I asked about this brand in the balun thread as well

http://www.qintar.com/html/tv/cs1000fp.htm
for their 4-way splitter CS-4-1000FP, they claim
Bandwidth: 5-1000 MHz
Insertion Loss: 6.5 dB max.
Isolation P to P: 25 dB min.
Return Loss: 20 dB min.

anyone had experience of this company and know if those figures are legit ?


and while we're at it, their AB switches
http://www.qintar.com/html/tv/tab.htm
claim an insertion loss of 0.1dB

Three Winegard SD-3700s were connected back-to-back, taken two at a time.

Two lengths of Channel Master 300 Ohm line (partially foam dielectric) were used to connect the units. The 300 Ohm lines, were as nearly the same length as practical. The measured lengths, chosen for convenience, were 8.75 inches.

Definition: A unit under test (UUT) is considered a pair of SD3700s connected back to back with the F-type ports available for input-output connections.

The units were labeled #1, #2 and #3.

Pairs of SD-3700s were selected:

#1 and #2
#1 and #3
#2 and #3
#2 and #1 (see Note)

Note: Repeat of first combo, with crossing of terminal pairs on SD-3700 (maintaining balanced line polarity)

Consistent terminal polarity was observed for all 300-Ohm connections.

Test equipment included a frequency synthesizer and a broadband signal power detector.

First, the signal synthesizer was connected to the power detector with short RG6 coaxial lines and through some fixed attenuators (FAM type). The attenuators were chosen to set a convenient power level and to ensure proper termination.

To obtain a base response, the synthesizer was stepped through frequencies chosen to represent the FM, VHF, and UHF bands, with a barrel (Female to Female connector) located where the UUT would be inserted. The frequency response was recorded

Then, the barrel (F-F) was removed and the UUT combinations were inserted one at a time and the frequency response recorded for each combination.

Using an Excel spreadsheet, the differences between the losses of the barrel and the UUT losses were calculated; this result was divided by two in order to represent the loss of a single SD-3700, and results were graphed.


http://www.digitalhome.ca/forum/picture.php?albumid=708&pictureid=4832


Comments:

The ripple effect (variation in loss vs. frequency) showing above in the relative wide UHF band is commonly seen in such configurations. Likely, most of the ripple is a result of imperfect matching of SD-3700s to either the 300-Ohm line or to each other. Practical lengths of transmission lines (at UHF) will be a significant fraction of a wavelength, or multiples. Such lengths of transmission line can exaggerate mismatch losses via impedance transformations. For example, a quarter wavelength line can invert the impedance from one end to another.

This loss variation can also be observed in actual installations, where the transmission line may be several wavelengths in length. For a particular frequency, one can minimize the effects by carefully trimming the line to a favorable length (although the trimmed length may not be favorable to other frequencies).

.

I'm surprised the loss is so high at UHF.

Have you measured 75-ohm power splitters at UHF? I've measured them at 98 MHz and I always get close to 3.3 dB loss at each port with the other terminated. That's only 0.3 dB more than ideal.

What sort of 75-ohm synthesizer and power meter are you using?

Brian

..Have you measured 75-ohm power splitters at UHF?

Yes

I've measured them at 98 MHz and I always get close to 3.3 dB loss at each port with the other terminated. That's only 0.3 dB more than ideal.Have measured in field test, spot frequencies, and comparisons against one another in actual installations at an antenna range. Don't have data handy.

Some splitters are much better than others (or worse). Found those used for CATV, to offer good performance (some versions of Antronix and Holland being good examples).

What sort of 75-ohm synthesizer and power meter are you using?Homebrew, of sorts:

- Synthesizer was made from kit parts obtained from SDR-Kits (http://sdr-kits.net/QRP2000_Description.html). It is based on synthesizer IC Silicon Devices SI570BBB (http://www.silabs.com/support%20documents/technicaldocs/si570.pdf).

- Power meter is homebrew, based on Linear Technology LT5534 (http://www.linear.com/product/LT5534) integrated circuit.

I just measured the excess loss at 584 MHz for four 75-ohm power splitters. I got 1.0, 1.6, 1.9, and 2.5 dB. After I was done I noticed that one splitter was rated to 500 MHz, another 600 MHz, another 1 GHz, and the last one said "UHF/VHF/FM." The best splitter was the 1-GHz Steren 201-222. I use this particular splitter as a return loss bridge because its port isolation at 98 MHz is > 40 dB. I measure 0.36 dB excess loss for it at 98 MHz.

Note that the loss from the worst splitter nullifies any gain from stacking two antennas.

Brian

antennahack measurements on several combiners was in 0.5 to 1.5+ dB range (divide by two):
http://www.antennahacks.com/

tripelo,

thanks for taking the time to perform the tests, and share the results here.

