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Some years ago we needed to use HF (3 - 30 MHz) T-type Moonraker Antenna with ATU. Good antenna. I have no any connection with Moonraker as well. Best regards, Stefan DImitrov








>-------- Оригинално писмо --------

>От: "Bob Ecclestone VK2ZRE" becclest@...

>Относно: Re: [nanovna-users] Double Discone VSWR

>До: [email protected]

>Изпратено на: 03.08.2023 07:19


I am surprised some folk on this group have rubbished Moonraker Antennas.

I know Moonraker HF antennas are used on some Australian Navy ships, so

I don't think they are really "Dollar Shop junk."

I don't have any connection with either Moonraker or the the Australian

Navy.

So perhaps those with complaints may need to examine their installation

practices.

Or contact Moonraker or their dealer for support.

Just my 2c worth.



Cheers...Bob VK2ZRE





On 3/08/2023 2:33 am, Clyde Spencer wrote:

one has to consider the environment, not discussed prior in this thread. If

there were any metal or other electrically conductive material near the

antenna when tested that could be a possible cause for the difference in

measurement data and that which is published.

*Clyde K. Spencer*

On Wed, Aug 2, 2023 at 11:09?AM Jim via groups.io <teotwaki=

[email protected] > wrote:

This antenna is related to what antenna design literature calls a

“产颈肠辞苍颈肠补濒“

- - Biconical antennas have dipole characteristics. The double cone

elements structure contributes to their wider bandwidth. The antenna

becomes more broadband as the cone angle increases. - -

Search on that name for design and results discussions

Jim

On Thu, Aug 3, 2023 at 11:33 PM, John Nightingale wrote:

Cheap used cable from the ham flea market is not the choice for those
interested in the frequencies in use with discone antennas as Manfred will
confirm. Also, painful though it is, what was installed as brand new,
expensive and high quality, cable is none of that twenty years later.

Interestingly I cannot confirm that coax cable necessarily degrades over time! Of course, if cable gets waterlogged, it will degrade. But properly used, which means avoiding water ingress, it can last for a very long time. I sometimes measure the loss of the various transmission lines in my station, and even a long piece of RG8, that is over 40 years old, still meets its specs!

It's right that I wouldn't buy a used flea-market-special cable without thoroughly checking it. But I would also not disregard it as being certainly bad. If the price is good, and I need it, I would test it, and buy it if it's still fine. It's easy enough to take the NanoVNA to the hamfest!

Three dB of power being lost in a run of cable across the yard and all
the way up the tower will produce a most misleading impression in the
mind of the unsophisticated investigator.

Yes, that error happens to many hams. I remember one who asked me to check why he couldn't hit the local UHF repeater. His radio and antenna were both new, he said, and the SWR was fine. I went to his place. He lived in a second floor of a 22 story building, had run an RG58 feedline through a ventilation shaft all the way to the roof, and installed his antenna there - and there was a solder short in his coax connector at the upper end of the cable. The SWR, as measured at his second floor shack, was absolutely great...

To be fair, I have to mention that he was a new ham. But many hams have real trouble understanding that the more lossy the coax cable is, the better will the SWR be, and that's still not a good idea to use bad cable to improve the SWR!

I did some more experiments last weekend. I manufactured a disc and tested the antenna with a traditional disc(one) configuration by changing the top part, tested a piled version against different 4dec2 simulations, etc.

Comments about the feedline and the need for a balun are interesting, thanks. There can be CM currents messing up the readings, it would make sense.

I ordered a set of ferrites for a balun that should allow me to eliminate CM noise from outer coax shield (>1k impedance broadband). I hope that would change readings.

(I think this antenna is simple compared to more complex antennas and the built quality is good. I optimistically also think that when the manufacturer (known brand) and a professional reseller are clearly marketing that there is a TX range on 2m and 70cm, both should be visible in VSWR reading.)

If you are connected to a pc I put a clamp on ferrite on the usb cable. Also have to be careful if you are holding the vna as you become part of the antenna.

I made a large metal ground plane fixture and calibrate the cable connected to it about 15 feet away from the whips I test. Usually having two different readings is an indication of coupling isolation issues.

K8HTB Joe

I think we should all consider that the Discone is actually and improved
version of rhe Biconical dipole and not the other way around.