Date   
Re: Fan Cooling at the Masthead

mike G6TRM
 


I missed a relevant bit out, I also fitted a sealed section of flexible tube (tumble trying tubing) from the inlet to the fan.
 
Mike G6TRM

----- Original Message -----
Sent: Sunday, June 09, 2019 11:43 AM
Subject: Re: [UKMicrowaves] Fan Cooling at the Masthead

My experience was to seal the electronics. fit a heatsink on the outside. fit it all inside a larger box with a fan blowing air on to the heatsink. Airflow is in through a hole in the bottom and blown out the top.
the bottom entry has a drip lip of 2-3 inches (tube) with a grill inside to prevent birds etc. the top has a similar tube with a inverted bowl on the top of that.( snorkel effect)
This prevents most rain/snow moisture form entering.
 
Mike G6TRM
----- Original Message -----
From: Ian White
Sent: Sunday, June 09, 2019 11:22 AM
Subject: Re: [UKMicrowaves] Fan Cooling at the Masthead

Definitely *blow* air directly at the baseplate from close range. A finned heatsink would be better, of course - and best of all, a ducted cooling system.

Blowing from close range gives a vast improvement in cooling compared with natural convection.  Left on its own, the surface of a heatsink becomes blanketed by a stagnant boundary layer of warm air, so the main purpose of the fan is to scrub away that insulating blanket. To do this efficiently needs turbulent air, which only exists immediately downstream of the fan. That is why it's so important to *blow* the air, and also to mount the fan close to the heatsink. Everywhere else (even immediately upstream of the fan) the airflow is much smoother and much less efficient for cooling.

So, the mistakes to *avoid* include:

= Sucking instead of blowing. The smooth airflow upstream of the fan is much less efficient for cooling, and meanwhile that useful turbulence goes somewhere else where it isn't needed.

= Mounting the fan too far away, just aiming hopefully in the general direction. Airflow always takes the easiest route, so it will not go between the fins of a heatsink until you have closed off all the easier options.

= Cooling the hottest components (usually the PA transistors) but then letting the hot air swirl around all the rest of the unit.

Attached is a photo of "one I made earlier" for a PA application where space was very limited. 50mm fans are the largest that would fit, so two fans are mounted side by side (rear of picture) and all the air  is ducted through the heatsink so none of the turbulent airflow is wasted. The hot air exits directly through the rear panel of the enclosure. Even with those two very small fans the cooling is very efficient, and also very quiet because the fans are buried deep inside the enclosure.

73 from Ian GM3SEK

On 09/06/2019 09:50, Andy G4JNT wrote:
I'm putting together a 24GHz personal beacon using white box modules and direct upconversion.  The Tx module is modified for direct drive to the mixer diodes, using modulated baseband generated  in a DDS.
Tested the whole assembly yesterday and it works OK, but the baseplate the whole assembly is mounted on gets far too warm - it is dissipating something like  18 Watts.
Testing with a small 12V fan blowing at the baseplate cooled it perfectly.  So if I want to run this in a box at the masthead for extended periods, the fan will be mandatory

Where and how is the best place to mount a fan on an external box?  and how do you keep out rain?   And where's the other port need to be to keep the air flow moving. 
 I think I want to blow air onto/past the baseplate rather than suck it past, simply because that works in practice sitting on the bench.  But don't have much experience of air cooling, especially in a closed environment.    Intuitively, sucking is better for keeping rain out, as the inlet port could be placed at the bottom of the box.  Or it could blow from the bottom.