That said, I have to agree with Brian that those losses are much higher than I would expect. They're so poor that they throw away most of the gains possible from combining two identical antennas! :o

That seems odd, considering that the SD-3700 is a fairly well respected combiner, and these results could be easily bested by a couple cheap baluns and a $2 UVSJ. In other words, it doesn't make sense. ;)

Are we sure that the patented mixer circuit in the SD-3700 works as well as a splitter, as it does a combiner? That symmetry is a fundamental assumption your testing was based on.

If I wanted to combine two 300-ohm antennas, I think would use short equal lengths of 300-ohm twinlead, tie those in parallel, and then match the resulting 150 ohms to 75 ohms with a 12th-wave transformer. The transformer consists of 1.3" lengths of 75-ohm and 150-ohm lines in series. SWR is less than 1.28 and mismatch loss less than 0.07 dB from 470 to 698 MHz when designed for 590 MHz. I know I have some 150-ohm twinlead and I may have some 75-ohm as well. If not, the lengths are so short you could make them from parallel solid wires. Put a couple ferrite beads over the 75-ohm coax and you're done.

A DOS program for designing series-section transformers, of which the 12th-wave is a specific case, is in this collection of transmission line utilities:

http://ham-radio.com/k6sti/TL.ZIP

A short tapered transmission line might be even simpler.

Brian

tripelo, what were the results on your equipment using 2 baluns and a splitter in a similar setup ?

Are we sure that the patented mixer circuit in the SD-3700 works as well as a splitter, as it does a combiner? That symmetry is a fundamental assumption your testing was based on.
Yeah I agree, I would think it may make a poor 75 ohm in to two 300 ohm out splitter.

Picture of the inside:
http://img153.imageshack.us/img153/9017/insidelayout.jpg

Basically, it looks an R/C circuit from one antenna to the other, then coupled thru a crossover in the ferrite bead, then out to a 2 : 1 current balun. Follows the patent closely. It doesnt look like a lot of loss should occur there. And their RF wiring looks good too with the short leads and clipped off ends on the other side of the board. (hmm, too much flux residue left on the F connector ???)

A DOS program for designing series-section transformers, of which the 12th-wave is a specific case, is in this collection of transmission line utilities:

http://ham-radio.com/k6sti/TL.ZIP

A short tapered transmission line might be even simpler.

Thanks for that.

The problem of course with the short tapered transmission line method is that it has to be modeled for each unique antenna stack, and with horizontal ganging other issues crop in. Something universal and with low loss would be nice.

holl_ands,
a long while back you asked about the Gemini CV72 VHF/UHF splitter/combiner. Heres some pics :

http://img412.imageshack.us/img412/4442/cv72outside.jpg

http://img14.imageshack.us/img14/7148/cv72insides.jpg

Some more:

http://img820.imageshack.us/img820/536/cv72insides2.jpg

http://img59.imageshack.us/img59/9974/cv72insides3.jpg

Completely different principles involved than in the Winegard above.
The RF wiring practices of the Gemini dont look anywhere as good as on the Winegard, to say the least, heh. (there was loose solder connections on two of the four 300ohm terminals when I took it apart)

The problem of course with the short tapered transmission line method is that it has to be modeled for each unique antenna stack, and with horizontal ganging other issues crop in. Something universal and with low loss would be nice.

Any network, lumped or distributed, that matches two 300-ohm sources to a 75-ohm load will do that regardless of the physical characteristics of the sources. All that matters is the impedance at the two ends. If it's a distributed network, it just needs to be put in an out-of-the-way place or located in a plane where fields cancel. The network doesn't need to be redesigned for each application unless you want to match different impedances.

Brian

The network doesn't need to be redesigned for each application unless you want to match different impedances.
So one all purpose tapered, designed for 300 ohm stacking harness should work for all (within the harness length limits) 300 ohm antennas with a low SWR [300] ?
The problem with most UHF antennas is that their impedance varies a lot (and differently from one design to another) depending on frequency, so the best harness is going to be one that levels the fluctuations and has the lowest average SWR. That should imply different tapers for each design.

All that matters is the impedance at the two ends. If it's a distributed network, it just needs to be put in an out-of-the-way place or located in a plane where fields cancel.
Where would be the best place to put the excess wire of a harness that is too long ? Bow or taper it out at the front or back ?

Ill have to try this on the UHF Shorted Bowtie Loop, which has a consistent very low SWR [300] throughout the UHF range.

The problem with most UHF antennas is that their impedance varies a lot (and differently from one design to another) depending on frequency, so the best harness is going to be one that levels the fluctuations and has the lowest average SWR. That should imply different tapers for each design.

A matching network just transfers the SWR at the source to the load, with a little extra near the band edges. Whatever SWR the antenna exhibits when fed alone is what a pair will exhibit. You can try to tame the SWR curve if you want, but if a single antenna has an adequate match, so will two.

