radio transmission trouble

I am hoping someone can help with a problem I am having in
mySZD55.while thermaling some transmissions are lost as I turn.it
seems to recieve fine no matter if I am turning or not.it's an older
avionic dittle 720c.how do I diagnose if it's antenna related or just
a bad radio?
Thanks, Dennis Vreeken. aka 4Q

On Oct 13, 9:17*pm, SD wrote:
I am hoping someone can help with a problem I am having in
mySZD55.while thermaling some transmissions are lost as I turn.it
seems to recieve fine no matter if I am turning or not.

Might it be caused by increased g-loading in a turn? Try transmitting
while pulling up. If you experience similar problems then look for a
loose connection somewhere in your radio.

Bart

On Oct 13, 10:49*pm, Bart wrote:
On Oct 13, 9:17*pm, SD wrote:

I am hoping someone can help with a problem I am having in
mySZD55.while thermaling some transmissions are lost as I turn.it
seems to recieve fine no matter if I am turning or not.

Might it be caused by increased g-loading in a turn? Try transmitting
while pulling up. If you experience similar problems then look for a
loose connection somewhere in your radio.

Bart

I found that my transmission clarity was strongly related to where my
mouth was relative to the Dittel boom mike I use - not the radio
itself. Do you use a boom mike? Does it move when you are pulling G's
in a turn?

9B

Blanking can occur in a cone in line with the antenna and the elevator
push-rod. This is perceived as fading in and fading out while
thermaling. The early LS-6 had this problem and the fix was to replace
the elevator push-rod with non metal rod.
JJ

SD wrote:
I am hoping someone can help with a problem I am having in
mySZD55.while thermaling some transmissions are lost as I turn.it
seems to recieve fine no matter if I am turning or not.it's an older
avionic dittle 720c.how do I diagnose if it's antenna related or just
a bad radio?
Thanks, Dennis Vreeken. aka 4Q

This isn't all that uncommon, depending on the antenna type and it's
location you may blanket the "line-of-sight" transmission to some degree. I
assume you have the standard tail mounted antenna from the factory, even
with this there can be some reflection from other grounding or metal
surfaces that will limit the transmission cone.
I've seen this with antennas mounted on the belly of airplanes reflecting
off landing gears, also transmitting essentially down to the ground so
ground communications are poor, even raspy as the signal is bounced from the
antenna off the ground or gears to the antenna again.. also poor
communications to the ground from the air with top mounted antennas where
the signal air-to-air is 5x5 because of the ground plane blocking this
transmission cone.
just a thought...try it, see if the direction of the transmission is in the
way you are in relation to the other gliders in the thermals or in a
straight line to see if this isolates your issue....if it doesn't then we'll
look for other suspect problems
tim

--
Please visit the Wings & Wheels website at www.wingsandwheels.com

"SD" wrote in message
...
I am hoping someone can help with a problem I am having in
mySZD55.while thermaling some transmissions are lost as I turn.it
seems to recieve fine no matter if I am turning or not.it's an older
avionic dittle 720c.how do I diagnose if it's antenna related or just
a bad radio?
Thanks, Dennis Vreeken. aka 4Q

On Oct 13, 9:17*pm, SD wrote:
I am hoping someone can help with a problem I am having in
mySZD55.while thermaling some transmissions are lost as I turn.it
seems to recieve fine no matter if I am turning or not.it's an older
avionic dittle 720c.how do I diagnose if it's antenna related or just
a bad radio?
Thanks, Dennis Vreeken. aka 4Q

If you recieve ok with a given aircraft attitude and heading but do do
not transmit at the same attitude and heading then the law of
reciprocity rules out an antenna problem. An antenna system works
just the same for receive and transmit.

You can expect the antenna performance to change as you circle.
Whether you receive ok depends on the received signal strength and
your receiver squelch setting. Whether others hear you depends on
their received signal strength (which will vary as you circle while
transmitting) and their squelch setting. What you are experiencing
may be completely normal. Try setting squelch off or at minimum at
both receivers and see if you can detect a slowly varying signal or
sudden loss as you circle.

I don't know of any aircraft VHF tranceivers that provide an S meter
but when I built my RST years ago I brought out the AGC line so I
could do signal strength tests.