Ideas, thoughts ...
(But beware - it could end up in a future RadCom column :-)

 

Virus-free. www.avg.com

Re: Radar Interference on 23cm

Murray Niman
 

On Sun, Jun 9, 2019 at 07:49 AM, Nicholas Shaxted wrote:
It is very likely to be from the radar system sitting by the motorway in Belgium, just outside Bruges in a small town called Jabbeke (51°11'30.01"N   3° 3'50.76"E), Take a look on GiggleEarth, or Bing, or OpenMap, or even a paper atlas.
Nick - that is rather unlikely - a bit more googling would have shown that particular one is one of many 5GHz C-band weather radars
http://radar.meteo.be/en/8243137-Jabbeke.html

73

 Murray G6JYB

Re: Fan Cooling at the Masthead

Reg Woolley
 

I have a large psu. When i got it the fan fitted sucked out air. I soon swapped to blow air. So it seems i did the right thing

Reg G8vhi 



Sent from Samsung tablet.

-------- Original message --------
From: Ian White <gm3sek@...>
Date: 09/06/2019 11:22 (GMT+00:00)
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] Fan Cooling at the Masthead

Definitely *blow* air directly at the baseplate from close range. A finned heatsink would be better, of course - and best of all, a ducted cooling system.

Blowing from close range gives a vast improvement in cooling compared with natural convection.  Left on its own, the surface of a heatsink becomes blanketed by a stagnant boundary layer of warm air, so the main purpose of the fan is to scrub away that insulating blanket. To do this efficiently needs turbulent air, which only exists immediately downstream of the fan. That is why it's so important to *blow* the air, and also to mount the fan close to the heatsink. Everywhere else (even immediately upstream of the fan) the airflow is much smoother and much less efficient for cooling.

So, the mistakes to *avoid* include:

= Sucking instead of blowing. The smooth airflow upstream of the fan is much less efficient for cooling, and meanwhile that useful turbulence goes somewhere else where it isn't needed.

= Mounting the fan too far away, just aiming hopefully in the general direction. Airflow always takes the easiest route, so it will not go between the fins of a heatsink until you have closed off all the easier options.

= Cooling the hottest components (usually the PA transistors) but then letting the hot air swirl around all the rest of the unit.

Attached is a photo of "one I made earlier" for a PA application where space was very limited. 50mm fans are the largest that would fit, so two fans are mounted side by side (rear of picture) and all the air  is ducted through the heatsink so none of the turbulent airflow is wasted. The hot air exits directly through the rear panel of the enclosure. Even with those two very small fans the cooling is very efficient, and also very quiet because the fans are buried deep inside the enclosure.

73 from Ian GM3SEK

On 09/06/2019 09:50, Andy G4JNT wrote:
I'm putting together a 24GHz personal beacon using white box modules and direct upconversion.  The Tx module is modified for direct drive to the mixer diodes, using modulated baseband generated  in a DDS.
Tested the whole assembly yesterday and it works OK, but the baseplate the whole assembly is mounted on gets far too warm - it is dissipating something like  18 Watts.
Testing with a small 12V fan blowing at the baseplate cooled it perfectly.  So if I want to run this in a box at the masthead for extended periods, the fan will be mandatory

Where and how is the best place to mount a fan on an external box?  and how do you keep out rain?   And where's the other port need to be to keep the air flow moving. 
 I think I want to blow air onto/past the baseplate rather than suck it past, simply because that works in practice sitting on the bench.  But don't have much experience of air cooling, especially in a closed environment.    Intuitively, sucking is better for keeping rain out, as the inlet port could be placed at the bottom of the box.  Or it could blow from the bottom.

Ideas, thoughts ...
(But beware - it could end up in a future RadCom column :-)
 

Virus-free. www.avg.com

Re: Fan Cooling at the Masthead

Neil Smith G4DBN
 

Tony G8DMU runs his 3.4/5.7/10GHz masthead PAs in closed thinwall plastic boxes with powerful internal circulation fans and no external heatsinking.  He has no problems of overheating despite dissipating 100W+ on transmit, so it is probably worth a test with a load and temp sensor on a bit of ally in a closed box with a decent fan and see what the steady-state temperature is in still air with 20W pumped in to the load.

H100 as water pipe - haha, brilliant.  One of the more stupid arrangements I tried was total-loss cooling with a PA on top of a 5m pole with a bung in the bottom of the 2 inch pipe and a hose attached to a standpipe in the garden. At the top, a bent bit of 10mm soft copper pipe directed a dribble of water on to the side of the masthead ally box.  Our water pressure is pretty low, but it only took a weak dribble to provide enough heat extraction. The flow rate was about half a litre per minute.

