Yes, that would make it an I.F. gain control, and that is what it is most of
the time. I don't know why manufacturers still use the misnomer "RF Gain"
for this control.
Concerning the ARRL, when they talk about having only enough gain to hear
the normal background noise they are usually talking about RF amplification
ahead of the 1st mixer. It is important to pay careful attention to the gain
distribution of the receiver, since any gain ahead of the 1st mixer degrades
the dynamic range by that same amount.
As an example, suppose a receiver has an IP3 of +30dBm. Now, if a
preamplifier with 10dB of gain is placed ahead of the 1st mixer the IP3 will
be degraded to +20dBm.
Typically, excess noise contributed by the environment is in the 15 to 20dB
range. Many shortwave receivers have a noise figure in the 10 to 12dB range.
The excess environmental noise can be between 3 to 5dB above any noise
contribution that the receiver has itself. For this reason, most modern
receivers don't use an RF amplifier ahead of the 1st mixer.
Some receivers, such as the AOR-7030 have a post-mixer amplifier. Any
amplification after the 1st mixer won't degrade out of band IMD performance
unless signals fall within the range of the roofing filter that follows the
1st mixer.
Now, another point comes into consideration..............close-in IP3
performance. Three major mechanisms affect this parameter. First of all, the
performance of the 2nd mixer itself. Most receivers use a "weaker" 2nd mixer
since the roofing filter protects this device from out of band signals. If a
stronger 2nd mixer with better IMD performance is used, the close-in IMD
will improve.
The 2nd parameter is the sideband noise of the synthesizer itself. If phase
noise can be improved, close-in IMD performance will improve.
Of course, the parameters of the roofing filter itself will directly affect
the close-in IMD performance. As an example, both the Racal 6790 and the JRC
NRD-515 are using at least an 8-pole crystal filter as the roofing filter at
the 1st I.F.
The 6790 has some amplification that follows the roofing filter, and another
roofing filter is added after that amplification.
The result is exceptional skirt selectivity at the 1st I.F. This affords
quite a bit of out of band protection for the 2nd mixer.
Another example is the Collins 651S-1. This is a triple conversion receiver.
At the 1st I.F. of 110.35MHz, an 8-pole crystal filter is used. At the 2nd
I.F. of 10.35MHz?, another 8-pole crystal filter is used. At the 3rd I.F. of
either 450 or 455kHz, depending on when the receiver was manufactured,
mechanical filters are used. These things are what set the "premium grade"
receivers apart from most of the consumer equipment.
Do we really need this kind of front end protection? Probably not, unless
the receiver is going to be used on an ocean going vessel that has
multi-kilowatt transmitters. Even in this scene, narrow band RF preselectors
are used ahead of the receivers to add additional IMD protection. I hope
this helps.

Pete

"Geoffrey S. Mendelson" wrote in message
...
Pete KE9OA wrote:

When you turn up the RF gain control, you don't desense the radio, but
you
do give the AGC loop more gain. Maybe this is what you meant.

Wouldn't that make it an IF GAIN control?

A while back I read a review by the ARRL of a transciver and they brought
up
an interesting point. Modern receivers have enough gain to "hear" the
normal background noise, so beyond that it really does not matter.

In my environment the noise is so high that almost anything can hear it,
my R-5000 often hears S9 level background noise on 40m and nearby SW
bands. (5-10mHz).

Geoff.

--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
IL Voice: (07)-7424-1667 Fax ONLY: 972-2-648-1443 U.S. Voice:
1-215-821-1838
Visit my 'blog at http://geoffstechno.livejournal.com/

That does add a bit of "nicety" to the recovered audio.

Pete

"Telamon" wrote in message
...
In article ,
David wrote:

On Fri, 5 Jan 2007 10:51:03 +0000 (UTC), (Geoffrey
S. Mendelson) wrote:

Pete KE9OA wrote:

When you turn up the RF gain control, you don't desense the radio, but
you
do give the AGC loop more gain. Maybe this is what you meant.

Wouldn't that make it an IF GAIN control?

