Using Hamitup on one antenna while transmitting on another

[N0IU]

Over the weekend, I ordered a Hamitup upconverter from Nooelec. I obviously don't have it yet, but I was curious about using it with SDR# as a panadapter. I have one antenna I can use to feed the converter (a dipole) and another for actually transmitting (a vertical). My radio is only 100 watts, but my fear is "blowing out" the front end of the upconverter since the antennas are in fairly close proximity.

I see that one of the features is, "Antenna protection on RF input; in-circuit in both enable and passthrough mode", but is that enough to protect it?

I wrote to Nooelec and they actually did not have a definitive answer to this.

So is anyone doing this?

[NI0Z]

While not specific to your question, this thread has some diagrams and references to equipment you may find useful in your pursuit of answers.

https://www.sdrzone.com/index.php?option=com_kunena&view=topic&Itemid=146&catid=18&id=86&limitstart=6

[N0IU]

Thanks for the link!

I ordered an RTL dongle to try out the Virtual Radar system as described in the January 2014 edition of QST. I have had it for about 10 days and every day brings something new and exciting to this new (to me!) world of SDR.

[N5INP]

I see that one of the features is, "Antenna protection on RF input; in-circuit in both enable and passthrough mode", but is that enough to protect it?

I wrote to Nooelec and they actually did not have a definitive answer to this. So is anyone doing this?

I ran into the same issue, and I wanted to protect my up converter which is on it's own long wire ant. I finally built my own circuit that uses a simple transistor/relay to disconnect the antenna when the rig is transmitting. If you are interested I can post the schematic and explain how it works.

[KA4POL]

By any means, ground the input while transmitting. There have been cases where regular transceivers suffered from RF even though they were off.

[N0IU]

By all means, please do post the schematic.

[N5INP]

This is designed for the FT-450 but the input can be changed to work with other types of signals. In this case the FT-450 has a pin on the Linear jack that goes low when transmitting. It's really nothing more than a line that goes to an open collector transistor in the radio, which can be used for anything you want within design limits. In this case I use it to trun on a transistor that closes a relay which connects the up converter input to ground. You still pick up RF because the up converter is not in a shielded box but it sure reduces the input a lot.

Any questions let me know.

[K9IUQ]

but my fear is "blowing out" the front end of the upconverter since the antennas are in fairly close proximity.

I see that one of the features is, "Antenna protection on RF input; in-circuit in both enable and passthrough mode", but is that enough to protect it?

I have used this for some time and it is excellent quality and fast switching It has been thru 3 contests running legal limit and protects my SDR 100%. What ever you use make SURE it works properly, 100 watts nearby and you can say bye bye to a RX.

I use a TS-590s and a QS1R sdr for a panafall with this device: http://www.dxengineering.com/parts/dxe-rtr-1a

Stan K9IUQ

[CHRISTOFERO]

One thing. Its my understanding that the Ham It Up is not using a MMIC or anything on the front end before the RF input.. so the signal goes through a low pass filter and into the mixer.. So it may not be so prone to getting blown out like a upconverter with an LNA in front of it.

There is a really good way to do antenna switching using PIN diodes which I have been reading about for years..

Also, there are ICs which are commonly used at UHF, Skyworks makes some very popular ones, so does Minicircuits, they are designed for more power, I think. It helps if you arent transmitting when the switch toggles.

Recently I've seen some PIN diode switch schematics, and bookmarked them. The nice thing about that is that its really fast and its non-mechanical. I suspect they could handle more power than the ICs, as long as they can handle a high enough voltage to keep them back biased and "off".

Lots of switching diodes might work for HF?

Or of course a relay would work but you have to make sure that the relay disconnects and preferably shorts the input of the receiver before the transmitter gets energized.

EDIT: Here is one PIN diode design (link below) This one is frequency dependent- it is just for one band (2 meters) But I think things like this can be done with DC and capacitors and work on all bands and its very fast. Faster than relays.

http://www.sm5bsz.com/pindiode.htm

[CHRISTOFERO]

The Nooelec Ham-it-up already has a circuit in it which you might be able to use in instantaneously switching it out of the circuit when you transmit.

Combined with a relay it would almost certainly be adequate.

I would go to the Skyworks site and look up whatever device they use.

http://www.skyworksinc.com/products_switches.aspx

They are very popular and I'm sure very good. Better than mechanical switches as far as loss at high frequencies.

The Ham-it-Up presents very little loss at VHF/UHF when its turned off.

The schematics for the entire Nooelect device are online.


Was looking for some data on Pin Diodes yesterday and found this:

http://www.microsemi.com/sites/default/files/micnotes/701.pdf

"PIN Diode Fundamentals

A PIN diode is a semiconductor
device that operates as a variable
resistor at RF and microwave
frequencies. The resistance value of
the PIN diode is determined only by
the forward biased dc current. In
switch and attenuator applications,
the PIN diode should ideally control
the RF signal level without
introducing distortion which might
change the shape of the RF signal.
An important additional feature of the
PIN diode is its ability to control large
RF signals while using much smaller
levels of dc excitation."

Since it doesn't have an LNA, I dont see why the Hamitup and similar simple converters wouldn't be able to be used in reverse for transmitting.

[CHRISTOFERO]

The oscillator on some of the upconverters is probably too noisy (at least it appears to be to me) to be used as is for transmitting. I'm not an expert, I'm just a beginner. But when I look at the LO in these upconverters to calibrate my LO offset I see enough noise to imply that they would not be clean enough to be used in transmitting.