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Blowing a masthead SSPA


DAVID G4ASR
 

Hi everyone,

Has anyone built a masthead SSPA with integral blowers?   I'm just looking for ideas of how to bring air in & out without bringing in rainwater.

Its actually going to be used on 70cm, bringing my total of masthead transverter/lna/sspa boxes to a total of 5, up to the 3cm band.
It won't be permanently on the tower. Just fired up for 1-day a month, maybe on the tower for 3 days or so.

On my 1296MHz masthead transverter/sspa I have 2 blowers and bring the air in/out on 32mm plastic plumbing fittings that I can swivel so that the inlet/outlet
point downwards.   

As an aside, I'm going to be rebuilding my 13cm masthead system with a 3xLDMOS sspa and will be shifting a fair bit of air.
Ideally I would love to have the heatsink fins external to the masthead box but can't see a way of making it waterproof and able to be easily removed when I blow it up.
Maybe some type of flexible gasket? 
 
Be interested to see how you do it ?         

73, David G4ASR


John Quarmby
 

For my 3 and 6cm systems the heatsinks are external to the diecast waterproof box, sealed round the edges with non-corrosive silicone sealant. The 3cm section has forced air cooling with a hood over the fans, the heatsink fins are covered so air is pulled up through the fins from bottom to the top and then expelled by the two minature fans into the hood which keeps water off. It does need annual maintenance to remove spiders webs which tend to gum up the fans. This arrangement has worked for 20 or so years with the box outside on the tower throughout that time. The heatsinking is compromised a little by having the diecast box body in between the PA and heatsink, it wouldn't be too difficult to calculate the resulting increase in thermal resistance.

73

John G3XDY

On 20/02/2021 13:48, DAVID G4ASR via groups.io wrote:
Hi everyone,

Has anyone built a masthead SSPA with integral blowers?   I'm just looking for ideas of how to bring air in & out without bringing in rainwater.

Its actually going to be used on 70cm, bringing my total of masthead transverter/lna/sspa boxes to a total of 5, up to the 3cm band.
It won't be permanently on the tower. Just fired up for 1-day a month, maybe on the tower for 3 days or so.

On my 1296MHz masthead transverter/sspa I have 2 blowers and bring the air in/out on 32mm plastic plumbing fittings that I can swivel so that the inlet/outlet
point downwards.   

As an aside, I'm going to be rebuilding my 13cm masthead system with a 3xLDMOS sspa and will be shifting a fair bit of air.
Ideally I would love to have the heatsink fins external to the masthead box but can't see a way of making it waterproof and able to be easily removed when I blow it up.
Maybe some type of flexible gasket? 
 
Be interested to see how you do it ?         

73, David G4ASR

Virus-free. www.avast.com


Neil Smith G4DBN
 

On 20/02/2021 13:48, DAVID G4ASR via groups.io wrote:

As an aside, I'm going to be rebuilding my 13cm masthead system with a 3xLDMOS sspa and will be shifting a fair bit of air.
Ideally I would love to have the heatsink fins external to the masthead box but can't see a way of making it waterproof and able to be easily removed when I blow it up.
Maybe some type of flexible gasket? 

Hi David, when I want to move lots of heat through the wall of a masthead box, I usually cut a rectangular hole in the back or lid, them mill a flat plate with a raised centre the same thickness as the case, leaving about 20mm rim around the edge. I fit that plate to the inside of the box, sealing the overlapping rim to the inside of the box with sanitary silicone. Then I machine another slab (or a heatsink) to fit flush with the surface of box and raised bit of the heatsink on the outside, overlapping by 20mm or so. I drill and counterbore that to fit a pattern of shallow tapped holes in the stepped internal plate. I apply a layer of thermal compound to the exposed bit of the inside slab, and a bead of silicone around the overlap. Then I tighten the bolts and squish it in a press.

As there are no holes from outside to inside, and all faces are sealed with silicone and nipped tight, I've never had any problem with water ingress. Obviously, such an effective cold-bridge does mean you have to be acutely aware of any diurnal pumping which could drag moist air as the unit cools down on a damp evening, causing condensation.