The weight of the mast increased by 8kg but it was well guyed and ran in a 2 inch ID ball race with a guy ring at the top on an extension pole.  Don't think I'd to that again though, EVER.  One of those ideas you have after waking at 3am after a steak supper and one-too-many glasses of claret.

I then worked out that if I used a pipe up and another down, and soldered a wiggle of the 10mm pipe to a slab of copper,  I could pump water under pressure up the first pipe, round the wiggles and then back down, and after that, just use the siphon effect with one bucket of water on a stepladder to another on the ground via the top of the mast.  That sort-of worked, but then I found that a centrifugal pond pump which can normally only manage a 1.5m head was perfectly happy pumping up 5m with the assistance of the siphon, so long as I started it with mains pressure.  Of course, it was a bit of a nightmare if any bubbles got into the pipe, then it needed repriming.

I never tried it any higher than 5m using the siphon approach because of the risk of the water near the top of the down pipe flashing to vapour under the reduced pressure.

I then used a positive displacement piston pump with a 10mm ID pipe to cool a PA on top of a SCAM using plain water and total loss.  That was a bit messy, but then found it worked fine as a closed loop so long as I used a restrictor valve at the output of the cooling plate to give some back pressure. I used that approach when testing the new 5.7GHz masthead PA, but then found that it stayed cool enough using passive cooling.

I am using fluid cooling on my new SHF PAs, but as it is a permanent installation designed to work outside, I use a strong solution of antifreeze in a closed loop.  It is only pumping to a max of 6m agl.  I have Hall effect flow monitors, pressure sensors and multiple temperature monitors to make sure the cooling is working effectively.

Neil G4DBN

On 09/06/2019 11:20, Mike Willis wrote:
Not about fans. Its always marginal with blowers outside. If its not water it's insects and birds. It is surprising how much heat a think aluminium pole takes away and also the dissipation of a large metal areas in free air. Failing that, water cooling is efficient and lightweight with a pair of hose pipes (or H100 coax) and a small pump.

Re: Fan Cooling at the Masthead

alwyn.seeds1
 

Dear Andy,

Sorry, this may all be a bit obvious, but is based on experience of masthead PAs, both commercial and amateur.

1. Isolate the airflow from the electronics, so that damp air cannot get at the electronics- otherwise condensation/corrosion can be a severe problem.

2. Use inlet and outlet tubes from the bottom of the enclosure, anything over 150mm long seems adequate for 70mm diameter tubes in British weather. The outlet tube draws air down from the top of the enclosure, of course. Fancy solutions include ducting to ensure uniform airflow across the width of the heatsink- but that is more necessary when you have 500W to shift than for the powers you are dealing with. 

3. Place the fan in the output tube, as the warmed drier air causes slower deterioration.

4. Use an airflow controller with alarm- Wisp or similar- to control fan speed and interlock for fan failure.

5. Insect screening- use flat perforated metal at the ends of the tubes for this to minimise insects being stuck and blocking airflow.

For 18W, I would have thought that coupling the plate to a vertical heatsink on the outside of the box with natural cooling would be ample, no forced air required.

Regards,

Alwyn G8DOH

 
_____________________________________________________

Alwyn Seeds, Director
SynOptika Ltd.,
114 Beaufort Street,
London,
SW3 6BU,
England.

Tel.: +44 (0) 20 7376 4110


SynOptika Ltd., Registered in England and Wales: No. 04606737
Registered Office: 114 Beaufort Street, London, SW3 6BU, United Kingdom.
_____________________________________________________

Re: 25mhz xtal

militaryoperator
 

I bought one of the Chinese small tcxo pcb units, about 30mm square.

It has a nice o/p on 25MHz, and 50Mhz and 75Mhz.............