... what were the results on your equipment using 2 baluns and a splitter in a similar setup ?

The performance of the SD-3700 was first noticed in the VHF band. Was building a long Yagi array to try to reliably receive a “Tropo Scatter” VHF station. Testing was done at an antenna range where the synthesized VHF signals were transmitted to the receiving array (UUT) from a distant antenna.

Tried half-wave coax baluns with ferrites, using various combiners, this arrangement provided reasonably low loss but was rejected for other concerns (See * below).

No amount of tuning, trimming, stub insertions, etc., could make SD-3700s match the performance of a combination of selected commercial baluns and selected commercial combiners.

----------------------------

For other UHF projects, bench tested a couple of dozen baluns and several combiners. The baluns and combiners were tested separately. The lowest-loss (for UHF) baluns always turned out to some versions of the small “for-inside-use baluns”. The combiner/splitters, that were best, were certain models of Holland and Antronix brands.

Have two labs (of sorts), one here in Dallas, another in KY where the antenna test range is located. So, some of the measurement data is there.

-----------------------------

The half-wave loop balun with selected commercial combiner can provide an option for low-loss UHF.

And, various forms of transmission line combining (some of which have been discussed in this thread) can be even lower loss (avoiding combiners altogether).

-----------------------------

Each method of combining has advantages and disadvantages (probably subject of another topic), some examples:In one UHF application used a “for-inside-use balun”, sealed with silicone, outside for over a year with good results. In another application, water got inside a similar balun and performance degraded.
* Half-wave coax baluns used with, or without commercial combiners, and various other transmission line combining configurations, can in some applications increase susceptibility of preamp to atmospheric discharge (lightning induced surges).

Half-wave coax baluns used with, or without commercial combiners, and various other transmission line combining configurations, can in some applications increase susceptibility of preamp to atmospheric discharge (lightning induced surges).

Why?

Brian

Brian, this may be of more concern to those using GaAs type preamps, i.e. those preamps without some nonlinear protection at input, as BJT preamps usually have.

As you probably know, this subject covers a wide area.

Lightning discharges release energy impulses that cover a large bandwidth, more intense at low frequencies and declining at higher frequencies. To suppress reception of atmospheric induced electrical impulses; a receiving system (without nonlinear protection) should reject before the preamp input, as much as practical, all but the desired range of frequencies.

Anything connected to the preamp, including the coaxial shield can contribute to voltage at preamp input.

Impulse protection (especially for lower frequencies) includes:



Low impedance across preamp input (as near to zero as practical)
High common mode rejection (over broadband)
Low capture area for undesired signals


The susceptibility concern is application specific.

Some thoughts on the half-wave coaxial balun vs. say a voltage balun:

- A commercial voltage balun probably provides a lower impedance across the preamp terminals, for lower frequencies, including near DC.

- The common mode rejection of a half-wave balun can be low for some out-of-band signals. Your analysis here touches on this topic. http://www.ham-radio.com/k6sti/balun.htm
The use of ferrite chokes help with common mode rejection, but their effectiveness falls with lower frequency.

- In some applications, half-wave coaxial baluns tend to increase capture area for impulse noise.

The half-wave balun and the elements, to which it is directly connected, can effectively become a single larger element, thus increasing antenna response to signals in the lower frequency range.

The only thing I can see that matters is the short-term power of the differential signal passed to the preamp input. Baluns with similar common-mode rejection and bandwidth should deliver a similar impulse energy. The smaller the bandwidth, the lower the energy delivered from a wideband pulse. Halfwave coaxial baluns provide a narrower bandwidth than ferrite baluns so I would expect them to be somewhat more forgiving of lightning. I do think it's a good idea to provide some sort of lightning protection at the preamp input in areas where it is frequent, especially for mast-mounted preamps that aren't easy to replace.

Brian

The only thing I can see that matters is the short-term power of the differential signal passed to the preamp input...

Yes, that summarizes the topic.

Lightning induced impulses can induce high common mode currents. Such that some of the current can be converted to differential voltages. This is related to differences in impedance in the common mode return paths.

Baluns with similar common-mode rejection and bandwidth should deliver a similar impulse energy. The smaller the bandwidth, the lower the energy delivered from a wideband pulse.Yes.

Halfwave coaxial baluns provide a narrower bandwidth than ferrite baluns so I would expect them to be somewhat more forgiving of lightning.Yes, the frequency response is somewhat narrow band, but the common mode rejection of a half-wave balun is probably more narrow band than a well-constructed voltage balun for the VHF/UHF band.

Wide band common-mode rejection is desirable.

I do think it's a good idea to provide some sort of lightning protection at the preamp input in areas where it is frequent, especially for mast-mounted preamps that aren't easy to replace.There are tradeoffs, probably another topic :)