OZ2M troubles

[M0NKA]

Hello,

I have a bit of a trouble with the OZ2M transverter tuning. According to the
builders page (http://www.rudius.net/oz2m/70mhz/transverter.htm) i should
achieve 75 dB on 84 Mhz harmonic of the LO and 60 dB on 140 Mhz on the
output. The best i could get is 35 dB on the 84 and 40 dB on the 140.

I also had to make some mods to get this - for example to get lowest second
harmonic on the output i had to put 10 pF in parallel on L16 because the min
was clearly not in the middle of the core position. In similar fashion i had to
add another 10 pF in parallel to L10.

The band pass filter (L13,L14) gets clear maximum on 70 Mhz in the middle
of core turning, but L12 seems to have little effect in any position.

I believe i have soldered all inductors according to the builders guide, but
for L1, L2, L3, L4, L12, L13, L14, L15 i didn't get part marked as 00 5231 03,
but 23871, so i assumed is equivalent and just used it.

I made a miserable attempt to measure L1 inductance, but my cheap
China meter can't catch such low value.

So i must be missing something obvious, but no luck to debug my own
work.

Again, any help will be appreciated. Thank you.

73, Chris

[M5TXJ]

Seamus G7ITT built one of these transverters and had problems initially, it turned out to be that the cans of the inductors were shorting out some of the tracks. Simply unsoldering and lifting slightly cured all his problems. Once aligned the transverter worked exactly to specs.

HTH 73 Dave 'TXJ

[M0NKA]

Hi,

Thank you very much for replying! I was getting to think that i am talking to
myself again, and maybe just being annoying posting such technical posts
here.

I will test as you suggested. Meanwhile i have ordered some parts to make
small pre-amp + bandpass filter. My amp seems to require at least 400 mW
for the logic to trigger it on. I can get that from the transverter, but only if
i leave the second harmonic on the output. With proper tuning and the harmonic
removed, i got 100 - 150 mW, but not enough to trigger the amp.

73, Chris

[M5TXJ]

Happy to shout up Chris, I may not be on the right track but it definitely caught Seamus out. As for the amp, would a better solution not be to hard wire the PTT to the transverter? I've never been a fan of RF switching.

73 Dave

[M0NKA]

Hi Dave,

Yes you could be right about that. But at this moment i have too many
unknowns in my project, the softrock has problems on transmit, the above
mentioned troubles with the oz2m, the amp is the only working thing right,
i prefer to not mod it too much right now.

This amp is part of a setup i had 15 years ago for a long range cordless
phone working in the 49/72 Mhz(base low, phone high). All has been gone
long time, but managed to find the amp when i visited my mother this summer.
Apparently been on he balcony for more than 10 years - exposed
to moisture and minus 10 degrees in the winter and 35 in the summer. But
hey, Japanese technology rocks - works like brand new.

Here some pics of the amp, so you can get a clue:






You can see on the inside that it has 49 Mhz basic duplexer between
in and out. I am reluctant to remove this one yet, as it might change the
in or out impedance. I also need to add some bias to the final as it is
clearly class C.

73, Chris

[EA7HV]

Hello Chris
By chance you will not have saved the scheme of service of this amplifier?
(This initial post is inappropriate question, excuse me)

73, Juanes

[G3CWI]

Hello,

I have a bit of a trouble with the OZ2M transverter tuning.

I have just built one. One of the inductors on mine did not tune correctly and, like you, I needed to add 10pF across it. Have you been able to sweep the filters with proper test gear? I did this and would not have liked to try to set it up without the right gear. It was fiddly to optimise. Mine is now working.

73

Richard
G3CWI

[GI0GDP]

Hi Richard
I suspect you used a certain VNA, perhaps you could enlighten others
Geoff

[G3CWI]

Hi Richard
I suspect you used a certain VNA, perhaps you could enlighten others
Geoff

Hi Geoff

This is the instrument that I used:

http://sdr-kits.net/VNWA3_Description.html

I have no commercial link with this company.

73

Richard
G3CWI

[M0NKA]

Hello Chris
By chance you will not have saved the scheme of service of this amplifier?
(This initial post is inappropriate question, excuse me)

73, Juanes

Hi,

I never had schematics or service manual for this. It was part of long distance
cordless phone. Bought second hand - the rest of the parts were sold long time ago, have only the car amp left.

I could maybe try to draw the schematics, but is nothing special - 2 transistors, LPF, switch logic and 6V regulator for the handset.

73

[M0NKA]

Hello,

I have a bit of a trouble with the OZ2M transverter tuning.

I have just built one. One of the inductors on mine did not tune correctly and, like you, I needed to add 10pF across it. Have you been able to sweep the filters with proper test gear? I did this and would not have liked to try to set it up without the right gear. It was fiddly to optimise. Mine is now working.

73

Richard
G3CWI

Hi Richard,

Yes, i have Hameg HSM1010. I wouldn't think of building this without a
spectrum analyzer. So far i found the biggest problem after e-mail exchange
with Bo (OZ2M). I was not using external attenuator with the analyzer,
so this i guess was causing some overload and the results were not
correct. But even i have managed to bring down the 2nd, 3rd and 4th
harmonic, i still have two spurious 'sidebands' 2.4 Mhz down and up.

About the capacitors values - i am really confused now. Based on the total
tuning, sometimes added values are needed, sometimes not. I have also
found that some of the critical value ones (in the tuned cuircuits) need
changing with small SMD ones, this gave me few dB improvement on the
harmonics.

73, Chris