Dummy aerial - 4 to 8 cm ( or specifically 5.5 Ghz) - suggestions?

[Al (astral highway)]

Originally Posted by Skywave

Al -

A further thought.



Would it be possible to reconfigure the PSU and its filters * so that you can use an external transformer + rectifiers running from domestic 50Hz mains to provide the necessary dc voltages for the unit and then build a low-power 400Hz oscillator to provide the required 400Hz for the time-base?

* e.g. increasing the value of the smoothing caps.

Al / Skywave.

Al,

That's a great idea. I think it would work very well, so thanks.

[Al (astral highway)]

Originally Posted by M0AFJ

Well it could need quite a lot of work if its not been run for a while, hope its not got Hunts in it !!

What data do you have?(Part number, manufacturer etc), so I can do some hunting around.

Cheers
Tim M0AFJ/G8GGP

Hi Tim, I'd certainly appreciate that. It's an RCA AVQ-10, whose power demands are now also the subject of this thread.

https://www.vintage-radio.net/forum/...ad.php?t=23008

[Al (astral highway)]

Originally Posted by ppppenguin

I don't know what anode voltage this radar uses but you don't get any Xrays below about 17kV.

And I don't know yet, but I do know that 20Kv isn't an unusual anode voltage for radar modulators and magnetrons. That's just a tad more than the 3,800 v that we have in our kitchen microwave ovens, right?

I read somewhere (a vintage article on the subject) that because of the very low duty-cycle, anode voltages were sometimes hugely exceeded. Oh, and tube heaters were also over-run (clearly reducing tube life) to increase electron emission.

[Phil G4SPZ]

Originally Posted by astral highway

I may be acquiring a vintage weather radar and instead of propogating hefty (75Kw for the 2us pulse duration) signals through a waveguide and antenna, was thinking how I could test it with a dummy aerial instead.

Does one need a licence to radiate amateur radar signals?! There is an amateur band at 5.7GHz but I don't think radar is a recognised mode of transmission!

Phil

[Al (astral highway)]

Originally Posted by G4SPZ

Does one need a licence to radiate amateur radar signals?! There is an amateur band at 5.7GHz but I don't think radar is a recognised mode of transmission!

Phil

Hi Phil and thanks. That's an interesting situation, isn't it? How do 'they' define radio? They must be focussing on the application rather than the means of propagation.

[Station X]

The amateur licence used to define what modes of modulation could be used and I think it included pulse type transmissions for radar experiments. However all that information has been removed from the latest licence. The licence does talk about communicating though and I don't think radar is a means of communication.

[MichaelR]

I think it would be prudent and the act of a responsible person to make absolutely sure that you can operate the radar.

Implications of interference ,safety etc

[Al (astral highway)]

Originally Posted by MichaelR

I think it would be prudent and the act of a responsible person to make absolutely sure that you can operate the radar.

Implications of interference ,safety etc

Indeed, you're absolutely right. That's why I've talked in earlier parts of this thread about using a dummy aerial/load, about conducting tests for durations of just milliseconds, about derating the HT+ power supply to reduce pulse power, isolating the magnetron and so on.

Rest assured that there's no question of my pointing the waveguide out of the window and firing the thing up blindly at full power!

[russell_w_b]

Originally Posted by Skywave

Provided, of course, that the electrons are moving in a vacuum - (which is applicable in this case).

Al / Skywave.

I thought the figure was as low as 8.9kV (for copper electrodes inside valves) before X-Rays started to be emitted?

[russell_w_b]

Originally Posted by G4SPZ

Does one need a licence to radiate amateur radar signals?!

One definitely needs a licence to radiate professional RADAR signals!

[Phil G4SPZ]

Originally Posted by Station X

The amateur licence used to... include pulse type transmissions for radar experiments. However all that information has been removed from the latest licence.

Yes, I remember that from my early days in the 80s, but I did check the latest regulations before posting, and it no longer seems to be permitted. Al, if you hold an amateur licence (or you know a licenced ham) you/he/she could always apply for a Notice of Variation. The amateur licence is still based on the notion of encouraging experimental work (though few do much these days) and NoVs can be issued for all sorts of experimental purposes.

I may be wrong, but if you don't hold an amateur licence, then it seems to me that the transmission of RF power into anything other than a non-radiating dummy load would contravene the Wireless Telegraphy Act unless you can find an ISM frequency allocation, and prove that your weather radar operates in that band, is type-approved and WT licence exempt... all highly unlikely, I expect...!

Phil

[Al (astral highway)]

Originally Posted by G4SPZ

...it seems to me that the transmission of RF power into anything other than a non-radiating dummy load would contravene the Wireless Telegraphy Act unless you can find an ISM frequency allocation, and prove that your weather radar operates in that band, is type-approved and WT licence exempt... all highly unlikely, I expect...!

Phil

Hi Phil, and thank you. Of course.

Just to reassure, you, let me plainly state that what I'm intending to do is to restore the radar, not operate it for its own sake.

In the process, I will:


1) initially isolate the magnetron
2) test each sub-circuit independently
3) test the entire set, including the magnetron at a voltage and into a non-radiating dummy load
4) test the entire set, including the magnetron, at full voltage into a suitable, non-radiating dummy load.

Once I have finished restoring the set, I will again remove the magnetron and keep it away from the rest of the set so that the apparatus can't be used by the unwary.

I'll then move on to restoring a suitable indicator unit, so plenty of other challenges lined up to keep my happy.

But that's another story and another thread, if it ever comes to that.

Thanks for your interest

[M0AFJ, Tim]

Al, I think it will be a while before you are ready for the load, PM me before the event and I'll arrange to come down, I'm sure I'll be able to find a suitable non-radiating load, I don't, however think I'll apply for a NoV to my amateur licence!!

Cheers
Tim M0AFJ

[M0AFJ, Tim]

When you get the unit can you let me have precise dimensions of the WG O/P, it looks like it should be WG14 (US WR137), and the flange mounting sizes.
Thanks
Tim M0AFJ

[Al (astral highway)]

Originally Posted by M0AFJ

When you get the unit can you let me have precise dimensions of the WG O/P, it looks like it should be WG14 (US WR137), and the flange mounting sizes.
Thanks
Tim M0AFJ

Hi Tim, yes I'll PM you when it comes down, with the WG dimensions. Many thanks for your interest and offer to help.

[Sean Williams]

Seeing as this thread has strayed so much I am going to close it