lmx2541 schm

Schematic diagram.


; Bill of Material=C:\Users\Brian\Desktop\LMX2541Support(1)\PCB_design\lmx2541.T3001           
; Date=10.May.2021  17:37           
; Variant=AllVars           
; PCB=<all component>           
; Author=           
Pos    Name    Value    Package
1    C1    loop    0805
2    C2    loop    0805
3    C3    1uF    0805
4    C4    100nF    0805
5    C5    1nF    0805
6    C6    1nF    0805
7    C7    100nF    0805
8    C8    1nF    0805
9    C9    1uF    0805
10    C10    100nF    0805
11    C11    4u7    0805
12    C12    100nF    0805
13    C13    100nF    0805
14    C14    100nF    0805
15    C15    100nF    0805
16    C16    100nF    0805
17    C17    47µF    2412_ELKO
18    C18    1nF    0805
19    C19    47µF    2412_ELKO
20    C20    47µF    2412_ELKO
21    C21    100nF    0805
22    J1    4 way    Pin Header
23    J2    2 way    Pin Header
24    J3    2 way    Pin Header
25    J4    SMA    SMA_EDGE_CONNECTOR(#2)
26    J5    SMA     SMA_EDGE_CONNECTOR(#2)
27    J6    6 way    Pin Header
28    L1    1uH    0805
29    L2    1 uH    0805
30    L3    1 uH    0805
31    L4    1 uH    0805
32    L5    1 uH    0805
33    L6    1 uH    0805
34    L7    1 uH    0805
35    LED1    RED    0805
36    R1    loop    0805
37    R2    loop    0805
38    R3    50 Ohm    0805
39    R4    50 Ohm    0805
40    R5    4.7 O    0805
41    R6    4.7 O    0805
42    R7    4.7 O    0805
43    R8    4k7    0805
44    R9    4k7    0805
45    R10    1k5    0805
46    R11    1k5    0805
47    R12    1k5    0805
48    R13    3k3    0805
49    R14    3k3    0805
50    R15    3k3    0805
51    R16    47O    0805
52    U1    LMX2541    TI_NATIONAL_SEMICONDUCTOR_LMX2541SQ3030E-NOPB_0(#7)
53    U2    LM1117MPX-3.3/NOPB    SOT223
54    U3    L78M05CDT-TR    DPAK
55    U4    PIC12F629(DIL8)    DIL8



lmx2541 layout

Parts placement.


 3 D PCB

3-D CAD view

lmx2541 CAD

CAD image


Tiled array of six boards (Top)



Tiled array of six boards (Bottom)

I think I need new coax!  The Lothians Radio Society net 21/4/2021.

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20200915 165802

Recently I was making some phase noise (PN) measurements using John Miles PN programme in his GPIB Toolkit using my 8566B spectrum analyser (SA) and was finding that there were spurrs occuring at 50/100 Hz intervals at the low frequency ends of the plots. A closer examination of the spectrum showed a series of close in spurs at 50 HZ intervals.  (The line frequency in Europe). The spurs were at around 45 to 50 dB below the carrier which seemed to be too high. They are not normally obvious but at a 1kHz span and a 10 Hz bandwidth became quite apparent.

12575GHz sidebands

The HP8566B Installation and Verification Manual (HP Part No. 08566-90169) gave a detailed table of the sideband spur specification which showed conclusively something was wrong. The spurs were around 15 to 20 dB to high. This table is below.

power line sidebands

I was confident that the 12575.5 MHz Herley PLL I was using as a signal source was clean and was not the source of the spurs, so they were from the SA itself. I opened it up and checked the power rails for ripple and they were all perfectlty clean and set to the  correct voltages. At this point I was assuming that the sidebands were being caused by some spurious modulation of the first YTO (first YIG local oscillator) in the analyser. I checked out the capacitors in the YTO driver circuitry and all seemed fine for both ESR and capacitance. On consulting the HP 8566B Service and Repair manual pages on the A6A7 module I discovered that the YTX (YIG tuned mixer) was a known source of power line spurii. The manual suggested that noise on the tuning current fed to the coil of the YTO modulated the incoming signal which became visible on the display as spurs at resolution bandwidths of 100Hz or less. The solution adopted was to switch a 100uF (A6A7C1) electrolytic capacitor across the the coil to bypass the residual ripple noise as shown below.  C1 is switched into circuit across the YTX coil by the  2N6073 triac, Q8.

A6A7C1 sch 

As a crusty old EE it struck me that this was not a good way to treat an electrolytic capacitor and expect it to have a long life. I was aware of the history of this particular 8566B (serial number 2332A02879) and I knew that I was its first custodian after HP/Agilent and that it was unlikely to have been used on narrow bandwidths very much. It had probably come from a HPIB automated production line environment. It was highly likely that the capacitor had been seldom switched into circuit to keep its dielectric "formed"..

The coil bypass capacitor (A6A7C1) is on module A6A7 which is located at the right hand side of the rf/mixer area accessed below the bottom cover. The module is easily removed by undoing two countersunk screws and unplugging a PCB header connector and a ribbon cable.  On checking C1 looked in excellent physical condition but on checking with an ESR meter was open circuit. The pictures below show the original capacitor and its replacement along with the board layout.

20200926 203911

20200926 205203

A6A7 pcb



The location of the A6A7 board is here.

20200926 203936

After replacing A6A7C1 the spectral plot looked like this with the spurs largely below the PN sidebands of the Herley PLL.

repaired line spurs at 12575GHz

A close-up of the offending capacitor. It is in excellent physical shape but not there!  Now perhaps I can remove that yellow  "Out of band responses OOS (Out of Spec)" sticker on the front panel.

20200928 114936

GM8BJF 28/09/2020

I have always been spurred on in my radio activities by the desire to get onto higher and higher frequencies so when I saw that kits for puting together a 122 GHz transceiver were becoming available I could not resist getting one. I ordered the 122 GHz populated PCB designed by Andrew Anderson VK3CV / WQ1S and produced by Tim Tuck VK2XAX. It duly arrived about six weeks ago. I decided to make the antennas myself as I have a small lathe and enjoy a bit of machining now and again.  I produced two antennas as per the original drawings supplied as part of the project. The board is pictured below.


I boxed up the board and mounted my circular horn on the PCB and arranged for the horn to protrude through the box.as shown below.

IMG 20200721 WA0000

Locally to me Peter bates GM4BYF had also bought a set of bits to build up a system so there was the possibility of having some QSOs! Earlier this week I visited Peter and we had a preliminary test acoss his garden and then went out to do a test over a longer path. Fortunately my home town of Edinburgh is endowed with plenty of hills. Peter went onto the Blackford hill and I set up shop on the Braid hill and we had a QSO over a path of 0.68 km.

1stGM GM122GHz


We believe this is the first GM to GM contact on the 122 GHz band. Once we got the horns lined up the signals were S5 to S7 and good copy on FM. There was some QSB on the signals which we attributed to a tree which was close into the path and it was quite windy. This test showed up a few deficiencies in my setup.and a couple of days later I improved the mounting and antenna pointing arrangement for my transceiver. It also was apparent that I was overdeviating and I corrected that.

Flushed with success from our first QSO we decided that we would try to have a cross border QSO GM to G!  We considered a number of locations around Coldstream on the A697 and Carter Bar on the A68. Finally Peter spotted a disused rail way line that crossed the border just east of the town of Kelso. As the Carter Bar site was likely to be busy with people visiting the border viewpoint the disused railway sounded better proposition! 


england Scotland border