I'm wondering if I need a LPF after it before feeding it into the LNB. Would the LNB 'see' the 50 or 75Mhz harmonic and get upset?

Ben.

Military Wireless Museum
Kidderminster, UK.


Re: 25mhz xtal

Andy G4JNT
 

The fist thing the chip does when  it gets its 25MHz reference input is square it up to g0 into a divider.

I've never really understood the urge many people seem to have to filter reference signals to a nice sine. 
 


Virus-free. www.avg.com


On Sun, 9 Jun 2019 at 16:15, militaryoperator via Groups.Io <Military1944=aol.com@groups.io> wrote:
I bought one of the Chinese small tcxo pcb units, about 30mm square.

It has a nice o/p on 25MHz, and 50Mhz and 75Mhz.............

I'm wondering if I need a LPF after it before feeding it into the LNB. Would the LNB 'see' the 50 or 75Mhz harmonic and get upset?

Ben.

Military Wireless Museum
Kidderminster, UK.


Re: Radar Interference on 23cm

alwyn.seeds1
 

Dear Sam,

Yes, this is certainly present, but at the site G6TRM refers to, there is sometimes extraordinarily strong interference in short irregular bursts- too short to be explained by A/S or tropo. shifts.

We’ll see how things are for VHF NFD and, if the interference occurs, I will take a look at spectrum and signature, other priorities permitting.

Regards,

Alwyn G8DOH

_____________________________________________________

Alwyn Seeds, Director
SynOptika Ltd.,
114 Beaufort Street,
London,
SW3 6BU,
England.

Tel.: +44 (0) 20 7376 4110


SynOptika Ltd., Registered in England and Wales: No. 04606737
Registered Office: 114 Beaufort Street, London, SW3 6BU, United Kingdom.
_____________________________________________________

Re: 25mhz xtal

militaryoperator
 

OK, I guess that's a NO then.

Sorry for asking what was obviously a stupid question. 

Ben.


-----Original Message-----
From: Andy G4JNT <andy.g4jnt@...>
To: UK Microwaves groups.io <UKMicrowaves@groups.io>
Sent: Sun, 9 Jun 2019 16:19
Subject: Re: [UKMicrowaves] 25mhz xtal

The fist thing the chip does when  it gets its 25MHz reference input is square it up to g0 into a divider.

I've never really understood the urge many people seem to have to filter reference signals to a nice sine. 
 


Virus-free. www.avg.com

On Sun, 9 Jun 2019 at 16:15, militaryoperator via Groups.Io <Military1944=aol.com@groups.io> wrote:
I bought one of the Chinese small tcxo pcb units, about 30mm square.

It has a nice o/p on 25MHz, and 50Mhz and 75Mhz.............

I'm wondering if I need a LPF after it before feeding it into the LNB. Would the LNB 'see' the 50 or 75Mhz harmonic and get upset?

Ben.

Re: 25mhz xtal

Mike Willis
 

I filter mine because to is combined with the IF on the coax. You don't want strong harmonics of the reference on the cable for several reasons. Also it cuts down any broadband noise and spurii from the reference that might otherwise cause trouble. In this case though if it is going inside the LNB I don't think its necessary.
--
Mike G0MJW

Re: Radar Interference on 23cm

SAM JEWELL
 

Thanks Alwyn,
Without hearing it (not always a reliable way to determine if its the same one) it is difficult to be sure.
However, not withstanding the more intermittent nature of what Mike hears, I would still be surprisedif the ‘Belgian’ radar was not heard regularly in that area. 
It will be interesting to see what you determine at  HF NFD.
Now I have our local rally (ESWR) involvement out of the way (today and very successful) I can spend a bit of time analysing the one I hear. Something I should have done long ago!
Prior to this one I used to hear a very ‘crackly’ sounding radar from that same direction. Then it disappeared and the one I hear now appeared. A change of radar type, perhaps?

Fascinating!.....

