DIY Radome?

[JERRY TAYLOR]

I am completing a portable system (yagi on telescope tripod, raspberry pi 4, battery operation) that I hope to operate for extended periods remotely.  I need to provide protection from the elements and was wondering if a small pvc pipe frame with heat shrink wrap covering would work without degrading the hydrogen signal.  Has anyone built a simple radome?   What kind of problems might I encounter?  Heat, condensation, etc.?

Jerry Taylor

[Marcus D. Leech]

On 14/07/2024 14:07, JERRY TAYLOR wrote:

I am completing a portable system (yagi on telescope tripod, raspberry pi 4, battery operation) that I hope to operate for extended periods remotely.  I need to provide protection from the elements and was wondering if a small pvc pipe frame with heat shrink wrap covering would work without degrading the hydrogen signal.  Has anyone built a simple radome?   What kind of problems might I encounter?  Heat, condensation, etc.?

Jerry Taylor

Heat and condensation would be the big ones.   The shrink-wrap that's used for boats is typically a modified LDPE, and
  should be fine at 21cm frequencies.  Will there be some loss?  Yes.  But it will be quite small.

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[JERRY TAYLOR]

Maybe a bucket of Damp Rid for condensation and white LDPE shrink wrap?

The area would be small, maybe 50cu ft.

Jerry

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[bsn...@gmail.com]

Greetings...

Have you considered Tyvek?

Water-proof but breathable. I have no idea of its electrical properties but I'm sure DuPont does and others as well.

A search on: Tyvek electrical properties turned up a lot of info.

....GL......bill.....

[JERRY TAYLOR]

Tube sounds like a good idea.  I will check it out.

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[Marcus D. Leech]

On 14/07/2024 16:16, bsn...@gmail.com wrote:

Greetings...

Have you considered Tyvek?

Water-proof but breathable. I have no idea of its electrical properties but I'm sure DuPont does and others as well.

A search on: Tyvek electrical properties turned up a lot of info.

....GL......bill.....

Would certainly be more robust than shrink-wrap.

Genuine Tyvek(tm) is a woven HDPE material, so similar loss tangent to LDPE and PTFE.  Avoid anything made with
  PVC--the PVC molecule is polar, which makes it quite a bit more lossy than PE or PTFE materials (by a factor of 50 to
  90!!!!!).

Your PVC support members will be fine, since nearly all of the energy is propagating through the membrane, and
  not the support structure.  Keep the support members as thin as practical, given the mechanical constraints.

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[JERRY TAYLOR]

I just checked and I have a large roll of polyethylene 4mil painters plastic.  Won’t shrink or last as long as Tyvek.  Should this be rf transparent?

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[Marcus D. Leech]

On 14/07/2024 16:36, JERRY TAYLOR wrote:

I just checked and I have a large roll of polyethylene 4mil painters plastic.  Won’t shrink or last as long as Tyvek.  Should this be rf transparent?

As long as it's actually polyethylene.  There are also PVC painters drop-clothes, and they wouldn't be suitable.

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[bsn...@gmail.com]

If you do decide to use Tyvek not sure how you would attach it to your plastic pipe frame.

When used in house construction in is always stapled to either the wooden underlayment of the roof or the wood sheathing on the walls.

It is remarkably resistant to winds. 

Most Tyvek I've seen is white, a decent reflective sufrace. Howerver, I've recently seen canary yellow and blue and pink!

Again, GL.....bill....

[Alex P]

Use a Leg to cover the Yagi ....

[Lester Veenstra]

To repeat a very old hoarse:  Put in microwave. If it heats up it is not rf transparent

 

Lester B Veenstra  K1YCM  MØYCM  W8YCM   6Y6Y W8YCM/6Y 6Y8LV (Reformed USNSG CTM1)

les...@veenstras.com

 

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[JERRY TAYLOR]

Good idea Alex!  Two for the price of one also.  Maybe four?

