Problems after moving aerial outside

Having some problems with some changes I’ve made to my installation due
to an ongoing loft conversion.

Previously I’ve had (in the loft) a DAT45/MRD feeding a Labgear PUH141
MHA, 2 outputs of which were used for TVs and a third output fed into a
Proception 310X amp which combined FM and DAB for other rooms in the
house. The local TX is Sandy Heath about 24 miles away. Performance has
been excellent with no drop outs or electrical interference.

I’ve had to move outside so decided that a Blake log periodic (DML26WB)
would be much neater. However, in tests where I’ve fixed it to some
scaffolding (giving a clear view in the direction of SH) the results are
not as good. There is interference on the Analog signals (important as I
have a computer monitor which has an analog tuner and is useful for PIP)
and the BER readings when checked on a Sony TV are higher.

Also, the bearing to SH is approx 70deg (all other aerials on other
houses are aligned on this bearing). However, I get the best results
pointing at approx 110deg. Pointing at 70 deg and re-scanning the TVs
results in only a limited number of channels being seen, all of which
are at low signal levels.

I could live with the aerial pointing in the “wrong” direction but if I
try to improve the analog signal by putting the PUH141 back in between
the blake PSU and the loft box results in any signal being lost. I can
only imagine the two PSUs are causing the problem.

Any suggestions? I'd like to fix this before the scaffolding comes down
and I have to balance at the top of a ladder....

Cheers - Kev

"Kevin Holohan" kevinholohan_at_hot_mail.com wrote in message
...
Having some problems with some changes I’ve made to my installation due to
an ongoing loft conversion.

Previously I’ve had (in the loft) a DAT45/MRD feeding a Labgear PUH141
MHA, 2 outputs of which were used for TVs and a third output fed into a
Proception 310X amp which combined FM and DAB for other rooms in the
house. The local TX is Sandy Heath about 24 miles away. Performance has
been excellent with no drop outs or electrical interference.

I’ve had to move outside so decided that a Blake log periodic (DML26WB)
would be much neater. However, in tests where I’ve fixed it to some
scaffolding (giving a clear view in the direction of SH) the results are
not as good. There is interference on the Analog signals (important as I
have a computer monitor which has an analog tuner and is useful for PIP)
and the BER readings when checked on a Sony TV are higher.

Also, the bearing to SH is approx 70deg (all other aerials on other houses
are aligned on this bearing). However, I get the best results pointing at
approx 110deg. Pointing at 70 deg and re-scanning the TVs results in only
a limited number of channels being seen, all of which are at low signal
levels.

I could live with the aerial pointing in the “wrong” direction but if I
try to improve the analog signal by putting the PUH141 back in between the
blake PSU and the loft box results in any signal being lost. I can only
imagine the two PSUs are causing the problem.

Any suggestions? I'd like to fix this before the scaffolding comes down
and I have to balance at the top of a ladder....

Cheers - Kev

You didn't say what you were connecting the log periodic to. By 'loft box'
do you mean the 310X amp?
It sounds as if you have a problem with the signal overloading an amp, but
it isn't clear from your description. I suggest you start from the beginning
and point the aerial at the TX and connect it directly to a digital and
analogue receiver/TV set/computer and see what the results are. Experiment
with the aerial off beam to prove to yourself that you do indeed have the
correct bearing. This could have a bearing on the problem (b-boom). Having
done that, connect the log to the 310X, ensure that the latter is powered,
and observe the results as before. If they are worse then either the 310X is
bust or the signal from the log is indeed mighty and is giving the 310X
indigestion. In the latter case, use an attenuator an the amplifier input.

It is also possible that you have chosen a location for the log where
signals are very poor. Such a location could be only 1m across, and it can
seem really freaky. Try a different location or three.

Is there any possibility that the log is not connected properly?

The elements of the log should be horizontal, and the short elements should
be nearest to the Tx..

Check that the two booms are not touching in the middle; a common problem if
the log has been abused in transit.

No conductive object should be affixed to the log other than at the clamp.
No piece of scaffolding tube should be near to the elements.

Bill

"Bill Wright" wrote in message
...

"Kevin Holohan" kevinholohan_at_hot_mail.com wrote in message
...
Having some problems with some changes I’ve made to my
installation due to
an ongoing loft conversion.

