Amplifiers

[Nick Orion]

Hi OMs,

I have an Expert 1.5k-fa PA. I am already using it with the HL2 together with predistortion connected like it is in this blog https://f5npv.wordpress.com/pure-signal-rf-sampler/  but without the described sampler because my PA has a -60db predistortion sma connector and it seems to be working fine  apart from some strange general behaviour sometimes maybe do to the PC which should be a faster one.

 
Now, the point is that my PA reads only 3w as drive power from the Hermes and as a consequence it does not deliver more than 300/350w pep (for 500w the drive power should be at least 5w). Measuring my Hermes output power on an external wattmeter and dummy load, it shows its 5w perfectly.

Question: if I want to use a pre-PA for my Expert so that I can get at least 5w for LOW, 10w for MID and 25w for HIGH output power, would this PA https://www.ebay.com/itm/175419175816 (or this https://www.ebay.com/itm/182260074503 ) be good for the purpose without loosing predistortion and without running the risk to produce spurious emission and/or burn something ?

Many thanks for your time.

Best regards,

Nico IT9PQJ  

[dh1tt]

Nick,

I changed the T-Pad ATT of my 1k3 (expecting equal to your's) to 3dB and it is working like a charm. 8/150/8 Ohm's TO220s The HL2 is running cool with maybe 1 to 1.5W and you're easily get out the max power of your amp.

 I'm running Thetis and I adjusted the output of the HL2 Settings in Setup for each band in a way, where it is never possible to overdrive the final amplifier. 

30minutes, 3 R's and your back to QRO

Good Luck !

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["Christoph v. Wüllen"]

Be careful,

the HL2 TX attenuator can be set from 0 to 7.5 dB in 0.5 dB steps,
this means that you cannot regulate down the HL2 to less than
1 ... 1.5 Watts, no matter how large the "PA calibration" value is.
For large calibration values, the "drive slider" has no effect.

I suggest to have a 6 dB / 10 Watt attenuator between the HL2 and
the PA, then the drive slider works and you know you won't overdrive
the PA.

Yours,

DL1YCF Christoph

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[V85NPV]

Hello Nico,

i know you have send me an email but today was really tough at the office and have no time to provide you a response.

Regarding your issue ,  Christoph and Oliver had provided you the right direction . I have choosen to build a sampler with step attenuator in order to assist me at the initial stage for PS . In fact it was finally very useful since i am using 2 ampliers (150w and 300w) , and the best result was for me to adjust the feedback level according the power i am using. i am sure other solution can be used but since it works for me i stick on it. As far i can recall the PS adjustment was more tedious when i was using my LDMOS amplier (i sold it) , but with my tubes amplifiers (Both homemade) the PS feature was easy to achieve. 

Adding an amplifier as a driver for my point of view is a bad idea since LDMOS amplifier are very sensitive regarding the input drive , you may kill your amplifier if just once you forget to adjust ther input power .

73s Didier

[DL1YCF]

The step attenuator in the sampler seems not necessary, since the RF frontend has the
combined preamp/attenuator that goes from -12 to + 48 dB. If you had problems with
the feedback level then possibly the software has not done well with automatic
attenuator setting.

The optimum PS feedback level is about -15 dBm if the HL2 gain is at +14 dB,
so it can cope with well above 0 dBm input (if the hardware stands it) just
by moving down the preamp. On the other hand, cranking up the preamp above 14 dB you
can easily handle feedback levels down to less than -30 dBm.

So a fixed -60dB coupler should work from 1W to 1 kW, just due to the very
large preamp/att range of the HL2.

Yours,

Christoph

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[V85NPV]

Hello Christoph,

In fact i have this idea initially since i was not sure where i am going. After reading your website it was better regarding my understanding. 2 years back i discover the PS feature thanks to the Hermes lite and your software. i was pretty lucky since it was working almost on the spot . My fear was in fact to damage the hermes lite with an improper feedback level (too high) . after few test with mostly PIHPSDR i found out a  TX ATT level from 10 to 20 roughly measured by PIHPSDR was providing me great results . Since this time i never come back with another sampler or variant solution since this one was ok . 

73s Didier

[Nick Orion]

Hi OM's,

many thanks for your kind and interesting reply.

Oliver, please, let me know more about what you wrote. Do you only have an HL2 or you use the amplifier with other radios as well? Thank you very much.

73,

Nico

[dh1tt]

Hello Nick,

my main and daily, nightly, weekly, monthly, DX and contest TRXs are two HL2s. On hold, Anan100 and 7000 acting more as dust collector's. Anan7000 is used in winter for low band DX, because of diversity RX, wich I hopefully can realize one day with HL2s. I'm running all of my stuff fully remote and max automated, installed seperated in my basement. Zero noise shack. HP scope fan is the last ear penetrating device here. 

Last ham related "luxurious" device is an optional, external ASIO device, if I'm operating from my captains chair in my office/bench/lab at the main floor.

This is a knob radio free household in general and I have no imagination to use something different.

I guess, you're question is related to old school 100W TRX and how to handle this with lower input attenuation?

My setup is vy consequent. QRP or QRO. I only know this 2 different status. There are NO practical REASONS to switch and use min/mid/max on the amp. NOT for  RF output! I'm always using mid because of lower drain voltage. Result is lower heat disipation. Beside the fact, that we have a max legal limit here, nobody notices 1 or 2 dB more output in max position. Linearity and some more headroom count's much more (for me).

Input and output is always measured inline with precise P.E.P. meter. This is essential and in my case a much bigger invest then 3 HL2s. If you can NOT measure precise P.E.P. RF power from mW to KWs, forget any modification, where a single dB input counts.... 

73s,

Oliver

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[Nick Orion]

Thank you very much Oliver! Many thanks to all for your kind replies!

Yes, how to handle this with old school 100W TRX? I presume by lowering power down on my IC-7300. SPE has told me that by doing that modification I loose some protections performed by the PA.

73,

Nico

[dh1tt]

Nick,

it's not related anymore to HL2.

Stay tuned, you will get direct answer....

cul,

Oliver

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[Nick Orion]

Sorry.

Thank you Oliver.

73,

Nico