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Diskussions- und Newsboard des DARC-Ortsverbandes I40  |  allgemeine Kategorie  |  mcHF Projekt Deutsch / English (here you can discuss everything related to mcHF) (Moderators: DF8OE, DL1PQ)  |  Topic: TX Intermod Meausements <- zurück vorwärts ->
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oz4hz
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TX Intermod Meausements
« on: 07. November 2022, 09:58:55 »

I have made a lot of TX IMD measurements both with  the original
PIN diode ant. switch and the relay modification.
See pics below

First picture is with the original PIN diode switch
and the second  with the relay modification.

There is quite a difference in IMD

Vy 73 OZ4HZ, Hans
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oz4hz
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Re:TX Intermod Meausements
« Reply #1 on: 07. November 2022, 10:00:29 »

IMD with PIN diode
 3.5MHz_5w_PIN.jpg
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oz4hz
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Re:TX Intermod Meausements
« Reply #2 on: 07. November 2022, 10:01:11 »

IMD with relay modification
 3.6MHz_5W_Relay.jpg
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DF8OE
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Re:TX Intermod Meausements
« Reply #3 on: 07. November 2022, 12:10:55 »

That's the reason I implemented relay switching few years ago...

vy 73
Andreas
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Re:TX Intermod Meausements
« Reply #4 on: 08. November 2022, 11:08:20 »

Totally agree to remove the PIN diodes.

I have some remarks to your measurement, be careful with measurements of such high signals because:
- you have performed different measurements because of TOI your SA, look at first measurement - you have 30dB attenuator set and signal level is over 3dBm at input mixer. SA itself may produce false intermodulation. With the second measurement, mixer signal is 10dB lower becuse you have 40dB attenuation. It is good to measure or find in manual IMD of SA mixer first to be sure the limits and reliable measurement. Believe me, R&S ESR (very expensive) has significant IMD3 rise at the level of -15dBm at input! Even worse  with cheap Siglent or Rigol...

- if you do not have proper external attenuator you may destroy the SA input mixer/attenuator with 2W power
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73 Slawek
oz4hz
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Re:TX Intermod Meausements
« Reply #5 on: 08. November 2022, 16:03:29 »

You are absolutely right, but there is also an external power attenuator of 30dB - so in the first picture the signal is -29dBm at the mixer input. In the pictures you can't see that there is a reference offset of 30dB from the external power attenuator-
.
Vy 73 OZ4HZ
(also eine alte Hase)
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Re:TX Intermod Meausements
« Reply #6 on: 08. November 2022, 18:28:07 »

Thank you for clarification - now everything is ok
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73 Slawek
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