Signal Selectivity

[blindfire]

Ok, here's the situation.

I have an Icom IC7100 with a Diamond X510 antenna.
I live in Shirley, MA (FN42en)
I frequent the Boston 2m repeater at 8pm daily for the EMA NTS Net.
That repeater is at 145.230
There is a DMR repeater up in Manchester...which is equidistant to me as Boston.
That repeater is at 145.220 (10 KHz below Boston).

The problem is, I get bleed over from 145.220 onto 145.230.

I emailed the main BARC guy who runs the repeater for advice. He reached out the the other repeater owner. They were nice enough to drop power a bit so as not to interfere with me. While it helped, it is not completely gone.

Below is a snipped from the email the BARC guy sent me.

Just checking in to see how your situation has been. I've been in contact with the folks that maintain W1RCF/R and I know that they have taken a few steps to reduce the interference, including a power reduction.

If you are still having some issues, I had a pair of solutions that could work for you (but they will involve station upgrades on your end!):

The X510 is an omnidirectional 8.3dB gain antenna. A directional antenna aimed at Boston and away from NH would null out the 145.22 repeater signal.
I looked up the selectivity numbers for the Icom and Kenwood you mentioned, and they aren't the best. The TM-281 and the IC-7100 are -6dB at 12 kHz, so essentially the 145.22 signal is still in the receiver passband when it keys up. A commercial VHF radio will typically have 12 kHz selectivity in the order of -60 dB! (I can talk from experience here in that my Yaesu FT8900 hears the signal from 145.22 when I'm listening to BARC's repeater in the Lowell/Tewksbury area, but my in my Motorola VHF radio 145.23 sounds good with no interference). Surplus commercial radios are easily found on ebay and in flea markets.

Hope this helps!

A beam / directional antenna is out of the question. No land or tower to put it on without major expense and other issues.

His second comment is interesting. Does this mean that the receivers only drop 6db 12KHz above / below the center frequency?

If that is the case, is there a circuit that can be built to increase this? It would have to be a box between the radio and the antenna, right?

Thanks

 

[Miamivice]

Cheapest solution, buy a used motorola cdm vhf mobile for $100- $150. Or an older maxtrac for $40-80 and use that.

Sent from my SAMSUNG-SM-G930A using Tapatalk

 

[cockpitbob]

I think Miamivice has the best suggestion, but would still consider a 3 or even 2 element Yagi. A 2m Yagi is small and you don't need a tower or rotator. And they can be fun to make.

 

[JDL]

cockpitbob has the best solution, if you have room for the Diamond X510 antenna you have room for the 3 or 2 element Yagi. The Yagi would take up less room then the antenna you are using now. You don't have to rotate the Yagi just point in in the direction of the repeater. Use a A/B antenna switch to switch back to the Diamond when you are using other repeaters.

 

[quincy]

I think Miamivice has the best suggestion, but would still consider a 3 or even 2 element Yagi. A 2m Yagi is small and you don't need a tower or rotator. And they can be fun to make.

FWIW, I am making a 3 element yagi so I can receive the 147.225 repeater from my QTH. Home Depot has aluminum rods 1/4" x 48" for about $4 each. The rest is just sched 40 pvc take your pick from 1 - 1.5" OD. Just google online for plans.


Sent from my iPhone using Tapatalk

 

[drgrant]

A beam / directional antenna is out of the question. No land or tower to put it on without major expense and other issues.

2M / 440 Yagis aren't that big, though. Hell when I lived with my parents, I had one stuffed in a tree (was a cushcraft dual bander) that was basically permanently pointed at Boston.

Out of curiosity have you tried a monoband 2M rig? A lot of the multiband rigs have front ends that easily get destroyed by strong
signals. It wouldn't surprise me if the 7100 is a little loose, like a hotdog down a hallway kind of loose on the front end, particularly on VHF/UHF. If you don't have one laying around I can let you borrow my FT2500M or one of the V8000s I have sitting around, just for experimentation. The V8Ks have a squelch that also has a 15db attenuator built into them as well. Have you seen if there is any difference punching ATT on 2M when listening to 230? Probably wont do much but its worth a try.

-Mike

 

[drgrant]

cockpitbob has the best solution, if you have room for the Diamond X510 antenna you have room for the 3 or 2 element Yagi. The Yagi would take up less room then the antenna you are using now. You don't have to rotate the Yagi just point in in the direction of the repeater. Use a A/B antenna switch to switch back to the Diamond when you are using other repeaters.

What I did back in the day with the Cushcraft was I took an HT up on the ladder with me and kept moving it on the mount a little bit till I got the favored stuff in range... just kept moving it for best signal.

-Mike