Sam

On Sunday, June 9, 2019, 4:22 pm, alwyn.seeds1 <a.seeds@...> wrote:

Dear Sam,

Yes, this is certainly present, but at the site G6TRM refers to, there is sometimes extraordinarily strong interference in short irregular bursts- too short to be explained by A/S or tropo. shifts.

We’ll see how things are for VHF NFD and, if the interference occurs, I will take a look at spectrum and signature, other priorities permitting.

Regards,

Alwyn G8DOH

_____________________________________________________

Alwyn Seeds, Director
SynOptika Ltd.,
114 Beaufort Street,
London,
SW3 6BU,
England.

Tel.: +44 (0) 20 7376 4110


SynOptika Ltd., Registered in England and Wales: No. 04606737
Registered Office: 114 Beaufort Street, London, SW3 6BU, United Kingdom.
_____________________________________________________

Re: 25mhz xtal

Clive, G3GJA
 

No, it isn’t a stupid question!

 

If you are intending to send the 25MHz reference as a square wave up a long length of coax to the LNB then you need to make sure that the impedance of the source is matched to the coax impedance as well as the terminating load in the LNB.

 

If you don’t, the square wave will become distorted due to the high levels of odd harmonics that get reflected. Using a low pass filter so that you end up with a sine wave solves all of these issues because the waveform will always fundamentally be sine no matter what mismatches you introduce.

 

I’ve seen counters and sig gens that failed to lock because the waveform was so badly distorted that the squaring circuit produced a multiple of the fundamental.

 

Clive G3GJA

 

 

From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> On Behalf Of militaryoperator via Groups.Io
Sent: 09 June 2019 16:24
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] 25mhz xtal

 

OK, I guess that's a NO then.

 

Sorry for asking what was obviously a stupid question. 

 

Ben.

 

-----Original Message-----
From: Andy G4JNT <andy.g4jnt@...>
To: UK Microwaves groups.io <UKMicrowaves@groups.io>
Sent: Sun, 9 Jun 2019 16:19
Subject: Re: [UKMicrowaves] 25mhz xtal

The fist thing the chip does when  it gets its 25MHz reference input is square it up to g0 into a divider.

 

I've never really understood the urge many people seem to have to filter reference signals to a nice sine. 

 

 

 

Virus-free. www.avg.com

 

On Sun, 9 Jun 2019 at 16:15, militaryoperator via Groups.Io <Military1944=aol.com@groups.io> wrote:

I bought one of the Chinese small tcxo pcb units, about 30mm square.

 

It has a nice o/p on 25MHz, and 50Mhz and 75Mhz.............

 

I'm wondering if I need a LPF after it before feeding it into the LNB. Would the LNB 'see' the 50 or 75Mhz harmonic and get upset?

 

Ben.

HESH Computer Services Limited Tel: (01482) 324936
12 Louis Pearlman Centre Web: www.hesh.co.uk
Goulton Street Registered in England No.: 3003479
Hull VAT No.: GB 647 3679 95
HU3 4DL

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Re: Radar Interference on 23cm

ian hope (2E0IJH)
 

At capel, near where you used to use Crete Down, There's really bad interence on 23cm and 70cm these days.
 
Ian
2E0IJH

 
Sent: Sunday, June 09, 2019 at 4:22 PM
From: "alwyn.seeds1" <a.seeds@...>
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] Radar Interference on 23cm
Dear Sam,
 
Yes, this is certainly present, but at the site G6TRM refers to, there is sometimes extraordinarily strong interference in short irregular bursts- too short to be explained by A/S or tropo. shifts.
 
We’ll see how things are for VHF NFD and, if the interference occurs, I will take a look at spectrum and signature, other priorities permitting.
 
Regards,
 
Alwyn G8DOH
 
_____________________________________________________
 
Alwyn Seeds, Director
SynOptika Ltd.,
114 Beaufort Street,
London,
SW3 6BU,
England.

