Well I've got all my TX problems sorted out fine now.
However I am beginning to think that the receiver is somewhat noisy.
When set up as per manual I am getting about a S3 internal noise level
on sideband.
My unit has had the RF stage modified as per the International Radio
mods and also the balanced mixer. In the next few days I hope to have a
look at this problem too, it is possible that the mixer balance is not
very perfect for example.
It was also fitted with back to back 1N4148 diodes across the RX input
and these might just have been damaged with the tx problem.
Has anyone else had a similar experience with this rig?
Regards Cliff Wright ZL1BDA ex G3NIA.

cliff wright wrote:
Well I've got all my TX problems sorted out fine now.
However I am beginning to think that the receiver is somewhat noisy.
When set up as per manual I am getting about a S3 internal noise level
on sideband.
My unit has had the RF stage modified as per the International Radio
mods and also the balanced mixer. In the next few days I hope to have a
look at this problem too, it is possible that the mixer balance is not
very perfect for example.
It was also fitted with back to back 1N4148 diodes across the RX input
and these might just have been damaged with the tx problem.
Has anyone else had a similar experience with this rig?
Regards Cliff Wright ZL1BDA ex G3NIA.
============================
Is it really the receiver ? Suggest you check by connecting a dummy
load inside a metal can . Are you sure that your house electrical power
wiring with attached equipment is NOT causing the noise?

Frank GM0CSZ / KN6WH

Highland Ham wrote:
cliff wright wrote:

Well I've got all my TX problems sorted out fine now.
However I am beginning to think that the receiver is somewhat noisy.
When set up as per manual I am getting about a S3 internal noise level
on sideband.
My unit has had the RF stage modified as per the International Radio
mods and also the balanced mixer. In the next few days I hope to have
a look at this problem too, it is possible that the mixer balance is
not very perfect for example.
It was also fitted with back to back 1N4148 diodes across the RX input
and these might just have been damaged with the tx problem.
Has anyone else had a similar experience with this rig?
Regards Cliff Wright ZL1BDA ex G3NIA.

============================
Is it really the receiver ? Suggest you check by connecting a dummy
load inside a metal can . Are you sure that your house electrical power
wiring with attached equipment is NOT causing the noise?

Frank GM0CSZ / KN6WH
Well Frank I've done just that. In the past I've had a lot of QRN from
"dirty" mains around here even if it is underground in this area.
So my first step was to ring the local power company.
However bad as it was when they had a faulty pole transformer about 600
metres or so away, it was variable according to loading etc.
This noise seems pretty constant under any conditions, just like the
noise from the mythical "Big Bang".
The mods I carried out are supposed to improve the noise floor of the
820S but although sensitivity is very good and any AGC action quietens
the noise considerably, I am still not entirely happy about the front
end of the RX. This is especially so as I have always been interested in
weak signal CW contacts on 20 metres especially to the Antipodes of New
Zealand in Spain and the western Med.
When it was done I had a few problems caused by a tiny solder bridge
on the IF board. This caused me to do a lot of messing around with the
front end before I found the problem as it had appeared to be RF stage
instabilty.
So I think that I will check out all the FET's and try and match even
more closely the pair in the balnced mixer.
Apparently Kenwood were not entirely happy with this circuit as
different units have at least 3 different source circuits for the
balanced mixer stage.
73"s Cliff Wright.

Highland Ham wrote:
cliff wright wrote:

Well I've got all my TX problems sorted out fine now.
However I am beginning to think that the receiver is somewhat noisy.
When set up as per manual I am getting about a S3 internal noise level
on sideband.
My unit has had the RF stage modified as per the International Radio
mods and also the balanced mixer. In the next few days I hope to have
a look at this problem too, it is possible that the mixer balance is
not very perfect for example.
It was also fitted with back to back 1N4148 diodes across the RX input
and these might just have been damaged with the tx problem.
Has anyone else had a similar experience with this rig?
Regards Cliff Wright ZL1BDA ex G3NIA.

============================
Is it really the receiver ? Suggest you check by connecting a dummy
load inside a metal can . Are you sure that your house electrical power
wiring with attached equipment is NOT causing the noise?

Frank GM0CSZ / KN6WH
Well Frank I've done just that. In the past I've had a lot of QRN from
"dirty" mains around here even if it is underground in this area.
So my first step was to ring the local power company.
However bad as it was when they had a faulty pole transformer about 600
metres or so away, it was variable according to loading etc.
This noise seems pretty constant under any conditions, just like the
noise from the mythical "Big Bang".
The mods I carried out are supposed to improve the noise floor of the
820S but although sensitivity is very good and any AGC action quietens
the noise considerably, I am still not entirely happy about the front
end of the RX. This is especially so as I have always been interested in
weak signal CW contacts on 20 metres especially to the Antipodes of New
Zealand in Spain and the western Med.
When it was done I had a few problems caused by a tiny solder bridge
on the IF board. This caused me to do a lot of messing around with the
front end before I found the problem as it had appeared to be RF stage
instabilty.
So I think that I will check out all the FET's and try and match even
more closely the pair in the balnced mixer.
Apparently Kenwood were not entirely happy with this circuit as
different units have at least 3 different source circuits for the
balanced mixer stage.
73"s Cliff Wright.

