5866	2011-02-22 07:35:05	Thomas S. Knutsen	microR2 gain
Message	Date	From	Subject
Hello. I'm planning an 70MHz transceiver using the W7ZOI hycas IF amplifier and an microR2 in the receiver. I have built most of the transmitter and IF parts, and with an microT2 and an crystal filter on 9MHz, the SSB generator have an excelent, clean signal. Then it's up-converted to 70MHz. Does anyone know what the total gain in the microR2 is? I'm afraid that I may have to much gain in the receiver, the hycas have approx 60db gain with AGC off, then the pre-amp have approx 15dB gain, but that may be equal to the loss in mixers and filters. This is going to be an experiment platform for testing of some different SAW filters, and I need an transceiver for the new 70MHz band that we just got. 73 de Thomas LA3PNA. -- Please avoid sending me Word or PowerPoint attachments. See <http://www.gnu.org/philosophy/no-word-attachments.html>
5867	2011-02-22 08:36:15	Mike Dinolfo	Re: microR2 gain
I'm a new subscriber to the emrfd yahoo group, so I'm not sure if this is appropriate, but here goes.... Some time back I put together a spreadsheet to try to quantify some of the calculations for various DC receiver audio sections, to look at gain, gain vs. supply voltage, etc. See attached spreadsheet (this was prepared using open office, but I think it can be opened and edited using excel). The spreadsheet provides calcs for not only the Micro R2, but also some of the earlier designs from SSDR (Solid State Design for the Radio Amateur), and also the QST November 68 direct conversion receiver article by Hayward & Bingham. According to my spreadsheet calcs, the MicroR2 audio amplifier voltage gain from the Q2 base to the output headphones (series connected as a single 64 ohm load) with a 9 volt supply is about 4.1 x 10^^6. But this spreadsheet has not been checked by anyone other than myself, so there might be errors in the calculation (and if anyone encounters any errors, please feel free to let me know.) Good luck with your new project; sounds very interesting! Mike Dinolfo N4MWP
5868	2011-02-22 08:46:38	Thomas S. Knutsen	Re: microR2 gain
Indeed I think it is appropriate, even better, put the file in the files section, so members of the group can take an look and perhaps correct if the numbers are not correct. Thanks. 73 de Thomas. 2011/2/22 Mike Dinolfo <mdinolfo@erols.com> > > > I'm a new subscriber to the emrfd yahoo group, so I'm not sure if this > is appropriate, but here goes.... > > Some time back I put together a spreadsheet to try to quantify some of > the calculations for various DC receiver audio sections, to look at > gain, gain vs. supply voltage, etc. See attached spreadsheet (this was > prepared using open office, but I think it can be opened and edited > using excel). The spreadsheet provides calcs for not only the Micro R2, > but also some of the earlier designs from SSDR (Solid State Design for > the Radio Amateur), and also the QST November 68 direct conversion > receiver article by Hayward & Bingham. > > According to my spreadsheet calcs, the MicroR2 audio amplifier voltage > gain from the Q2 base to the output headphones (series connected as a > single 64 ohm load) with a 9 volt supply is about 4.1 x 10^^6. But this > spreadsheet has not been checked by anyone other than myself, so there > might be errors in the calculation (and if anyone encounters any errors, > please feel free to let me know.) > > Good luck with your new project; sounds very interesting! > > Mike Dinolfo N4MWP > > >
5870	2011-02-22 12:33:27	Mike Dinolfo	Re: microR2 gain
I will post the spreadsheet on the server within a few days. I probably will make a few last minute tweaks, and label it as "rev 0."
5871	2011-02-22 19:02:47	kb1gmx	Re: microR2 gain
That will be far to much gain. Do not forget the uR2 is a complete receiver of adequate sensitvity. The uR2 has enough sensitivity to hear a -131dbm signal (it's MDS is -131dbm). That means you will be hearing the IF noise as the overloading signal and even with AGC the headroom of the uR2 will be severely compromised. To use a uR2 after down conversion you need to keep the total gain down in the 0 to 15db range to avoid overload. The uR2 with a suitable LO is almost sensitive enough as is for VHF. it only needs a few more db of very low noise gain to be hot by VHF standards. I have done this for 6M and the gain needed to hear -140dbm was quite small. The test setup was RF amp(low noise) of 16db driving DBM and a low gain common gate Jfet (8db gain) to insure the IF port was well matched. I wanted enough RF gain to set the NF of the radio and overcome the triple tuned image stripping filter that was placed before the DBM. The SAW filter may have higher losses than the triple tuned filter (about 4db) I used but that layout does not require Hycas. I am currently trying the uR2 as a fixed high IF (32mhz) with either down conversion from 6M or up-conversion from lower HF and the gain needs do not change much as the uR2 design holds it's performance to VHF. So far tests at 6M say 12-15db converter gain over all is more than enough to hit the noise floor and about 6db converter gain for lower HF is maybe excess. If you do not pay attention to gain distributi