[Premium-Rx] receivers with 20Mhz IF?...slight clarification

[Gary Geissinger]

Eugene,
 
I probably should clarify what, "sweeps by the 10.7 MHz IF and output into the 20 MHz IF" means.
 
My VCO sweeps from 25.7 MHz to 35.7 MHz when in the 1 MHz/cm position.  I tend to run VCOs above the IF in circuits like this; that way the tuning range is a smaller proportion of the output frequency.  This improves tuning linearity.  I've had good luck with making the oscillator a Hartley type circuit, this can improve the linearity as well (since there won't be fixed capacitors in the tank circuit for feedback which tend to "dilute" the varactor diodes.)
 
Gary 

________________________________

From: premium-rx-bounces at ml.skirrow.org on behalf of Gary Geissinger
Sent: Tue 5/24/2005 8:57 PM
To: premium-rx at ml.skirrow.org
Subject: RE: [Premium-Rx] receivers with 20Mhz IF?


Eugene,
 
I've done this and it works great.  It puts the LCD panadapters in some HF transceivers to shame.
 
I use it with my Icom R-7000 with a 10.7 MHz IF.
 
In addition to the 20 MHz input, it has a sweep output.  The rest of the BNC connectors and the "blue ribbon" connector on the back are not used.
 
I scaled the sweep and drive a VCO with it.  The VCO sweeps by the 10.7 MHz IF and outputs into the 20 MHz IF.  The 20 MHz IF input on the 851 is fixed; the RF sweep is done by the RF section.  As a result, you will be in the VCO business on this project.
 
Hints:
 
1.  Put an LNA on the output of an Icom receiver 10.7 MHz IF tap.  The amplitude is very low.  Watch out, ICOM puts DC out on some of the IF output jacks!
2.  Use a balanced (or better yet a double balanced) mixer to eliminate feed-thru of the input and LO.
3.  You may want to consider putting a filter (Mini-Circuits has a good choice) in front of the mixer.  The ICOM receivers put out some spurs a few MHz from 10.7 MHz.
4.  The gain on some 851 display sections changes with IF bandwidth.  You may find the 1 MHz bandwidth to be pretty unusable, except to look at your local TV station's spectrum.
5.  On the VCO, use a back to back pair of varactor diodes for tuning; the linearity is much better than with a single diode.
 
6.  Parts I chose:
     LNA:  40673 RCA dual gate MOSFET
     VCO: MPF-102
     Mixer: MC-1496
     Op-Amp: LM324 (sweep scaling, offset, calibration)
 
The sweep was calibrated at 10 KHz/cm, 100 KHz/cm, and 1 MHz/cm.
 
Currently K0UE (Skip) is building one for his ICOM receiver as well.  You may want to compare notes with him.
 
Good Luck,
 
Gary WA0SPM
  

________________________________

From: premium-rx-bounces at ml.skirrow.org on behalf of Eugene Hertz
Sent: Tue 5/24/2005 8:16 PM
To: premium-rx at ml.skirrow.org
Subject: [Premium-Rx] receivers with 20Mhz IF?



Ok, here's one I know you will all laugh at me on.  I came across an old HP spectrum analyzer, specifically, 851B display and an 8551B RF section. For those of you fortunate to have never seen one, here's a picture. http://www.fairradio.com/hp-851b.html

It weighs about as much as my 1961 MGA.  So I started thinking about what I could use this for. Asking around on the HP/Agilent list, I found out that the 851B Display takes an IF input of 20Mhz.  Asking around further I discovered that I could not easily locate a more modern RF section (at say 1/10 the size) because the 20Mhz IF was abandoned by HP.

So I got ta thinkin.  Are there any receivers that use 20Mhz as IF output? I thought the display section alone could make for a neat panadapter/sdu.

(Ok, you can stop laughing now!)
Eugene

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman.qth.net/pipermail/premium-rx/attachments/20050524/462e3968/attachment.htm