[time-nuts] Difference in antennas

Fri Nov 22 16:07:08 UTC 2019

I would like to tag on to this.  I have a large Leica L1 choke ring antenna.  It has an indicator for “N”.  Not sure why.  I placed it on the roof without respect to directionality.  I will rotate it with “N” facing north in a month or so to see if there is any effect.

Bill Dailey

Negativity always wins the short game. But positivity wins the long game. - Gary Vaynerchuk

Don’t be easy to understand, 
Be impossible to misunderstand 
- Steve Sims

> On Nov 21, 2019, at 6:00 PM, Dana Whitlow <k8yumdoober at gmail.com> wrote:
> 
> Most modern GPS receivers are very quiet even barefoot.  So, one could
> argue that one should
> not have much more LNA gain in the antenna than required to make up for
> feedline loss, which
> should be easily calculable.  While excess gain  in the antenna can improve
> overall system noise
> figure a small amount, it will degrade intermod performance, which is
> likely to be a worse problem
> than simple weak signals.  It's likely that the cure is worse than the
> disease, as my doctor likes to
> say.
> 
> Dana
> 
> 
> 
>> On Thu, Nov 21, 2019 at 4:00 PM Taka Kamiya via time-nuts <
>> time-nuts at lists.febo.com> wrote:
>> 
>> So.... concensus is, 50dB gain antenna is too much gain, unless feed line
>> is too long, reception is poor, or there are other circumstances extra gain
>> is desired?
>> 
>> ---------------------------------------
>> (Mr.) Taka Kamiya
>> KB4EMF / ex JF2DKG
>> 
>> 
>>    On Thursday, November 21, 2019, 3:00:14 PM EST, Bob kb8tq <
>> kb8tq at n1k.org> wrote:
>> 
>> Hi
>> 
>> That is indeed the gotcha. Once you get past a certain amount of gain in
>> the
>> preamp, the C/N levels don’t change enough to notice. Looking today vs
>> looking
>> tomorrow is unlikely to be of any help if you are after a fraction of a
>> db.
>> 
>> About the only way to check would be to fast switch an attenuator in and
>> out of
>> the signal path. Watch things for a minute at one setting and then do the
>> same at
>> another setting. Run for a while and log all the deltas. If you see a
>> degradation of
>> more than a few tenths of a db, you are getting towards the minimum gain
>> point.
>> 
>> Indeed there are some receivers that have an AGC built in. *IF* your
>> receiver has one
>> and *IF* you can get at it, that would be a great way to work this out.
>> Indeed anybody
>> who makes it past both of those constraints has a pretty unique device.
>> 
>> ====
>> 
>> Simple answer for a 50 db antenna is to put an attenuator in after the DC
>> has
>> been eliminated from the circuit. It’s not idea, but it’s the best you can
>> do. Running
>> a great big splitter is one great way to come up with attenuation …..
>> 
>> Bob
>> 
>> 
>>>> On Nov 21, 2019, at 10:29 AM, John Ackermann N8UR <jra at febo.com> wrote:
>>> 
>>> Bob, this is a great summary, thanks!
>>> 
>>> One related question, especially with mixed systems -- how do you tell
>>> if you have optimum signal level at the receiver?
>>> 
>>> Most show some sort of SNR or Cn value.  What should we look for?  What
>>> are the indication of *too much* signal?  One issue in particular is how
>>> to handle a modern GPS that expects modest antenna gain when it's
>>> plugged into a system with a 50dB gain antenna at the top.
>>> 
>>> Thanks!
>>> John
>>> ----
>>> 
>>> On 11/21/19 8:00 AM, Bob kb8tq wrote:
>>>> Hi
>>>> 
>>>> Way back in time, the first gear out there to use what we now look at
>> as “normal” antennas
>>>> was survey gear. For various reasons they decided on a 12V power supply
>> and 40 to 50 db
>>>> of gain in the preamp mounted in the antenna. They also got into L1 /
>> L2 pretty quickly.
>>>> 
>>>> A bit later the cell phone (and later broadcast) guys got into this. In
>> a location with a lot of
>>>> RF (like a cell site) having a lot of gain at the antenna didn’t work
>> all that well. IMD issues
>>>> got into the act pretty quickly. In addition, front end filtering was
>> required to reduce overload
>>>> issues. The focus was on L1 only so filtering was relatively easy.
>>>> 
>>>> There is a whole separate set of antennas that put a big chunk of the
>> RF portion of the radio
>>>> in the antenna. Those still survive here and there. I have one of them
>> and probably a couple
>>>> of dozen of the more “normal” antennas.
>>>> 
>>>> As time marched on, supplying 12V to antennas became a bit less
>> popular. Most of the cell
>>>> guys went over to a 5V antenna supply. The net result was 12V 50 db
>> survey antennas that did
>>>> L1/L2 and much smaller 5V 25 db antennas for “timing”. The timing
>> antennas didn’t do L1/L2 so
>>>> not going to work for survey. The survey antennas had way to much gain
>> and no filtering so
>>>> not going to work for a cell site.
>>>> 
>>>> Indeed things did and do get crossed up in various pro and basement
>> systems. With care and
>>>> the right set of circumstances things may work. In other cases the
>> result can be an ongoing set
>>>> of systems issues over an entire network of stations.
>>>> 
>>>> Prices for a good new survey antenna are up in the many thousands of
>> dollars range. They have
>>>> very stable phase centers and (usually) test results to allow
>> correction of any residual phase
>>>> issues. This is part of what lets you get into the “couple of mm” range
>> on a survey.
>>>> 
>>>> For timing, you have to dig a bit and answer a few questions. Is your
>> concern how close you
>>>> are to BIH? If so you will need to know all the delays in your system.
>> This includes the delays
>>>> in the antenna filters and the preamp. Is your concern (or measure) the
>> ADEV at 1 second?
>>>> If so the delays are not a concern. Your antenna choice may be a bit
>> different depending on
>>>> this focus.
>>>> 
>>>> Bob
>>>> 
>>>> 
>>>> 
>>>>> On Nov 21, 2019, at 1:25 AM, Taka Kamiya via time-nuts <
>> time-nuts at lists.febo.com> wrote:
>>>>> 
>>>>> I have been looking antennas.  Prices seem to range less than 30
>> dollars to more than 500 dollars.  Some are 20db gain and some are 40 db
>> gain.  Some are specified as marine use only.  Some are specified as timing
>> use.  Some doesn't say anything at all.  Power supplies are different.
>>>>> Other than obvious, antenna is an antenna, isn't it?  It captures L1
>> signal, amplify it and send it down the coax.  What makes one more costly
>> than others?  What makes one timing antenna and one navigation antenna?  It
>> doesn't make sense to me.
>>>>> 
>>>>> I did some simple experiment with 26db, 40db, and magnetic stick on
>> type.  I didn't really see significant difference.  Signal level itself
>> even wasn't all that different.  I have nearly a clear sky view 360 degrees
>> above 30 degrees above horizon.  In some directions, clear view to
>> horizon.  My feed is Timewave type.  So It may not be the best but nearly
>> ideal.
>>>>> 
>>>>> Can someone shed light on this topic?  (of course, I know some antenna
>> has integrated receiver.  I am not talking about those)
>>>>> 
>>>>> ---------------------------------------
>>>>> (Mr.) Taka Kamiya
>>>>> KB4EMF / ex JF2DKG
>>>>> _______________________________________________
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>>>> 
>>>> 
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>>> 
>>> 
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