Previously I’ve had (in the loft) a DAT45/MRD feeding a
Labgear PUH141
MHA, 2 outputs of which were used for TVs and a third output
fed into a
Proception 310X amp which combined FM and DAB for other rooms
in the
house. The local TX is Sandy Heath about 24 miles away.
Performance has
been excellent with no drop outs or electrical interference.

I’ve had to move outside so decided that a Blake log periodic
(DML26WB)
would be much neater. However, in tests where I’ve fixed it to
some
scaffolding (giving a clear view in the direction of SH) the
results are
not as good. There is interference on the Analog signals
(important as I
have a computer monitor which has an analog tuner and is
useful for PIP)
and the BER readings when checked on a Sony TV are higher.

Also, the bearing to SH is approx 70deg (all other aerials on
other houses
are aligned on this bearing). However, I get the best results
pointing at
approx 110deg. Pointing at 70 deg and re-scanning the TVs
results in only
a limited number of channels being seen, all of which are at
low signal
levels.

I could live with the aerial pointing in the “wrong” direction
but if I
try to improve the analog signal by putting the PUH141 back in
between the
blake PSU and the loft box results in any signal being lost. I
can only
imagine the two PSUs are causing the problem.

Any suggestions? I'd like to fix this before the scaffolding
comes down
and I have to balance at the top of a ladder....

Cheers - Kev

You didn't say what you were connecting the log periodic to. By
'loft box'
do you mean the 310X amp?
It sounds as if you have a problem with the signal overloading
an amp, but
it isn't clear from your description. I suggest you start from
the beginning
and point the aerial at the TX and connect it directly to a
digital and
analogue receiver/TV set/computer and see what the results are.
Experiment
with the aerial off beam to prove to yourself that you do
indeed have the
correct bearing. This could have a bearing on the problem
(b-boom). Having
done that, connect the log to the 310X, ensure that the latter
is powered,
and observe the results as before. If they are worse then
either the 310X is
bust or the signal from the log is indeed mighty and is giving
the 310X
indigestion. In the latter case, use an attenuator an the
amplifier input.

It is also possible that you have chosen a location for the log
where
signals are very poor. Such a location could be only 1m across,
and it can
seem really freaky. Try a different location or three.

Is there any possibility that the log is not connected
properly?

The elements of the log should be horizontal, and the short
elements should
be nearest to the Tx..

Check that the two booms are not touching in the middle; a
common problem if
the log has been abused in transit.

No conductive object should be affixed to the log other than at
the clamp.
No piece of scaffolding tube should be near to the elements.

Bill





One other thing Bill. He has gone from a 17dB gain antenna with
13dB amp, to a 7dB gain antenna, a loss of 23dB less the loss
through the roof. How many TV signals can stand a 20dB or so
loss?

I know Sandy is in the flatlands, but there are hills around
there and at 24 miles there could be anything in the way.

Just a simple gain problem?



--
Woody

harrogate three at ntlworld dot com

"Woody" wrote in message
...
"Bill Wright" wrote in message
...
One other thing Bill. He has gone from a 17dB gain antenna with 13dB amp,
to a 7dB gain antenna, a loss of 23dB less the loss through the roof. How
many TV signals can stand a 20dB or so loss?

I know Sandy is in the flatlands, but there are hills around there and at
24 miles there could be anything in the way.

Just a simple gain problem?

1. The gain of a DAT 45 is quoted at 17dBi, which is about 14.5dBd. In fact
the gain is likely to be below 14.5dB across almost all of the band.
Wideband yagis tend to peak near the top end and can be very poor at the
bottom. Some of them have gain of 7dBd on the lower channels.
2. A log has gain of about 8.5dBd across the whole band, except for a slight
drop-off at the very top.
3. Loss due to loft mounting relative to outdoor mounting at the same height
could be anything from 6dB to 20dB, quite normally. Taking the 6dB figure,
the signal entering the amp should be about the same. In reality, if you
said to me, 'log outside versus DAT45 inside?' I would unhesitatingly reply,
'No contest, the log will **** it.'
4. Q: "How many TV signals can stand a 20dB or so loss?" A: Any that are
20dB or more above threshold.
5. The fact that he reports better results with the aerial off beam seems to
preclude a simple lack of field strength.