Jerry

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[Joe McCauley]

I'm following this one with interest as I have a requirement for weatherproofing an L-band system (40cm diameter feed). I'm in Ireland and we get a reasonable ammount of rain & some of our winter storms are impressive.

I could just buy a marine type radome like https://www.osculati.com/en/11610-m-040591/glomex-spare-radome, but they are surprisingly expensive for what is essentially an empty box. These radomes are usually used to house radar or other antennas where the RX signal strength would be relatively high compared to a signal of galactic origin. I've asked a few manufacturers about RF attenuation figures, but no response so far. Another consideration is that these empty box units are actually essentially decorations to 'solve a problem of aesthetics and visual balance on the boat. To compensate for the installation of an antenna, you can install an empty antenna on the opposite side.'  In other words it seems people install them because lack of symmetry on their boats is somehow annoying.... They are probably identical in all respects to the one containing the antenna, but there is no info to confirm this I can find.

Anyone have any links to studies on various materiels from an RF point of view? A colleague suggested to me this morning that he could mould some PETG into a suitable domed cover. Google searches suggest PETG may not be great for this though I have not found anything particularly authoritative so far.

One doc I found suggested polyurethane foam might be a good option, but not sure how you'd shape it. (https://www.generalplastics.com/wp-content/uploads/2016/12/White-Paper-PU-Foam-Dielectric-Materials-for-Use-in-Radomes-and-Other_Applications.pdf)

Any advice on this would be gratefully received.

Thanks,

Joe

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[bsn...@gmail.com]

Joe,

Pretty sure PETG is NOT someting you want to use.

" PETG has applications in a range of industries due to being resistant to heat, impact and solvents. It is widely used for packaging (both retail and medical), advertising displays and electronic insulators."

https://www.twi-global.com/technical-knowledge/faqs/what-is-petg

[Joe McCauley]

Being an insulator is not a problem surely? But that website you gave does list one property which I imagine is a good reason not to use it -  'PETG can quickly take in moisture'. So in a damp environment, PETG may absorbe enough moisture to cause additional attenuation of signals you'd like to pass through it.

I think my colleague (who is not an RF expert) suggested PETG as its easily enough worked with. 

Thanks,

Joe

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[Marcus D. Leech]

On 16/07/2024 08:28, Joe McCauley wrote:

Being an insulator is not a problem surely? But that website you gave does list one property which I imagine is a good reason not to use it -  'PETG can quickly take in moisture'. So in a damp environment, PETG may absorbe enough moisture to cause additional attenuation of signals you'd like to pass through it.

I think my colleague (who is not an RF expert) suggested PETG as its easily enough worked with. 

Thanks,

Joe

Chemistry matters a LOT.  One would have to look up the loss tangent on the material (if it has ever been evaluated), and
  compare it to other, known-to-be-better materials like PTFE and PE.

There are many dielectric materials that have never been considered for RF applications, and thus there is little
  data on their loss tangent and other related properties.

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[Brad Thomas]

The article on polyurethane foam has an interesting graph of common materials and their loss tangent.  Plywood is quite bad, for example. Anything polar, as was said.

--Brad Thomas

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[JERRY TAYLOR]

I am going to try Alex’s idea of using parts from a Tyvek suit to protect components.  It is simple, cheap and I really don’t need a permanent solution although that is what I started to design.  Enough protection for a few days should suffice.  I am able to attach my H1 LNA, SDR and Raspberry Pi in one continuous line without coax or USB cables.  The Raspberry Pi is headless, controlled via VNC and my iPhone.

The total length is a little over a meter so parts from the Tyvek suit should cover everything nicely. I will add a little support for the components.  Power for everything comes from a deep cycle marine battery and a DC/AC converter which I already have.  I will do some drift scans for a few days to see how things work out.