On Oct 25, 1:27 pm, cliff wright wrote:
Well I've got all my TX problems sorted out fine now.
However I am beginning to think that the receiver is somewhat noisy.
When set up as per manual I am getting about a S3 internal noise level
on sideband.
My unit has had the RF stage modified as per the International Radio
mods and also the balanced mixer. In the next few days I hope to have a
look at this problem too, it is possible that the mixer balance is not
very perfect for example.
It was also fitted with back to back 1N4148 diodes across the RX input
and these might just have been damaged with the tx problem.
Has anyone else had a similar experience with this rig?
Regards Cliff Wright ZL1BDA ex G3NIA.

Remove ALL the mods. Take it back to original - that way, you will be
looking for a fault rather than trying to figure out if its the mods,
faulty mods, something else, etc etc.

The original design engineers had a pretty good idea of how it was
supposed to work, published specifications in the manual, are based on
this. Your battling with "mods" - how can find any fault with
extraneous mods?

Get an established reference point, ie the service manual. Go forward
from there.....

Andrew VK3BFA.

Andrew VK3BFA wrote:
On Oct 25, 1:27 pm, cliff wright wrote:

Well I've got all my TX problems sorted out fine now.
However I am beginning to think that the receiver is somewhat noisy.
When set up as per manual I am getting about a S3 internal noise level
on sideband.
My unit has had the RF stage modified as per the International Radio
mods and also the balanced mixer. In the next few days I hope to have a
look at this problem too, it is possible that the mixer balance is not
very perfect for example.
It was also fitted with back to back 1N4148 diodes across the RX input
and these might just have been damaged with the tx problem.
Has anyone else had a similar experience with this rig?
Regards Cliff Wright ZL1BDA ex G3NIA.


Remove ALL the mods. Take it back to original - that way, you will be
looking for a fault rather than trying to figure out if its the mods,
faulty mods, something else, etc etc.

The original design engineers had a pretty good idea of how it was
supposed to work, published specifications in the manual, are based on
this. Your battling with "mods" - how can find any fault with
extraneous mods?

Get an established reference point, ie the service manual. Go forward
from there.....

Andrew VK3BFA.

Hi Andrew.
Well I ran it for over a year before making the modifications.
These were basically using more advanced MOSFET's in the rf and balanced
mixer stages with some bias adjustments to suit.
From my measurements (I have a pretty well equipped home electronics
workshop) it did make some improvement to the internal noise floor and
about a 6 to 10 dB improvement in overload capacity.
I must actually beg to differ a little about the original design
engineers. As I pointed out the 820S was produced with a least 5
different 1st mixer source circuits in production and the coupling to
the balanced mixer is not optimum by any means. This doesn't look to me
like a fully optimised design!
BTW I did actually restore things the way they were and it just went
back the way it was, and the noise was still there.
Perhaps I should point out that I have designed and built 10 different
communication receivers in the last 40 years and have owned most of the
well known older commercial units too, in fact in the late 1970s I
worked 200 countries confirmed and got my WAC with a completely homebrew
station running 100 watts to a TT21 final.
Further investigation has confirmed so far that we have a serious local
problem with mains radiated QRN here.
Some experiments the other evening showed that the noise has decided
polarisation characteristics as a 5/8 wave 20 metre vertical produces
a similar noise level to my G5RV but with greater impulsive
characteristics, a bit like auto ignition noise.
The jury is still out but fortunately another local ham works for the
power distribution company and I'm going to get in contact with him to s
share our experiences.
Very dissapointing though as I have a nice elevated site and had great
hopes of getting some good DX.
I'll post anything I find out further.
73's Cliff Wright ZL1BDA ex G3NIA

cliff wright wrote:
Andrew VK3BFA wrote:

On Oct 25, 1:27 pm, cliff wright wrote:

Well I've got all my TX problems sorted out fine now.
However I am beginning to think that the receiver is somewhat noisy.
When set up as per manual I am getting about a S3 internal noise level
on sideband.
My unit has had the RF stage modified as per the International Radio
mods and also the balanced mixer. In the next few days I hope to have a
look at this problem too, it is possible that the mixer balance is not
very perfect for example.
It was also fitted with back to back 1N4148 diodes across the RX input
and these might just have been damaged with the tx problem.
Has anyone else had a similar experience with this rig?
Regards Cliff Wright ZL1BDA ex G3NIA.



Remove ALL the mods. Take it back to original - that way, you will be
looking for a fault rather than trying to figure out if its the mods,
faulty mods, something else, etc etc.

The original design engineers had a pretty good idea of how it was
supposed to work, published specifications in the manual, are based on
this. Your battling with "mods" - how can find any fault with
extraneous mods?

Get an established reference point, ie the service manual. Go forward
from there.....

Andrew VK3BFA.