Bill

On Sun, 25 Oct 2009 20:28:39 -0000, Woody wrote:

One other thing Bill. He has gone from a 17dB gain antenna with
13dB amp, to a 7dB gain antenna, a loss of 23dB less the loss
through the roof. How many TV signals can stand a 20dB or so
loss?

This is a rather simplistic analysis. A 17dB gain antenna with a 13dB amp.
doesn't give you the equivalent of a 30dB antenna, which is what you seem
to be implying. Loss through the roof only 3dB? I don't think so...

On Mon, 26 Oct 2009 02:49:24 -0000, "Bill Wright"
wrote:

One other thing Bill. He has gone from a 17dB gain antenna with 13dB amp,
to a 7dB gain antenna, a loss of 23dB less the loss through the roof. How
many TV signals can stand a 20dB or so loss?

I know Sandy is in the flatlands, but there are hills around there and at
24 miles there could be anything in the way.

Just a simple gain problem?

1. The gain of a DAT 45 is quoted at 17dBi, which is about 14.5dBd. In fact
the gain is likely to be below 14.5dB across almost all of the band.
Wideband yagis tend to peak near the top end and can be very poor at the
bottom. Some of them have gain of 7dBd on the lower channels.
2. A log has gain of about 8.5dBd across the whole band, except for a slight
drop-off at the very top.
3. Loss due to loft mounting relative to outdoor mounting at the same height
could be anything from 6dB to 20dB, quite normally. Taking the 6dB figure,
the signal entering the amp should be about the same. In reality, if you
said to me, 'log outside versus DAT45 inside?' I would unhesitatingly reply,
'No contest, the log will **** it.'
4. Q: "How many TV signals can stand a 20dB or so loss?" A: Any that are
20dB or more above threshold.
5. The fact that he reports better results with the aerial off beam seems to
preclude a simple lack of field strength.

Bill


http://www.hdtvprimer.com/ANTENNAS/comparing.html

....snip...

http://www.hdtvprimer.com/ANTENNAS/comparing.html

Interesting but most US TV is wideband (as are all the antenna here) and
often mixed UHF/VHF antenna. Next time you are in the US, take a look up
and marvel at the contraptions up on the roof of most houses.

Paul DS

On Mon, 26 Oct 2009 02:49:24 -0000, "Bill Wright"
wrote:

5. The fact that he reports better results with the aerial off beam seems to
preclude a simple lack of field strength.

and also suggests that perhaps the scaffolding is not entirely
innocent.

lid wrote:
On Mon, 26 Oct 2009 02:49:24 -0000, "Bill Wright"
wrote:

5. The fact that he reports better results with the aerial off beam seems to
preclude a simple lack of field strength.

and also suggests that perhaps the scaffolding is not entirely
innocent.

Well, I've got the aerial on the top corner of the scaffolding on a pole
4 feet above any other scaffolding, but when I get chance I'll put it on
the 8 foot mast I intend to use I have and walk around the scaffolding
to see what results I get. I'll report back once I've done this but it
won't be before the weekend.

I did as Bill suggested and connected the aerial directly into the TV
bypassing the 310X and saw relatively little difference in the BER
reported by the Sony TV (this confirms the problem I had when originally
installing the 310X - it didn't seem to offer much in the way of gain
which is why I added the mast head amp). Finally I've re-checked all my
connections and they seem sound enough.

Thanks for the suggestions.

Paul D.Smith wrote:

...snip...

http://www.hdtvprimer.com/ANTENNAS/comparing.html

Interesting but most US TV is wideband (as are all the antenna here) and
often mixed UHF/VHF antenna. Next time you are in the US, take a look up
and marvel at the contraptions up on the roof of most houses.

Paul DS

I couldn't resist having a look at that site too.

What's most interesting is all the detail on trying to get rid of multipath.
Evidently the American DTTV system can't cope with that at all.

I'd have thought the receivers would have adaptive echo cancellers but
apparently not. Maybe they chose that system (VSB!!!) so they could be made
as cheaply as possible.

From personal observation, the European COFDM system copes perfectly with
multipath/ghosting that makes analogue pictures from the same transmitter
(Wenvoe) unwatchable. And our set-top boxes couldn't be much cheaper.

--
Steve Hayes, South Wales, UK
----Remove colours from reply address----