Ascom SE550 Mk3

[Kaon]

Hi,

Has anyone had experience of a deaf receiver on an Ascom SE 550 Mk3, the
receive does not seem to perform as I would have expected.
Is there a common problem on the RX? Are they inherently deaf? This is the
second radio that exhibits the same problem.

Any help will be gratefully received.

Cheers

Andy

[Jeff]

Post by Kaon
Hi,
Has anyone had experience of a deaf receiver on an Ascom SE 550 Mk3, the
receive does not seem to perform as I would have expected.
Is there a common problem on the RX? Are they inherently deaf? This is the
second radio that exhibits the same problem.
Any help will be gratefully received.
Cheers
Andy

Have you just upgraded the software to Mk 3 I wonder?

A lot of the tuning inside the Ascom is s/w controlled
via d/a, you may find that the tuning voltages are not
what they were with the Mk2 s/w. The easiest fix is
to re-tune the rx.

Jeff

[blank]

The one I have, believed a Mk2, is and has always been excellent. Not
certain if there are any differences to the RX front end(?). Have fitted
new firmware via a new e-prom but forgot to check the VCO control volts
before removing the old prom. This necessitated retuning the RF RX front
end, but with a sig gen to hand, this was easy. Squelch threshold on 4m is
around -124dBm (0.15uV pd) across the 4m band which is acceptable
considering there is double tuned circuit before the first RF amp. The
tracking is ok but the sensititvity does go off a little as you tune well hf
of 4m.

Chris

Post by Jeff

Post by Kaon
Hi,
Has anyone had experience of a deaf receiver on an Ascom SE 550 Mk3, the
receive does not seem to perform as I would have expected.
Is there a common problem on the RX? Are they inherently deaf? This is the
second radio that exhibits the same problem.
Any help will be gratefully received.
Cheers
Andy

Have you just upgraded the software to Mk 3 I wonder?
A lot of the tuning inside the Ascom is s/w controlled
via d/a, you may find that the tuning voltages are not
what they were with the Mk2 s/w. The easiest fix is
to re-tune the rx.
Jeff

[Gareth (G1LVN)]

Post by Kaon
Hi,
Has anyone had experience of a deaf receiver on an Ascom SE 550 Mk3, the
receive does not seem to perform as I would have expected.
Is there a common problem on the RX? Are they inherently deaf? This is the
second radio that exhibits the same problem.

no experience with ascoms. But have had the same problem with a motorolla
M110. Similar radio in that it is software controlled. After moving freq (a
couple of megs) it was extremely deaf - TX was fully quieting 2 km away but
2 watts back couldn't break the squelch. Seems like the front end was very
narrow (less than a Meg or 2).

Simply tuned up the cores on the front end (should be obvious which cans to
tune without a schematic etc) on a low level on air signal and peaked the RX
that way. Works a treat now.

further investigation shows that the workshop procedure for frequency
changing is not just a simple software change. It has to be followed up with
a complete tune up particularly if you are swinging it a MHz or so.

Gareth (G1LVN)
www.g1lvn.org.uk

[Jeff]

Just as a follow-up to my first post;

when you say deaf do you mean poor sensitivity or receiving
absolutely nothing??
I assumed that poor sensitivity meant just that not totally dead,
but on reflection if you are getting nothing at all then see below:

It is quite common when upgrading from Mk2 to Mk3 s/w for the
vco to be out of lock on 4m.

If one of the red leds is on below the display then the vco
is out of lock. If you tune up to about 75MHz it usually goes out.
If this is the case the the vco needs resetting.

Select 70.0125MHz and set the vco voltage for 5V +/-0.2V
measaured on MP2 (test pad in bottom LH corner of screened area
to the right of the vco screning can.
with R110 (right hand of the 2 variable resistors next to the vco
screening can)

Note that the red led will come on at 70MHz and below.

Jeff

Post by Jeff

Post by Kaon
Hi,
Has anyone had experience of a deaf receiver on an Ascom SE 550 Mk3, the
receive does not seem to perform as I would have expected.
Is there a common problem on the RX? Are they inherently deaf? This is the
second radio that exhibits the same problem.
Any help will be gratefully received.
Cheers
Andy

Have you just upgraded the software to Mk 3 I wonder?
A lot of the tuning inside the Ascom is s/w controlled
via d/a, you may find that the tuning voltages are not
what they were with the Mk2 s/w. The easiest fix is
to re-tune the rx.
Jeff

[Kaon]

Hi,
Thanks for the all the replies, the VCO LED is not on when tuning
through the 4m band, it illuminates at 70.000 Mhz as you described below.
The radio seems to receive poorly, I can hear stations but very weakly and
when I hold a QSO the stations report I am 59, I have held brief
conversations with another station using an Ascom radio (on the same output
power) although due to my limited RX capabilities it was very short.
I have re-tuned the front-end filters and gained a small improvement,
although the radio still does not perform as well as I would have expected.
If I set the radio to a smaller frequency step, i.e. 5Khz, the radio will
not lock on the RX VCO.
The radio was purchased as a Mk3, and this is the second radio exhibiting
the same behaviour, I shall check my antenna at the weekend although my VSWR
is fine and I do not have a problem with TX.
Thanks to everyone that helped,
best regards Andy

Post by Jeff
Just as a follow-up to my first post;
when you say deaf do you mean poor sensitivity or receiving
absolutely nothing??
I assumed that poor sensitivity meant just that not totally dead,
It is quite common when upgrading from Mk2 to Mk3 s/w for the
vco to be out of lock on 4m.
If one of the red leds is on below the display then the vco
is out of lock. If you tune up to about 75MHz it usually goes out.
If this is the case the the vco needs resetting.
Select 70.0125MHz and set the vco voltage for 5V +/-0.2V
measaured on MP2 (test pad in bottom LH corner of screened area
to the right of the vco screning can.
with R110 (right hand of the 2 variable resistors next to the vco
screening can)
Note that the red led will come on at 70MHz and below.
Jeff

Post by Jeff

Post by Kaon
Hi,
Has anyone had experience of a deaf receiver on an Ascom SE 550 Mk3, the
receive does not seem to perform as I would have expected.
Is there a common problem on the RX? Are they inherently deaf? This is the
second radio that exhibits the same problem.
Any help will be gratefully received.
Cheers
Andy

Have you just upgraded the software to Mk 3 I wonder?
A lot of the tuning inside the Ascom is s/w controlled
via d/a, you may find that the tuning voltages are not
what they were with the Mk2 s/w. The easiest fix is
to re-tune the rx.
Jeff