Fox Receiver 2m

Sam weeks ago i found that the ARDF resources from G3ZOI was updated. URL fox description I like this design wary good. So I ordered one bored and this arrived a few days later, PCB + 2 potentiometers, 3.5 mm jack for earphone and 2 Led, soldered and aligned. Order a box from Elfa 10-431-36 Aluminium 115 x 64 x 30 mm 1550B. I won’t little different setup see picture, possible to operate attenuator and pejel with one hand. Already use a old antenna. Fox Antenna Is made after this info. Use Isolated SMA connector and can easy change antenna.

Testing on Lab bench.

 

Current 13.6 mA.

Frequency 143,6 – 145,0 MHz

 

Input            RSSI pin 7.

-100 dBm    0,98V

-90                1,16

-80                1,40

-70                1.66

-60                1,84

-50                2,0

-40                2,23

-30                2,45

-26                2,5 max.

 

MinDetectebelSignal  around -120dBm

 

To turn on led1 red it needs maximum signal -30 dBm.

I measure Led1 Vforward around 1.8V if I remember correct.

I use one Elfa 75-036-76 it turns on 1,6V with the same current. Now Led1 turns on earlier.

 

Practice at home 3 Km away strong signals excellent reception.

Red diode lightning 100 - 150m before Fox.

2015-04-24 First Competition. Bad result, but excellent receiver especial I like the pitch it helps to determine the exact direction, When Red diode on, take exact bearing and catch the fox.

 

It is my third 2m Fox receiver and the best I have.

Minima Input-filter

This is the 15 MHz filter RF OUT - C13

This is the 30 MHz filter RF OUT - C8

This is the notch L7, CT3, L9, CT2, L11, CT1

This is the 30 MHz filter RF OUT - C8 and notch.

This is the 30 MHz filter RF OUT - C8 and notch and K1.

First comment  L1, L5 is 0,68uH and L2, L3, L4 is 0,82uH. Notch L7, L9, L11 is 3,3uH I check in filter-program Elsie before I order inductor and the effect was small.

I think the vna-plot says more than a lot of data or word. The notch is not so selective so it effect the 21MHz band, perhaps it is possible to compensate with preamplifier. Locking at the plot it can be possible to change IF to 16 MHz -1,65 to 14MHz and + 2,68 MHz to 18 MHz band. Chang lo-filter to 10 to 12 MHz cut off.

I think it is better to have tow small relays in sted of one, the K1 on this solution I work with (pp2kr pcb). I think this is the reason way there is les attenuations in the last plot. K1 serves out and in of the filters.

  Here is the result a finished board.

Next step is to load original sw and start playing with it the receiver. I will be back in May stay tuned.

SM5CJW Fox-Receiver 2014

Now the fox receiver is working, murphy is in the first one it has bad sensitivity. I will fix this later. The PCB was shown in this blog 8 October. This second one I can here -130 dBm signal from my generator.  So I have start the mechanical work to put it in a metal box. There is needed a sense antenna.  Lock forward to the spring and nice fox-orienting.

Minima Crystal filter

Started to measure all 30 pcs i have. 2 was really bad i put them in the wastebasket (nr 15, 19 ). Putt all f values in a spread sheet. Then it is simple to select the 8 X-tal with the closest frequencies. I put them on a pcb. and use 100pF as original loading capacitor, this give around 4kHz bw, try 200 pF but tis give below 2 kHz bw. Then I order 180 pF.

After testing this I try to change order of the X-tal, the effect was minimal, time to put them on the minima board. This measurement is on the minima board. Note the 3dB point and try to adjust BFO to +/- 400 Hz was not possible so i must change the circuit to succeed.

In teori the X-tal should not be mor spred then +/- 5% off BW 2.4 kHz means +/- 120 Hz the best 8 pcs i have spred -160 + 145 Hz, here is the result measured when mounting on the pcb.

After all I put murphy out of the shack and will son start the last step with the LP- filter,

stay tuned SM4HNG Leif.

Minima Mixer

The mixer is now on the board. I start winding the two BN43–2402 5,5 turn. Then select 2 off the 10 pcs J310 fet, with the closest Ids current. Mounted all mixer components on  the pcb. First try to adjust the bias to the fet. I have seen youtube video saying there is no difference in output, but I could see 3 dB change in amplitude on IF signal at 20MHz and also around 5dB in change of Noise-Flore best on 3,5 MHz was 2,5V and best on 28 MHz was 3,5V so I set bias in middle 3,0 V.

The spectrum is, what coms in coms out.

This measurement give me the conversion loss. Input 3,75, 17,2 and 28,4 Mhz around -52 dBm, this result in around 7 dB conversen loss, i also check @ 144 MHz input around 12dB loss.

The Isolation on IF port and RF port.  Lo is +16 dBm

Isolation @ IF port23,75 around 44 dB 37,2 around 41 dB 48,4 MHz around 38 dB.

it is worse on RF port.

Isolation @ RF port 37,2 MHz around 17 dB, its better at lower and higher freqv. 27 dB. 

After that I check impedance on the port.

Lo Port

 IF Port

RF port 

Perhaps it possible to get better figures more close to 50 ohm, but life is not always perfect!

I am glad that its time for X-Tal filer Test……….

73 de Leif SM4HNG

Minima QRP the BiDirection IF Amplifier

This is no build and tested.

RX  

R24 0,4mA, 

R26 8,17V 2k2 -> 3,7 mA

R27 7,47 V 220 ohm  -> 34 mA

Total current R22 0,39V 10 ohm -> 39 mA.

Put in 10,4 mV 20 MHz from generator 50 ohm to C34.

Get 40,8 mV out @ C38 this means 11,9 dB ?, but in Z is not 50 ohm.

More then -25 dBm in @ C34 is clipping in T11

TX

R13 1,28V 220 ohm -> 0,6mA

R17 8,8V 2k2 -> 4 mA

R18 8,13V 220 ohm -> 37 mA

Total current R10 0,48 V 10 ohm 48mA.

Put in 32 mV 20 MHz from generator 50 ohm to C29.

Get 56 mV out @ C33 this means 4,9 dB ?, but in Z is not 50 ohm.

50 mV 1kHz to MIC in measure @ C33 with 50 ohm power meter -23 dBm.

100 mV 1kHz to MIC in measure @ C33 with 50 ohm power meter -16 dBm.

172 mV 1kHz to MIC in measure @ C33 with 50 ohm power meter -10 dBm.

It start clipping at higher inputs!

After this i test Rx put generator to C34 -107 dBm. 20,001 MHz.

Give me a audio around 12 dB SINAD, i can clear hear a toggle on/off generator @ -120 dBm.

For me it seems that this part is working, better then expected.

Next time i start with the X-tal filter lock forward to test the 30 X-tal i have in my box.

Fox Hunting Transmitter for 80m

As i mention in this blog Fox transmitter 2m that this work has start.

After Christmas i received this PCB to start work with. Most work left is to set output level and make the tuning to the short vertical antenna to optimal. There is also little sw upgrade to do.

I will put info here when working.