Minicircuits ZFL-500 directivity question

On 11/8/2023 5:02 PM, upsidedown@downunder.com wrote:
> On Wed, 8 Nov 2023 11:11:31 -0500, bitrex <user@example.net> wrote:
> 
>> They're nice lil modules, I didn't have this purpose in mind but I
>> wonder if they make a LNA suitable to replace the shit ass front end on
>> my DTV antenna, I live in a fringe area so reception varies by the day.
>> and I'm in a condo so mounting stuff outdoors not really feasible
> 
> That ZFL-500 is not very suitable as antenna amplifier for DTV. First
> of all it is quite noisy, noise figure NF = 4.2 dB (typical). These
> days a good antenna amplifier the NF should be below 3 dB. That
> amplifier is specified only up to 500 MHz, thus most UHF channels are
> out of range. However, it might still work since the specs are good at
> 500 MHz, wonder why the specs ends at 500 MHz.

Yeah it has gain for days. S21 is above 20dB well past 1 GHz.

> An antenna amplifier should be installed _at_ the antenna, thus the
> cable between amplifier and DTV receiver can be long.
> 
> You seem to suffer from tropospheric fading and the signal nulls can
> be quite deep and the signal is still momentary lost no matter what
> antenna amplifier you use. Only a proper outdoor antenna will really
> help.

I'll see if high pressure systems seem to make it better...atm with a 
planar antenna and associated amp I'm getting a station with a purported 
field strength of -70 dBm at 36 miles no problem if I kinda point it in 
that direction, but a station at 16 miles -50 dBm doesn't come in at all 
/shrug

On 2023-11-07 17:45, Simon S Aysdie wrote:
> On Tuesday, November 7, 2023 at 2:42:48 PM UTC-8, Simon S Aysdie wrote:
>> On Saturday, November 4, 2023 at 1:55:09 PM UTC-7, bitrex wrote:
>>> How is "directivity" defined for these Minicircuits gain blocks?
>>> Datasheet here:
>>>
>>> <https://www.mouser.com/datasheet/2/1030/ZFL_500_2b-3305829.pdf>
>>>
>>> Across the bandwidth of interest I'm measuring S21 as about 20-something
>>> dB give or take a dB which seems fine, S12 is at -40.
>>>
>>> If "directivity" in this context is just S12 then that seems within spec
>>> but if it's |S21 - S12| then something seems wrong with my setup and/or
>>> the amp.
>>>
>>> Doing the measurements on a (unfortunately not my personal home-lab
>>> machine!) Keysight 5080.
>> They give S-params for 2 units. Conveniently, they are in dB/angle. The table just says 38 dB, more or less for directivity. By a quick look at the S-params and comparing to the datasheet table, I think they are just saying D = |S12| (dB), which you noted.
>>
>> Example:
>> For "unit 1" and at 100 MHz, forward gain is +24.47859 dB.
>> For "unit 1" and at 100 MHz, reverse gain is -38.36183 dB.
>>
>> Because the "directivity" looks to be about same as |S12|, it is safe to say they mean D = |S12| (dB)
>>
>> !Freq S11:SOLT2(ON) S21:SOLT2(ON) S12:SOLT2(ON) S22:SOLT2(ON)
>> # Hz S dB R 50
>> 100000000 -3.318152e+001 -2.120138e+001 2.447859e+001 -1.975411e+001 -3.836183e+001 -1.134106e+001 -2.672768e+001 -1.570933e+002
> 
> 
> I should say:
> D = -|S12| (dB)
> 

(Supernews doesn't seem to be registering my 3 PM EST reply just 
now--apologies for duplication if it shows up eventually.)

It makes no sense to take the absolute value of a quantity expressed in 
decibels--that's saying that there's no difference between, say, a 100X 
voltage amp (+40 dB) and a 40-dB attenuator (-40 dB).

The directivity is just |S12 * S21|,  i.e. the effects at one port of a 
short-circuit load reflecting all of the signal backwards through the 
network. In decibels, it's

D = 20 log(|S12 * S21|).  Symmetrical. No big mystery.

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

On Wednesday, November 8, 2023 at 1:12:11 PM UTC-5, bitrex wrote:
> On 11/8/2023 11:47 AM, Fred Bloggs wrote: 
> > On Wednesday, November 8, 2023 at 11:11:40 AM UTC-5, bitrex wrote: 
> >> On 11/7/2023 5:42 PM, Simon S Aysdie wrote: 
> >>> On Saturday, November 4, 2023 at 1:55:09 PM UTC-7, bitrex wrote: 
> >>>> How is "directivity" defined for these Minicircuits gain blocks? 
> >>>> Datasheet here: 
> >>>> 
> >>>> <https://www.mouser.com/datasheet/2/1030/ZFL_500_2b-3305829.pdf> 
> >>>> 
> >>>> Across the bandwidth of interest I'm measuring S21 as about 20-something 
> >>>> dB give or take a dB which seems fine, S12 is at -40. 
> >>>> 
> >>>> If "directivity" in this context is just S12 then that seems within spec 
> >>>> but if it's |S21 - S12| then something seems wrong with my setup and/or 
> >>>> the amp. 
> >>>> 
> >>>> Doing the measurements on a (unfortunately not my personal home-lab 
> >>>> machine!) Keysight 5080. 
> >>> 
> >>> They give S-params for 2 units. Conveniently, they are in dB/angle. The table just says 38 dB, more or less for directivity. By a quick look at the S-params and comparing to the datasheet table, I think they are just saying D = |S12| (dB), which you noted. 
> >>> 
> >>> Example: 
> >>> For "unit 1" and at 100 MHz, forward gain is +24.47859 dB. 
> >>> For "unit 1" and at 100 MHz, reverse gain is -38.36183 dB. 
> >>> 
> >>> Because the "directivity" looks to be about same as |S12|, it is safe to say they mean D = |S12| (dB) 
> >>> 
> >>> !Freq S11:SOLT2(ON) S21:SOLT2(ON) S12:SOLT2(ON) S22:SOLT2(ON) 
> >>> # Hz S dB R 50 
> >>> 100000000 -3.318152e+001 -2.120138e+001 2.447859e+001 -1.975411e+001 -3.836183e+001 -1.134106e+001 -2.672768e+001 -1.570933e+002 
> >> Thanks Simon, yes that seems right, this amp was bang on within spec 
> >> otherwise so I'd have been surprised if it was way off there. 
> >> 
> >> They're nice lil modules, I didn't have this purpose in mind but I 
> >> wonder if they make a LNA suitable to replace the shit ass front end on 
> >> my DTV antenna, I live in a fringe area so reception varies by the day. 
> >> and I'm in a condo so mounting stuff outdoors not really feasible 
> > 
> > Your reception is probably being degraded by suboptimal antenna pointing, the sun, and unpredictable multi-path signal impingement [ coastal is littoral causes no end of propagation anomalies ]. It doesn't cost the manufacturer anything to provide a high performance front end amplifier
> It doesn't?
> all of which intended for satellite reception are LN-A's. The 
> customers pay for everything, do you think it's wise then for them to 
> provide junk performance parts making customers into ex-customers?
> Could apply the same argument to many other industries...and conclude 
> all products are high-quality because otherwise the manufacturer might 
> lose customers. 

The business is going to provide the best part suited for the application and price range.  It doesn't take state-of-the-art. 

Your reception is problematic because of the location and other factors. Nothing by way of more expensive parts is going to fix it.


> 
> Hey, I have a cool idea, I'll see if I can put it on the 5080 next time 
> I have a chance and see how it compares to a Minicircuits gain block for 
> similar bandwidth, I think I can get a hold of one..