Tel.: +44 (0) 20 7376 4110


SynOptika Ltd., Registered in England and Wales: No. 04606737
Registered Office: 114 Beaufort Street, London, SW3 6BU, United Kingdom.
_____________________________________________________

Re: Radar Interference on 23cm

alwyn.seeds1
 

Dear Sam,

Sorry, what I wrote was unclear. The ATC radars are audible pretty well continuously at that site, not usually loud enough to be a problem and with a rich amalgam of A/S.

This thing, though, is very strong- can pin the K3 S-meter to near end of scale- and you know how many dB above noise that is (about 110 dB for the non-K3 users). We have an interdigital filter before the pre-amp, so I think it is an in-band source.

Perhaps we can enlist the help of a military chum with some ARMs, in case we have trouble during VHF NFD.

Cheers,

Alwyn

_____________________________________________________

Alwyn Seeds, Director
SynOptika Ltd.,
114 Beaufort Street,
London,
SW3 6BU,
England.

Tel.: +44 (0) 20 7376 4110


SynOptika Ltd., Registered in England and Wales: No. 04606737
Registered Office: 114 Beaufort Street, London, SW3 6BU, United Kingdom.
_____________________________________________________

Re: Fan Cooling at the Masthead

John G3UUT
 

Andy,
I'm not an active microwaver but I lurk on this site because of the more erudite technical content than on your average forum (Boo Boo) a lot of which is relevant to VHF and HF anyway.  This preamble is necessary because my suggestion for cooling may be completely bonkers as I'm not up to speed on the dimensions of the various components involved, but if so have a laugh at my expensive anyway.

It seems to me that as it's "microwave" you may be or could be using waveguide which could be dual purposed to remove hot air upwards.  As it's a personal beacon it's likely to need some sort of slot antenna which I suspect is likely to be hollow and I'm sure some sort of cap could be devised to stop the rain getting in.  You may not need a fan at all as during hot weather when the waveguide and antenna are hot then there will be a higher flow of hot air upwards by convection effects anyway.  You will of course need an opening at the bottom of your box to let cool air in.  This will need to be protected by a pipe sticking down to stop rain getting in and a fine mesh gauze to stop the spiders. 
During cold weather you may have a problem with condensation forming on the inside of the waveguide/antenna.  As this is distilled water, with careful organisation of your plumbing you could utilise this distilled water for evaporative cooling of your PA.  Wait a minute, that sounds bonkers even to me. However you may need to ensure that it won't escape to places where it could cause damage.
Any mileage?
John G3UUT

On 09/06/2019 15:54, alwyn.seeds1 wrote:
Dear Andy,

Sorry, this may all be a bit obvious, but is based on experience of masthead PAs, both commercial and amateur.

1. Isolate the airflow from the electronics, so that damp air cannot get at the electronics- otherwise condensation/corrosion can be a severe problem.

2. Use inlet and outlet tubes from the bottom of the enclosure, anything over 150mm long seems adequate for 70mm diameter tubes in British weather. The outlet tube draws air down from the top of the enclosure, of course. Fancy solutions include ducting to ensure uniform airflow across the width of the heatsink- but that is more necessary when you have 500W to shift than for the powers you are dealing with. 

3. Place the fan in the output tube, as the warmed drier air causes slower deterioration.

4. Use an airflow controller with alarm- Wisp or similar- to control fan speed and interlock for fan failure.

5. Insect screening- use flat perforated metal at the ends of the tubes for this to minimise insects being stuck and blocking airflow.

For 18W, I would have thought that coupling the plate to a vertical heatsink on the outside of the box with natural cooling would be ample, no forced air required.

Regards,

Alwyn G8DOH

 
_____________________________________________________

Alwyn Seeds, Director
SynOptika Ltd.,
114 Beaufort Street,
London,
SW3 6BU,
England.

Tel.: +44 (0) 20 7376 4110


SynOptika Ltd., Registered in England and Wales: No. 04606737
Registered Office: 114 Beaufort Street, London, SW3 6BU, United Kingdom.
_____________________________________________________



Virus-free. www.avast.com

Re: Fan Cooling at the Masthead

Andy G4JNT
 

John
See the photo I posted earlier.  

