best antenna

[ccz]

Double bi-quad works visibly better for longer range.
For medium range I can't say anything yet, I have to do at least some 24h tests on same weekdays.

Bi-quads are excellent for window antennas. I am picking up reflections up to 120nm on the opposite side of the antenna.

Calculator link:

http://buildyourownantenna.blogspot.com/2014/07/double-biquad-antenna-calculator.html

Tips:
The reflector plate should not be smaller than recommended size.
Thicker wire seems to work better than thinner wire. For 1090MHz 2.6mm diameter is recommended - I used 1.78mm dia (2.5 sq.mm)


To do:
- try a better wire thickness: 2.6mm diameter (5.30sq.mm)
- try a mesh for reflector - thin mesh - simply because it is available at a nearby store
- try a rounded double bi-quad - regular double bi-quad turned around a can as reflector

@abcd
If you have the spare time and if it is also possible to simulate the rounded double bi-quad, that would be interesting.


Edit:
found the omnidirectional biquad here: https://www.youtube.com/watch?v=4t6OliwhJ5g
going to test it tonight!

[abcd567]

@ccz
Wow great!
Bi-quad & double bi-quad. I never tried this, but you inspire me to make one. Will do it on some week-end.

Mixing RF signals of 4 antennas and feeding to 1 receiver is tricky, and requires accurate phasing harness.

Mixing in software (VRS, modeSMixer etc) 4 bi-quad is possible if each antenna is connected to its own dedicated receiver. For 4 antennas, 4 receivers (dvb-t) are required. This is a costly solution, but possible.

Yes, I did use idea of integral whip, but it did not allow use of a connector. Your idea to pass the integral whip all the way through the F female barrel connector is brilliant.

[ccz]

I've seen them both a long time ago.
I think that the inspiration for the integral whip came from your no.2 post.


I had holidays but managed to finish 2 new antennas before leaving and tested them today.

They are pretty directional after 80-90nm but before that distance I seem to receive a lot of planes too. Maybe a lot of them are due to reflections.
The beam seems to be about 90 degrees wide. It catches double the amount of planes in that direction (compared to a 1/4 whip).
The message rate at ranges over 80nm is greatly improved indicating that it really has more gain.

It would be nice if it would be possible to stack 4-6 of these and feed them into 1 receiver but sadly it isn't possible from what I have read.


Construction:

Simple one:
1 x sheet 25/25cm of aluminum
1 x F connector
copper wire (from RG cable or other sources)

Double version:
1 x sheet of 50/25cm of aluminum
1 x F connector
copper wire

For both versions the sides of the sqares are 68.8mm.
The antenna is mounted 34.4mm away from the reflector.
I read that most people are shielding the main 2 posts that connect the antenna to F connector/joiner.
I have used the shielding from the RG cable for that.



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[abcd567]

@ccz
Great! Very innovative!
Thanks for detailed explanation.

Did you see my following two posts?

(1) Radials tightened by the nut. Click here (post #5) .


(2) The coax core continues to make an integeral whip. Click here.

.

[ccz]

@ccz
At last, after long wait...
Nice to read detailed report. At microwave, the hardware often behave unexpectedly. The net result is combination of many factors, and combination of little difference in each can result in substatial difference in overall performance.

Amazingly unexpected and the slightest misalignment/length mistakes produces a unworkable fixture.

Glad to see you broke the tradition of using SO239 connector (good only for VHF) and N connector (for UHF) and used F connector which is designed for microwave frequencies. The idea of soldering the radials to the nut is good. Others who used F connector, have soldered radials on the washer.

To be sincere, I was put off by the price of those connectors and the fact that F ones are readily available in almost any stores. Plus that they are used for SAT frequencies was reassuring enough.
The only specialty connectors I've bought are the MCX ones. I'm trying to avoid adapters or any other connectors on the cable run. As short as needed and as directly connected as possible seems to give the best results here.

I did try at first soldering to the washer but it was not sturdy enough for me. The nut, if soldered properly gives a much tougher result.

Since in the new spider you have placed few turns of wire below the nut, raising radials to the level where the whip starts, this might have improved the performance of your new spider.

This and using a continous center wire from cable trough F connector then the F joiner and to the whip also helped a lot too.

For outdoor use put few drops of hot melt glue or a sealent to prevent rain water or moisture entering the coax and corroding its braid and center conductor.

I will mix some fluid bicomponent gle and pour it around. That should take care of any moisture even better than silicone.

@ccz:
I did not understand your photo below. What is this? If you passed the core wire of feed coax all the way through the F female barrel to make the whip, then this is a very smart idea. I will also try this.

Exactly what I did, that picture is just to show an example that it is possible. At least with part of the F female barrels that I got.
I hated the fact that the whip was always moving around and the connection is actually pretty flimsy since there is no cable and F connector to support it. Plus the fact that from whip to MCX connector there's nothing else besides the small cable run.

I will have to post a picture of how I soldered the MCX connector to the RG59 cable.

PS: the wire through the barrel was at one time a radial for a spider connected just by tightening the nut. They were each (3 doubles making 6 total radials) at different height on the F connector. Not the best option but it worked nicely for a few tests.

