Monday, April 24, 2017

"Telrad" board to work


Just spent part of the weekend populating the "gig" with auxiliary circuits for the "Telrad" board testing, following previous posts.

Nothing special, a 9.000 Mhz BFO an LM386 audio amplifier and the power circuit, vfo is external. Not using the +12/0/-12 for supply, only +/- 9V from small batteries.

VFO is from a si5351 controled by the Arduino, signal level from the VFO is reduced to show around 100mV on the mixer carrier input pin (10)

BFO is from the Bitx and other designs directly connected to the board BFO input #11:

No provision with serial inductance or capacitance, at the moment, to "tune" the frequency.

Audio amplifier is a stock LM386 design and interestingly got some audio oscillation from the circuit that I will fix on latter experiments, probably with a RC low pass filter on the supply voltage. Connection was made at the audio output of the board and now is at the isolation transformer out.

Test signal is injected from my S9 signal generator to the front end and I do get audio ! Success...but only with injection bypassing the inboard front end filter and directly to pin 1 of the first MC1496 mixer.
Signal level injected from the signal generator even without proper measurement and calibration is probably around S4.
Audio is on the low side so more testing is needed.
I didn't managed to get LSB, only USB, have to check why (proably switching circuit) although if injecting 9Mhz directly on the LSB filter output I could be ear the signal with low level.

Another view of the first success:

I chosed 3.6Mhz since, apparently, that's around the front end filter center frequency...I start to suspect it's not, still need to bypass the filter to get audio out.
Probably in the future will remove the filter components from the board (last resource) and use a pre-amp also.
Injecting 9 Mhz on the front end is also audible as an audio tone, that's expected and is also a confirmation the board is working.

Will post more info as soon as more experiments are made.

Have a nice week!

Sunday, April 09, 2017

More filters III - "Telrad" board".

Just another update to these filters and boards as on More filters I and update II

Found the page of GW4SAE/ZL4SAE with an updated schematic of the board, no question, Will made an excellent work.

Basically just confirms the schematic from here as referenced on the previous post about this boards.

Also in regards to the filters in the board, some time ago I found the following: (From here and here)

XF-9 S 44
XF-9 S 42
XF-9 S 43

S42: bande passante=+/- 3k6 à -3db : fréquence centrale 9.000000 MHZ
S43: +/-1K55 à -3db : 8.998200 MHZ
S44: +/-1K55 à -3db : 9.001800 MHZ

Capa d'entrée et de sortie: 25 pF
Z entrée/sortie 560 ohms (mesurés)  ..."

In the mean time I started to prepare the board to make also some experiments, maybe a future receiver.

Backside of board:

Removing the extra hardware:

Have a nice week!

P.S. Just made a small jig to take on the underside the audio amp, bfo and vfo for further testing, time permits:

Sunday, April 02, 2017

S9 signal generator, another one.

This is not my first one, anyhow since the other is 1600Km away and I needed to tune a receiver, here's the "new" one:

 Allready helping tunning IF coils of a transceiver in kit form (will write more on that latter):

Here's the schematic:

It's similar to the Elecrat signal generator ( and the Norcal one.

The schematic I loosely followed is from here: KV4QB has a nice write-up on the generator.

I didn't placed the capacitor in series with the crystals and the attenuators are both in line since I'm interested on the lowest possible signal.

Construction and boxing, an house electrical junction box and some pcb made the trick:

The power clip for the 9V battery was made reusing one old battery terminal and then glued for rigidity:

Testing connected to the FT-707 it displays around S1 but since I calibrate the s-meter by ear, guess might be getting wrong results, If time permits will test with the AD8307 ...anyhow that one needs calibration also.

Here's level to s-meter table:

Have a nice week!