On one system, the outside slab has a cylindrical hollow face machined in it so it fits perfectly to the face of a 50.8 mm thickwalled ally tube to which it is clamped. A smear of thermal compound and I get a lot of extra heatsinking for free.

http://www.g4dbn.uk/?p=917

Neil G4DBN



Paul G8AQA
 

There is a spray product called Midas Spider EX that is supposed to keep the spiders out of things.  I have tested it for flies and it works very well. I now use it on all box on the tower.  Read the can for precautions. Ideal for outside heat sinks.

73
Paul G8AQA

On 20/02/2021 15:13, John Quarmby via groups.io wrote:

For my 3 and 6cm systems the heatsinks are external to the diecast waterproof box, sealed round the edges with non-corrosive silicone sealant. The 3cm section has forced air cooling with a hood over the fans, the heatsink fins are covered so air is pulled up through the fins from bottom to the top and then expelled by the two minature fans into the hood which keeps water off. It does need annual maintenance to remove spiders webs which tend to gum up the fans. This arrangement has worked for 20 or so years with the box outside on the tower throughout that time. The heatsinking is compromised a little by having the diecast box body in between the PA and heatsink, it wouldn't be too difficult to calculate the resulting increase in thermal resistance.

73

John G3XDY

On 20/02/2021 13:48, DAVID G4ASR via groups.io wrote:
Hi everyone,

Has anyone built a masthead SSPA with integral blowers?   I'm just looking for ideas of how to bring air in & out without bringing in rainwater.

Its actually going to be used on 70cm, bringing my total of masthead transverter/lna/sspa boxes to a total of 5, up to the 3cm band.
It won't be permanently on the tower. Just fired up for 1-day a month, maybe on the tower for 3 days or so.

On my 1296MHz masthead transverter/sspa I have 2 blowers and bring the air in/out on 32mm plastic plumbing fittings that I can swivel so that the inlet/outlet
point downwards.   

As an aside, I'm going to be rebuilding my 13cm masthead system with a 3xLDMOS sspa and will be shifting a fair bit of air.
Ideally I would love to have the heatsink fins external to the masthead box but can't see a way of making it waterproof and able to be easily removed when I blow it up.
Maybe some type of flexible gasket? 
 
Be interested to see how you do it ?         

73, David G4ASR

Virus-free. www.avast.com


DAVID G4ASR
 

Thank you John XDY, Neil DBN, Paul AQA & Rainer DF6NA (email).

Excellent solutions.

I could either:

cut a slot in the 13cm masthead box and mount a suitable copper spreader etc  

or 

have a look in my outbuilding for a "Whitebox" I picked up a few months ago. It is very solid with heatsinking and designed for outdoor mounting.
I need to look first to see how easy it is to use, but that might be my preferred option. The 3 x LDMOS SSPA can potentially give 400W output. 

I've also got 4 x 100W C-band 6GHz solid state amplifiers with huge blowers that may prove useful. 
 
73, David G4ASR
 


Colin Ranson
 

Dave, 400w on 6cm ? that’ll QRM the Mars Lander !

 

De G8LBS.

 

 

Sent from Mail for Windows 10

 

From: DAVID G4ASR via groups.io
Sent: 25 February 2021 18:17
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] Blowing a masthead SSPA

 

Thank you John XDY, Neil DBN, Paul AQA & Rainer DF6NA (email).

Excellent solutions.

I could either:

cut a slot in the 13cm masthead box and mount a suitable copper spreader etc  

or 

have a look in my outbuilding for a "Whitebox" I picked up a few months ago. It is very solid with heatsinking and designed for outdoor mounting.
I need to look first to see how easy it is to use, but that might be my preferred option. The 3 x LDMOS SSPA can potentially give 400W output. 

I've also got 4 x 100W C-band 6GHz solid state amplifiers with huge blowers that may prove useful. 
 
73, David G4ASR