[abcd567]

@ccz:
I did not understand your photo below. What is this? If you passed the core wire of feed coax all the way through the F female barrel to make the whip, then this is a very smart idea. I will also try this.

[abcd567]

@ccz
At last, after long wait...
Nice to read detailed report. At microwave, the hardware often behave unexpectedly. The net result is combination of many factors, and combination of little difference in each can result in substatial difference in overall performance.

Glad to see you broke the tradition of using SO239 connector (good only for VHF) and N connector (for UHF) and used F connector which is designed for microwave frequencies. The idea of soldering the radials to the nut is good. Others who used F connector, have soldered radials on the washer.

Since in the new spider you have placed few turns of wire below the nut, raising radials to the level where the whip starts, this might have improved the performance of your new spider.

I have once tried to avoid SO239 and use an F connector, but also avoided soldering as I have very poor soldering skills. Click here (post #5) to see it.

I also have tried to make a Spider without any connector at all. Click here to see.

For outdoor use put few drops of hot melt glue or a sealent to prevent rain water or moisture entering the coax and corroding its braid and center conductor.

[ccz]

Time flies... but in the meantime I managed to work a little on the air gap coco, ordered one antenna from ebay, and soldered my best spider until now.
The ebay coco is worthless, will try to sort it out with the seller.

The new spider antenna works really great, over 200nm coverage, bulk of received messages is at around 100-130nm.
It's a ~50nm improvement over my normal spiders/cantennas.

For this spider I used one male F connector and one F female joiner. RTL side is covered by a MCX connector adapted (soldered) to the RG59/U cable I used.
The cable is all copper with 0.6mm dia center wire. Attenuation is 13.02dB/100m at 100MHz, I expect it to be a lot over 30dB at 1000MHz.
Since the cable length is about half meter, it should be fine.
The second spider uses 11m of the same cable with identical reception. Weird, right?

The only different thing that I did comparing to other spiders is that the central coax wire was left longer by an extra F joiner + whip length.
The male F connector was mounted on the cable and the central wire was protruding by 10-11cm.
This was mounted through the F joiner with the central wire coming through and exiting for about 70-80mm. I trimmed it to 68.8mm.
On the F joiner I added some copper wire to allow the fixing nut to sit flush on the open end.
4 copper wires (I used 1.5mm appliance cable here) were soldered on the fixing nut and trimmed to 68.8mm length each.

[abcd567]

just wanted to make that clear to anyone reading the post.

A wise step to cover my mistake of not mentioning "add to these lengths, the length of pins at both the ends" . Thanks.

[SpaxmoidJAm]

just wanted to make that clear to anyone reading the post.

[abcd567]

your plan wont work, because if you cut to those lengths by the time you have trimmed of the outer needed to push the elements together they will non longer be the right length.

see image, [ATTACH=CONFIG]7875[/ATTACH]

that's your corrected wavelength

Yes, sure the lengths given by me do not include the pins on both ends. This is the way element lengths are specified in all designs on internet. The maker has to add required extra length for pins as it suits him. Pin length is not critical to design, and can be anything from say 10mm to 30mm.

Have you noted I mentioned to cut 6 lengths of 1.5 meters each? The length required without pins is 8 x 117 = 940 mm, say 1 m only. This additional 0.5 meter is for pins (8x2x0.025=0.4m).

[SpaxmoidJAm]

your plan wont work, because if you cut to those lengths by the time you have trimmed of the outer needed to push the elements together they will non longer be the right length.

see image, length.jpg

that's your corrected wavelength

[abcd567]

miniVNA €450
and a Signal generator, may be same price!

I can buy 20 very good quality commercial antennas for this money.

Purchase a 100 ft/30 m coil of cheap TV or Satellite coax, and a tape measure. Then cut 6 lengths of 1.50 meters each from this coil, and start cutting pieces.

8 pieces x 110mm (vf=0.8),
8 x 112mm (vf=0.81),
8 x 113 mm (vf=0.82),
8 x 114 (vf=0.83),
8 x 116mm (vf=0.84), and
8 x 117mm (vf=0.85).

Assemble the 6 cocos and try. At least one of the 6 will be good! Use the balance coax in the reel as your feeder coax. Cost < €10

[Rooster]

ALL TV sticks are 75 Ohm... but I wouldnt loose much sleep over the impedance, the rest of the homebrew antennae are going to be nowhere near calculated !!!!
As for using a 'scope - you are going to need very deep pockets for a 1 gHz version ! not to mention a sig gen that covers the frequencies.

If you are intent on spending money - you wont go far wrong with an analyser... such as :

http://miniradiosolutions.com/54-2/

[ccz]

That's right, but since I didn't have time to print the spacers, I assembled first the one with dielectric.

The version without will follow soon. First I want to try the oscilloscope method for tuning, it seems pretty bad that I can only do 1/4 wave antennas. I have to find out where I am making mistakes.


Are our RTL sticks 75 or 50 ohms? I saw it mentioned somewhere but can't put my finger on it right now.

Ahh, got it:

What is the RTL-SDR input impedance?

Since these dongles are intended for TV, all dongles will have an input impedance of about 75 Ohms. However, the mismatch loss when using 50 Ohm cabling will be very minimal at around 0.177 dB.

The 75 Ohm impedance for the R820T can be checked on the datasheet which can be downloaded here.