The baseplate is 210 x 160mm
There is waveguide, and a small antenna - but they don't have much bulk at 24GHz
And you certainly don't want to mix water and mm band RF

I'm going to investigate the idea for rapid closed circulation of air, with a fan blowing directly on the baseplate, using the surface of the box for cooling
Neil's comment on how G8DMU does it.
Sounds a rather neat idea - if the box surface is adequate



On Sun, 9 Jun 2019 at 18:41, John G3UUT <g3uut@...> wrote:
Andy,
I'm not an active microwaver but I lurk on this site because of the more erudite technical content than on your average forum (Boo Boo) a lot of which is relevant to VHF and HF anyway.  This preamble is necessary because my suggestion for cooling may be completely bonkers as I'm not up to speed on the dimensions of the various components involved, but if so have a laugh at my expensive anyway.

It seems to me that as it's "microwave" you may be or could be using waveguide which could be dual purposed to remove hot air upwards.  As it's a personal beacon it's likely to need some sort of slot antenna which I suspect is likely to be hollow and I'm sure some sort of cap could be devised to stop the rain getting in.  You may not need a fan at all as during hot weather when the waveguide and antenna are hot then there will be a higher flow of hot air upwards by convection effects anyway.  You will of course need an opening at the bottom of your box to let cool air in.  This will need to be protected by a pipe sticking down to stop rain getting in and a fine mesh gauze to stop the spiders. 
During cold weather you may have a problem with condensation forming on the inside of the waveguide/antenna.  As this is distilled water, with careful organisation of your plumbing you could utilise this distilled water for evaporative cooling of your PA.  Wait a minute, that sounds bonkers even to me. However you may need to ensure that it won't escape to places where it could cause damage.
Any mileage?
John G3UUT

On 09/06/2019 15:54, alwyn.seeds1 

Re: Radar Interference on 23cm

SAM JEWELL
 

Umm, that does sound like something else again. Such is the nature of our shared band!
I got  diverted earlier. I brought the EME dish down towards the horizon to check the radar but the Belgian EME beacon on 1296MHz was being received at good strength (by EME) so I went off to investigate any activity on the moon!
Just a W......
Sam

On Sunday, June 9, 2019, 5:53 pm, alwyn.seeds1 <a.seeds@...> wrote:

Dear Sam,

Sorry, what I wrote was unclear. The ATC radars are audible pretty well continuously at that site, not usually loud enough to be a problem and with a rich amalgam of A/S.

This thing, though, is very strong- can pin the K3 S-meter to near end of scale- and you know how many dB above noise that is (about 110 dB for the non-K3 users). We have an interdigital filter before the pre-amp, so I think it is an in-band source.

Perhaps we can enlist the help of a military chum with some ARMs, in case we have trouble during VHF NFD.

Cheers,

Alwyn

_____________________________________________________

Alwyn Seeds, Director
SynOptika Ltd.,
114 Beaufort Street,
London,
SW3 6BU,
England.

Tel.: +44 (0) 20 7376 4110


SynOptika Ltd., Registered in England and Wales: No. 04606737
Registered Office: 114 Beaufort Street, London, SW3 6BU, United Kingdom.
_____________________________________________________

Re: 25mhz xtal

militaryoperator
 

No, it isn’t a stupid question!
 
If you are intending to send the 25MHz reference as a square wave up a long length of coax to the LNB then you need to make sure that the impedance of the source is matched to the coax impedance as well as the terminating load in the LNB.
 
If you don’t, the square wave will become distorted due to the high levels of odd harmonics that get reflected. Using a low pass filter so that you end up with a sine wave solves all of these issues because the waveform will always fundamentally be sine no matter what mismatches you introduce.
 
I’ve seen counters and sig gens that failed to lock because the waveform was so badly distorted that the squaring circuit produced a multiple of the fundamental.
 
Clive G3GJA
 
 
Many thanks Clive.

