Bert Modderman Engineer


Products for Sale
13cm 12 watt
13cm 40 watt
MRF284 proj.
Lot sales
Custom build

13cm filters
23cm filters

Dish calcs.
Quad ant.


ATV Hobby
Dro Modulator
Echostar Mod
Received ATV


Before i continue with building more 250 watt amplifiers, i want to see if they are able to be cooled for atv.
If not, i must change the design or make an option available for an amp that consist of a copper base.
For now it looks ok, i can cool a 250 watt atv amplifier with water. (the acryl version below)
I cant rush with selling these 250 watt amps, the design is mostly done, what remains is filters and protection.
the 250 watt amp goes beyond 400 watt in saturation. such a pitty that the p1db kicks in so early.

This cooler is menth for the 500 watt atv amp:

Acryl must not get hot during milling or it will crack. It leaks a little bit. will replace it later with a delrin top.
If it didnt crack, it would have been one of the most beautifull things i ever made.

I finished a 4 transistor 500 watt 1252mhz atv amplifier today.
This means the 1296mhz 250 watt versions are not far away now.
Probably continue with them this week.

The 500watt amp is watercooled and probably later 200 watt or 400 watt peltier elements will be added to the waterloop.
I can only transmit a few minutes before the water gets warm, even with a big radiator with 2 24 volt blowers.
With every power increment from 50 watt on to 500 watt i could notice improvements in picture quality.
Picture showed some packet disturbance in the picture which got less on 500 watt.
PI6ATV is 115 km away from me and there was some temp inversion going on so i was stronger then usual.
In normal nice weather conditions im received with extreme fading and with cloudy weather not at all.

Local repeater station had a little bit of trouble with the harmonic from the 23cm amplifier so i made a simple 28db
harmonic suppressor with only 0.1db loss at 1280mhz. filter works best at its designed frequency.
this version was made waterproof.
1 connector is missing to show rubber ring for water protection..
Filter could be expended with another 1/4 stub to reach near double its suppresion
but also double its losses in the passband.
If you want 60db + harmonic suppression look in 23cm filters section.

Finished the new 150 watt 23cm model today.
1296MHz 7 watt in and approx 150 watt out or 10 watt in 180watt out (saturation).
The fets are mrf286 or xrf286.
Amplifier can also be used for atv but requires a big heatsink.
Thermal stability is good, fets are soldered directly onto big brass plates.
harmonic suppression is good with an additional filter, without filter the suppresion at 2600 is only 30db.
price for ready build in alu case: 250 euro.
i also make bigger amplifiers 250 watt 500 watt or 1 kw. ask for prices.

Improved again my amplifier design with new low loss pcb.
The single transistor amplifier version for 23cm is now making 80 watt with only 3watt input.
Below is the first prototype with this kind of pcb.

build a few weeks ago for an eme amateur, a 500 watt 1296mhz amplifier. watercooled. crazy.
and offcourse its made with filters. without filter the amp would make 500mw on 2600mhz.
this amp was capable of warming up a few meters of h2000.

And another awsome watercooled amplifier.
Its a single fet 13cm 150 watt out 4 watt in. Such fets can only opperate proper with watercooling.
This amplifier is 240 euro.
At 32volt and approx 6 watt in it reaches 200 watt but then a case of brass or copper is needed.

In the test process i had two 8meter H2000 cables connected together via cheap N couplings.
At this point it caries approx. 100 watt at 2380mhz and it liquified the plastic inside.
The left one is molten and the right one is ok which only had to carry only 60 watt.

An 8420 MHz septumfeed with horn. Its made for

Pictures at the links in the metalworking section have been added to 'milling' and a new section lathe (dutch: draaibank) has been made.

More and more people are switching to watercooling.
Here is another pillar design for the 170watt 23cm amplifier:

We had huge thunderstorms last night. It was amazing.
Stayed awake till 5:30, made 500+ pictures from which 125 had a lightning.
Click on the picture for more.

