Combining 2 antennas

[bearcatrp]

This is just a what if question. Say I want to combine a loop and a discone. Connect the 2 on the mast, then run coax down from there. Even though my discone picks up HF fairly well, just wondering if the loop would help. It would be around 30 feet in the air. Would side mount the loop. OR, get a Omni X and combine it with the discone.

 

[Ubbe]

Wouldn't a loop be amplified and be powered from the coax? It makes it difficult to combine the antennas. Otherwise a diplexer or some simple low/high pass filters can be used. Just connecting two antennas might not work satisfactory but needs to be tested to see the impact.

/Ubbe

 

[sonm10]

diplexer is what you need - diamond, comet, mfj
just have to find one with the proper split

 

[bearcatrp]

Have been looking at loops lately. So many different ones out there. Don't want to run power to it unless it comes from the radio. Have seen smaller ones but not sure how well they function. Some of these loops cost a kidney. Will have to continue my research on loops.

 

[prcguy]

In my experience a passive or non amplified loop is way down in signal level, although you will have the ability to null out interference, etc. I have a home made 1m loop and a commercial one about 12" dia and my amplified loops pick up much more.

As others have mentioned a simple diplexer that separates the HF band from VHF/UHF is an easy way to combine a loop and Discone with virtually no loss. You can run the power inserter for the loop right after the diplexer on the coax to the loop. Finding a loop powered by the radio is probably not going to happen.

I'm a big fan of the W6LVP loop which is reasonably priced and you can make a passive loop for just a few $$ then stick a loop amplifier circuit board at the base and a power inserter near the radio for less than $30. If your looking at more expensive loops consider you do have two kidneys and really only need one (good one).

Have been looking at loops lately. So many different ones out there. Don't want to run power to it unless it comes from the radio. Have seen smaller ones but not sure how well they function. Some of these loops cost a kidney. Will have to continue my research on loops.

 

[iMONITOR]

I would not recommend a diplexer or triplexer when working with VHF, UHF and HF. I would use a separate dedicated antenna and feed line for the HF.

 

[900mhz]

I would not recommend a diplexer or triplexer when working with VHF, UHF and HF. I would use a separate dedicated antenna and feed line for the HF.

I agree. Perhaps, if you are working dedicated for 10 meter FM only and combine it with the higher frequencies, you could make an exception, but anything else will invite more headaches...HF is a totally different animal which requires direct attention.

 

[prcguy]

Why?

I would not recommend a diplexer or triplexer when working with VHF, UHF and HF. I would use a separate dedicated antenna and feed line for the HF.

 

[bearcatrp]

This is for receive only folks. With a loop covering 1-50 mhz, and the discone covering 25 mhx to 3000 mhz, wouldn't think there would be issues. But, thats why I posted this question, to find out.

 

[prcguy]

In my opinion using a diplexer to combine the two will work perfectaly and I'm doing the same thing right now and have been for years. The only thing I would recommend is placing a good ferrite common mode choke in line near the loop to decouple the coax. That will help keep some noise out of the loop antenna and will preserve its directivity.

This is for receive only folks. With a loop covering 1-50 mhz, and the discone covering 25 mhx to 3000 mhz, wouldn't think there would be issues. But, thats why I posted this question, to find out.

 

[n5ims]

the discone covering 25 mhx to 3000 mhz

That's probably what their marketing department wants you to believe but don't count it working very well over all of that range. The typical discone generally covers the VHF-Hi and UHF bands (basically 140 - 500) pretty well and drops off both above and below rather quickly. Now some discones have a piece that fits above the standard discone design (above the horizontal elements) that will help on the lower frequencies, but these are designed for a fairly narrow range and once you exceed that range the performance degrades quickly as well. It's hard to tell what range they're designed for since they never really give the specifications for that extension. If it works good for you, great but if things change (such as band conditions) it might go from good to great or good to bad.

As far as the second part of your original post (mixing two random antennas to share the same feed line), using a diplexer is really the only way to go. That will have your HF antenna feed the HF signals and the VHF/UHF antenna feed the VHF/UHF signals. You won't have issues with out of phase signals cancelling the signal(s) that are received by both. Using some very simple math to explain this (very simplified but helps to explain the issue). Signals in perfect phase you get 1 + 1 = 2 (more signal). Signals perfectly out of phase you get 1 + (-1) = 0 (no signal). Mixing random signals together will give you random results (sometimes better, sometimes very worse). Combining two antennas that were specifically designed to be combined (on the frequency range in use) you'll get some very good gain or coverage (this is why they sell phasing kits for specific antennas and frequency ranges). Combining two antennas that were not designed specifically to be combined (or combining them using something other than the specifically designed phasing kit) you will most likely not get good results.

 

[bearcatrp]

Do these diplexers or other multiport things need to be inside or is outside ok provided weatherized? Looking at some of these, they don't use PL259. Small jumpers? Are adapters available?

 

[AM909]

Do these diplexers or other multiport things need to be inside or is outside ok provided weatherized? ...

Being in MN, you might have an issue with temperature – check the specs for operating temp range. Seems to me I've seen people build heaters into tower-mounted electronics in extreme environments.

 

[bearcatrp]

Will try to do my research on it before buying. For now, I need a 2 port diplexer/other kind for my R8500 for both HF and higher frequencies for my discone for now. Will be getting a loop in the new future but won't go up until spring. On waiting list for the one I want. Do they make adapters for these multiport connections or do I need jumpers since all I have looked at don't use PL259?

 

[merlin]

They did that for years with NTSC TV, The separate VHF/UHF antenna combined onto a single cable.
Then, those old TVs had an F connector for VHF and 300 ohm screws for the UHF.
Quite easy to do. If your loop needs power, there are combiners with a DC pass line.
In the shack, just another combiner to separate HF from VHF/UHF and go to their respective receivers.
Yes, there are adapters from anything to about anything.

 

[bearcatrp]

Am starting to reconsider selling my R75 I have listed for sale (not sure yet). Could use that for the loop (when I get one) but use the R8500 for quick scanning on HF using the discone. Thanks for the replies.

 

[bearcatrp]

Considering this loop:
MFJ-1886TR

 

[prcguy]

Instead of some Mighty Fine Junk, take a look at this one which is cheaper and probably much better. I have both the receive only version and the experimenters kit and am thrilled with them. I can't say that for any MFJ product I've ever had the displeasure of owning.

https://www.w6lvp.com/

Considering this loop:
MFJ-1886TR

 

[bearcatrp]

Does the w6lvp require a power cord? From just looking at the picture, seems I need to run power to it. But not sure if that was for the rotor or the loop. The MFJ is still on back order I just found out.

 

[prcguy]

They have a power inserter you put near the radio and it feeds power up the coax. The W6LVP guy will also look at your receive location and any high power AM transmitters nearby and he can put in a notch filter to reduce potential interfering stations if you want. Nobody else will do that.

Does the w6lvp require a power cord? From just looking at the picture, seems I need to run power to it. But not sure if that was for the rotor or the loop. The MFJ is still on back order I just found out.