A while back I read a review by the ARRL of a transciver and they
brought up
an interesting point. Modern receivers have enough gain to "hear" the
normal background noise, so beyond that it really does not matter.

In my environment the noise is so high that almost anything can hear it,
my R-5000 often hears S9 level background noise on 40m and nearby SW
bands. (5-10mHz).

Geoff.
The RF gain control can be very handy for reducing noise to the point
where SSB voice comms sound extremely HiFi.

Putting the AGC on slow also helps for a similar reason.

--
Telamon
Ventura, California

"Telamon" wrote in message
...
In article ,
"Pete KE9OA" wrote:

How do you figure that this is nonsense?

Well let's quote the the statement that I responded to OK?

In article , BDK
wrote: You can't even be sure identical
radios will have the same S-Meter readings, in most cases. The
reading is pretty meaningless, except to compare antennas, or if a
preselector is used, to adjust for max reading.

You already answered one exception to this blanket statement about
radios calibrated in an absolute scale.

Here is another exception, you can be reasonably sure that the same
model radio will have similar readings.

Typically, SWL radios would have their S-Meter calibrated at 14MHz,
so that S9 would equal 50uV. You are correct when you mention
S-Meters that are calibrated in dBm as being absolute, as long as the
system in in calibration for gain distribution, etc. Receivers that
have this function do provide for setting up the gain distribution.
Now, the mystery continues.................what exactly do you mean
by the following statement?

"The RF gain control just sets maximum sensitivity of the radio and
does not change the gain of the radio so by turning all the way down
you are at the radios published maximum sensitivity. As you turn it
up you are desensitizing the radio."

The above statement, in quotes, is a new one to me. Could be showing
my young 54 year old age. The RF gain control only sets the maximum
sensitivity of the radio when it is controlling the bias to the RF
stage in addition to the I.F. stages, and this usually isn't the
case, except for some of the older tubed equipment. Most RF gain
controls USUALLY only set the gain of the I.F. stage. This has
nothing to do with the sensitivity of the system, if we are talking
about noise figure (I realize that you didn't mention that, so I
won't put words in you mouth on this one). When you turn up the RF
gain control, you don't desense the radio, but you do give the AGC
loop more gain. Maybe this is what you meant.

Man, you are ancient.

How did you know? Have you looked at the service manuals of the more recent
equipment? I don't think so.


No I pretty much meant what the user would experience using the radio.
Looking at the radio as a black box and not understanding how all the
circuits inside actually operate I described what would happen as the
RF gain control is operated with the AGC circuit on.

The perspective here is what to expect from the operation of the RF
gain control not unlike what to expect from the S-meter, which is the
subject of the thread.

--
Telamon
Ventura, California

That still doesn't make sense. As you advance the setting on the RF gain
control, the S-Meter reading will increase, unless you are talking about
some of the older tubed units that used a negative AGC and had the S-Meter
at full-scale when the receiver was powered down. Now, about being
ancient........................................... ....

Pete

It's been a great discussion. Great group!

Pete

"BDK" wrote in message
...
In article , says...
S-UNIT DISCUSSIONS AT URL:

http://www.ac6v.com/sunit.htm

CL





Good page.

BDK

In article ,
"Pete KE9OA" wrote:

"Telamon" wrote in message
...
In article ,
"Pete KE9OA" wrote:

How do you figure that this is nonsense?

Well let's quote the the statement that I responded to OK?

In article , BDK
wrote: You can't even be sure identical
radios will have the same S-Meter readings, in most cases. The
reading is pretty meaningless, except to compare antennas, or if a
preselector is used, to adjust for max reading.

You already answered one exception to this blanket statement about
radios calibrated in an absolute scale.

Here is another exception, you can be reasonably sure that the same
model radio will have similar readings.

Typically, SWL radios would have their S-Meter calibrated at 14MHz,
so that S9 would equal 50uV. You are correct when you mention
S-Meters that are calibrated in dBm as being absolute, as long as the
system in in calibration for gain distribution, etc. Receivers that
have this function do provide for setting up the gain distribution.
Now, the mystery continues.................what exactly do you mean
by the following statement?

