in most places, one earth stake is not going to give the best performance, there won't be much "forces the power up and out"

Unless you have a perfect ground, you will end up with many of the features you need to deal with using a 9:1 unun, which do work just as well if used effectively.

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Tue Mar 23, 2021 5:46 am
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 Where has my RF gone ? 
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Post Re: Where has my RF gone ?
My fault I should have said a 380 ohm resister to earth , as an inverted U. |I do on times lift the wire from earth and use it straight unterminated wire. It is just an opinion after 60 years in the hobby.


Wed Mar 24, 2021 6:39 pm
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