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uBitx as IF rig for transverter

John Kemker
 

Ordering a uBitx v6 Thursday to use as a transverter rig for a transverter that needs between 1 mW to 750 mW input on 10m.? Anybody have any suggestions on how to mod the uBitx to limit output to around 500 mW?

73 de W5NNH
 

John, realizing it¡¯s not quite what you are asking for you might take a look at the Transverter-Store attenuator board.? It¡¯s got on board in/out switching and is only 20 bucks shipped.? I went that way rather than modifying the uBITX.

73 Scott Ka9p

On Mon, Jun 14, 2021 at 11:13 AM John Kemker <kemkerj3@...> wrote:
Ordering a uBitx v6 Thursday to use as a transverter rig for a transverter that needs between 1 mW to 750 mW input on 10m.? Anybody have any suggestions on how to mod the uBitx to limit output to around 500 mW?

73 de W5NNH

 

John - Couldn't you just turn down the PA BIAS until you get the output you need?

73,

Justin
KI5GKD
 

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he can turn down "drive" to get lower output

turning down bias makes distorcion (clas c and not class a or class ab)

so drive lower ... yes ... bias lower ... no

in fact a higher bias gives cleaner signals (with a bit more heat)

greetz sigi dg9bfc

Am 14.06.2021 um 19:52 schrieb Justin Bowser - KI5GKD:

John - Couldn't you just turn down the PA BIAS until you get the output you need?

73,

Justin
KI5GKD

 

You need to keep the PA operating within its linear range.? Turning down the bias?
may make it operate in its non-linear range.? Take a look at the load line diagram
in the device datasheet to see how much you can adjust the bias without causing?
problems.

Arv
_._


On Mon, Jun 14, 2021 at 11:52 AM Justin Bowser - KI5GKD <justin.bowser@...> wrote:
John - Couldn't you just turn down the PA BIAS until you get the output you need?

73,

Justin
KI5GKD

 

John

Well one step is to remove and bypass the pa devices. One can imagine the transmit drive will reduce to the vicinity of what you seek. I would use search engine ubitx transverse to see what has been reported.?

Curt
John Kemker
 

Curt, that was my first step, before posting.? However, I'll admit, I just searched the site, not the entire web.? I'll try that and see what crops up.

--
--John E Kemker III
 

Hello John,
the simplest way to solve any power problem transmitted by the ?BITX to the transverter is to insert a FIXED ATTENUATOR on the TX input of the transverter that brings the level from about 5W output to the required 750mW (about 8 or 10 dB of attenuation).
A dispassionate advice, dictated by the experience of almost 50 years of OM, is better to also insert a 3 or 6 dB attenuator also on the reception side so as not to overload the RX input of the ?BITX and generate unpleasant intermodulations.
Basically (except checking that the output to the Tranverter is correct) putting a 6dB FIXED ATTENUATOR with a power of 5 or 10 Watt between the ?BITX and the Transverter, you should have an optimal coupling.
If you think that 6dB of attenuation in RX (medium frequency for the transverter) is too much, remember that it is always better to act on the input amplification of the tranverter with an amplifier and low noise that increases the sensitivity of the whole system that also improvs the S/N ratio ?and that (in medium frequency) a lower amplification is useful to reduce intermodulation disturbances.
A dear greeting from IW4AJR Loris
John Kemker
 

Thank you very much, Loris!

Now, to make sure I understand you fully, you're recommending?I put a 6dB attenuator with no T/R switching between the uBITX and the transverter?? Don't sweat the 6dB attenuation?I'll see on the input, but put an LNA (Low Noise Amplifier) style preamp between the antenna and the transverter?? Or, should I place the LNA someplace else?

FYI, the transverter (a Microwave Modules 144/28 model) has the ability to split out receive and transmit, if desired.

73 de W5NNH

--
--John E Kemker III
 

Hello John,
OK the 6dB attenuator between the antenna output of the ?BITX and the 28MHz output of the transverter without separation between TX and RX (28MHz side).
LNA in RX transverter input side 144.
For a better performance in RX, the LNA would be better to place it directly under the antenna with a couple of coaxial relays, but be careful, in this case the TX switching of the ?BITX + transverter system must take place after the switching of the LNA (sequencer) to avoid replace the MOSFET or MESFET very often!
73 de IW4AJR Loris

On Tue, Jun 15, 2021 at 04:17 PM, John Kemker wrote:
Thank you very much, Loris!
?
Now, to make sure I understand you fully, you're recommending?I put a 6dB attenuator with no T/R switching between the uBITX and the transverter?? Don't sweat the 6dB attenuation?I'll see on the input, but put an LNA (Low Noise Amplifier) style preamp between the antenna and the transverter?? Or, should I place the LNA someplace else?
?
FYI, the transverter (a Microwave Modules 144/28 model) has the ability to split out receive and transmit, if desired.
?
 

Look at the pot after Q90. It allow to set output to almost zere.

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