¿ªÔÆÌåÓý

  1. BITX20
  2. Topics

24 volt

 

Hi, got my BITX40 working and all looking good. Looking at doing some improving and read the final stage can be driven from 24 volt to give more transmission? power. It also looked at changing the heat-sink, as more power will produce more heat. I do not have much room for another heat-sink, so I thought I'd add a fan.?

Now the problem I have is the size of the fan. I found a nice PC cooling fan, only some 30mm square, trouble is on fitting it was very noisy., possibly as its a brush less one.

Still like the idea of a fan, so can anyone offer tips on how to remove the rf noise it makes, or where i can get a better fan of a similar size?

Many thanks Vaughn
 

Hi Vaughn,

The rule of thumb is: The smaller the fan, the noisier it is.? ?If You're short on room for bigger heat sink, is it not possible to lead the heat to the box?

Best Regards,
Jonas - SM4VEY

Den tors 6 juni 2019 kl 16:57 skrev Vaughn <vlkteach@...>:

Hi, got my BITX40 working and all looking good. Looking at doing some improving and read the final stage can be driven from 24 volt to give more transmission? power. It also looked at changing the heat-sink, as more power will produce more heat. I do not have much room for another heat-sink, so I thought I'd add a fan.?

Now the problem I have is the size of the fan. I found a nice PC cooling fan, only some 30mm square, trouble is on fitting it was very noisy., possibly as its a brush less one.

Still like the idea of a fan, so can anyone offer tips on how to remove the rf noise it makes, or where i can get a better fan of a similar size?

Many thanks Vaughn

 

Vaughn,

You might want to do some investigation on small linear amps that can be built for under <$100. uBitx.net has some references and there are several choices. There is one designed by a ham that won some price from the ARRL a while back that gets good reviews. (Wish I could remember his call letters - any help here?) Several ham kit suppliers, including the folks that make the cases for the ubitx sell a two board set (amp + filter). You can also get some on ebay for under $20, but you have to put them together. As designed, they are not that great. However, there are several blogs/websites that will help you fix them so they are respectable and on 12v give you between 40-60w (depending on band).?

Because I like a challenge, I bought the inexpensive one on ebay. Search for?

DIY Kits 70w SSB Linear HF Power Amplifier for Yaesu Ft-817 Kx3
There is a blog that also identifies a heat sink and box. Again you will want a filter system, and in my case, that cost several times more than the amp kit...

73
Mark





73
Mark
AJ6CU
 

I've been very happy with this fan /g/BITX20/message/53168
I've been using it for close to a year and still no noticeable noise in my ears or antenna.
--

 

A few years back ARRL had a PA contesting aiming for 40 watts or so.? Perhaps you are referring to the design by NM0S?? I can't find the schematic on the web - so this is little help to folk outside US that likely don't belong to ARRL (I wish they would make articles open source after 1 year !)

Here are some comments on it --



Please note some designs are optimized or configured for C -- careful bias adjustment is needed (as in the ubitx) for SSB linearity.?

On the ubitx - given expense of making a full set of 40 watt low pass filters - perhaps consider? building a PA for just 2 or 3 bands - where you may 'need' QRO.?

My first advice on the BITX and uBITX -- enjoy it some as is!? 5 watts on 40m SSB can cross oceans when the bands allow.?

73 Curt
 

Found the reference.... ?WA2EBY. ?Take a look at:

http://www.golddredgervideo.com/kc0wox/wa2ebyamp/??(pointer to availability of boards) and??and?

Although I am already committed to the ?ebay cheap amp, (nice construction with pointers to heat sync etc. at?. ) certainly tempted to look at. WA2EBY...

73
Mark
 

The WA2EBY is a great little qrp amp. I built one and love it, finding some of the boards might be tough but its a great amp.

?

Try Taydaelectronics for a Fan the sell some nice little ones I use for Pi's.
--
David

?N8DAH
 

Vaughn,
A brush-less fan is normally low on radiated EMI and is more likely problematic on conducted EMI (e.g. EMI current in the power and ground wires) There can be EMI radiated from the power / ground wires too, just like any signal wire.