Hi Andrew.
Well I ran it for over a year before making the modifications.
These were basically using more advanced MOSFET's in the rf and balanced
mixer stages with some bias adjustments to suit.
From my measurements (I have a pretty well equipped home electronics
workshop) it did make some improvement to the internal noise floor and
about a 6 to 10 dB improvement in overload capacity.
I must actually beg to differ a little about the original design
engineers. As I pointed out the 820S was produced with a least 5
different 1st mixer source circuits in production and the coupling to
the balanced mixer is not optimum by any means. This doesn't look to me
like a fully optimised design!
BTW I did actually restore things the way they were and it just went
back the way it was, and the noise was still there.
Perhaps I should point out that I have designed and built 10 different
communication receivers in the last 40 years and have owned most of the
well known older commercial units too, in fact in the late 1970s I
worked 200 countries confirmed and got my WAC with a completely homebrew
station running 100 watts to a TT21 final.
Further investigation has confirmed so far that we have a serious local
problem with mains radiated QRN here.
Some experiments the other evening showed that the noise has decided
polarisation characteristics as a 5/8 wave 20 metre vertical produces
a similar noise level to my G5RV but with greater impulsive
characteristics, a bit like auto ignition noise.
The jury is still out but fortunately another local ham works for the
power distribution company and I'm going to get in contact with him to s
share our experiences.
Very dissapointing though as I have a nice elevated site and had great
hopes of getting some good DX.
I'll post anything I find out further.
73's Cliff Wright ZL1BDA ex G3NIA

Well things are in progress here. I've finally got the power company
looking at a 33KV line about 600 metres away. This seems to be the
source of most of the noise.
My fellow ham down the rad has exactly the same problems, in fact he has
taken down his all band vertical because the noise level it picked up
was so high. His multiband 3 el Yagi is somewhat better but then of
course you can use the front to back and front to side ratio to reduce
the noise pickup.
The powere boys are looking at the line right now and I am hoping to get
a quieter QTH in the near future.
Cliff Wright ZL1BDA ex G3NIA

On Oct 31, 5:43 pm, cliff wright wrote:
Andrew VK3BFA wrote:
On Oct 25, 1:27 pm, cliff wright wrote:

Well I've got all my TX problems sorted out fine now.
However I am beginning to think that the receiver is somewhat noisy.
When set up as per manual I am getting about a S3 internal noise level
on sideband.
My unit has had the RF stage modified as per the International Radio
mods and also the balanced mixer. In the next few days I hope to have a
look at this problem too, it is possible that the mixer balance is not
very perfect for example.
It was also fitted with back to back 1N4148 diodes across the RX input
and these might just have been damaged with the tx problem.
Has anyone else had a similar experience with this rig?
Regards Cliff Wright ZL1BDA ex G3NIA.

Remove ALL the mods. Take it back to original - that way, you will be
looking for a fault rather than trying to figure out if its the mods,
faulty mods, something else, etc etc.

The original design engineers had a pretty good idea of how it was
supposed to work, published specifications in the manual, are based on
this. Your battling with "mods" - how can find any fault with
extraneous mods?

Get an established reference point, ie the service manual. Go forward
from there.....

Andrew VK3BFA.

Hi Andrew.
Well I ran it for over a year before making the modifications.
These were basically using more advanced MOSFET's in the rf and balanced
mixer stages with some bias adjustments to suit.
From my measurements (I have a pretty well equipped home electronics
workshop) it did make some improvement to the internal noise floor and
about a 6 to 10 dB improvement in overload capacity.
I must actually beg to differ a little about the original design
engineers. As I pointed out the 820S was produced with a least 5
different 1st mixer source circuits in production and the coupling to
the balanced mixer is not optimum by any means. This doesn't look to me
like a fully optimised design!
BTW I did actually restore things the way they were and it just went
back the way it was, and the noise was still there.
Perhaps I should point out that I have designed and built 10 different
communication receivers in the last 40 years and have owned most of the
well known older commercial units too, in fact in the late 1970s I
worked 200 countries confirmed and got my WAC with a completely homebrew
station running 100 watts to a TT21 final.
Further investigation has confirmed so far that we have a serious local
problem with mains radiated QRN here.
Some experiments the other evening showed that the noise has decided
polarisation characteristics as a 5/8 wave 20 metre vertical produces
a similar noise level to my G5RV but with greater impulsive
characteristics, a bit like auto ignition noise.
The jury is still out but fortunately another local ham works for the
power distribution company and I'm going to get in contact with him to s
share our experiences.
Very dissapointing though as I have a nice elevated site and had great
hopes of getting some good DX.
I'll post anything I find out further.
73's Cliff Wright ZL1BDA ex G3NIA

I stand corrected - it was from my own experience of fixing other
peoples radios where a bizarre collection of "mods" had degraded the
actual performance!. But, as you point out, you have the test gear and
the knowledge to eliminate this.

In the end, its going to be something very simple (isnt it always?)
and possibly related to an error made while doing something else in
there........(been there, done that - still drives me NUTS!!!)

Andrew VK3BFA.