"The RF gain control just sets maximum sensitivity of the radio and
does not change the gain of the radio so by turning all the way down
you are at the radios published maximum sensitivity. As you turn it
up you are desensitizing the radio."

The above statement, in quotes, is a new one to me. Could be showing
my young 54 year old age. The RF gain control only sets the maximum
sensitivity of the radio when it is controlling the bias to the RF
stage in addition to the I.F. stages, and this usually isn't the
case, except for some of the older tubed equipment. Most RF gain
controls USUALLY only set the gain of the I.F. stage. This has
nothing to do with the sensitivity of the system, if we are talking
about noise figure (I realize that you didn't mention that, so I
won't put words in you mouth on this one). When you turn up the RF
gain control, you don't desense the radio, but you do give the AGC
loop more gain. Maybe this is what you meant.

Man, you are ancient.

How did you know? Have you looked at the service manuals of the more recent
equipment? I don't think so.

None of the manuals I read had anything about your age in them.

No I pretty much meant what the user would experience using the radio.
Looking at the radio as a black box and not understanding how all the
circuits inside actually operate I described what would happen as the
RF gain control is operated with the AGC circuit on.

The perspective here is what to expect from the operation of the RF
gain control not unlike what to expect from the S-meter, which is the
subject of the thread.

--
Telamon
Ventura, California

That still doesn't make sense. As you advance the setting on the RF gain
control, the S-Meter reading will increase, unless you are talking about
some of the older tubed units that used a negative AGC and had the S-Meter
at full-scale when the receiver was powered down. Now, about being
ancient........................................... ....

Well, I don't think I can help you then.

--
Telamon
Ventura, California

In article ,
"Pete KE9OA" wrote:

Yes, that would make it an I.F. gain control, and that is what it is most of
the time. I don't know why manufacturers still use the misnomer "RF Gain"
for this control.

Snip

If the signal has not gone through a demodulation stage it it still a
modulated carrier so even if it is a mixed IF product it is all a part
of the RF gain stage in the radio.

I agree with you that it would be better to call it a IF gain control.

--
Telamon
Ventura, California

In article ,
"Pete KE9OA" wrote:

Snip

As an example, suppose a receiver has an IP3 of +30dBm. Now, if a
preamplifier with 10dB of gain is placed ahead of the 1st mixer the
IP3 will be degraded to +20dBm. Typically, excess noise contributed
by the environment is in the 15 to 20dB range. Many shortwave
receivers have a noise figure in the 10 to 12dB range. The excess
environmental noise can be between 3 to 5dB above any noise
contribution that the receiver has itself. For this reason, most
modern receivers don't use an RF amplifier ahead of the 1st mixer.

Snip

Most of the better modern receivers have a switchable RF amplifier
because the background noise is higher at lower frequencies and as you
noted can reduce the intermodulation performance so with adjustable or
switchable RF gain you can use it at higher frequencies or actually at
any frequency as conditions permit.

--
Telamon
Ventura, California

In article ,
"Pete KE9OA" wrote:

Snip

Now, another point comes into consideration..............close-in IP3
performance. Three major mechanisms affect this parameter. First of
all, the performance of the 2nd mixer itself. Most receivers use a
"weaker" 2nd mixer since the roofing filter protects this device from
out of band signals. If a stronger 2nd mixer with better IMD
performance is used, the close-in IMD will improve.

Snip

Every stage in the radio that the signal has to pass through will add
its own set of intermodulation products. RF amplifiers, RF attenuators,
all and any mixers, IF amplifiers, filters, and demodulators.

--
Telamon
Ventura, California

In article ,
BDK wrote:

In article telamon_spamshield-C9BF19.20290005012007
@newsclstr03.news.prodigy.net,
lid says...
In article ,
BDK wrote:

In article telamon_spamshield-F6523C.20501704012007
@newsclstr02.news.prodigy.com,
lid says...
In article ,
BDK wrote:

In article m,
says...

David wrote:
On Fri, 05 Jan 2007 02:17:32 GMT, Telamon
wrote:

In article
s.com,
"john" wrote:


An exception would be radios that have a signal strength meter
in
dBm,
which is an absolute scale.