I would suggest running the fan from an isolated / separate power supply (e.g. wall wart), with fan wiring away from your BITX40, and see if the "RF noise" persists.? If you are happy with the results, than discuss build options.? How the fan is physically wired, ways to filter.? In the case that the EMI affects RX quality, but not TX quality: one possible solution is to just power the fan on transmit, which would be fine if your total thermal solution can handle 100% TX duty cycle.

Simple filtering schemes have a series resistor on both power and ground close to the fan and a capacitor (or numerous capacitors of different decade values in parallel)? electrically shunted across the fan.

Regards,
Gary
 

N8DAH,

Boards are easy for the EBY amp.? FARCircuits has them.

Its a good design and allwos for getting good performance at higher frequencies.
Mine with a little effort does 37W on 10M (1.8W drive) and with the same drive at?
40M about 55W.? 80 and 20 are about 50.? Never though to try 15 or 17m but
I'd expect about 44w.? The 1.8W is because I use an attenuator at the amp input
as most of my HB radios do 4W which is excessive power or the amp.
FYI I run it at 28V.

It is a good amp mine is now 13 years old and still running the same set of IRF510s.
I did use a large heatsink (4x8" with 1" fins and the base thickness was .300").??
Some call it overkill but no fan with a brick on the key for 10 minutes is easy.

At least one of the "70W DIY AMP" I've seen did do that power for about 1 minute
into a dummy load?before it? blew up.? Likely self oscillation or overheat the
supplied heatsink was maybe pentium II vintage? with mounting points for
a fan and not at all large or highly finned.

Allison
 

Even Sunil vu3sua sells set of pcbs for EBY . BLACK MASKED PCBS.


On Fri, 7 Jun 2019, 9:43 pm ajparent1/KB1GMX <kb1gmx@... wrote:
N8DAH,

Boards are easy for the EBY amp.? FARCircuits has them.

Its a good design and allwos for getting good performance at higher frequencies.
Mine with a little effort does 37W on 10M (1.8W drive) and with the same drive at?
40M about 55W.? 80 and 20 are about 50.? Never though to try 15 or 17m but
I'd expect about 44w.? The 1.8W is because I use an attenuator at the amp input
as most of my HB radios do 4W which is excessive power or the amp.
FYI I run it at 28V.

It is a good amp mine is now 13 years old and still running the same set of IRF510s.
I did use a large heatsink (4x8" with 1" fins and the base thickness was .300").??
Some call it overkill but no fan with a brick on the key for 10 minutes is easy.

At least one of the "70W DIY AMP" I've seen did do that power for about 1 minute
into a dummy load?before it? blew up.? Likely self oscillation or overheat the
supplied heatsink was maybe pentium II vintage? with mounting points for
a fan and not at all large or highly finned.

Allison

 

HERE IS the related link




On Fri, 7 Jun 2019, 10:28 pm MVS Sarma via Groups.Io <mvssarma=[email protected] wrote:
Even Sunil vu3sua sells set of pcbs for EBY . BLACK MASKED PCBS.

On Fri, 7 Jun 2019, 9:43 pm ajparent1/KB1GMX <kb1gmx@... wrote:
N8DAH,

Boards are easy for the EBY amp.? FARCircuits has them.

Its a good design and allwos for getting good performance at higher frequencies.
Mine with a little effort does 37W on 10M (1.8W drive) and with the same drive at?
40M about 55W.? 80 and 20 are about 50.? Never though to try 15 or 17m but
I'd expect about 44w.? The 1.8W is because I use an attenuator at the amp input
as most of my HB radios do 4W which is excessive power or the amp.
FYI I run it at 28V.

It is a good amp mine is now 13 years old and still running the same set of IRF510s.
I did use a large heatsink (4x8" with 1" fins and the base thickness was .300").??
Some call it overkill but no fan with a brick on the key for 10 minutes is easy.

At least one of the "70W DIY AMP" I've seen did do that power for about 1 minute
into a dummy load?before it? blew up.? Likely self oscillation or overheat the
supplied heatsink was maybe pentium II vintage? with mounting points for
a fan and not at all large or highly finned.

Allison

 

That is where I got mine last I check though he was out of them. The one I made was overkill on the Heatsink as well, I did end up putting in the T-Pad so I could use 5W drive. It was a nice project and fun to build/use. I am running mine at 24v since I couldn't find a good solution to a nice 28v supply.
--
David

?N8DAH

1 - 12 of 12