10 GHz  low power exciter/marker transmitter

Introduction

It just happens that if you replace the 10 MHz TCXO in the receive converter with a 14.4 MHz one, and operate the first multiplier at x2, the UHF multiplier pcb will output at 432 MHz instead of 450 MHz - and it will tune up without any other component changes. Likewise, if the 'x23' multiplier is tuned to the 24th harmonic, the output will appear at 10 368 MHz.
With this in mind, connections to the TCXO were added to allow both NBFM and CW to be applied. Voltage tuning of the TCXO allows an output frequency variation of 10 368.000 to 10 368.200 MHz.

A small Tx audio board, the same size as the mixer pcb, has been added to the pcb matrix. This takes mic audio, amplifies and clips it before adding pre-emphasis and finally low-pass filtering the result.

Tx block dia

Output power is only -30 dBm, so amplification is required for transmitter use. An easy source of gain is the front end of a satellite LNB, which will normally give 20 dB. Occasionally, LNBs with three stages of gain before the mixer can be found, and these will provide 30 dB or so gain. There is some information about this here. .

lnb tx 4                         tx lnb5                        tx lnb3



432 MHz 20 dBm multiplier pcb

layout   smd side

Tx mult pcb cct

C1     0.1uF 0805
 C30   0.1uF 0805
 R5    2k2 0805
 IC3   78M05 DPAK
C2     22uF tant
 C31   0.1uF 0805
 R6    220R 0805
 IC4   BGA6489 DPAK
C3     22uF tant
 C32   0.1uF 0805
 R7    100R 1206
C4     22uF tant
 C33   1nF 0805
 R8    1k 0805
 Q1    BFS17
C5     22uF tant
 C34   1nF 0805
 R9    12k 0805
 Q2    BFS17
C6     0.1uF 1206
 C35   1nF 0805
 R10   2k2 0805
 Q3    BFS17
C7     10nF 0805
 C36   1nF 0805
 R11   47R 0805
 Q4    nf
C8     0.1uF 1206
 C37   1nF 0805
 R12   100R 1206
 Q5    nf
C9     0.1uF 0805
 C38   22uF tant
 R13   12k 0805
 Q6    BSS84 **
C10   39pF 0805
C39   22uF tant
 R14   2k2 0805
C11   0.1uF 0805
 C40   1nF 0805
 R15   100R 0805
 D1    LLSD103A-07
C12   82pF 0805
 C41   0.1uF 0805
 R16   100R 1206
C13   2.2pF 0805
 C42   1nF 0805
 R17   22R 0805
 TCXO1    14.4 MHz  Modified Meiden CO-T67PZ **
C14   2.2pF 0805
 C43   1nF 0805
 R18   22R 0805
C15   82pF 0805
 C44   nf   (no pads)
 R19   220R
 L1    Toko 378008 - green
C16   100pF 0805
 C45   nf
 R20   10k leaded pot
 L2    Toko 378008 - green
C17   470pF 0805
 C46   nf
 R21   2k2
 L3    Toko 378008 - green
C18   0.1uF 0805
 C47   nf
 R22   nf
 L4    Toko 371044 - red
C19   0.1uF 0805
 C48   nf
 R23   nf
 L5    Toko 371044 - red
C20   0.1uF 0805
 C49   nf
 R24   nf
 L6    Toko 371044 - red
C21   0.1uF 0805
 C50   nf
 R25   nf
 L7    10uH 1206
C22   10nF 0805
 C51   10n    0805
 R26   100k  0805
 L8    10uH 1206
C23   15pF 0805
 C52   100n  1206
 R27   12k    0805
 L9    10uH 1206
C24   1pF 0805
R28   100R  0805
 L10   10uH 1206
C25   15pF 0805
R29   100k  0805
 L11   Toko 1550 93474 - yellow
C26   1pF 0805
 R1    0R 0805
L12   Toko 1550 93474 - yellow
C27   22pF 0805            
R2    100R 1206               
 
L13   10uH 1206
C28   82pF 0805
 R3    1k 0805
 IC1   78M05   DPAK           

C29   10nF 0805
 R4    12k 0805
 IC2   78L03 SOT89
 
** Due to incorrect tracking, Q6 must be fitted upside down (ie, the drain connect is correct, but the gate and source tracks have been interchanged)

A stocklist version of this might also be useful:
1pF     0805    2    C24, 26,
22uF    tant     6    C2-5, 38, 39 78L03     SOT89     1     IC2
2p2     0805    2    C13, 14
 0R     0805    1    R1 78M08    DPAK      2     IC1, 3
15pF   0805   2    C23, 25
 22R   0805    2    R17, 18 BGA6489 DPAK     1    IC4
22pF   0805   1    C27
 47R   0805    1    R15 BFS17   SOT23      3    Q1-3
39pF   0805   1    C10
 100R 0805    2    R11, 28 BSS84   SOT23      1    Q6 **
82pF   0805   3    C12, 15, 28 100R 1206    4    R2, 7, 12, 16 LLSD103A-07         1     D1
100pF 0805   1    C16 220R 0805    2    R6, 19   
Meiden CO-T67PZ  1    TCXO1 (modified) **
470pF 0805   1    C17 1k     0805     2    R3, 8
1nF     0805   8    C33-37, 40, 42, 43 2k2   0805     4    R5, 10, 14, 21 10uH 1206                5    L7-10, 13
10nF   0805   4    C7, 22, 29, 51 10k     pot      1    R20                  Toko 378008            3    L1-3        (green)
100nF 1206   3    C6, 8,  52
 12k   0805     4    R4, 9, 13, 27  Toko 371044            3    L4-6        (red)
100nF 0805   11  C1, 9, 11, 18-21, 30-32, 41 100k 0805     2    R26, 29
 Toko 1550 93474     2    L11, 12    (yellow)