Millivolts?

actually the palstar and the drake scales are in Decibels, while
the
kenwoods scale is in Db at the top and millivolts at the bottom.
also
before anyone asks my rf gain is fully clockwise on both the drake
and
kenwood. the palstar doesn't have a rf gain control.



You can't even be sure identical radios will have the same S-Meter
readings, in most cases. The reading is pretty meaningless, except to
compare antennas, or if a preselector is used, to adjust for max
reading.

Nonsense.



Wanna bet? In most cases, side by side, identical models have different
meter readings. Usually it's slight, but sometimes it's huge. My JRC
NRD-515 has a "tight" meter. SSB audio can be clearly heard with the
meter at the left peg. Another 515 I had here for interconnect repair
was just as sensitive as mine, but the same signal would read S-2 or 3.
Same thing has happened with Kenwood R5000's, R2000's, and JRC NRD-525s.
(The first ones had a "spastic" S-Meter, later ones were cured of this)

In "pro" radios it might be true, but in hobby receivers, it's not true
that S-meters have any real correlation with signal strength in
comparing one radio to another.

Oh come on. The same model with the same factory adjustment would have
the same reading or very close. It would be reasonable to see a small
variation but a "huge" difference would indicate a problem with one of
the radios.



Obviously, your and my idea of "tolerances" isn't what theirs is. A
whole lot of radios are aligned "just good enough", or they need
touching up due to aging after a really short time. Some just are not
right at all out of the box, and a slight adjustment works wonders. I've
seen huge differences between Icom R-71A's. Some, like the last one I
had were dead on freq, the PBT was aligned right, etc, but some I had
previously owned, and worked on weren't even close. Some of these were
brand new, and I was helping the owner install a filter or something.
when compared to a good one, it was obvious something was wrong.

Electronic Equipment Bank (EEB) sold a lot of alignments on brand new
radios, as the factories weren't doing a real good job of it. They would
turn on your brand new R71A, R5000, Yaesu FRG-8800, and let it cook for
a couple days, then align it.

Then there is the thing all the major brands of ham and SW equipment
have in common, the lack of ability to tighten screws. Most were just
snugged, and by the time the thing had ridden across the country in a
UPS or Fedex truck, gone through a few heat/cool cycles in the process,
they weren't even close to being tight anymore. Even after an EEB
alignment, the S-Meter's could still be off a little from one to the
next.


Then you have techs who forget to tighten screws in your $1000 receiver
before they ship it, and not only does the alignment get messed up, but
you are overjoyed that something wasn't broken. Yes, it happened to me
about 15 years ago. I sent my NRD-515 in for a minor problem, more an
annoyance than anything else. When it came back, it rattled, and two
screws holding the top PC board had fallen out, and the rest were so
loose they were about to fall out. I ended up checking around and
finding a good freq counter and realigned it myself. Close, but not 100%
right, I need to do it again. I also fixed the original problem that
they "couldn't duplicate". Odd, since it did it as soon as I turned it
on after I put the screws back in and tightened it all up.

The only real way to compare (without any equipment) two radios is to
hook them up to a coax switch and then to the same antenna, and switch
them back and forth to compare.

Sure there are many reasons a radio may not perform to specifications.

Specifications can only get you so far. You do have to actually operate
the radio to find out if its total performance is in line with your
expectations.

--
Telamon
Ventura, California

On 4 Jan 2007 17:54:40 -0800, "john" wrote:

hi,

i'm noticing a discrepancy between the s-meter readings of these three
radios. all three radios are connected to the same antenna for the test
and signals can be heard equally well on all three, but the kenwood
r-5000 always has the highest signal levels, by quite a bit - followed
by the palstar and then the drake. the palstar and the drake are the
closest. when i turn the pre-amp on the drake closes in on the palstar,
but still a little low. are s-meter readings standardized - is this a
fair way to test for a radios sensitivity.

The readings are more or less standardized...

http://www.algonet.se/~k-jarl/ssa/IARU/smeter.html

.... but the meterings can be "off" and in need of recalibration.

bob
k5qwg