Andy

On Oct 14, 2:29*pm, Andy wrote:
On Oct 13, 9:17*pm, SD wrote:

I am hoping someone can help with a problem I am having in
mySZD55.while thermaling some transmissions are lost as I turn.it
seems to recieve fine no matter if I am turning or not.it's an older
avionic dittle 720c.how do I diagnose if it's antenna related or just
a bad radio?
Thanks, Dennis Vreeken. aka 4Q

If you recieve ok with a given aircraft attitude and heading but do do
not transmit at the same attitude and heading then the law of
reciprocity rules out an antenna problem. *An antenna system works
just the same for receive and transmit.

You can expect the antenna performance to change as you circle.
Whether you receive ok depends on the received signal strength and
your receiver squelch setting. *Whether *others hear you depends on
their received signal strength (which will vary as you circle while
transmitting) and their squelch setting. *What you are experiencing
may be completely normal. *Try setting squelch off or at minimum at
both receivers and see if you can detect a slowly varying signal or
sudden loss as you circle.

I don't know of any aircraft VHF tranceivers that provide an S meter
but when I built my RST years ago I brought out the AGC line so I
could do signal strength tests.

Andy

I had a similar problem just this last month. I had a bad push to talk
switch on the control stick. Seems I had to really push hard on the
button to transmit. Replaced the switch and it now works OK. This was
in a SZD55 #096 N55SZ. Hope this helps, Paul

On Tue, 13 Oct 2009 21:17:49 -0700 (PDT), SD wrote:

I am hoping someone can help with a problem I am having in
mySZD55.while thermaling some transmissions are lost as I turn.it
seems to recieve fine no matter if I am turning or not.it's an older
avionic dittle 720c.how do I diagnose if it's antenna related or just
a bad radio?
Thanks, Dennis Vreeken. aka 4Q

Not sure how to recommend diagnosis, but I can relate a problem I had
last year with my Dittel radio cutting out intermittently. My problem
turned out to be caused by a broken center pin on the coax cable
carrying the antenna into the radio. It was completely detached at the
point where it was soldered to the coax center wire, but contained in
the coax connector, it would sometimes contact, and other times not.
This is the sort of fault that could be g-effected, depending on how
your antenna wiring harness is supported.

Easy enough to check.

Good luck.

Bob

On Oct 14, 8:24*pm, Bob Gibbons wrote:
On Tue, 13 Oct 2009 21:17:49 -0700 (PDT), SD wrote:
I am hoping someone can help with a problem I am having in
mySZD55.while thermaling some transmissions are lost as I turn.it
seems to recieve fine no matter if I am turning or not.it's an older
avionic dittle 720c.how do I diagnose if it's antenna related or just
a bad radio?
Thanks, Dennis Vreeken. aka 4Q

Not sure how to recommend diagnosis, but I can relate a problem I had
last year with my Dittel radio cutting out intermittently. My problem
turned out to be caused by a broken center pin on the coax cable
carrying the antenna into the radio. It was completely detached at the
point where it was soldered to the coax center wire, but contained in
the coax connector, it would sometimes contact, and other times not.
This is the sort of fault that could be g-effected, depending on how
your antenna wiring harness is supported.

Easy enough to check.

Good luck.

Bob

thank you to all that have responded, you have given me lots of things
to check!! as usual this group is always helpful. 4Q

In article Andy writes:
On Oct 13, 9:17=A0pm, SD wrote:
I am hoping someone can help with a problem I am having in
mySZD55.while thermaling some transmissions are lost as I turn.it
seems to recieve fine no matter if I am turning or not.it's an older
avionic dittle 720c.how do I diagnose if it's antenna related or just
a bad radio?
Thanks, Dennis Vreeken. aka 4Q

If you recieve ok with a given aircraft attitude and heading but do do
not transmit at the same attitude and heading then the law of
reciprocity rules out an antenna problem. An antenna system works
just the same for receive and transmit.

True for most VHF systems, but not true in general.

The reciprocity will provide the same ratio of received power to
transmitted power, but will not guarantee the same signal/noise in
the received signal.

This is easily seen on HF, where atmospheric noise is substantially
more than the front end noise of the radio. The poor antenna receives
the signal attenuated by (for example) 20 dB, but also attenuates the
noise by 20 dB. The resulting signal/noise ratio as heard by the radio
is pretty much the same as when heard with an excellent antenna. However,
the 20 dB attenuation on transmit with the poor antenna means that the
signal received at the other end will be 20 dB down with unattenuated
noise, so that end has a 20 dB s/n loss of receive performance.

Normally the aircraft radio will not have as much atmospheric noise,
but I have heard precipitation static and ignition noise being pretty
bad.


Alan