A filter is now available for 100 euro and completely adjustable with 2 notch filters.
Thanx to PE1KYC who improved and adjusted the design of DC9XG for atv use (below on this page)

Here the filter is tuned for 2345-2390 bandpass and its blocking wifi and everything from 2410 and above:

The bandpass has 0.5db loss. The 40db value could be more becuase that was the end of my watt meter.
This is the best the filter can do, i could not get the bandpass wider or the bandstop closer.
Without network analyzer it is very hard to allign the filter like this.

A picture given to me from PE3ATV, who bought a strong 23cm amplifier from me, showing that RG213 cannot withstand 500 watt on 23cm for a long time.

I have been working now for half a year on the new design of the 23cm amplifiers.
The design has been greatly improved on several points:
The drain resistors have been removed, they got to hot.
The input 50ohm dummy which also got hot, has been replaced by a flange type.
The entire pcb is now teflon, instead of just the combiner. In some occasions the epoxy started burning.
I have put more effort into the precision of the hybrid couplers.

The continuous effort in perfecting this amp has resulted that i have managed to get a 1296 version peak to 210watt in complete saturation.
Offcourse in continuous use it is not recommended to use the amp in saturation this far.
I could rate this particular amp at 170 watt linear.
But 160 watt should be considered ok for continuous use in FM/ATV.
Those versions need to be tuned more broadband and power and gain is lost in this process.
Linearity of the new design varies around 160 watt. Minimal 150 watt at which i will put them for sale.
Although it costs more money to make now, the price will remain the same, 250 euro.
Also couplers can be ordered which are usable up to at least 350 watt.

Watercooling milled in a 1296mhz 2 transistor 150 watt amplifier.
(case is not yet finished)

A 76 GHz fresnel from acrylic made on my milling machine. diameter 9.5cm and 1cm thick

Another custom horn for 47ghz. 20.3DBi gain with 4mm waveguide and holes simular to WR10 flange.

I made a youtube channel and i got some movies on it.
my milling machine moves a bit silly and its all not finished.
but it works and mills nice things for me.

a 5mw prototype atv transmitter on 6cm with baseband in. working on pcb 125 euro. (better looking then this one but with no display or rotory encoder)
vco oscillates on 6cm and is locked will pll on 250khz steps. 200khz steps is also possible with different crystal.
this version works from 5150 to 5900. a rotory encoder can be connected and/or up-down buttons. stepsize adjustable for the rotory encoder.
1 programmable memory so it can power up on a desired frequency.
custom designs, based on this system, can be ordered.

custom made horns can now also be ordered. horns for 24ghz and 47ghz are 50 euro a piece.
47ghz custom horns:

24ghz custom horn

another waterblock experiment, this time with o ring in a milled groove and pillars for more heat transfer.

The 100 watt amps i sell do get a little hot so i suggested watercooling for a recent purchaser of the amp.
With a radiator and blowers and a small aquarium pump it works awesome.
power dropped only 2 or 3 watt after 2 minutes and stays like that.
Heatsinks cant compete with that.
I used tapered bsp threaded water connectors with sealing tape.
On the right you can see my first actual works of CNC machining with feedback from the table.
The amp does 95 watt on 2320 with 2 watt input.

Finished working today on a DC9XG 13cm filter for harry PA2HOS.
Originaly intended filter for 2320 but can be used on 2350 with almost same characteristics.
i measured 0.6db loss at 2330 mhz with a usable bandwidth of about 8-10mhz.
-3db bandwidth is little under 50 mhz.

A Friend came to me (PE1JTU) with an oscillating M57762. Looking at its casing and design i made a new case and pcb for him.
For those who also have problems with their M57762, this pcb is available for 8 euro.

i still had the old watercooling laying around from my previous computer so i figured,
why not an amp on watercooling.
the fet is normaly pretty hot on aircooling and is now almost cold and the aluminium is even colder.
fet dissipates 40 watt and makes 40 watt on 13cm with 1.3 watt drive.
tested pcb and fet is available for 60 euro.
that is without watercooling system which is only a testsetup and normaly not required but
it should do nice on a 100+ watt system which im gonna build soon for 13cm.

made for a recent project: a dj9bv coupler to combine two 120 watt amps and make 240 watt ssb on 1296mhz.

the old 13cm 8 watt amp =)