Ben G4BXD

Re: 25mhz xtal

Paul G8KFW
 

Hi I think a lot of use will be requiring

 

10 Mhz distribution amplifiers and filters  any one found a good value solution  

 

Regards Paul

 


From: UKMicrowaves@groups.io [mailto:UKMicrowaves@groups.io] On Behalf Of militaryoperator via Groups.Io
Sent: 09 June 2019 21:43
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] 25mhz xtal

 

No, it isn’t a stupid question!

 

If you are intending to send the 25MHz reference as a square wave up a long length of coax to the LNB then you need to make sure that the impedance of the source is matched to the coax impedance as well as the terminating load in the LNB.

 

If you don’t, the square wave will become distorted due to the high levels of odd harmonics that get reflected. Using a low pass filter so that you end up with a sine wave solves all of these issues because the waveform will always fundamentally be sine no matter what mismatches you introduce.

 

I’ve seen counters and sig gens that failed to lock because the waveform was so badly distorted that the squaring circuit produced a multiple of the fundamental.

 

Clive G3GJA

 

 

Many thanks Clive.

 

Ben G4BXD

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--
Paul Bicknell G8KFW   South Coast UK

Re: Fan Cooling at the Masthead

PAUL NICKALLS
 

Andy,

As no-one else has mentioned it I will repeat the recommendation from GM3SEK to spray the exposed electronics with a conformal coating.
Electrolube "Acrylic Protective Lacquer"  CPC Order code SA00362 is an example. Datasheet is found at:-
http://www.farnell.com/datasheets/2032232.pdf

I have the fan in box problem on the bench at the moment.  It is the stepper motor driver for a high speed rotator I am making.  I get very bored with a 1 RPM commercial rotator during a contest.  As I have a surplus well finned box I think I will mill a flat inside to get good conduction to the side of the heatsink and allow the small incorporated fan to do a bit of stirring inside.

I have recently installed a heatpipe cooler for the CPU in the new computer. It has a big radiator with 2 x 100mm fans.  There must be mileage in these to separate weather from the electronics.  My personal preference however is no moving parts but a big external heat sink.

Paul G8AQA


On 09/06/2019 18:58, Andy G4JNT wrote:
John
See the photo I posted earlier.  

The baseplate is 210 x 160mm
There is waveguide, and a small antenna - but they don't have much bulk at 24GHz
And you certainly don't want to mix water and mm band RF

I'm going to investigate the idea for rapid closed circulation of air, with a fan blowing directly on the baseplate, using the surface of the box for cooling
Neil's comment on how G8DMU does it.
Sounds a rather neat idea - if the box surface is adequate



On Sun, 9 Jun 2019 at 18:41, John G3UUT <g3uut@...> wrote:
Andy,
I'm not an active microwaver but I lurk on this site because of the more erudite technical content than on your average forum (Boo Boo) a lot of which is relevant to VHF and HF anyway.  This preamble is necessary because my suggestion for cooling may be completely bonkers as I'm not up to speed on the dimensions of the various components involved, but if so have a laugh at my expensive anyway.

It seems to me that as it's "microwave" you may be or could be using waveguide which could be dual purposed to remove hot air upwards.  As it's a personal beacon it's likely to need some sort of slot antenna which I suspect is likely to be hollow and I'm sure some sort of cap could be devised to stop the rain getting in.  You may not need a fan at all as during hot weather when the waveguide and antenna are hot then there will be a higher flow of hot air upwards by convection effects anyway.  You will of course need an opening at the bottom of your box to let cool air in.  This will need to be protected by a pipe sticking down to stop rain getting in and a fine mesh gauze to stop the spiders. 
During cold weather you may have a problem with condensation forming on the inside of the waveguide/antenna.  As this is distilled water, with careful organisation of your plumbing you could utilise this distilled water for evaporative cooling of your PA.  Wait a minute, that sounds bonkers even to me. However you may need to ensure that it won't escape to places where it could cause damage.
Any mileage?
John G3UUT

On 09/06/2019 15:54, alwyn.seeds1 


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