Items printed in blue are leaded - all else are smd

 
** For those obtaining the Meiden TCXO themselves, here are details of the mods required
 modified TCXOs



x24 multiplier pcb assembly  
 
x23 pcb
 x23 pcb top


HSMS-8202 back to back schottky diode (SOT-23 package)
 D70
Inductor link
 L70
Pre-tuned pipecap (with 6BA x 1/2" brass screw and brass nut)  2 off
Input coax (75mm RG178)
Cavity to cavity coax link (50mm Quickform 86)
output coax lead assy (70mm Quickform 86 with one end terminated in an sma single hole bulkhead socket
Input probe wire (5mm length of RG-405 inner - see text)


Build notes

Assembly of this pcb is a little agricultural, nontheless it is very important to maintain the dimensions detailed below. Also, it is advisable to follow the build order below – if you must ‘do it your own way’, at least leave the cavity soldering until all the probes have been fitted (so that you check/readjust the probe heights).
Start by fitting the input probe. This is a short length of semi-rigid coax inner, and is supplied cut to length. It fits through a plated-through hole (the plating-through providing the outer conductor as it passes through the board).  The ptfe sleeve is an interference fit, but if for some reason it has been pushed out of the hole, beware that it may be harder to fit with the inner probe wire fitted, so in this case, remove this and insert the ptfe first – then push the probe wire back through the sleeve.

Once the probe is fitted, ensure that its ptfe shoulder is flush with the non-cavity side of the board, and then solder the shotkky diode pair (D70) into place, soldering the common lead to the probe first, before soldering the two ground pins

        input probe

Fit the sma bulkhead socket to the 70mm length of output coax, and prepare the other end so that, say 5mm, of inner is exposed. Likewise expose 5mm of inner at each end of the cavity-to-cavity coax lead, and bend into a 'U' shape with 10mm spacing between centres. Push the coax cables through the board holes as below, and ensure that the coax outer extends 1mm through the board. Solder the coax outers to rhe board. Finally, cut back the 5mm exposed inner core to 1mm, as per the rest of the pic above.
  
                       

         coax fitment		 input probe

              pipecap dimentions

Fitting the cavities onto the top side of the board

The two cavities have been pre-tinned on their bottom face, and the pcb solder resist pattern provides a good guidance for their accurate placement.

A good hefty and hot bit is required to solder each cavity. For those using a Weller soldering station, the PT-E9 tip is ideal.


 
Alignment

Alignment is carried out at the unit assembly stage.




Tx AF pcb
 
tx af layout
 tx af pcb

Tx AF pcb
C81   10uF tant   case 'B'
 C92   1uF tant   case 'A'   
R83   3k9    0805
 R94   100k   0805
C82   nf
 C93   1uF tant   case 'A'
R84   3k9    0805         
R95   10k     0805     
C83   100n         1206
 C94   na
 R85   18k    0805
 R96   18k     0805
C84   10uF tant   case 'B'
 C95   1uF tant   case 'A'
 R86   22k    0805
 R97   68k     0805
C85   1uF tant     case 'A'
 C96   22nF       1206
 R87   3k9    0805
 R98   9k1     0805
C86   nf
 C97   220pF     1206
 R88   100k   pot
 R99   10k     0805 
C87   10uF tant   case 'B'       
C98   10nF       1206               
R89   3k9    0805                    
R100  100k    pot
C88   1uF tant     case 'A'
 C99   1uF tant   case 'A'
 R90   100k  0805
C89   nf
R91   100k  1206
 IC82   MC34072 or LM833M
C90   3.3nF        1206
 R81   3k9          0805
 R92   6k8    0805
 IC81   MC34072 or LM833M
C91   10uF tant   case 'B'
 R82   3k9          0805
 R93   6k8    1206
 
If you are using an electric mic which requires some dc supply, you should solder-blob LK1.

The first pot, R88, sets the mic sensitivity. This should be set high enough to run IC82a into a small amount of (rail to rail) clipping, prior to feeding the low pass filter stage configured arround IC82b. Peak deviation is set by pot R100, and should be adjusted with a hefty audio input at the mic socket to ensure that IC82a is well into clipping.

If you have an AF signal generator, you can set R88 and R100 in the following manner: With LK1 not blobbed, set both pots to mid travel. Input a 100mV signal at 1 KHz to the mic socket. Set the deviation (R100) at 10 GHz to +- 5 KHz. Reduce the audio generator output to 2mV, and set R88 to give a deviation at 10 GHz of 3 KHz.

Pre-emphasis is provided by R91/C90 shunted by R92, interfacing the output of IC81a with the input of IC82a.

Note that all the op-amps are operating at unity dc gain, and are dc interconnected, so you should see the half rail voltage defined at the junction of R85/86 appearing at all the output pins


Pcb  interconnections

  interconnection