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 70MHz PA For Flex 6500 
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Post 70MHz PA For Flex 6500
I have a Kalmus 172F 200W linear amp. The spec. sheet states that It's a 50 dB amp, so if my calculations are correct it needs 0.5 mW drive to get the 200W out. I understand that the transverter TX port on my 6500 outputs 1mW? so that's in the ballpark with some attenuation between the port and the amp.
I also have a BER 4 Metre amp. that I could strip the PA from, and fit the Kalmus in the case, making use of the substantial heat sink and RF relay switching.
Can anyone see any problems with this set-up? and are my figures correct?


Mon Jul 11, 2016 3:35 pm
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 70MHz PA For Flex 6500 
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Post Re: 70MHz PA For Flex 6500
1 mw is 0dbm x 30 db = 1 watt

so I think 1 mw x 50 db = 100 watt

Im sure 50 dbw is 100kw watts

Mind, Im a bit rusty so check

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Mon Jul 11, 2016 5:44 pm
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 70MHz PA For Flex 6500 
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Post Re: 70MHz PA For Flex 6500
It might be a idea to make several attenuators and be able to switch them, to give a way to have lower power.


Mon Jul 11, 2016 6:30 pm
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 70MHz PA For Flex 6500 
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Post Re: 70MHz PA For Flex 6500
I may be wrong and not understand what your trying to do, but the flex doesn't output 70mhz from the transverter port it outputs what ever frequency you need to drive your transverter which is usually 28mhz at low power,

So you still need to transvert to 70mhz and then amplify

Trevor
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Mon Jul 11, 2016 7:07 pm
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 70MHz PA For Flex 6500 
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Post Re: 70MHz PA For Flex 6500
I think you will find that the Flex 6500 can output an IF of 100khz to 72Mhz on the transverter port!

Peter


Wed Jul 13, 2016 11:19 am
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 70MHz PA For Flex 6500 
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Post Re: 70MHz PA For Flex 6500
That's interesting I must investigate further

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Trevor
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MM0CEZ wrote:
I think you will find that the Flex 6500 can output an IF of 100khz to 72Mhz on the transverter port!

Peter

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Wed Jul 13, 2016 3:17 pm
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 70MHz PA For Flex 6500 
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Post Re: 70MHz PA For Flex 6500
I believe down east microwave were developing power amps for the flex series for 2 and 4m

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Wed Jul 13, 2016 7:55 pm
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 70MHz PA For Flex 6500 
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Post Re: 70MHz PA For Flex 6500
G4HTZ wrote:
I believe down east microwave were developing power amps for the flex series for 2 and 4m

I had a look at them. Hell of a price.


Thu Jul 14, 2016 5:41 pm
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 70MHz PA For Flex 6500 
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Post Re: 70MHz PA For Flex 6500
Just noticed dx shop are now doing their 300w 2 and 4m amps with 0db pre distortian drive from sdr radios
At extra cost

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Thu Jul 14, 2016 8:58 pm
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 70MHz PA For Flex 6500 
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Post Re: 70MHz PA For Flex 6500
Attachment:
DSC_2194b.jpg
DSC_2194b.jpg [ 161.81 KiB | Viewed 2285 times ]


The photo of the resistive attenuator circuit appears to show a Bridged T with 51 Ohm i/p and o/p resistors (50 Ohm in and out with no impedance matching)
The bridge resistor is 15 Ohm, and the shunt resistor 120 Ohm. If my calculations are correct then this is an approximately 3 dB attenuator.
What I don't understand is that the data sheet for the amp. states that it is a 50 dB amplifier, but the seller states that approximately 1W drive is required to get 200W out.
The first device in the amp. is an MRF136


Mon Jul 18, 2016 3:04 pm
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 70MHz PA For Flex 6500 
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Post Re: 70MHz PA For Flex 6500
Can you give the diagram of that attenuator?


Mon Jul 18, 2016 3:10 pm
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 70MHz PA For Flex 6500 
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Post Re: 70MHz PA For Flex 6500
I don't know the amplifier, but if it's spec'd at 1W in for 200W out that's a gain of 23dB.

If it is a 50dB module than at 200W output it must be being driven well into compression, you wouldn't be very popular on the bands with the resulting dirty signal :shock:

it may be that the attenuator drops the drive to the correct level. Too hot here atm to calculate it from your picture. But guess it would need to be around 27dB

Can you find any data for linearity tests?

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Mon Jul 18, 2016 5:59 pm
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 70MHz PA For Flex 6500 
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Post Re: 70MHz PA For Flex 6500
Attachment:
20160718_185414.jpg
20160718_185414.jpg [ 41.13 KiB | Viewed 2264 times ]


My fag-packet interpretation of the attenuator


Mon Jul 18, 2016 6:00 pm
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 70MHz PA For Flex 6500 
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Post Re: 70MHz PA For Flex 6500
gm0gtu wrote:
Attachment:
20160718_185414.jpg


My fag-packet interpretation of the attenuator



It's going to be less than 3db, the 15ohm resistor is too small for 3db


Mon Jul 18, 2016 6:26 pm
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 70MHz PA For Flex 6500 
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Post Re: 70MHz PA For Flex 6500
I've decided to buy one of Sam G4DDK's 7W PA kits to boost the output of the 6500 to a high enough level to drive the Kalmus to 160W. There is enough room in the box I'll be using to mount them both.


Tue Jul 19, 2016 4:55 pm
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