Function over form!😊

Jerry

 

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[Joe McCauley]

I phrased that clumsily I guess. Apologies. PETG has been looked at at least at lower frequencies - https://www.mdpi.com/2227-9717/10/9/1881. Section 5 of their conclusions are not optimistic on its utility, but I'll try to understand the rest of the paper anyhow.

They reference these guys - https://www.proquest.com/docview/2557220898/fulltextPDF/9999CC48A1AD4B06PQ/1?accountid=14404&sourcetype=Scholarly%20Journals Not read this yet, but maybe others here are interested.

Lots of other references in there that could drag you down a rabbit hole:).

Joe

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[Alex P]

Polyurethane Foam: Dielectric Materials for
Use in Radomes and Other Applications
November 3, 2015

https://www.generalplastics.com/wp-content/uploads/2016/12/White-Paper-PU-Foam-Dielectric-Materials-for-Use-in-Radomes-and-Other_Applications.pdf

[Marcus D. Leech]

On 16/07/2024 10:13, Joe McCauley wrote:

I phrased that clumsily I guess. Apologies. PETG has been looked at at least at lower frequencies - https://www.mdpi.com/2227-9717/10/9/1881. Section 5 of their conclusions are not optimistic on its utility, but I'll try to understand the rest of the paper anyhow.

They reference these guys - https://www.proquest.com/docview/2557220898/fulltextPDF/9999CC48A1AD4B06PQ/1?accountid=14404&sourcetype=Scholarly%20Journals Not read this yet, but maybe others here are interested.

Lots of other references in there that could drag you down a rabbit hole:).

Joe

Something to keep in mind with lossy materials is that you pay two different, but related, prices.

One is the loss itself -- let's say it's 0.2dB (about 4.5% loss).    That also translates to a related Black-body equivalent
  emission temperature of about 13K at 20C or so.  As the material gets warmer, its apparent blackbody emission will
  track its physical temperature.   The limit is approached at 3dB loss, where the material will "look" like a
  Black-body at its physical temperature.

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[duncan campbell-wilson]

Hi,

Marcus is correct in  the above comment.

Protective environment requirement for a linearly  phased antenna array :

In the past I have used a polyethylene core flute for a rigid protective structure (radome). The material was a compromise between both signal loss /black body  radiation and environmental damage. Experience showed that native birds  would destroy, nest or deposit corrosive material on  the antennas.  The persistent  avian destruction would far outweigh the core flute material loss so an engineering trade off was made due to local environmental operating conditions .

Rgds Duncan

  

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[Marcus D. Leech]

On 16/07/2024 20:33, duncan campbell-wilson wrote:

Hi,

Marcus is correct in  the above comment.

Protective environment requirement for a linearly  phased antenna array :

In the past I have used a polyethylene core flute for a rigid protective structure (radome). The material was a compromise between both signal loss /black body  radiation and environmental damage. Experience showed that native birds  would destroy, nest or deposit corrosive material on  the antennas.  The persistent  avian destruction would far outweigh the core flute material loss so an engineering trade off was made due to local environmental operating conditions .

Rgds Duncan

Years ago, Ken Tapping discovered wasps nesting in his feed horn assembly.  Which actually wasn't much of a problem
  until the larvae-count started to climb.  The loss tangent of wasp larvae seems to be a couple of orders of magnitude
  larger than the loss tangent of adult wasps :)

We don't have any animal problems to contend with at our new observatory site, owing to the radome.  But at the two
  previous sites, it was an ongoing thing.  Even for the less-than-a-year we were at the Rideau Ferry site, we had
  a bird nest in our feed.  We also had a serious tick problem, and I had to be very vigilant about them when I was
  there.  Oh, also saw an Ontario Lynx at that site once.  It never nested in our feeds, however :) :)


At our Smiths Falls/Gallipeau Centre site, I twice disturbed the most magnificent snowy owl up on top of the roof.
  It occasionally liked to perch on the rim of our dish.  It was so very splendid that I didn't begrudge its occasional
  resting on our dish.

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