Help Identify Device: DB Products DB4326

[tropiradio]

Hi,

Came across this DB Products DB4326, looks to be a UHF isolator, but aside from the usual IN, OUT, and LOAD ports, it has two additional unmarked ports. Perhaps additional inputs? Could this be a combiner/isolator? Nothing online on the model number whatsoever, not really unusual as brand is long defunct.

Two pictures that I hope will help with identification. Thank you for looking.

 

[tropiradio]

Anybody? Just wanted to give this thread one last try.

 

[rescue161]

The ports on the bottom are for dummy loads. It is an isolator or circulator device that only allows RF to travel in one direction, but not the other. See the arrow on the label. The label on the edge should give a frequency range as there don't appear to be any tuning adjustments on this one.

 

[tropiradio]

Yes someone already confirmed that these are 3-stage UHF 450-512MHz wide-band (no tuning required) circulators. What threw me off was the two unlabeled load ports, and zero info out there on this model. Awaiting for them to arrive and test. I just hope they where packed well to protect them during shipping and not end up with a pair of doorstops. Will update soon, hopefully.

 

[rescue161]

The other two unlabeled ports are just to catch any RF that makes it past the first load. Typically they will be much smaller dummy loads. The first one labeled "LOAD" would generally be about 50 Watts or so and the other unlabeled ones would be around 15-25 Watts or so. You can test it with a spec-an with a tracking generator. Just make sure you terminate the unused ports with 50 Ohm loads.

 

[tropiradio]

Thank you for the information, this should arrive next week so will be testing it soon and hopefully it will be found to be working fine.

 

[tropiradio]

I finally received the isolators. They both measure about 60-62dB reverse isolation, with between -0.4 to -1.0db insertion forward loss, depending on the frequency. Tested with 50-ohm loads at each port, and at 450, 470, and 500MHz resting on a non metallic surface.

Would these results be consisted with the expected performance of wide band untuned isolators like these?

 

[rescue161]

Yes, that sounds about right. They would be used in conjunction with a pass filter to construct a combiner with two or more tied together to a single antenna. The ones I have are adjustable, so they can be aligned to have a little better rejection, but I like the ease of the non-adjustable units.

 

[tropiradio]

Yes I do have harmonic the filters, couple of DB4332B 450-470MHz. These came from a decommissioned IM panel, they where checked and aligned with NanoVNA and show about -55db at second harmonic, and only about 0.3dB insertion loss at close to 470MHz operating Tx frequency.

Well I am happy with the results of these 3-stage isolators. I also have a pair of untunned DB4325B single stage isolators from same brand and vintage (80s-90s) that came from that same IM panel, and they measured each about 20-22dB isolation and around 0.3-0.4dB forward loss at around 470MHz. So these 3-stage ones seem to be in line with those numbers.

The single stage isolators are each one now mounted on two separate repeaters along with Sinclair Q3220E duplexers. Repeaters are set to just 20W out of the Tx port which leaves about 15W at the antenna. That will provide plenty strong enough coverage within the required 1-mile radius of the repeater for the portables, and that along those single isolators will hopefully minimize possibility of IM inside each others the Tx's. One repeater is Moto SLR5000 and the other is Hytera RD982i.

So far the first repeater (SLR) has been in operation for several months now. The second repeater will be put online later this week at same location, with same configuration, and R/T spaced 100KHz away of the first one. I will try to achieve as much physical isolation between both repeater antennas, and was hoping the single stage islolators will do their thing and pick up the rest. Otherwise I'll replace them with these 3-stage babies which was the whole "just in case" intention of the last minute purchase. I was just not sure if they where going to even work given the $50/each price.

 

[rescue161]

That was a very good price.

 

[tropiradio]

Well guess I took my chances and got lucky.

So what about combining 2 channels, since you mentioned I started thinking about putting the two repeaters TXs on a single antenna.
So if I understand this correctly, each transmitter would go into one of the 3-stage isolators, then the output each with its own LP filter and then the output of the LPFs is combined into a coaxial "T" with equal length cables, and then into the TX side of the QT3220E duplexer that is then connected to the antenna (via a Polyphaser surge protector).

For the RX side guess would then need a RX multicoupler connected to the RX side of the duplexer, and then one output port of the power divider goes to each receiver. Altough dealing with only strong signals from nearby portables I wonder if a simple 50-ohm 2-port splitter might even be workable enough in this scenario, it would be just 3dB down to each receiver side without any active amplification.

 

[rescue161]

On my sites, I have 5 channel combiners exactly the way you are describing the TX side. On the RX side, I have a multi-coupler to the receivers and am just using the pre-selectors inside the repeaters (Quantars). It works very good. No duplexer involved. You are limited to the minimum freq separation based on the pass filters that you use. Mine are rated at 250 kHz. All of my channels are farther away than that, so I'm good to go.

 

[tropiradio]

I purchased two more of them, just to have them handy and play around. Besides one never knows when something like this will come up again as such a low price.

Yesterday installed repeater #2, and so far there does not seem to be any interference between one and the other when both are transmitting, so for now left them both with the single stage isolators in place.