A High-Level Accessory Front End for the HF Amateur Bands
Additional info NOT given in time for press about the preamplifier performance:
IN3LNC, Claudio has performed for us an accurate set of tests of our preamplifier alone and here are the results that fully confirm our preliminary data:
Gain: 12 dB (12.7 dB at 7 Mhz, 11.3 dB at 30 Mhz, flat
within 2 dB over all 30 Mhz range)
Output third order IP3 (OIP3) = + 43 dBm (with 7L14 by Tektronix and 2x HP8640B, -6 dB hybrid coupler, 10 dB attenuator each leg, the two tones at 20, 50,100 Khz spacing and for all three offsets that OIP3 data has been confirmed)
Input third order IP3 (IIP3) = (OIP3 - Gain) = + 31 dBm
Output second order IP2 (OIP2) = + 41 dBm (so ie. with a band pass filter with 60 db of stopband at the two outside test frequencies (our QRM signals) the total OIP2 will be much much better. IP2 has a 2:1 relation with power input).
NF: 3.9 dB (measured with a calibrated noise source at 30 Mhz)
1dB Compression point: +24.5dBm (input + 11.5dBm)
The output impedance resulted to be lower than 50 Ohm, but in this
application this is not a problem, performance are not degraded and maybe useful
ie. when paralleling two 50 Ohm receiver without any 2:1 three way-combiner.
It is interesting to compare this 2x2N5109 push-pull with a single transistor Norton noiseless feedback circuit:
our friend IN3LNC compared for us our 2x 2N5109 push-pull with one transistor Norton circuit noiseless feedback (transistor type BFG135 or BFR134 or BFG34 with same results) with + 13 Vdc, I= 35 to 40 mA, G=11dB NF=2 dB, OIP3= + 41 dBm, but OIP2 was only +31 dBm (10 dB poorer). He confirmed to us that our pushpull is a better performer. Norton feedback amplifier is also very much load impedence sensitive inverse isolation is low.
Please compare the above data with W8JI, Tom, PREAMPLIFIERS SUMMARY test report <----click here the link.
Useful software tools:
I have discovered a very powerful tool to play with receiver gain, noise,
IP3, MDS, per stage and cumulatives data to simulate with a complete receiver
system without getting tired about long calculations.
Try this professional-nice and available for free software by AGILENT:
Download file name: setup251.exe
Choose the menu function "Noise Calc". And enjoy it.
I have some more info, and dBm to dBmicroV easy conversion relations, in my web site at
http://www.qsl.net/ik4auy/article_5.htm (under Measures & simulations an article in Italian which is under future publication in our ARI magazine, but the relations are easy to read).
Best Regards. Sergio Cartoceti, IK4AUY
Down load here May/June 2003 QEX .pdf file "Letter to
a link to Neoamateur.org download page
Last update: 20 Dec 2003